GCC(1)                                GNU                               GCC(1)



NAME
       gcc - GNU project C and C++ compiler

SYNOPSIS
       gcc [-c|-S|-E] [-std=standard]
           [-g] [-pg] [-Olevel]
           [-Wwarn...] [-Wpedantic]
           [-Idir...] [-Ldir...]
           [-Dmacro[=defn]...] [-Umacro]
           [-foption...] [-mmachine-option...]
           [-o outfile] [@file] infile...

       Only the most useful options are listed here; see below for the
       remainder.  g++ accepts mostly the same options as gcc.

DESCRIPTION
       When you invoke GCC, it normally does preprocessing, compilation,
       assembly and linking.  The "overall options" allow you to stop this
       process at an intermediate stage.  For example, the -c option says not
       to run the linker.  Then the output consists of object files output by
       the assembler.

       Other options are passed on to one stage of processing.  Some options
       control the preprocessor and others the compiler itself.  Yet other
       options control the assembler and linker; most of these are not
       documented here, since you rarely need to use any of them.

       Most of the command-line options that you can use with GCC are useful
       for C programs; when an option is only useful with another language
       (usually C++), the explanation says so explicitly.  If the description
       for a particular option does not mention a source language, you can use
       that option with all supported languages.

       The gcc program accepts options and file names as operands.  Many
       options have multi-letter names; therefore multiple single-letter
       options may not be grouped: -dv is very different from -d -v.

       You can mix options and other arguments.  For the most part, the order
       you use doesn't matter.  Order does matter when you use several options
       of the same kind; for example, if you specify -L more than once, the
       directories are searched in the order specified.  Also, the placement
       of the -l option is significant.

       Many options have long names starting with -f or with -W---for example,
       -fmove-loop-invariants, -Wformat and so on.  Most of these have both
       positive and negative forms; the negative form of -ffoo is -fno-foo.
       This manual documents only one of these two forms, whichever one is not
       the default.

OPTIONS
   Option Summary
       Here is a summary of all the options, grouped by type.  Explanations
       are in the following sections.

       Overall Options
           -c  -S  -E  -o file  -no-canonical-prefixes -pipe  -pass-exit-codes
           -x language  -v  -###  --help[=class[,...]]  --target-help
           --version -wrapper @file -fplugin=file -fplugin-arg-name=arg
           -fdump-ada-spec[-slim] -fada-spec-parent=unit -fdump-go-spec=file

       C Language Options
           -ansi  -std=standard  -fgnu89-inline -aux-info filename
           -fallow-parameterless-variadic-functions -fno-asm  -fno-builtin
           -fno-builtin-function -fhosted  -ffreestanding -fopenmp
           -fms-extensions -fplan9-extensions -trigraphs  -traditional
           -traditional-cpp -fallow-single-precision  -fcond-mismatch
           -flax-vector-conversions -fsigned-bitfields  -fsigned-char
           -funsigned-bitfields  -funsigned-char

       C++ Language Options
           -fabi-version=n  -fno-access-control  -fcheck-new
           -fconstexpr-depth=n  -ffriend-injection -fno-elide-constructors
           -fno-enforce-eh-specs -ffor-scope  -fno-for-scope
           -fno-gnu-keywords -fno-implicit-templates
           -fno-implicit-inline-templates -fno-implement-inlines
           -fms-extensions -fno-nonansi-builtins  -fnothrow-opt
           -fno-operator-names -fno-optional-diags  -fpermissive
           -fno-pretty-templates -frepo  -fno-rtti  -fstats
           -ftemplate-backtrace-limit=n -ftemplate-depth=n
           -fno-threadsafe-statics -fuse-cxa-atexit  -fno-weak  -nostdinc++
           -fno-default-inline  -fvisibility-inlines-hidden
           -fvisibility-ms-compat -fext-numeric-literals -Wabi
           -Wconversion-null  -Wctor-dtor-privacy -Wdelete-non-virtual-dtor
           -Wliteral-suffix -Wnarrowing -Wnoexcept -Wnon-virtual-dtor
           -Wreorder -Weffc++  -Wstrict-null-sentinel -Wno-non-template-friend
           -Wold-style-cast -Woverloaded-virtual  -Wno-pmf-conversions
           -Wsign-promo

       Objective-C and Objective-C++ Language Options
           -fconstant-string-class=class-name -fgnu-runtime  -fnext-runtime
           -fno-nil-receivers -fobjc-abi-version=n -fobjc-call-cxx-cdtors
           -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck
           -fobjc-std=objc1 -freplace-objc-classes -fzero-link -gen-decls
           -Wassign-intercept -Wno-protocol  -Wselector
           -Wstrict-selector-match -Wundeclared-selector

       Language Independent Options
           -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
           -fno-diagnostics-show-option -fno-diagnostics-show-caret

       Warning Options
           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors -w
           -Wextra  -Wall  -Waddress  -Waggregate-return
           -Waggressive-loop-optimizations -Warray-bounds -Wno-attributes
           -Wno-builtin-macro-redefined -Wc++-compat -Wc++11-compat
           -Wcast-align  -Wcast-qual -Wchar-subscripts -Wclobbered  -Wcomment
           -Wconversion  -Wcoverage-mismatch  -Wno-cpp  -Wno-deprecated
           -Wno-deprecated-declarations -Wdisabled-optimization
           -Wno-div-by-zero -Wdouble-promotion -Wempty-body  -Wenum-compare
           -Wno-endif-labels -Werror  -Werror=* -Wfatal-errors  -Wfloat-equal
           -Wformat  -Wformat=2 -Wno-format-contains-nul
           -Wno-format-extra-args -Wformat-nonliteral -Wformat-security
           -Wformat-y2k -Wframe-larger-than=len -Wno-free-nonheap-object
           -Wjump-misses-init -Wignored-qualifiers -Wimplicit
           -Wimplicit-function-declaration  -Wimplicit-int -Winit-self
           -Winline -Wmaybe-uninitialized -Wno-int-to-pointer-cast
           -Wno-invalid-offsetof -Winvalid-pch -Wlarger-than=len
           -Wunsafe-loop-optimizations -Wlogical-op -Wlong-long -Wmain
           -Wmaybe-uninitialized -Wmissing-braces
           -Wmissing-field-initializers -Wmissing-include-dirs -Wno-mudflap
           -Wno-multichar  -Wnonnull  -Wno-overflow -Woverlength-strings
           -Wpacked  -Wpacked-bitfield-compat  -Wpadded -Wparentheses
           -Wpedantic-ms-format -Wno-pedantic-ms-format -Wpointer-arith
           -Wno-pointer-to-int-cast -Wredundant-decls  -Wno-return-local-addr
           -Wreturn-type  -Wsequence-point  -Wshadow -Wsign-compare
           -Wsign-conversion  -Wsizeof-pointer-memaccess -Wstack-protector
           -Wstack-usage=len -Wstrict-aliasing -Wstrict-aliasing=n
           -Wstrict-overflow -Wstrict-overflow=n
           -Wsuggest-attribute=[pure|const|noreturn|format]
           -Wmissing-format-attribute -Wswitch  -Wswitch-default
           -Wswitch-enum -Wsync-nand -Wsystem-headers  -Wtrampolines
           -Wtrigraphs  -Wtype-limits  -Wundef -Wuninitialized
           -Wunknown-pragmas  -Wno-pragmas -Wunsuffixed-float-constants
           -Wunused  -Wunused-function -Wunused-label  -Wunused-local-typedefs
           -Wunused-parameter -Wno-unused-result -Wunused-value
           -Wunused-variable -Wunused-but-set-parameter
           -Wunused-but-set-variable -Wuseless-cast -Wvariadic-macros
           -Wvector-operation-performance -Wvla -Wvolatile-register-var
           -Wwrite-strings -Wzero-as-null-pointer-constant

       C and Objective-C-only Warning Options
           -Wbad-function-cast  -Wmissing-declarations
           -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
           -Wold-style-declaration  -Wold-style-definition -Wstrict-prototypes
           -Wtraditional  -Wtraditional-conversion
           -Wdeclaration-after-statement -Wpointer-sign

       Debugging Options
           -dletters  -dumpspecs  -dumpmachine  -dumpversion -fsanitize=style
           -fdbg-cnt-list -fdbg-cnt=counter-value-list -fdisable-ipa-pass_name
           -fdisable-rtl-pass_name -fdisable-rtl-pass-name=range-list
           -fdisable-tree-pass_name -fdisable-tree-pass-name=range-list
           -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links
           -fdump-translation-unit[-n] -fdump-class-hierarchy[-n]
           -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-passes
           -fdump-statistics -fdump-tree-all -fdump-tree-original[-n]
           -fdump-tree-optimized[-n] -fdump-tree-cfg -fdump-tree-alias
           -fdump-tree-ch -fdump-tree-ssa[-n] -fdump-tree-pre[-n]
           -fdump-tree-ccp[-n] -fdump-tree-dce[-n] -fdump-tree-gimple[-raw]
           -fdump-tree-mudflap[-n] -fdump-tree-dom[-n] -fdump-tree-dse[-n]
           -fdump-tree-phiprop[-n] -fdump-tree-phiopt[-n]
           -fdump-tree-forwprop[-n] -fdump-tree-copyrename[-n] -fdump-tree-nrv
           -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra[-n]
           -fdump-tree-forwprop[-n] -fdump-tree-fre[-n] -fdump-tree-vrp[-n]
           -ftree-vectorizer-verbose=n -fdump-tree-storeccp[-n]
           -fdump-final-insns=file -fcompare-debug[=opts]
           -fcompare-debug-second -feliminate-dwarf2-dups
           -fno-eliminate-unused-debug-types -feliminate-unused-debug-symbols
           -femit-class-debug-always -fenable-kind-pass
           -fenable-kind-pass=range-list -fdebug-types-section
           -fmem-report-wpa -fmem-report -fpre-ipa-mem-report
           -fpost-ipa-mem-report -fprofile-arcs -fopt-info
           -fopt-info-options[=file] -frandom-seed=string -fsched-verbose=n
           -fsel-sched-verbose -fsel-sched-dump-cfg
           -fsel-sched-pipelining-verbose -fstack-usage  -ftest-coverage
           -ftime-report -fvar-tracking -fvar-tracking-assignments
           -fvar-tracking-assignments-toggle -g  -glevel  -gtoggle  -gcoff
           -gdwarf-version -ggdb  -grecord-gcc-switches
           -gno-record-gcc-switches -gstabs  -gstabs+  -gstrict-dwarf
           -gno-strict-dwarf -gvms  -gxcoff  -gxcoff+ -fno-merge-debug-strings
           -fno-dwarf2-cfi-asm -fdebug-prefix-map=old=new
           -femit-struct-debug-baseonly -femit-struct-debug-reduced
           -femit-struct-debug-detailed[=spec-list] -p  -pg
           -print-file-name=library  -print-libgcc-file-name
           -print-multi-directory  -print-multi-lib  -print-multi-os-directory
           -print-prog-name=program  -print-search-dirs  -Q -print-sysroot
           -print-sysroot-headers-suffix -save-temps -save-temps=cwd
           -save-temps=obj -time[=file]

       Optimization Options
           -faggressive-loop-optimizations -falign-functions[=n]
           -falign-jumps[=n] -falign-labels[=n] -falign-loops[=n]
           -fassociative-math -fauto-inc-dec -fbranch-probabilities
           -fbranch-target-load-optimize -fbranch-target-load-optimize2
           -fbtr-bb-exclusive -fcaller-saves -fcheck-data-deps
           -fcombine-stack-adjustments -fconserve-stack -fcompare-elim
           -fcprop-registers -fcrossjumping -fcse-follow-jumps
           -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range
           -fdata-sections -fdce -fdelayed-branch -fdelete-null-pointer-checks
           -fdevirtualize -fdse -fearly-inlining -fipa-sra
           -fexpensive-optimizations -ffat-lto-objects -ffast-math
           -ffinite-math-only -ffloat-store -fexcess-precision=style
           -fforward-propagate -ffp-contract=style -ffunction-sections -fgcse
           -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity
           -fgcse-sm -fhoist-adjacent-loads -fif-conversion -fif-conversion2
           -findirect-inlining -finline-functions
           -finline-functions-called-once -finline-limit=n
           -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-pta
           -fipa-profile -fipa-pure-const -fipa-reference
           -fira-algorithm=algorithm -fira-region=region -fira-hoist-pressure
           -fira-loop-pressure -fno-ira-share-save-slots
           -fno-ira-share-spill-slots -fira-verbose=n -fivopts
           -fkeep-inline-functions -fkeep-static-consts -floop-block
           -floop-interchange -floop-strip-mine -floop-nest-optimize
           -floop-parallelize-all -flto -flto-compression-level
           -flto-partition=alg -flto-report -fmerge-all-constants
           -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves
           -fmove-loop-invariants fmudflap -fmudflapir -fmudflapth
           -fno-branch-count-reg -fno-default-inline -fno-defer-pop
           -fno-function-cse -fno-guess-branch-probability -fno-inline
           -fno-math-errno -fno-peephole -fno-peephole2 -fno-sched-interblock
           -fno-sched-spec -fno-signed-zeros -fno-toplevel-reorder
           -fno-trapping-math -fno-zero-initialized-in-bss
           -fomit-frame-pointer -foptimize-register-move
           -foptimize-sibling-calls -fpartial-inlining -fpeel-loops
           -fpredictive-commoning -fprefetch-loop-arrays -fprofile-report
           -fprofile-correction -fprofile-dir=path -fprofile-generate
           -fprofile-generate=path -fprofile-use -fprofile-use=path
           -fprofile-values -freciprocal-math -free -fregmove
           -frename-registers -freorder-blocks -freorder-blocks-and-partition
           -freorder-functions -frerun-cse-after-loop
           -freschedule-modulo-scheduled-loops -frounding-math
           -fsched2-use-superblocks -fsched-pressure -fsched-spec-load
           -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=n]
           -fsched-stalled-insns[=n] -fsched-group-heuristic
           -fsched-critical-path-heuristic -fsched-spec-insn-heuristic
           -fsched-rank-heuristic -fsched-last-insn-heuristic
           -fsched-dep-count-heuristic -fschedule-insns -fschedule-insns2
           -fsection-anchors -fselective-scheduling -fselective-scheduling2
           -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops
           -fshrink-wrap -fsignaling-nans -fsingle-precision-constant
           -fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector
           -fstack-protector-all -fstrict-aliasing -fstrict-overflow
           -fthread-jumps -ftracer -ftree-bit-ccp -ftree-builtin-call-dce
           -ftree-ccp -ftree-ch -ftree-coalesce-inline-vars
           -ftree-coalesce-vars -ftree-copy-prop -ftree-copyrename -ftree-dce
           -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre
           -ftree-loop-if-convert -ftree-loop-if-convert-stores -ftree-loop-im
           -ftree-phiprop -ftree-loop-distribution
           -ftree-loop-distribute-patterns -ftree-loop-ivcanon
           -ftree-loop-linear -ftree-loop-optimize -ftree-parallelize-loops=n
           -ftree-pre -ftree-partial-pre -ftree-pta -ftree-reassoc -ftree-sink
           -ftree-slsr -ftree-sra -ftree-switch-conversion -ftree-tail-merge
           -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp
           -funit-at-a-time -funroll-all-loops -funroll-loops
           -funsafe-loop-optimizations -funsafe-math-optimizations
           -funswitch-loops -fvariable-expansion-in-unroller -fvect-cost-model
           -fvpt -fweb -fwhole-program -fwpa -fuse-ld=linker
           -fuse-linker-plugin --param name=value -O  -O0  -O1  -O2  -O3  -Os
           -Ofast -Og

       Preprocessor Options
           -Aquestion=answer -A-question[=answer] -C  -dD  -dI  -dM  -dN
           -Dmacro[=defn]  -E  -H -idirafter dir -include file  -imacros file
           -iprefix file  -iwithprefix dir -iwithprefixbefore dir  -isystem
           dir -cxx-isystem dir -imultilib dir -isysroot dir -M  -MM  -MF  -MG
           -MP  -MQ  -MT  -nostdinc -P  -fdebug-cpp -ftrack-macro-expansion
           -fworking-directory -remap -trigraphs  -undef  -Umacro -Wp,option
           -Xpreprocessor option -no-integrated-cpp

       Assembler Option
           -Wa,option  -Xassembler option

       Linker Options
           object-file-name  -llibrary -nostartfiles  -nodefaultlibs
           -nostdlib -pie -rdynamic -s  -static -static-libgcc
           -static-libstdc++ -static-libasan -static-libtsan -shared
           -shared-libgcc  -symbolic -T script  -Wl,option  -Xlinker option -u
           symbol

       Directory Options
           -Bprefix  -Idir  -iquotedir -iremapsrc:dst  -Ldir -specs=file  -I-
           --sysroot=dir

       Target Options
           -V version  -b machine -Bprefix -Idir -iplugindir=dir -iquotedir
           -Ldir -specs=file -I- --sysroot=dir --no-sysroot-suffix

       Machine Dependent Options
           AArch64 Options -mbig-endian  -mlittle-endian -mgeneral-regs-only
           -mcmodel=tiny  -mcmodel=small  -mcmodel=large -mstrict-align
           -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
           -mtls-dialect=desc  -mtls-dialect=traditional -march=name
           -mcpu=name  -mtune=name

           Adapteva Epiphany Options -mhalf-reg-file -mprefer-short-insn-regs
           -mbranch-cost=num -mcmove -mnops=num -msoft-cmpsf -msplit-lohi
           -mpost-inc -mpost-modify -mstack-offset=num -mround-nearest
           -mlong-calls -mshort-calls -msmall16 -mfp-mode=mode -mvect-double
           -max-vect-align=num -msplit-vecmove-early -m1reg-reg

           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name
           -mapcs-stack-check  -mno-apcs-stack-check -mapcs-float
           -mno-apcs-float -mapcs-reentrant  -mno-apcs-reentrant
           -msched-prolog  -mno-sched-prolog -mlittle-endian  -mbig-endian
           -mwords-little-endian -mfloat-abi=name -mfp16-format=name
           -mthumb-interwork  -mno-thumb-interwork -mcpu=name  -march=name
           -mfpu=name -mstructure-size-boundary=n -mabort-on-noreturn
           -mlong-calls  -mno-long-calls -msingle-pic-base
           -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport
           -mpoke-function-name -mthumb  -marm -mtpcs-frame  -mtpcs-leaf-frame
           -mcaller-super-interworking  -mcallee-super-interworking -mtp=name
           -mtls-dialect=dialect -mword-relocations -mfix-cortex-m3-ldrd
           -munaligned-access

           AVR Options -mmcu=mcu -maccumulate-args -mbranch-cost=cost
           -mcall-prologues -mint8 -mno-interrupts -mrelax -mstrict-X
           -mtiny-stack -Waddr-space-convert

           Blackfin Options -mcpu=cpu[-sirevision] -msim
           -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
           -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly
           -mno-csync-anomaly -mlow-64k -mno-low64k  -mstack-check-l1
           -mid-shared-library -mno-id-shared-library  -mshared-library-id=n
           -mleaf-id-shared-library  -mno-leaf-id-shared-library -msep-data
           -mno-sep-data  -mlong-calls  -mno-long-calls -mfast-fp -minline-plt
           -mmulticore  -mcorea  -mcoreb  -msdram -micplb

           C6X Options -mbig-endian  -mlittle-endian -march=cpu -msim
           -msdata=sdata-type

           CRIS Options -mcpu=cpu  -march=cpu  -mtune=cpu -mmax-stack-frame=n
           -melinux-stacksize=n -metrax4  -metrax100  -mpdebug  -mcc-init
           -mno-side-effects -mstack-align  -mdata-align  -mconst-align
           -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue  -mno-gotplt
           -melf  -maout  -melinux  -mlinux  -sim  -sim2 -mmul-bug-workaround
           -mno-mul-bug-workaround

           CR16 Options -mmac -mcr16cplus -mcr16c -msim -mint32 -mbit-ops
           -mdata-model=model

           Darwin Options -all_load  -allowable_client  -arch
           -arch_errors_fatal -arch_only  -bind_at_load  -bundle
           -bundle_loader -client_name  -compatibility_version
           -current_version -dead_strip -dependency-file  -dylib_file
           -dylinker_install_name -dynamic  -dynamiclib
           -exported_symbols_list -filelist  -flat_namespace
           -force_cpusubtype_ALL -force_flat_namespace
           -headerpad_max_install_names -iframework -image_base  -init
           -install_name  -keep_private_externs -multi_module
           -multiply_defined  -multiply_defined_unused -noall_load
           -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs
           -noprebind  -noseglinkedit -pagezero_size  -prebind
           -prebind_all_twolevel_modules -private_bundle  -read_only_relocs
           -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate
           -sectobjectsymbols  -sectorder -segaddr -segs_read_only_addr
           -segs_read_write_addr -seg_addr_table  -seg_addr_table_filename
           -seglinkedit -segprot  -segs_read_only_addr  -segs_read_write_addr
           -single_module  -static  -sub_library  -sub_umbrella
           -twolevel_namespace  -umbrella  -undefined -unexported_symbols_list
           -weak_reference_mismatches -whatsloaded -F -gused -gfull
           -mmacosx-version-min=version -mkernel -mone-byte-bool

           DEC Alpha Options -mno-fp-regs  -msoft-float -mieee
           -mieee-with-inexact  -mieee-conformant -mfp-trap-mode=mode
           -mfp-rounding-mode=mode -mtrap-precision=mode  -mbuild-constants
           -mcpu=cpu-type  -mtune=cpu-type -mbwx  -mmax  -mfix  -mcix
           -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data
           -mlarge-data -msmall-text  -mlarge-text -mmemory-latency=time

           FR30 Options -msmall-model -mno-lsim

           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float
           -msoft-float -malloc-cc  -mfixed-cc  -mdword  -mno-dword -mdouble
           -mno-double -mmedia  -mno-media  -mmuladd  -mno-muladd -mfdpic
           -minline-plt -mgprel-ro  -multilib-library-pic -mlinked-fp
           -mlong-calls  -malign-labels -mlibrary-pic  -macc-4  -macc-8 -mpack
           -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
           -moptimize-membar -mno-optimize-membar -mscc  -mno-scc  -mcond-exec
           -mno-cond-exec -mvliw-branch  -mno-vliw-branch -mmulti-cond-exec
           -mno-multi-cond-exec  -mnested-cond-exec -mno-nested-cond-exec
           -mtomcat-stats -mTLS -mtls -mcpu=cpu

           GNU/Linux Options -mglibc -muclibc -mbionic -mandroid
           -tno-android-cc -tno-android-ld

           H8/300 Options -mrelax  -mh  -ms  -mn  -mexr -mno-exr  -mint32
           -malign-300

           HPPA Options -march=architecture-type -mbig-switch
           -mdisable-fpregs  -mdisable-indexing -mfast-indirect-calls  -mgas
           -mgnu-ld   -mhp-ld -mfixed-range=register-range -mjump-in-delay
           -mlinker-opt -mlong-calls -mlong-load-store  -mno-big-switch
           -mno-disable-fpregs -mno-disable-indexing  -mno-fast-indirect-calls
           -mno-gas -mno-jump-in-delay  -mno-long-load-store
           -mno-portable-runtime  -mno-soft-float -mno-space-regs
           -msoft-float  -mpa-risc-1-0 -mpa-risc-1-1  -mpa-risc-2-0
           -mportable-runtime -mschedule=cpu-type  -mspace-regs  -msio  -mwsio
           -munix=unix-std  -nolibdld  -static  -threads

           i386 and x86-64 Options -mtune=cpu-type  -march=cpu-type
           -mfpmath=unit -masm=dialect  -mno-fancy-math-387 -mno-fp-ret-in-387
           -msoft-float -mno-wide-multiply  -mrtd  -malign-double
           -mpreferred-stack-boundary=num -mincoming-stack-boundary=num -mcld
           -mcx16 -msahf -mmovbe -mcrc32 -mrecip -mrecip=opt -mvzeroupper
           -mprefer-avx128 -mmmx  -msse  -msse2 -msse3 -mssse3 -msse4.1
           -msse4.2 -msse4 -mavx -mavx2 -maes -mpclmul -mfsgsbase -mrdrnd
           -mf16c -mfma -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4
           -mxop -mlzcnt -mbmi2 -mrtm -mlwp -mthreads -mno-align-stringops
           -minline-all-stringops -minline-stringops-dynamically
           -mstringop-strategy=alg -mpush-args  -maccumulate-outgoing-args
           -m128bit-long-double -m96bit-long-double -mlong-double-64
           -mlong-double-80 -mregparm=num  -msseregparm -mveclibabi=type
           -mvect8-ret-in-mem -mpc32 -mpc64 -mpc80 -mstackrealign
           -momit-leaf-frame-pointer  -mno-red-zone -mno-tls-direct-seg-refs
           -mcmodel=code-model -mabi=name -maddress-mode=mode -m32 -m64 -mx32
           -mlarge-data-threshold=num -msse2avx -mfentry -m8bit-idiv
           -mavx256-split-unaligned-load -mavx256-split-unaligned-store

           i386 and x86-64 Windows Options -mconsole -mcygwin -mno-cygwin
           -mdll -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows
           -fno-set-stack-executable

           IA-64 Options -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld
           -mno-pic -mvolatile-asm-stop  -mregister-names  -msdata -mno-sdata
           -mconstant-gp  -mauto-pic  -mfused-madd
           -minline-float-divide-min-latency
           -minline-float-divide-max-throughput -mno-inline-float-divide
           -minline-int-divide-min-latency -minline-int-divide-max-throughput
           -mno-inline-int-divide -minline-sqrt-min-latency
           -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm
           -mearly-stop-bits -mfixed-range=register-range -mtls-size=tls-size
           -mtune=cpu-type -milp32 -mlp64 -msched-br-data-spec
           -msched-ar-data-spec -msched-control-spec -msched-br-in-data-spec
           -msched-ar-in-data-spec -msched-in-control-spec -msched-spec-ldc
           -msched-spec-control-ldc -msched-prefer-non-data-spec-insns
           -msched-prefer-non-control-spec-insns
           -msched-stop-bits-after-every-cycle
           -msched-count-spec-in-critical-path
           -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost
           -msched-max-memory-insns-hard-limit -msched-max-memory-insns=max-
           insns

           LM32 Options -mbarrel-shift-enabled -mdivide-enabled
           -mmultiply-enabled -msign-extend-enabled -muser-enabled

           M32R/D Options -m32r2 -m32rx -m32r -mdebug -malign-loops
           -mno-align-loops -missue-rate=number -mbranch-cost=number
           -mmodel=code-size-model-type -msdata=sdata-type -mno-flush-func
           -mflush-func=name -mno-flush-trap -mflush-trap=number -G num

           M32C Options -mcpu=cpu -msim -memregs=number

           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020
           -m68020-40  -m68020-60  -m68030  -m68040 -m68060  -mcpu32  -m5200
           -m5206e  -m528x  -m5307  -m5407 -mcfv4e  -mbitfield  -mno-bitfield
           -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div
           -mshort -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
           -malign-int  -mstrict-align  -msep-data  -mno-sep-data
           -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
           -mxgot -mno-xgot

           MCore Options -mhardlit  -mno-hardlit  -mdiv  -mno-div
           -mrelax-immediates -mno-relax-immediates  -mwide-bitfields
           -mno-wide-bitfields -m4byte-functions  -mno-4byte-functions
           -mcallgraph-data -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes
           -mno-lsim -mlittle-endian  -mbig-endian  -m210  -m340
           -mstack-increment

           MeP Options -mabsdiff -mall-opts -maverage -mbased=n -mbitops -mc=n
           -mclip -mconfig=name -mcop -mcop32 -mcop64 -mivc2 -mdc -mdiv -meb
           -mel -mio-volatile -ml -mleadz -mm -mminmax -mmult -mno-opts
           -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf -mtiny=n

           MicroBlaze Options -msoft-float -mhard-float -msmall-divides
           -mcpu=cpu -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift
           -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss
           -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt -mbig-endian
           -mlittle-endian -mxl-reorder -mxl-mode-app-model

           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2
           -mips3  -mips4  -mips32  -mips32r2 -mips64  -mips64r2 -mips16
           -mno-mips16  -mflip-mips16 -minterlink-mips16
           -mno-interlink-mips16 -mabi=abi  -mabicalls  -mno-abicalls -mshared
           -mno-shared  -mplt  -mno-plt  -mxgot  -mno-xgot -mgp32  -mgp64
           -mfp32  -mfp64  -mhard-float  -msoft-float -mno-float
           -msingle-float  -mdouble-float -mdsp  -mno-dsp  -mdspr2  -mno-dspr2
           -mmcu -mmno-mcu -mfpu=fpu-type -msmartmips  -mno-smartmips
           -mpaired-single  -mno-paired-single  -mdmx  -mno-mdmx -mips3d
           -mno-mips3d  -mmt  -mno-mt  -mllsc  -mno-llsc -mlong64  -mlong32
           -msym32  -mno-sym32 -Gnum  -mlocal-sdata  -mno-local-sdata
           -mextern-sdata  -mno-extern-sdata  -mgpopt  -mno-gopt
           -membedded-data  -mno-embedded-data -muninit-const-in-rodata
           -mno-uninit-const-in-rodata -mcode-readable=setting
           -msplit-addresses  -mno-split-addresses -mexplicit-relocs
           -mno-explicit-relocs -mcheck-zero-division
           -mno-check-zero-division -mdivide-traps  -mdivide-breaks -mmemcpy
           -mno-memcpy  -mlong-calls  -mno-long-calls -mmad  -mno-mad
           -mfused-madd  -mno-fused-madd  -nocpp -mfix-24k -mno-fix-24k
           -mfix-r4000  -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400
           -mfix-r10000 -mno-fix-r10000  -mfix-vr4120  -mno-fix-vr4120
           -mfix-vr4130  -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1
           -mflush-func=func  -mno-flush-func -mbranch-cost=num
           -mbranch-likely  -mno-branch-likely -mfp-exceptions
           -mno-fp-exceptions -mvr4130-align -mno-vr4130-align -msynci
           -mno-synci -mrelax-pic-calls -mno-relax-pic-calls
           -mmcount-ra-address

           MMIX Options -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon
           -mabi=gnu -mabi=mmixware  -mzero-extend  -mknuthdiv
           -mtoplevel-symbols -melf  -mbranch-predict  -mno-branch-predict
           -mbase-addresses -mno-base-addresses  -msingle-exit
           -mno-single-exit

           MN10300 Options -mmult-bug  -mno-mult-bug -mno-am33 -mam33 -mam33-2
           -mam34 -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0  -mrelax
           -mliw -msetlb

           Moxie Options -meb -mel -mno-crt0

           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45
           -m10 -mbcopy  -mbcopy-builtin  -mint32  -mno-int16 -mint16
           -mno-int32  -mfloat32  -mno-float64 -mfloat64  -mno-float32
           -mabshi  -mno-abshi -mbranch-expensive  -mbranch-cheap -munix-asm
           -mdec-asm

           picoChip Options -mae=ae_type -mvliw-lookahead=N
           -msymbol-as-address -mno-inefficient-warnings

           PowerPC Options See RS/6000 and PowerPC Options.

           RL78 Options -msim -mmul=none -mmul=g13 -mmul=rl78

           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type
           -mcmodel=code-model -mpowerpc64 -maltivec  -mno-altivec
           -mpowerpc-gpopt  -mno-powerpc-gpopt -mpowerpc-gfxopt
           -mno-powerpc-gfxopt -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb
           -mpopcntd -mno-popcntd -mfprnd  -mno-fprnd -mcmpb -mno-cmpb
           -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp -mfull-toc
           -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc -m64  -m32
           -mxl-compat  -mno-xl-compat  -mpe -malign-power  -malign-natural
           -msoft-float  -mhard-float  -mmultiple  -mno-multiple
           -msingle-float -mdouble-float -msimple-fpu -mstring  -mno-string
           -mupdate  -mno-update -mavoid-indexed-addresses
           -mno-avoid-indexed-addresses -mfused-madd  -mno-fused-madd
           -mbit-align  -mno-bit-align -mstrict-align  -mno-strict-align
           -mrelocatable -mno-relocatable  -mrelocatable-lib
           -mno-relocatable-lib -mtoc  -mno-toc  -mlittle  -mlittle-endian
           -mbig  -mbig-endian -mdynamic-no-pic  -maltivec -mswdiv
           -msingle-pic-base -mprioritize-restricted-insns=priority
           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme
           -mcall-sysv  -mcall-netbsd -maix-struct-return
           -msvr4-struct-return -mabi=abi-type -msecure-plt -mbss-plt
           -mblock-move-inline-limit=num -misel -mno-isel -misel=yes
           -misel=no -mspe -mno-spe -mspe=yes  -mspe=no -mpaired
           -mgen-cell-microcode -mwarn-cell-microcode -mvrsave -mno-vrsave
           -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mfloat-gprs=yes
           -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double -mprototype
           -mno-prototype -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
           -msdata=opt  -mvxworks  -G num  -pthread -mrecip -mrecip=opt
           -mno-recip -mrecip-precision -mno-recip-precision -mveclibabi=type
           -mfriz -mno-friz -mpointers-to-nested-functions
           -mno-pointers-to-nested-functions -msave-toc-indirect
           -mno-save-toc-indirect

           RX Options -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu -mcpu=
           -mbig-endian-data -mlittle-endian-data -msmall-data -msim  -mno-sim
           -mas100-syntax -mno-as100-syntax -mrelax -mmax-constant-size=
           -mint-register= -mpid -mno-warn-multiple-fast-interrupts
           -msave-acc-in-interrupts

           S/390 and zSeries Options -mtune=cpu-type  -march=cpu-type
           -mhard-float  -msoft-float  -mhard-dfp -mno-hard-dfp
           -mlong-double-64 -mlong-double-128 -mbackchain  -mno-backchain
           -mpacked-stack  -mno-packed-stack -msmall-exec  -mno-small-exec
           -mmvcle -mno-mvcle -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
           -mtpf-trace -mno-tpf-trace  -mfused-madd  -mno-fused-madd
           -mwarn-framesize  -mwarn-dynamicstack  -mstack-size -mstack-guard
           -mhotpatch[=halfwords] -mno-hotpatch

           Score Options -meb -mel -mnhwloop -muls -mmac -mscore5 -mscore5u
           -mscore7 -mscore7d

           SH Options -m1  -m2  -m2e -m2a-nofpu -m2a-single-only -m2a-single
           -m2a -m3  -m3e -m4-nofpu  -m4-single-only  -m4-single  -m4
           -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -m5-64media
           -m5-64media-nofpu -m5-32media  -m5-32media-nofpu -m5-compact
           -m5-compact-nofpu -mb  -ml  -mdalign  -mrelax -mbigtable -mfmovd
           -mhitachi -mrenesas -mno-renesas -mnomacsave -mieee -mno-ieee
           -mbitops  -misize  -minline-ic_invalidate -mpadstruct -mspace
           -mprefergot  -musermode -multcost=number -mdiv=strategy
           -mdivsi3_libfunc=name -mfixed-range=register-range
           -mindexed-addressing -mgettrcost=number -mpt-fixed
           -maccumulate-outgoing-args -minvalid-symbols -matomic-model=atomic-
           model -mbranch-cost=num -mzdcbranch -mno-zdcbranch -mcbranchdi
           -mcmpeqdi -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra
           -mno-fsrra -mpretend-cmove -mtas

           Solaris 2 Options -mimpure-text  -mno-impure-text -pthreads
           -pthread

           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model
           -mmemory-model=mem-model -m32  -m64  -mapp-regs  -mno-app-regs
           -mfaster-structs  -mno-faster-structs  -mflat  -mno-flat -mfpu
           -mno-fpu  -mhard-float  -msoft-float -mhard-quad-float
           -msoft-quad-float -mstack-bias  -mno-stack-bias -munaligned-doubles
           -mno-unaligned-doubles -mv8plus  -mno-v8plus  -mvis  -mno-vis
           -mvis2  -mno-vis2  -mvis3  -mno-vis3 -mcbcond -mno-cbcond -mfmaf
           -mno-fmaf  -mpopc  -mno-popc -mfix-at697f -mfix-ut699

           SPU Options -mwarn-reloc -merror-reloc -msafe-dma -munsafe-dma
           -mbranch-hints -msmall-mem -mlarge-mem -mstdmain
           -mfixed-range=register-range -mea32 -mea64
           -maddress-space-conversion -mno-address-space-conversion
           -mcache-size=cache-size -matomic-updates -mno-atomic-updates

           System V Options -Qy  -Qn  -YP,paths  -Ym,dir

           TILE-Gx Options -mcpu=cpu -m32 -m64 -mcmodel=code-model

           TILEPro Options -mcpu=cpu -m32

           V850 Options -mlong-calls  -mno-long-calls  -mep  -mno-ep
           -mprolog-function  -mno-prolog-function  -mspace -mtda=n  -msda=n
           -mzda=n -mapp-regs  -mno-app-regs -mdisable-callt
           -mno-disable-callt -mv850e2v3 -mv850e2 -mv850e1 -mv850es -mv850e
           -mv850 -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float
           -mhard-float -mgcc-abi -mrh850-abi -mbig-switch

           VAX Options -mg  -mgnu  -munix

           VMS Options -mvms-return-codes -mdebug-main=prefix -mmalloc64
           -mpointer-size=size

           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy
           -Xbind-now

           x86-64 Options See i386 and x86-64 Options.

           Xstormy16 Options -msim

           Xtensa Options -mconst16 -mno-const16 -mfused-madd  -mno-fused-madd
           -mforce-no-pic -mserialize-volatile  -mno-serialize-volatile
           -mtext-section-literals  -mno-text-section-literals -mtarget-align
           -mno-target-align -mlongcalls  -mno-longcalls

           zSeries Options See S/390 and zSeries Options.

       Code Generation Options
           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions
           -fnon-call-exceptions  -fdelete-dead-exceptions  -funwind-tables
           -fasynchronous-unwind-tables -finhibit-size-directive
           -finstrument-functions
           -finstrument-functions-exclude-function-list=sym,sym,...
           -finstrument-functions-exclude-file-list=file,file,...  -fno-common
           -fno-ident -fpcc-struct-return  -fpic  -fPIC -fpie -fPIE
           -fno-jump-tables -frecord-gcc-switches -freg-struct-return
           -fshort-enums -fshort-double  -fshort-wchar -fverbose-asm
           -fpack-struct[=n]  -fstack-check -fstack-limit-register=reg
           -fstack-limit-symbol=sym -fno-stack-limit -fsplit-stack
           -fleading-underscore  -ftls-model=model -fstack-reuse=reuse_level
           -ftrapv  -fwrapv  -fbounds-check -fvisibility
           -fstrict-volatile-bitfields -fsync-libcalls

   Options Controlling the Kind of Output
       Compilation can involve up to four stages: preprocessing, compilation
       proper, assembly and linking, always in that order.  GCC is capable of
       preprocessing and compiling several files either into several assembler
       input files, or into one assembler input file; then each assembler
       input file produces an object file, and linking combines all the object
       files (those newly compiled, and those specified as input) into an
       executable file.

       For any given input file, the file name suffix determines what kind of
       compilation is done:

       file.c
           C source code that must be preprocessed.

       file.i
           C source code that should not be preprocessed.

       file.ii
           C++ source code that should not be preprocessed.

       file.m
           Objective-C source code.  Note that you must link with the libobjc
           library to make an Objective-C program work.

       file.mi
           Objective-C source code that should not be preprocessed.

       file.mm
       file.M
           Objective-C++ source code.  Note that you must link with the
           libobjc library to make an Objective-C++ program work.  Note that
           .M refers to a literal capital M.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.h
           C, C++, Objective-C or Objective-C++ header file to be turned into
           a precompiled header (default), or C, C++ header file to be turned
           into an Ada spec (via the -fdump-ada-spec switch).

       file.cc
       file.cp
       file.cxx
       file.cpp
       file.CPP
       file.c++
       file.C
           C++ source code that must be preprocessed.  Note that in .cxx, the
           last two letters must both be literally x.  Likewise, .C refers to
           a literal capital C.

       file.mm
       file.M
           Objective-C++ source code that must be preprocessed.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.hh
       file.H
       file.hp
       file.hxx
       file.hpp
       file.HPP
       file.h++
       file.tcc
           C++ header file to be turned into a precompiled header or Ada spec.

       file.f
       file.for
       file.ftn
           Fixed form Fortran source code that should not be preprocessed.

       file.F
       file.FOR
       file.fpp
       file.FPP
       file.FTN
           Fixed form Fortran source code that must be preprocessed (with the
           traditional preprocessor).

       file.f90
       file.f95
       file.f03
       file.f08
           Free form Fortran source code that should not be preprocessed.

       file.F90
       file.F95
       file.F03
       file.F08
           Free form Fortran source code that must be preprocessed (with the
           traditional preprocessor).

       file.go
           Go source code.

       file.ads
           Ada source code file that contains a library unit declaration (a
           declaration of a package, subprogram, or generic, or a generic
           instantiation), or a library unit renaming declaration (a package,
           generic, or subprogram renaming declaration).  Such files are also
           called specs.

       file.adb
           Ada source code file containing a library unit body (a subprogram
           or package body).  Such files are also called bodies.

       file.s
           Assembler code.

       file.S
       file.sx
           Assembler code that must be preprocessed.

       other
           An object file to be fed straight into linking.  Any file name with
           no recognized suffix is treated this way.

       You can specify the input language explicitly with the -x option:

       -x language
           Specify explicitly the language for the following input files
           (rather than letting the compiler choose a default based on the
           file name suffix).  This option applies to all following input
           files until the next -x option.  Possible values for language are:

                   c  c-header  cpp-output
                   c++  c++-header  c++-cpp-output
                   objective-c  objective-c-header  objective-c-cpp-output
                   objective-c++ objective-c++-header objective-c++-cpp-output
                   assembler  assembler-with-cpp
                   ada
                   f77  f77-cpp-input f95  f95-cpp-input
                   go
                   java

       -x none
           Turn off any specification of a language, so that subsequent files
           are handled according to their file name suffixes (as they are if
           -x has not been used at all).

       -pass-exit-codes
           Normally the gcc program exits with the code of 1 if any phase of
           the compiler returns a non-success return code.  If you specify
           -pass-exit-codes, the gcc program instead returns with the
           numerically highest error produced by any phase returning an error
           indication.  The C, C++, and Fortran front ends return 4 if an
           internal compiler error is encountered.

       If you only want some of the stages of compilation, you can use -x (or
       filename suffixes) to tell gcc where to start, and one of the options
       -c, -S, or -E to say where gcc is to stop.  Note that some combinations
       (for example, -x cpp-output -E) instruct gcc to do nothing at all.

       -c  Compile or assemble the source files, but do not link.  The linking
           stage simply is not done.  The ultimate output is in the form of an
           object file for each source file.

           By default, the object file name for a source file is made by
           replacing the suffix .c, .i, .s, etc., with .o.

           Unrecognized input files, not requiring compilation or assembly,
           are ignored.

       -S  Stop after the stage of compilation proper; do not assemble.  The
           output is in the form of an assembler code file for each non-
           assembler input file specified.

           By default, the assembler file name for a source file is made by
           replacing the suffix .c, .i, etc., with .s.

           Input files that don't require compilation are ignored.

       -E  Stop after the preprocessing stage; do not run the compiler proper.
           The output is in the form of preprocessed source code, which is
           sent to the standard output.

           Input files that don't require preprocessing are ignored.

       -o file
           Place output in file file.  This applies to whatever sort of output
           is being produced, whether it be an executable file, an object
           file, an assembler file or preprocessed C code.

           If -o is not specified, the default is to put an executable file in
           a.out, the object file for source.suffix in source.o, its assembler
           file in source.s, a precompiled header file in source.suffix.gch,
           and all preprocessed C source on standard output.

       -v  Print (on standard error output) the commands executed to run the
           stages of compilation.  Also print the version number of the
           compiler driver program and of the preprocessor and the compiler
           proper.

       -###
           Like -v except the commands are not executed and arguments are
           quoted unless they contain only alphanumeric characters or "./-_".
           This is useful for shell scripts to capture the driver-generated
           command lines.

       -pipe
           Use pipes rather than temporary files for communication between the
           various stages of compilation.  This fails to work on some systems
           where the assembler is unable to read from a pipe; but the GNU
           assembler has no trouble.

       --help
           Print (on the standard output) a description of the command-line
           options understood by gcc.  If the -v option is also specified then
           --help is also passed on to the various processes invoked by gcc,
           so that they can display the command-line options they accept.  If
           the -Wextra option has also been specified (prior to the --help
           option), then command-line options that have no documentation
           associated with them are also displayed.

       --target-help
           Print (on the standard output) a description of target-specific
           command-line options for each tool.  For some targets extra target-
           specific information may also be printed.

       --help={class|[^]qualifier}[,...]
           Print (on the standard output) a description of the command-line
           options understood by the compiler that fit into all specified
           classes and qualifiers.  These are the supported classes:

           optimizers
               Display all of the optimization options supported by the
               compiler.

           warnings
               Display all of the options controlling warning messages
               produced by the compiler.

           target
               Display target-specific options.  Unlike the --target-help
               option however, target-specific options of the linker and
               assembler are not displayed.  This is because those tools do
               not currently support the extended --help= syntax.

           params
               Display the values recognized by the --param option.

           language
               Display the options supported for language, where language is
               the name of one of the languages supported in this version of
               GCC.

           common
               Display the options that are common to all languages.

           These are the supported qualifiers:

           undocumented
               Display only those options that are undocumented.

           joined
               Display options taking an argument that appears after an equal
               sign in the same continuous piece of text, such as:
               --help=target.

           separate
               Display options taking an argument that appears as a separate
               word following the original option, such as: -o output-file.

           Thus for example to display all the undocumented target-specific
           switches supported by the compiler, use:

                   --help=target,undocumented

           The sense of a qualifier can be inverted by prefixing it with the ^
           character, so for example to display all binary warning options
           (i.e., ones that are either on or off and that do not take an
           argument) that have a description, use:

                   --help=warnings,^joined,^undocumented

           The argument to --help= should not consist solely of inverted
           qualifiers.

           Combining several classes is possible, although this usually
           restricts the output so much that there is nothing to display.  One
           case where it does work, however, is when one of the classes is
           target.  For example, to display all the target-specific
           optimization options, use:

                   --help=target,optimizers

           The --help= option can be repeated on the command line.  Each
           successive use displays its requested class of options, skipping
           those that have already been displayed.

           If the -Q option appears on the command line before the --help=
           option, then the descriptive text displayed by --help= is changed.
           Instead of describing the displayed options, an indication is given
           as to whether the option is enabled, disabled or set to a specific
           value (assuming that the compiler knows this at the point where the
           --help= option is used).

           Here is a truncated example from the ARM port of gcc:

                     % gcc -Q -mabi=2 --help=target -c
                     The following options are target specific:
                     -mabi=                                2
                     -mabort-on-noreturn                   [disabled]
                     -mapcs                                [disabled]

           The output is sensitive to the effects of previous command-line
           options, so for example it is possible to find out which
           optimizations are enabled at -O2 by using:

                   -Q -O2 --help=optimizers

           Alternatively you can discover which binary optimizations are
           enabled by -O3 by using:

                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled

       -no-canonical-prefixes
           Do not expand any symbolic links, resolve references to /../ or
           /./, or make the path absolute when generating a relative prefix.

       --version
           Display the version number and copyrights of the invoked GCC.

       -wrapper
           Invoke all subcommands under a wrapper program.  The name of the
           wrapper program and its parameters are passed as a comma separated
           list.

                   gcc -c t.c -wrapper gdb,--args

           This invokes all subprograms of gcc under gdb --args, thus the
           invocation of cc1 is gdb --args cc1 ....

       -fplugin=name.so
           Load the plugin code in file name.so, assumed to be a shared object
           to be dlopen'd by the compiler.  The base name of the shared object
           file is used to identify the plugin for the purposes of argument
           parsing (See -fplugin-arg-name-key=value below).  Each plugin
           should define the callback functions specified in the Plugins API.

       -fplugin-arg-name-key=value
           Define an argument called key with a value of value for the plugin
           called name.

       -fdump-ada-spec[-slim]
           For C and C++ source and include files, generate corresponding Ada
           specs.

       -fada-spec-parent=unit
           In conjunction with -fdump-ada-spec[-slim] above, generate Ada
           specs as child units of parent unit.

       -fdump-go-spec=file
           For input files in any language, generate corresponding Go
           declarations in file.  This generates Go "const", "type", "var",
           and "func" declarations which may be a useful way to start writing
           a Go interface to code written in some other language.

       @file
           Read command-line options from file.  The options read are inserted
           in place of the original @file option.  If file does not exist, or
           cannot be read, then the option will be treated literally, and not
           removed.

           Options in file are separated by whitespace.  A whitespace
           character may be included in an option by surrounding the entire
           option in either single or double quotes.  Any character (including
           a backslash) may be included by prefixing the character to be
           included with a backslash.  The file may itself contain additional
           @file options; any such options will be processed recursively.

   Compiling C++ Programs
       C++ source files conventionally use one of the suffixes .C, .cc, .cpp,
       .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or
       (for shared template code) .tcc; and preprocessed C++ files use the
       suffix .ii.  GCC recognizes files with these names and compiles them as
       C++ programs even if you call the compiler the same way as for
       compiling C programs (usually with the name gcc).

       However, the use of gcc does not add the C++ library.  g++ is a program
       that calls GCC and automatically specifies linking against the C++
       library.  It treats .c, .h and .i files as C++ source files instead of
       C source files unless -x is used.  This program is also useful when
       precompiling a C header file with a .h extension for use in C++
       compilations.  On many systems, g++ is also installed with the name
       c++.

       When you compile C++ programs, you may specify many of the same
       command-line options that you use for compiling programs in any
       language; or command-line options meaningful for C and related
       languages; or options that are meaningful only for C++ programs.

   Options Controlling C Dialect
       The following options control the dialect of C (or languages derived
       from C, such as C++, Objective-C and Objective-C++) that the compiler
       accepts:

       -ansi
           In C mode, this is equivalent to -std=c90. In C++ mode, it is
           equivalent to -std=c++98.

           This turns off certain features of GCC that are incompatible with
           ISO C90 (when compiling C code), or of standard C++ (when compiling
           C++ code), such as the "asm" and "typeof" keywords, and predefined
           macros such as "unix" and "vax" that identify the type of system
           you are using.  It also enables the undesirable and rarely used ISO
           trigraph feature.  For the C compiler, it disables recognition of
           C++ style // comments as well as the "inline" keyword.

           The alternate keywords "__asm__", "__extension__", "__inline__" and
           "__typeof__" continue to work despite -ansi.  You would not want to
           use them in an ISO C program, of course, but it is useful to put
           them in header files that might be included in compilations done
           with -ansi.  Alternate predefined macros such as "__unix__" and
           "__vax__" are also available, with or without -ansi.

           The -ansi option does not cause non-ISO programs to be rejected
           gratuitously.  For that, -Wpedantic is required in addition to
           -ansi.

           The macro "__STRICT_ANSI__" is predefined when the -ansi option is
           used.  Some header files may notice this macro and refrain from
           declaring certain functions or defining certain macros that the ISO
           standard doesn't call for; this is to avoid interfering with any
           programs that might use these names for other things.

           Functions that are normally built in but do not have semantics
           defined by ISO C (such as "alloca" and "ffs") are not built-in
           functions when -ansi is used.

       -std=
           Determine the language standard.   This option is currently only
           supported when compiling C or C++.

           The compiler can accept several base standards, such as c90 or
           c++98, and GNU dialects of those standards, such as gnu90 or
           gnu++98.  When a base standard is specified, the compiler accepts
           all programs following that standard plus those using GNU
           extensions that do not contradict it.  For example, -std=c90 turns
           off certain features of GCC that are incompatible with ISO C90,
           such as the "asm" and "typeof" keywords, but not other GNU
           extensions that do not have a meaning in ISO C90, such as omitting
           the middle term of a "?:" expression. On the other hand, when a GNU
           dialect of a standard is specified, all features supported by the
           compiler are enabled, even when those features change the meaning
           of the base standard.  As a result, some strict-conforming programs
           may be rejected.  The particular standard is used by -Wpedantic to
           identify which features are GNU extensions given that version of
           the standard. For example -std=gnu90 -Wpedantic warns about C++
           style // comments, while -std=gnu99 -Wpedantic does not.

           A value for this option must be provided; possible values are

           c90
           c89
           iso9899:1990
               Support all ISO C90 programs (certain GNU extensions that
               conflict with ISO C90 are disabled). Same as -ansi for C code.

           iso9899:199409
               ISO C90 as modified in amendment 1.

           c99
           c9x
           iso9899:1999
           iso9899:199x
               ISO C99.  Note that this standard is not yet fully supported;
               see <http://gcc.gnu.org/c99status.html> for more information.
               The names c9x and iso9899:199x are deprecated.

           c11
           c1x
           iso9899:2011
               ISO C11, the 2011 revision of the ISO C standard.  Support is
               incomplete and experimental.  The name c1x is deprecated.

           gnu90
           gnu89
               GNU dialect of ISO C90 (including some C99 features). This is
               the default for C code.

           gnu99
           gnu9x
               GNU dialect of ISO C99.  When ISO C99 is fully implemented in
               GCC, this will become the default.  The name gnu9x is
               deprecated.

           gnu11
           gnu1x
               GNU dialect of ISO C11.  Support is incomplete and
               experimental.  The name gnu1x is deprecated.

           c++98
           c++03
               The 1998 ISO C++ standard plus the 2003 technical corrigendum
               and some additional defect reports. Same as -ansi for C++ code.

           gnu++98
           gnu++03
               GNU dialect of -std=c++98.  This is the default for C++ code.

           c++11
           c++0x
               The 2011 ISO C++ standard plus amendments.  Support for C++11
               is still experimental, and may change in incompatible ways in
               future releases.  The name c++0x is deprecated.

           gnu++11
           gnu++0x
               GNU dialect of -std=c++11. Support for C++11 is still
               experimental, and may change in incompatible ways in future
               releases.  The name gnu++0x is deprecated.

           c++1y
               The next revision of the ISO C++ standard, tentatively planned
               for 2017.  Support is highly experimental, and will almost
               certainly change in incompatible ways in future releases.

           gnu++1y
               GNU dialect of -std=c++1y.  Support is highly experimental, and
               will almost certainly change in incompatible ways in future
               releases.

       -fgnu89-inline
           The option -fgnu89-inline tells GCC to use the traditional GNU
           semantics for "inline" functions when in C99 mode.
             This option is accepted and ignored by GCC versions 4.1.3 up to
           but not including 4.3.  In GCC versions 4.3 and later it changes
           the behavior of GCC in C99 mode.  Using this option is roughly
           equivalent to adding the "gnu_inline" function attribute to all
           inline functions.

           The option -fno-gnu89-inline explicitly tells GCC to use the C99
           semantics for "inline" when in C99 or gnu99 mode (i.e., it
           specifies the default behavior).  This option was first supported
           in GCC 4.3.  This option is not supported in -std=c90 or -std=gnu90
           mode.

           The preprocessor macros "__GNUC_GNU_INLINE__" and
           "__GNUC_STDC_INLINE__" may be used to check which semantics are in
           effect for "inline" functions.

       -aux-info filename
           Output to the given filename prototyped declarations for all
           functions declared and/or defined in a translation unit, including
           those in header files.  This option is silently ignored in any
           language other than C.

           Besides declarations, the file indicates, in comments, the origin
           of each declaration (source file and line), whether the declaration
           was implicit, prototyped or unprototyped (I, N for new or O for
           old, respectively, in the first character after the line number and
           the colon), and whether it came from a declaration or a definition
           (C or F, respectively, in the following character).  In the case of
           function definitions, a K&R-style list of arguments followed by
           their declarations is also provided, inside comments, after the
           declaration.

       -fallow-parameterless-variadic-functions
           Accept variadic functions without named parameters.

           Although it is possible to define such a function, this is not very
           useful as it is not possible to read the arguments.  This is only
           supported for C as this construct is allowed by C++.

       -fno-asm
           Do not recognize "asm", "inline" or "typeof" as a keyword, so that
           code can use these words as identifiers.  You can use the keywords
           "__asm__", "__inline__" and "__typeof__" instead.  -ansi implies
           -fno-asm.

           In C++, this switch only affects the "typeof" keyword, since "asm"
           and "inline" are standard keywords.  You may want to use the
           -fno-gnu-keywords flag instead, which has the same effect.  In C99
           mode (-std=c99 or -std=gnu99), this switch only affects the "asm"
           and "typeof" keywords, since "inline" is a standard keyword in ISO
           C99.

       -fno-builtin
       -fno-builtin-function
           Don't recognize built-in functions that do not begin with
           __builtin_ as prefix.

           GCC normally generates special code to handle certain built-in
           functions more efficiently; for instance, calls to "alloca" may
           become single instructions which adjust the stack directly, and
           calls to "memcpy" may become inline copy loops.  The resulting code
           is often both smaller and faster, but since the function calls no
           longer appear as such, you cannot set a breakpoint on those calls,
           nor can you change the behavior of the functions by linking with a
           different library.  In addition, when a function is recognized as a
           built-in function, GCC may use information about that function to
           warn about problems with calls to that function, or to generate
           more efficient code, even if the resulting code still contains
           calls to that function.  For example, warnings are given with
           -Wformat for bad calls to "printf" when "printf" is built in and
           "strlen" is known not to modify global memory.

           With the -fno-builtin-function option only the built-in function
           function is disabled.  function must not begin with __builtin_.  If
           a function is named that is not built-in in this version of GCC,
           this option is ignored.  There is no corresponding
           -fbuiltin-function option; if you wish to enable built-in functions
           selectively when using -fno-builtin or -ffreestanding, you may
           define macros such as:

                   #define abs(n)          __builtin_abs ((n))
                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))

       -fhosted
           Assert that compilation targets a hosted environment.  This implies
           -fbuiltin.  A hosted environment is one in which the entire
           standard library is available, and in which "main" has a return
           type of "int".  Examples are nearly everything except a kernel.
           This is equivalent to -fno-freestanding.

       -ffreestanding
           Assert that compilation targets a freestanding environment.  This
           implies -fno-builtin.  A freestanding environment is one in which
           the standard library may not exist, and program startup may not
           necessarily be at "main".  The most obvious example is an OS
           kernel.  This is equivalent to -fno-hosted.

       -fopenmp
           Enable handling of OpenMP directives "#pragma omp" in C/C++ and
           "!$omp" in Fortran.  When -fopenmp is specified, the compiler
           generates parallel code according to the OpenMP Application Program
           Interface v3.0 <http://www.openmp.org/>.  This option implies
           -pthread, and thus is only supported on targets that have support
           for -pthread.

       -fgnu-tm
           When the option -fgnu-tm is specified, the compiler generates code
           for the Linux variant of Intel's current Transactional Memory ABI
           specification document (Revision 1.1, May 6 2009).  This is an
           experimental feature whose interface may change in future versions
           of GCC, as the official specification changes.  Please note that
           not all architectures are supported for this feature.

           For more information on GCC's support for transactional memory,

           Note that the transactional memory feature is not supported with
           non-call exceptions (-fnon-call-exceptions).

       -fms-extensions
           Accept some non-standard constructs used in Microsoft header files.

           In C++ code, this allows member names in structures to be similar
           to previous types declarations.

                   typedef int UOW;
                   struct ABC {
                     UOW UOW;
                   };

           Some cases of unnamed fields in structures and unions are only
           accepted with this option.

       -fplan9-extensions
           Accept some non-standard constructs used in Plan 9 code.

           This enables -fms-extensions, permits passing pointers to
           structures with anonymous fields to functions that expect pointers
           to elements of the type of the field, and permits referring to
           anonymous fields declared using a typedef.    This is only
           supported for C, not C++.

       -trigraphs
           Support ISO C trigraphs.  The -ansi option (and -std options for
           strict ISO C conformance) implies -trigraphs.

       -traditional
       -traditional-cpp
           Formerly, these options caused GCC to attempt to emulate a pre-
           standard C compiler.  They are now only supported with the -E
           switch.  The preprocessor continues to support a pre-standard mode.
           See the GNU CPP manual for details.

       -fcond-mismatch
           Allow conditional expressions with mismatched types in the second
           and third arguments.  The value of such an expression is void.
           This option is not supported for C++.

       -flax-vector-conversions
           Allow implicit conversions between vectors with differing numbers
           of elements and/or incompatible element types.  This option should
           not be used for new code.

       -funsigned-char
           Let the type "char" be unsigned, like "unsigned char".

           Each kind of machine has a default for what "char" should be.  It
           is either like "unsigned char" by default or like "signed char" by
           default.

           Ideally, a portable program should always use "signed char" or
           "unsigned char" when it depends on the signedness of an object.
           But many programs have been written to use plain "char" and expect
           it to be signed, or expect it to be unsigned, depending on the
           machines they were written for.  This option, and its inverse, let
           you make such a program work with the opposite default.

           The type "char" is always a distinct type from each of "signed
           char" or "unsigned char", even though its behavior is always just
           like one of those two.

       -fsigned-char
           Let the type "char" be signed, like "signed char".

           Note that this is equivalent to -fno-unsigned-char, which is the
           negative form of -funsigned-char.  Likewise, the option
           -fno-signed-char is equivalent to -funsigned-char.

       -fsigned-bitfields
       -funsigned-bitfields
       -fno-signed-bitfields
       -fno-unsigned-bitfields
           These options control whether a bit-field is signed or unsigned,
           when the declaration does not use either "signed" or "unsigned".
           By default, such a bit-field is signed, because this is consistent:
           the basic integer types such as "int" are signed types.

   Options Controlling C++ Dialect
       This section describes the command-line options that are only
       meaningful for C++ programs.  You can also use most of the GNU compiler
       options regardless of what language your program is in.  For example,
       you might compile a file "firstClass.C" like this:

               g++ -g -frepo -O -c firstClass.C

       In this example, only -frepo is an option meant only for C++ programs;
       you can use the other options with any language supported by GCC.

       Here is a list of options that are only for compiling C++ programs:

       -fabi-version=n
           Use version n of the C++ ABI.  The default is version 2.

           Version 0 refers to the version conforming most closely to the C++
           ABI specification.  Therefore, the ABI obtained using version 0
           will change in different versions of G++ as ABI bugs are fixed.

           Version 1 is the version of the C++ ABI that first appeared in G++
           3.2.

           Version 2 is the version of the C++ ABI that first appeared in G++
           3.4.

           Version 3 corrects an error in mangling a constant address as a
           template argument.

           Version 4, which first appeared in G++ 4.5, implements a standard
           mangling for vector types.

           Version 5, which first appeared in G++ 4.6, corrects the mangling
           of attribute const/volatile on function pointer types, decltype of
           a plain decl, and use of a function parameter in the declaration of
           another parameter.

           Version 6, which first appeared in G++ 4.7, corrects the promotion
           behavior of C++11 scoped enums and the mangling of template
           argument packs, const/static_cast, prefix ++ and --, and a class
           scope function used as a template argument.

           See also -Wabi.

       -fno-access-control
           Turn off all access checking.  This switch is mainly useful for
           working around bugs in the access control code.

       -fcheck-new
           Check that the pointer returned by "operator new" is non-null
           before attempting to modify the storage allocated.  This check is
           normally unnecessary because the C++ standard specifies that
           "operator new" only returns 0 if it is declared throw(), in which
           case the compiler always checks the return value even without this
           option.  In all other cases, when "operator new" has a non-empty
           exception specification, memory exhaustion is signalled by throwing
           "std::bad_alloc".  See also new (nothrow).

       -fconstexpr-depth=n
           Set the maximum nested evaluation depth for C++11 constexpr
           functions to n.  A limit is needed to detect endless recursion
           during constant expression evaluation.  The minimum specified by
           the standard is 512.

       -fdeduce-init-list
           Enable deduction of a template type parameter as
           "std::initializer_list" from a brace-enclosed initializer list,
           i.e.

                   template <class T> auto forward(T t) -> decltype (realfn (t))
                   {
                     return realfn (t);
                   }

                   void f()
                   {
                     forward({1,2}); // call forward<std::initializer_list<int>>
                   }

           This deduction was implemented as a possible extension to the
           originally proposed semantics for the C++11 standard, but was not
           part of the final standard, so it is disabled by default.  This
           option is deprecated, and may be removed in a future version of
           G++.

       -ffriend-injection
           Inject friend functions into the enclosing namespace, so that they
           are visible outside the scope of the class in which they are
           declared.  Friend functions were documented to work this way in the
           old Annotated C++ Reference Manual, and versions of G++ before 4.1
           always worked that way.  However, in ISO C++ a friend function that
           is not declared in an enclosing scope can only be found using
           argument dependent lookup.  This option causes friends to be
           injected as they were in earlier releases.

           This option is for compatibility, and may be removed in a future
           release of G++.

       -fno-elide-constructors
           The C++ standard allows an implementation to omit creating a
           temporary that is only used to initialize another object of the
           same type.  Specifying this option disables that optimization, and
           forces G++ to call the copy constructor in all cases.

       -fno-enforce-eh-specs
           Don't generate code to check for violation of exception
           specifications at run time.  This option violates the C++ standard,
           but may be useful for reducing code size in production builds, much
           like defining NDEBUG.  This does not give user code permission to
           throw exceptions in violation of the exception specifications; the
           compiler still optimizes based on the specifications, so throwing
           an unexpected exception results in undefined behavior at run time.

       -fextern-tls-init
       -fno-extern-tls-init
           The C++11 and OpenMP standards allow thread_local and threadprivate
           variables to have dynamic (runtime) initialization.  To support
           this, any use of such a variable goes through a wrapper function
           that performs any necessary initialization.  When the use and
           definition of the variable are in the same translation unit, this
           overhead can be optimized away, but when the use is in a different
           translation unit there is significant overhead even if the variable
           doesn't actually need dynamic initialization.  If the programmer
           can be sure that no use of the variable in a non-defining TU needs
           to trigger dynamic initialization (either because the variable is
           statically initialized, or a use of the variable in the defining TU
           will be executed before any uses in another TU), they can avoid
           this overhead with the -fno-extern-tls-init option.

           On targets that support symbol aliases, the default is
           -fextern-tls-init.  On targets that do not support symbol aliases,
           the default is -fno-extern-tls-init.

       -ffor-scope
       -fno-for-scope
           If -ffor-scope is specified, the scope of variables declared in a
           for-init-statement is limited to the for loop itself, as specified
           by the C++ standard.  If -fno-for-scope is specified, the scope of
           variables declared in a for-init-statement extends to the end of
           the enclosing scope, as was the case in old versions of G++, and
           other (traditional) implementations of C++.

           If neither flag is given, the default is to follow the standard,
           but to allow and give a warning for old-style code that would
           otherwise be invalid, or have different behavior.

       -fno-gnu-keywords
           Do not recognize "typeof" as a keyword, so that code can use this
           word as an identifier.  You can use the keyword "__typeof__"
           instead.  -ansi implies -fno-gnu-keywords.

       -fno-implicit-templates
           Never emit code for non-inline templates that are instantiated
           implicitly (i.e. by use); only emit code for explicit
           instantiations.

       -fno-implicit-inline-templates
           Don't emit code for implicit instantiations of inline templates,
           either.  The default is to handle inlines differently so that
           compiles with and without optimization need the same set of
           explicit instantiations.

       -fno-implement-inlines
           To save space, do not emit out-of-line copies of inline functions
           controlled by #pragma implementation.  This causes linker errors if
           these functions are not inlined everywhere they are called.

       -fms-extensions
           Disable Wpedantic warnings about constructs used in MFC, such as
           implicit int and getting a pointer to member function via non-
           standard syntax.

       -fno-nonansi-builtins
           Disable built-in declarations of functions that are not mandated by
           ANSI/ISO C.  These include "ffs", "alloca", "_exit", "index",
           "bzero", "conjf", and other related functions.

       -fnothrow-opt
           Treat a "throw()" exception specification as if it were a
           "noexcept" specification to reduce or eliminate the text size
           overhead relative to a function with no exception specification.
           If the function has local variables of types with non-trivial
           destructors, the exception specification actually makes the
           function smaller because the EH cleanups for those variables can be
           optimized away.  The semantic effect is that an exception thrown
           out of a function with such an exception specification results in a
           call to "terminate" rather than "unexpected".

       -fno-operator-names
           Do not treat the operator name keywords "and", "bitand", "bitor",
           "compl", "not", "or" and "xor" as synonyms as keywords.

       -fno-optional-diags
           Disable diagnostics that the standard says a compiler does not need
           to issue.  Currently, the only such diagnostic issued by G++ is the
           one for a name having multiple meanings within a class.

       -fpermissive
           Downgrade some diagnostics about nonconformant code from errors to
           warnings.  Thus, using -fpermissive allows some nonconforming code
           to compile.

       -fno-pretty-templates
           When an error message refers to a specialization of a function
           template, the compiler normally prints the signature of the
           template followed by the template arguments and any typedefs or
           typenames in the signature (e.g. "void f(T) [with T = int]" rather
           than "void f(int)") so that it's clear which template is involved.
           When an error message refers to a specialization of a class
           template, the compiler omits any template arguments that match the
           default template arguments for that template.  If either of these
           behaviors make it harder to understand the error message rather
           than easier, you can use -fno-pretty-templates to disable them.

       -frepo
           Enable automatic template instantiation at link time.  This option
           also implies -fno-implicit-templates.

       -fno-rtti
           Disable generation of information about every class with virtual
           functions for use by the C++ run-time type identification features
           (dynamic_cast and typeid).  If you don't use those parts of the
           language, you can save some space by using this flag.  Note that
           exception handling uses the same information, but G++ generates it
           as needed. The dynamic_cast operator can still be used for casts
           that do not require run-time type information, i.e. casts to "void
           *" or to unambiguous base classes.

       -fstats
           Emit statistics about front-end processing at the end of the
           compilation.  This information is generally only useful to the G++
           development team.

       -fstrict-enums
           Allow the compiler to optimize using the assumption that a value of
           enumerated type can only be one of the values of the enumeration
           (as defined in the C++ standard; basically, a value that can be
           represented in the minimum number of bits needed to represent all
           the enumerators).  This assumption may not be valid if the program
           uses a cast to convert an arbitrary integer value to the enumerated
           type.

       -ftemplate-backtrace-limit=n
           Set the maximum number of template instantiation notes for a single
           warning or error to n.  The default value is 10.

       -ftemplate-depth=n
           Set the maximum instantiation depth for template classes to n.  A
           limit on the template instantiation depth is needed to detect
           endless recursions during template class instantiation.  ANSI/ISO
           C++ conforming programs must not rely on a maximum depth greater
           than 17 (changed to 1024 in C++11).  The default value is 900, as
           the compiler can run out of stack space before hitting 1024 in some
           situations.

       -fno-threadsafe-statics
           Do not emit the extra code to use the routines specified in the C++
           ABI for thread-safe initialization of local statics.  You can use
           this option to reduce code size slightly in code that doesn't need
           to be thread-safe.

       -fuse-cxa-atexit
           Register destructors for objects with static storage duration with
           the "__cxa_atexit" function rather than the "atexit" function.
           This option is required for fully standards-compliant handling of
           static destructors, but only works if your C library supports
           "__cxa_atexit".

       -fno-use-cxa-get-exception-ptr
           Don't use the "__cxa_get_exception_ptr" runtime routine.  This
           causes "std::uncaught_exception" to be incorrect, but is necessary
           if the runtime routine is not available.

       -fvisibility-inlines-hidden
           This switch declares that the user does not attempt to compare
           pointers to inline functions or methods where the addresses of the
           two functions are taken in different shared objects.

           The effect of this is that GCC may, effectively, mark inline
           methods with "__attribute__ ((visibility ("hidden")))" so that they
           do not appear in the export table of a DSO and do not require a PLT
           indirection when used within the DSO.  Enabling this option can
           have a dramatic effect on load and link times of a DSO as it
           massively reduces the size of the dynamic export table when the
           library makes heavy use of templates.

           The behavior of this switch is not quite the same as marking the
           methods as hidden directly, because it does not affect static
           variables local to the function or cause the compiler to deduce
           that the function is defined in only one shared object.

           You may mark a method as having a visibility explicitly to negate
           the effect of the switch for that method.  For example, if you do
           want to compare pointers to a particular inline method, you might
           mark it as having default visibility.  Marking the enclosing class
           with explicit visibility has no effect.

           Explicitly instantiated inline methods are unaffected by this
           option as their linkage might otherwise cross a shared library
           boundary.

       -fvisibility-ms-compat
           This flag attempts to use visibility settings to make GCC's C++
           linkage model compatible with that of Microsoft Visual Studio.

           The flag makes these changes to GCC's linkage model:

           1.  It sets the default visibility to "hidden", like
               -fvisibility=hidden.

           2.  Types, but not their members, are not hidden by default.

           3.  The One Definition Rule is relaxed for types without explicit
               visibility specifications that are defined in more than one
               shared object: those declarations are permitted if they are
               permitted when this option is not used.

           In new code it is better to use -fvisibility=hidden and export
           those classes that are intended to be externally visible.
           Unfortunately it is possible for code to rely, perhaps
           accidentally, on the Visual Studio behavior.

           Among the consequences of these changes are that static data
           members of the same type with the same name but defined in
           different shared objects are different, so changing one does not
           change the other; and that pointers to function members defined in
           different shared objects may not compare equal.  When this flag is
           given, it is a violation of the ODR to define types with the same
           name differently.

       -fno-weak
           Do not use weak symbol support, even if it is provided by the
           linker.  By default, G++ uses weak symbols if they are available.
           This option exists only for testing, and should not be used by end-
           users; it results in inferior code and has no benefits.  This
           option may be removed in a future release of G++.

       -nostdinc++
           Do not search for header files in the standard directories specific
           to C++, but do still search the other standard directories.  (This
           option is used when building the C++ library.)

       In addition, these optimization, warning, and code generation options
       have meanings only for C++ programs:

       -fno-default-inline
           Do not assume inline for functions defined inside a class scope.
             Note that these functions have linkage like inline functions;
           they just aren't inlined by default.

       -Wabi (C, Objective-C, C++ and Objective-C++ only)
           Warn when G++ generates code that is probably not compatible with
           the vendor-neutral C++ ABI.  Although an effort has been made to
           warn about all such cases, there are probably some cases that are
           not warned about, even though G++ is generating incompatible code.
           There may also be cases where warnings are emitted even though the
           code that is generated is compatible.

           You should rewrite your code to avoid these warnings if you are
           concerned about the fact that code generated by G++ may not be
           binary compatible with code generated by other compilers.

           The known incompatibilities in -fabi-version=2 (the default)
           include:

              A template with a non-type template parameter of reference type
               is mangled incorrectly:

                       extern int N;
                       template <int &> struct S {};
                       void n (S<N>) {2}

               This is fixed in -fabi-version=3.

              SIMD vector types declared using "__attribute ((vector_size))"
               are mangled in a non-standard way that does not allow for
               overloading of functions taking vectors of different sizes.

               The mangling is changed in -fabi-version=4.

           The known incompatibilities in -fabi-version=1 include:

              Incorrect handling of tail-padding for bit-fields.  G++ may
               attempt to pack data into the same byte as a base class.  For
               example:

                       struct A { virtual void f(); int f1 : 1; };
                       struct B : public A { int f2 : 1; };

               In this case, G++ places "B::f2" into the same byte as "A::f1";
               other compilers do not.  You can avoid this problem by
               explicitly padding "A" so that its size is a multiple of the
               byte size on your platform; that causes G++ and other compilers
               to lay out "B" identically.

              Incorrect handling of tail-padding for virtual bases.  G++ does
               not use tail padding when laying out virtual bases.  For
               example:

                       struct A { virtual void f(); char c1; };
                       struct B { B(); char c2; };
                       struct C : public A, public virtual B {};

               In this case, G++ does not place "B" into the tail-padding for
               "A"; other compilers do.  You can avoid this problem by
               explicitly padding "A" so that its size is a multiple of its
               alignment (ignoring virtual base classes); that causes G++ and
               other compilers to lay out "C" identically.

              Incorrect handling of bit-fields with declared widths greater
               than that of their underlying types, when the bit-fields appear
               in a union.  For example:

                       union U { int i : 4096; };

               Assuming that an "int" does not have 4096 bits, G++ makes the
               union too small by the number of bits in an "int".

              Empty classes can be placed at incorrect offsets.  For example:

                       struct A {};

                       struct B {
                         A a;
                         virtual void f ();
                       };

                       struct C : public B, public A {};

               G++ places the "A" base class of "C" at a nonzero offset; it
               should be placed at offset zero.  G++ mistakenly believes that
               the "A" data member of "B" is already at offset zero.

              Names of template functions whose types involve "typename" or
               template template parameters can be mangled incorrectly.

                       template <typename Q>
                       void f(typename Q::X) {}

                       template <template <typename> class Q>
                       void f(typename Q<int>::X) {}

               Instantiations of these templates may be mangled incorrectly.

           It also warns about psABI-related changes.  The known psABI changes
           at this point include:

              For SysV/x86-64, unions with "long double" members are passed
               in memory as specified in psABI.  For example:

                       union U {
                         long double ld;
                         int i;
                       };

               "union U" is always passed in memory.

       -Wctor-dtor-privacy (C++ and Objective-C++ only)
           Warn when a class seems unusable because all the constructors or
           destructors in that class are private, and it has neither friends
           nor public static member functions.  Also warn if there are no non-
           private methods, and there's at least one private member function
           that isn't a constructor or destructor.

       -Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
           Warn when delete is used to destroy an instance of a class that has
           virtual functions and non-virtual destructor. It is unsafe to
           delete an instance of a derived class through a pointer to a base
           class if the base class does not have a virtual destructor.  This
           warning is enabled by -Wall.

       -Wliteral-suffix (C++ and Objective-C++ only)
           Warn when a string or character literal is followed by a ud-suffix
           which does not begin with an underscore.  As a conforming
           extension, GCC treats such suffixes as separate preprocessing
           tokens in order to maintain backwards compatibility with code that
           uses formatting macros from "<inttypes.h>".  For example:

                   #define __STDC_FORMAT_MACROS
                   #include <inttypes.h>
                   #include <stdio.h>

                   int main() {
                     int64_t i64 = 123;
                     printf("My int64: %"PRId64"\n", i64);
                   }

           In this case, "PRId64" is treated as a separate preprocessing
           token.

           This warning is enabled by default.

       -Wnarrowing (C++ and Objective-C++ only)
           Warn when a narrowing conversion prohibited by C++11 occurs within
           { }, e.g.

                   int i = { 2.2 }; // error: narrowing from double to int

           This flag is included in -Wall and -Wc++11-compat.

           With -std=c++11, -Wno-narrowing suppresses the diagnostic required
           by the standard.  Note that this does not affect the meaning of
           well-formed code; narrowing conversions are still considered ill-
           formed in SFINAE context.

       -Wnoexcept (C++ and Objective-C++ only)
           Warn when a noexcept-expression evaluates to false because of a
           call to a function that does not have a non-throwing exception
           specification (i.e. throw() or noexcept) but is known by the
           compiler to never throw an exception.

       -Wnon-virtual-dtor (C++ and Objective-C++ only)
           Warn when a class has virtual functions and an accessible non-
           virtual destructor, in which case it is possible but unsafe to
           delete an instance of a derived class through a pointer to the base
           class.  This warning is also enabled if -Weffc++ is specified.

       -Wreorder (C++ and Objective-C++ only)
           Warn when the order of member initializers given in the code does
           not match the order in which they must be executed.  For instance:

                   struct A {
                     int i;
                     int j;
                     A(): j (0), i (1) { }
                   };

           The compiler rearranges the member initializers for i and j to
           match the declaration order of the members, emitting a warning to
           that effect.  This warning is enabled by -Wall.

       -fext-numeric-literals (C++ and Objective-C++ only)
           Accept imaginary, fixed-point, or machine-defined literal number
           suffixes as GNU extensions.  When this option is turned off these
           suffixes are treated as C++11 user-defined literal numeric
           suffixes.  This is on by default for all pre-C++11 dialects and all
           GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++1y.
           This option is off by default for ISO C++11 onwards (-std=c++11,
           ...).

       The following -W... options are not affected by -Wall.

       -Weffc++ (C++ and Objective-C++ only)
           Warn about violations of the following style guidelines from Scott
           Meyers' Effective C++, Second Edition book:

              Item 11:  Define a copy constructor and an assignment operator
               for classes with dynamically-allocated memory.

              Item 12:  Prefer initialization to assignment in constructors.

              Item 14:  Make destructors virtual in base classes.

              Item 15:  Have "operator=" return a reference to *this.

              Item 23:  Don't try to return a reference when you must return
               an object.

           Also warn about violations of the following style guidelines from
           Scott Meyers' More Effective C++ book:

              Item 6:  Distinguish between prefix and postfix forms of
               increment and decrement operators.

              Item 7:  Never overload "&&", "||", or ",".

           When selecting this option, be aware that the standard library
           headers do not obey all of these guidelines; use grep -v to filter
           out those warnings.

       -Wstrict-null-sentinel (C++ and Objective-C++ only)
           Warn about the use of an uncasted "NULL" as sentinel.  When
           compiling only with GCC this is a valid sentinel, as "NULL" is
           defined to "__null".  Although it is a null pointer constant rather
           than a null pointer, it is guaranteed to be of the same size as a
           pointer.  But this use is not portable across different compilers.

       -Wno-non-template-friend (C++ and Objective-C++ only)
           Disable warnings when non-templatized friend functions are declared
           within a template.  Since the advent of explicit template
           specification support in G++, if the name of the friend is an
           unqualified-id (i.e., friend foo(int)), the C++ language
           specification demands that the friend declare or define an
           ordinary, nontemplate function.  (Section 14.5.3).  Before G++
           implemented explicit specification, unqualified-ids could be
           interpreted as a particular specialization of a templatized
           function.  Because this non-conforming behavior is no longer the
           default behavior for G++, -Wnon-template-friend allows the compiler
           to check existing code for potential trouble spots and is on by
           default.  This new compiler behavior can be turned off with
           -Wno-non-template-friend, which keeps the conformant compiler code
           but disables the helpful warning.

       -Wold-style-cast (C++ and Objective-C++ only)
           Warn if an old-style (C-style) cast to a non-void type is used
           within a C++ program.  The new-style casts (dynamic_cast,
           static_cast, reinterpret_cast, and const_cast) are less vulnerable
           to unintended effects and much easier to search for.

       -Woverloaded-virtual (C++ and Objective-C++ only)
           Warn when a function declaration hides virtual functions from a
           base class.  For example, in:

                   struct A {
                     virtual void f();
                   };

                   struct B: public A {
                     void f(int);
                   };

           the "A" class version of "f" is hidden in "B", and code like:

                   B* b;
                   b->f();

           fails to compile.

       -Wno-pmf-conversions (C++ and Objective-C++ only)
           Disable the diagnostic for converting a bound pointer to member
           function to a plain pointer.

       -Wsign-promo (C++ and Objective-C++ only)
           Warn when overload resolution chooses a promotion from unsigned or
           enumerated type to a signed type, over a conversion to an unsigned
           type of the same size.  Previous versions of G++ tried to preserve
           unsignedness, but the standard mandates the current behavior.

   Options Controlling Objective-C and Objective-C++ Dialects
       (NOTE: This manual does not describe the Objective-C and Objective-C++
       languages themselves.

       This section describes the command-line options that are only
       meaningful for Objective-C and Objective-C++ programs.  You can also
       use most of the language-independent GNU compiler options.  For
       example, you might compile a file "some_class.m" like this:

               gcc -g -fgnu-runtime -O -c some_class.m

       In this example, -fgnu-runtime is an option meant only for Objective-C
       and Objective-C++ programs; you can use the other options with any
       language supported by GCC.

       Note that since Objective-C is an extension of the C language,
       Objective-C compilations may also use options specific to the C front-
       end (e.g., -Wtraditional).  Similarly, Objective-C++ compilations may
       use C++-specific options (e.g., -Wabi).

       Here is a list of options that are only for compiling Objective-C and
       Objective-C++ programs:

       -fconstant-string-class=class-name
           Use class-name as the name of the class to instantiate for each
           literal string specified with the syntax "@"..."".  The default
           class name is "NXConstantString" if the GNU runtime is being used,
           and "NSConstantString" if the NeXT runtime is being used (see
           below).  The -fconstant-cfstrings option, if also present,
           overrides the -fconstant-string-class setting and cause "@"...""
           literals to be laid out as constant CoreFoundation strings.

       -fgnu-runtime
           Generate object code compatible with the standard GNU Objective-C
           runtime.  This is the default for most types of systems.

       -fnext-runtime
           Generate output compatible with the NeXT runtime.  This is the
           default for NeXT-based systems, including Darwin and Mac OS X.  The
           macro "__NEXT_RUNTIME__" is predefined if (and only if) this option
           is used.

       -fno-nil-receivers
           Assume that all Objective-C message dispatches ("[receiver
           message:arg]") in this translation unit ensure that the receiver is
           not "nil".  This allows for more efficient entry points in the
           runtime to be used.  This option is only available in conjunction
           with the NeXT runtime and ABI version 0 or 1.

       -fobjc-abi-version=n
           Use version n of the Objective-C ABI for the selected runtime.
           This option is currently supported only for the NeXT runtime.  In
           that case, Version 0 is the traditional (32-bit) ABI without
           support for properties and other Objective-C 2.0 additions.
           Version 1 is the traditional (32-bit) ABI with support for
           properties and other Objective-C 2.0 additions.  Version 2 is the
           modern (64-bit) ABI.  If nothing is specified, the default is
           Version 0 on 32-bit target machines, and Version 2 on 64-bit target
           machines.

       -fobjc-call-cxx-cdtors
           For each Objective-C class, check if any of its instance variables
           is a C++ object with a non-trivial default constructor.  If so,
           synthesize a special "- (id) .cxx_construct" instance method which
           runs non-trivial default constructors on any such instance
           variables, in order, and then return "self".  Similarly, check if
           any instance variable is a C++ object with a non-trivial
           destructor, and if so, synthesize a special "- (void)
           .cxx_destruct" method which runs all such default destructors, in
           reverse order.

           The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods
           thusly generated only operate on instance variables declared in the
           current Objective-C class, and not those inherited from
           superclasses.  It is the responsibility of the Objective-C runtime
           to invoke all such methods in an object's inheritance hierarchy.
           The "- (id) .cxx_construct" methods are invoked by the runtime
           immediately after a new object instance is allocated; the "- (void)
           .cxx_destruct" methods are invoked immediately before the runtime
           deallocates an object instance.

           As of this writing, only the NeXT runtime on Mac OS X 10.4 and
           later has support for invoking the "- (id) .cxx_construct" and "-
           (void) .cxx_destruct" methods.

       -fobjc-direct-dispatch
           Allow fast jumps to the message dispatcher.  On Darwin this is
           accomplished via the comm page.

       -fobjc-exceptions
           Enable syntactic support for structured exception handling in
           Objective-C, similar to what is offered by C++ and Java.  This
           option is required to use the Objective-C keywords @try, @throw,
           @catch, @finally and @synchronized.  This option is available with
           both the GNU runtime and the NeXT runtime (but not available in
           conjunction with the NeXT runtime on Mac OS X 10.2 and earlier).

       -fobjc-gc
           Enable garbage collection (GC) in Objective-C and Objective-C++
           programs.  This option is only available with the NeXT runtime; the
           GNU runtime has a different garbage collection implementation that
           does not require special compiler flags.

       -fobjc-nilcheck
           For the NeXT runtime with version 2 of the ABI, check for a nil
           receiver in method invocations before doing the actual method call.
           This is the default and can be disabled using -fno-objc-nilcheck.
           Class methods and super calls are never checked for nil in this way
           no matter what this flag is set to.  Currently this flag does
           nothing when the GNU runtime, or an older version of the NeXT
           runtime ABI, is used.

       -fobjc-std=objc1
           Conform to the language syntax of Objective-C 1.0, the language
           recognized by GCC 4.0.  This only affects the Objective-C additions
           to the C/C++ language; it does not affect conformance to C/C++
           standards, which is controlled by the separate C/C++ dialect option
           flags.  When this option is used with the Objective-C or
           Objective-C++ compiler, any Objective-C syntax that is not
           recognized by GCC 4.0 is rejected.  This is useful if you need to
           make sure that your Objective-C code can be compiled with older
           versions of GCC.

       -freplace-objc-classes
           Emit a special marker instructing ld(1) not to statically link in
           the resulting object file, and allow dyld(1) to load it in at run
           time instead.  This is used in conjunction with the Fix-and-
           Continue debugging mode, where the object file in question may be
           recompiled and dynamically reloaded in the course of program
           execution, without the need to restart the program itself.
           Currently, Fix-and-Continue functionality is only available in
           conjunction with the NeXT runtime on Mac OS X 10.3 and later.

       -fzero-link
           When compiling for the NeXT runtime, the compiler ordinarily
           replaces calls to "objc_getClass("...")" (when the name of the
           class is known at compile time) with static class references that
           get initialized at load time, which improves run-time performance.
           Specifying the -fzero-link flag suppresses this behavior and causes
           calls to "objc_getClass("...")"  to be retained.  This is useful in
           Zero-Link debugging mode, since it allows for individual class
           implementations to be modified during program execution.  The GNU
           runtime currently always retains calls to "objc_get_class("...")"
           regardless of command-line options.

       -gen-decls
           Dump interface declarations for all classes seen in the source file
           to a file named sourcename.decl.

       -Wassign-intercept (Objective-C and Objective-C++ only)
           Warn whenever an Objective-C assignment is being intercepted by the
           garbage collector.

       -Wno-protocol (Objective-C and Objective-C++ only)
           If a class is declared to implement a protocol, a warning is issued
           for every method in the protocol that is not implemented by the
           class.  The default behavior is to issue a warning for every method
           not explicitly implemented in the class, even if a method
           implementation is inherited from the superclass.  If you use the
           -Wno-protocol option, then methods inherited from the superclass
           are considered to be implemented, and no warning is issued for
           them.

       -Wselector (Objective-C and Objective-C++ only)
           Warn if multiple methods of different types for the same selector
           are found during compilation.  The check is performed on the list
           of methods in the final stage of compilation.  Additionally, a
           check is performed for each selector appearing in a
           "@selector(...)"  expression, and a corresponding method for that
           selector has been found during compilation.  Because these checks
           scan the method table only at the end of compilation, these
           warnings are not produced if the final stage of compilation is not
           reached, for example because an error is found during compilation,
           or because the -fsyntax-only option is being used.

       -Wstrict-selector-match (Objective-C and Objective-C++ only)
           Warn if multiple methods with differing argument and/or return
           types are found for a given selector when attempting to send a
           message using this selector to a receiver of type "id" or "Class".
           When this flag is off (which is the default behavior), the compiler
           omits such warnings if any differences found are confined to types
           that share the same size and alignment.

       -Wundeclared-selector (Objective-C and Objective-C++ only)
           Warn if a "@selector(...)" expression referring to an undeclared
           selector is found.  A selector is considered undeclared if no
           method with that name has been declared before the "@selector(...)"
           expression, either explicitly in an @interface or @protocol
           declaration, or implicitly in an @implementation section.  This
           option always performs its checks as soon as a "@selector(...)"
           expression is found, while -Wselector only performs its checks in
           the final stage of compilation.  This also enforces the coding
           style convention that methods and selectors must be declared before
           being used.

       -print-objc-runtime-info
           Generate C header describing the largest structure that is passed
           by value, if any.

   Options to Control Diagnostic Messages Formatting
       Traditionally, diagnostic messages have been formatted irrespective of
       the output device's aspect (e.g. its width, ...).  You can use the
       options described below to control the formatting algorithm for
       diagnostic messages, e.g. how many characters per line, how often
       source location information should be reported.  Note that some
       language front ends may not honor these options.

       -fmessage-length=n
           Try to format error messages so that they fit on lines of about n
           characters.  The default is 72 characters for g++ and 0 for the
           rest of the front ends supported by GCC.  If n is zero, then no
           line-wrapping is done; each error message appears on a single line.

       -fdiagnostics-show-location=once
           Only meaningful in line-wrapping mode.  Instructs the diagnostic
           messages reporter to emit source location information once; that
           is, in case the message is too long to fit on a single physical
           line and has to be wrapped, the source location won't be emitted
           (as prefix) again, over and over, in subsequent continuation lines.
           This is the default behavior.

       -fdiagnostics-show-location=every-line
           Only meaningful in line-wrapping mode.  Instructs the diagnostic
           messages reporter to emit the same source location information (as
           prefix) for physical lines that result from the process of breaking
           a message which is too long to fit on a single line.

       -fno-diagnostics-show-option
           By default, each diagnostic emitted includes text indicating the
           command-line option that directly controls the diagnostic (if such
           an option is known to the diagnostic machinery).  Specifying the
           -fno-diagnostics-show-option flag suppresses that behavior.

       -fno-diagnostics-show-caret
           By default, each diagnostic emitted includes the original source
           line and a caret '^' indicating the column.  This option suppresses
           this information.

   Options to Request or Suppress Warnings
       Warnings are diagnostic messages that report constructions that are not
       inherently erroneous but that are risky or suggest there may have been
       an error.

       The following language-independent options do not enable specific
       warnings but control the kinds of diagnostics produced by GCC.

       -fsyntax-only
           Check the code for syntax errors, but don't do anything beyond
           that.

       -fmax-errors=n
           Limits the maximum number of error messages to n, at which point
           GCC bails out rather than attempting to continue processing the
           source code.  If n is 0 (the default), there is no limit on the
           number of error messages produced.  If -Wfatal-errors is also
           specified, then -Wfatal-errors takes precedence over this option.

       -w  Inhibit all warning messages.

       -Werror
           Make all warnings into errors.

       -Werror=
           Make the specified warning into an error.  The specifier for a
           warning is appended; for example -Werror=switch turns the warnings
           controlled by -Wswitch into errors.  This switch takes a negative
           form, to be used to negate -Werror for specific warnings; for
           example -Wno-error=switch makes -Wswitch warnings not be errors,
           even when -Werror is in effect.

           The warning message for each controllable warning includes the
           option that controls the warning.  That option can then be used
           with -Werror= and -Wno-error= as described above.  (Printing of the
           option in the warning message can be disabled using the
           -fno-diagnostics-show-option flag.)

           Note that specifying -Werror=foo automatically implies -Wfoo.
           However, -Wno-error=foo does not imply anything.

       -Wfatal-errors
           This option causes the compiler to abort compilation on the first
           error occurred rather than trying to keep going and printing
           further error messages.

       You can request many specific warnings with options beginning with -W,
       for example -Wimplicit to request warnings on implicit declarations.
       Each of these specific warning options also has a negative form
       beginning -Wno- to turn off warnings; for example, -Wno-implicit.  This
       manual lists only one of the two forms, whichever is not the default.
       For further language-specific options also refer to C++ Dialect Options
       and Objective-C and Objective-C++ Dialect Options.

       When an unrecognized warning option is requested (e.g.,
       -Wunknown-warning), GCC emits a diagnostic stating that the option is
       not recognized.  However, if the -Wno- form is used, the behavior is
       slightly different: no diagnostic is produced for -Wno-unknown-warning
       unless other diagnostics are being produced.  This allows the use of
       new -Wno- options with old compilers, but if something goes wrong, the
       compiler warns that an unrecognized option is present.

       -Wpedantic
       -pedantic
           Issue all the warnings demanded by strict ISO C and ISO C++; reject
           all programs that use forbidden extensions, and some other programs
           that do not follow ISO C and ISO C++.  For ISO C, follows the
           version of the ISO C standard specified by any -std option used.

           Valid ISO C and ISO C++ programs should compile properly with or
           without this option (though a rare few require -ansi or a -std
           option specifying the required version of ISO C).  However, without
           this option, certain GNU extensions and traditional C and C++
           features are supported as well.  With this option, they are
           rejected.

           -Wpedantic does not cause warning messages for use of the alternate
           keywords whose names begin and end with __.  Pedantic warnings are
           also disabled in the expression that follows "__extension__".
           However, only system header files should use these escape routes;
           application programs should avoid them.

           Some users try to use -Wpedantic to check programs for strict ISO C
           conformance.  They soon find that it does not do quite what they
           want: it finds some non-ISO practices, but not all---only those for
           which ISO C requires a diagnostic, and some others for which
           diagnostics have been added.

           A feature to report any failure to conform to ISO C might be useful
           in some instances, but would require considerable additional work
           and would be quite different from -Wpedantic.  We don't have plans
           to support such a feature in the near future.

           Where the standard specified with -std represents a GNU extended
           dialect of C, such as gnu90 or gnu99, there is a corresponding base
           standard, the version of ISO C on which the GNU extended dialect is
           based.  Warnings from -Wpedantic are given where they are required
           by the base standard.  (It does not make sense for such warnings to
           be given only for features not in the specified GNU C dialect,
           since by definition the GNU dialects of C include all features the
           compiler supports with the given option, and there would be nothing
           to warn about.)

       -pedantic-errors
           Like -Wpedantic, except that errors are produced rather than
           warnings.

       -Wall
           This enables all the warnings about constructions that some users
           consider questionable, and that are easy to avoid (or modify to
           prevent the warning), even in conjunction with macros.  This also
           enables some language-specific warnings described in C++ Dialect
           Options and Objective-C and Objective-C++ Dialect Options.

           -Wall turns on the following warning flags:

           -Waddress -Warray-bounds (only with -O2) -Wc++11-compat
           -Wchar-subscripts -Wenum-compare (in C/ObjC; this is on by default
           in C++) -Wimplicit-int (C and Objective-C only)
           -Wimplicit-function-declaration (C and Objective-C only) -Wcomment
           -Wformat -Wmain (only for C/ObjC and unless -ffreestanding)
           -Wmaybe-uninitialized -Wmissing-braces (only for C/ObjC) -Wnonnull
           -Wparentheses -Wpointer-sign -Wreorder -Wreturn-type
           -Wsequence-point -Wsign-compare (only in C++) -Wstrict-aliasing
           -Wstrict-overflow=1 -Wswitch -Wtrigraphs -Wuninitialized
           -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value
           -Wunused-variable -Wvolatile-register-var

           Note that some warning flags are not implied by -Wall.  Some of
           them warn about constructions that users generally do not consider
           questionable, but which occasionally you might wish to check for;
           others warn about constructions that are necessary or hard to avoid
           in some cases, and there is no simple way to modify the code to
           suppress the warning. Some of them are enabled by -Wextra but many
           of them must be enabled individually.

       -Wextra
           This enables some extra warning flags that are not enabled by
           -Wall. (This option used to be called -W.  The older name is still
           supported, but the newer name is more descriptive.)

           -Wclobbered -Wempty-body -Wignored-qualifiers
           -Wmissing-field-initializers -Wmissing-parameter-type (C only)
           -Wold-style-declaration (C only) -Woverride-init -Wsign-compare
           -Wtype-limits -Wuninitialized -Wunused-parameter (only with
           -Wunused or -Wall) -Wunused-but-set-parameter (only with -Wunused
           or -Wall)

           The option -Wextra also prints warning messages for the following
           cases:

              A pointer is compared against integer zero with <, <=, >, or
               >=.

              (C++ only) An enumerator and a non-enumerator both appear in a
               conditional expression.

              (C++ only) Ambiguous virtual bases.

              (C++ only) Subscripting an array that has been declared
               register.

              (C++ only) Taking the address of a variable that has been
               declared register.

              (C++ only) A base class is not initialized in a derived class's
               copy constructor.

       -Wchar-subscripts
           Warn if an array subscript has type "char".  This is a common cause
           of error, as programmers often forget that this type is signed on
           some machines.  This warning is enabled by -Wall.

       -Wcomment
           Warn whenever a comment-start sequence /* appears in a /* comment,
           or whenever a Backslash-Newline appears in a // comment.  This
           warning is enabled by -Wall.

       -Wno-coverage-mismatch
           Warn if feedback profiles do not match when using the -fprofile-use
           option.  If a source file is changed between compiling with
           -fprofile-gen and with -fprofile-use, the files with the profile
           feedback can fail to match the source file and GCC cannot use the
           profile feedback information.  By default, this warning is enabled
           and is treated as an error.  -Wno-coverage-mismatch can be used to
           disable the warning or -Wno-error=coverage-mismatch can be used to
           disable the error.  Disabling the error for this warning can result
           in poorly optimized code and is useful only in the case of very
           minor changes such as bug fixes to an existing code-base.
           Completely disabling the warning is not recommended.

       -Wno-cpp
           (C, Objective-C, C++, Objective-C++ and Fortran only)

           Suppress warning messages emitted by "#warning" directives.

       -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
           Give a warning when a value of type "float" is implicitly promoted
           to "double".  CPUs with a 32-bit "single-precision" floating-point
           unit implement "float" in hardware, but emulate "double" in
           software.  On such a machine, doing computations using "double"
           values is much more expensive because of the overhead required for
           software emulation.

           It is easy to accidentally do computations with "double" because
           floating-point literals are implicitly of type "double".  For
           example, in:

                   float area(float radius)
                   {
                      return 3.14159 * radius * radius;
                   }

           the compiler performs the entire computation with "double" because
           the floating-point literal is a "double".

       -Wformat
       -Wformat=n
           Check calls to "printf" and "scanf", etc., to make sure that the
           arguments supplied have types appropriate to the format string
           specified, and that the conversions specified in the format string
           make sense.  This includes standard functions, and others specified
           by format attributes, in the "printf", "scanf", "strftime" and
           "strfmon" (an X/Open extension, not in the C standard) families (or
           other target-specific families).  Which functions are checked
           without format attributes having been specified depends on the
           standard version selected, and such checks of functions without the
           attribute specified are disabled by -ffreestanding or -fno-builtin.

           The formats are checked against the format features supported by
           GNU libc version 2.2.  These include all ISO C90 and C99 features,
           as well as features from the Single Unix Specification and some BSD
           and GNU extensions.  Other library implementations may not support
           all these features; GCC does not support warning about features
           that go beyond a particular library's limitations.  However, if
           -Wpedantic is used with -Wformat, warnings are given about format
           features not in the selected standard version (but not for
           "strfmon" formats, since those are not in any version of the C
           standard).

           -Wformat=1
           -Wformat
               Option -Wformat is equivalent to -Wformat=1, and -Wno-format is
               equivalent to -Wformat=0.  Since -Wformat also checks for null
               format arguments for several functions, -Wformat also implies
               -Wnonnull.  Some aspects of this level of format checking can
               be disabled by the options: -Wno-format-contains-nul,
               -Wno-format-extra-args, and -Wno-format-zero-length.  -Wformat
               is enabled by -Wall.

           -Wno-format-contains-nul
               If -Wformat is specified, do not warn about format strings that
               contain NUL bytes.

           -Wno-format-extra-args
               If -Wformat is specified, do not warn about excess arguments to
               a "printf" or "scanf" format function.  The C standard
               specifies that such arguments are ignored.

               Where the unused arguments lie between used arguments that are
               specified with $ operand number specifications, normally
               warnings are still given, since the implementation could not
               know what type to pass to "va_arg" to skip the unused
               arguments.  However, in the case of "scanf" formats, this
               option suppresses the warning if the unused arguments are all
               pointers, since the Single Unix Specification says that such
               unused arguments are allowed.

           -Wno-format-zero-length
               If -Wformat is specified, do not warn about zero-length
               formats.  The C standard specifies that zero-length formats are
               allowed.

           -Wformat=2
               Enable -Wformat plus additional format checks.  Currently
               equivalent to -Wformat -Wformat-nonliteral -Wformat-security
               -Wformat-y2k.

           -Wformat-nonliteral
               If -Wformat is specified, also warn if the format string is not
               a string literal and so cannot be checked, unless the format
               function takes its format arguments as a "va_list".

           -Wformat-security
               If -Wformat is specified, also warn about uses of format
               functions that represent possible security problems.  At
               present, this warns about calls to "printf" and "scanf"
               functions where the format string is not a string literal and
               there are no format arguments, as in "printf (foo);".  This may
               be a security hole if the format string came from untrusted
               input and contains %n.  (This is currently a subset of what
               -Wformat-nonliteral warns about, but in future warnings may be
               added to -Wformat-security that are not included in
               -Wformat-nonliteral.)

           -Wformat-y2k
               If -Wformat is specified, also warn about "strftime" formats
               that may yield only a two-digit year.

       -Wnonnull
           Warn about passing a null pointer for arguments marked as requiring
           a non-null value by the "nonnull" function attribute.

           -Wnonnull is included in -Wall and -Wformat.  It can be disabled
           with the -Wno-nonnull option.

       -Winit-self (C, C++, Objective-C and Objective-C++ only)
           Warn about uninitialized variables that are initialized with
           themselves.  Note this option can only be used with the
           -Wuninitialized option.

           For example, GCC warns about "i" being uninitialized in the
           following snippet only when -Winit-self has been specified:

                   int f()
                   {
                     int i = i;
                     return i;
                   }

           This warning is enabled by -Wall in C++.

       -Wimplicit-int (C and Objective-C only)
           Warn when a declaration does not specify a type.  This warning is
           enabled by -Wall.

       -Wimplicit-function-declaration (C and Objective-C only)
           Give a warning whenever a function is used before being declared.
           In C99 mode (-std=c99 or -std=gnu99), this warning is enabled by
           default and it is made into an error by -pedantic-errors. This
           warning is also enabled by -Wall.

       -Wimplicit (C and Objective-C only)
           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This
           warning is enabled by -Wall.

       -Wignored-qualifiers (C and C++ only)
           Warn if the return type of a function has a type qualifier such as
           "const".  For ISO C such a type qualifier has no effect, since the
           value returned by a function is not an lvalue.  For C++, the
           warning is only emitted for scalar types or "void".  ISO C
           prohibits qualified "void" return types on function definitions, so
           such return types always receive a warning even without this
           option.

           This warning is also enabled by -Wextra.

       -Wmain
           Warn if the type of main is suspicious.  main should be a function
           with external linkage, returning int, taking either zero arguments,
           two, or three arguments of appropriate types.  This warning is
           enabled by default in C++ and is enabled by either -Wall or
           -Wpedantic.

       -Wmissing-braces
           Warn if an aggregate or union initializer is not fully bracketed.
           In the following example, the initializer for a is not fully
           bracketed, but that for b is fully bracketed.  This warning is
           enabled by -Wall in C.

                   int a[2][2] = { 0, 1, 2, 3 };
                   int b[2][2] = { { 0, 1 }, { 2, 3 } };

           This warning is enabled by -Wall.

       -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
           Warn if a user-supplied include directory does not exist.

       -Wparentheses
           Warn if parentheses are omitted in certain contexts, such as when
           there is an assignment in a context where a truth value is
           expected, or when operators are nested whose precedence people
           often get confused about.

           Also warn if a comparison like x<=y<=z appears; this is equivalent
           to (x<=y ? 1 : 0) <= z, which is a different interpretation from
           that of ordinary mathematical notation.

           Also warn about constructions where there may be confusion to which
           "if" statement an "else" branch belongs.  Here is an example of
           such a case:

                   {
                     if (a)
                       if (b)
                         foo ();
                     else
                       bar ();
                   }

           In C/C++, every "else" branch belongs to the innermost possible
           "if" statement, which in this example is "if (b)".  This is often
           not what the programmer expected, as illustrated in the above
           example by indentation the programmer chose.  When there is the
           potential for this confusion, GCC issues a warning when this flag
           is specified.  To eliminate the warning, add explicit braces around
           the innermost "if" statement so there is no way the "else" can
           belong to the enclosing "if".  The resulting code looks like this:

                   {
                     if (a)
                       {
                         if (b)
                           foo ();
                         else
                           bar ();
                       }
                   }

           Also warn for dangerous uses of the GNU extension to "?:" with
           omitted middle operand. When the condition in the "?": operator is
           a boolean expression, the omitted value is always 1.  Often
           programmers expect it to be a value computed inside the conditional
           expression instead.

           This warning is enabled by -Wall.

       -Wsequence-point
           Warn about code that may have undefined semantics because of
           violations of sequence point rules in the C and C++ standards.

           The C and C++ standards define the order in which expressions in a
           C/C++ program are evaluated in terms of sequence points, which
           represent a partial ordering between the execution of parts of the
           program: those executed before the sequence point, and those
           executed after it.  These occur after the evaluation of a full
           expression (one which is not part of a larger expression), after
           the evaluation of the first operand of a "&&", "||", "? :" or ","
           (comma) operator, before a function is called (but after the
           evaluation of its arguments and the expression denoting the called
           function), and in certain other places.  Other than as expressed by
           the sequence point rules, the order of evaluation of subexpressions
           of an expression is not specified.  All these rules describe only a
           partial order rather than a total order, since, for example, if two
           functions are called within one expression with no sequence point
           between them, the order in which the functions are called is not
           specified.  However, the standards committee have ruled that
           function calls do not overlap.

           It is not specified when between sequence points modifications to
           the values of objects take effect.  Programs whose behavior depends
           on this have undefined behavior; the C and C++ standards specify
           that "Between the previous and next sequence point an object shall
           have its stored value modified at most once by the evaluation of an
           expression.  Furthermore, the prior value shall be read only to
           determine the value to be stored.".  If a program breaks these
           rules, the results on any particular implementation are entirely
           unpredictable.

           Examples of code with undefined behavior are "a = a++;", "a[n] =
           b[n++]" and "a[i++] = i;".  Some more complicated cases are not
           diagnosed by this option, and it may give an occasional false
           positive result, but in general it has been found fairly effective
           at detecting this sort of problem in programs.

           The standard is worded confusingly, therefore there is some debate
           over the precise meaning of the sequence point rules in subtle
           cases.  Links to discussions of the problem, including proposed
           formal definitions, may be found on the GCC readings page, at
           <http://gcc.gnu.org/readings.html>.

           This warning is enabled by -Wall for C and C++.

       -Wno-return-local-addr
           Do not warn about returning a pointer (or in C++, a reference) to a
           variable that goes out of scope after the function returns.

       -Wreturn-type
           Warn whenever a function is defined with a return type that
           defaults to "int".  Also warn about any "return" statement with no
           return value in a function whose return type is not "void" (falling
           off the end of the function body is considered returning without a
           value), and about a "return" statement with an expression in a
           function whose return type is "void".

           For C++, a function without return type always produces a
           diagnostic message, even when -Wno-return-type is specified.  The
           only exceptions are main and functions defined in system headers.

           This warning is enabled by -Wall.

       -Wswitch
           Warn whenever a "switch" statement has an index of enumerated type
           and lacks a "case" for one or more of the named codes of that
           enumeration.  (The presence of a "default" label prevents this
           warning.)  "case" labels outside the enumeration range also provoke
           warnings when this option is used (even if there is a "default"
           label).  This warning is enabled by -Wall.

       -Wswitch-default
           Warn whenever a "switch" statement does not have a "default" case.

       -Wswitch-enum
           Warn whenever a "switch" statement has an index of enumerated type
           and lacks a "case" for one or more of the named codes of that
           enumeration.  "case" labels outside the enumeration range also
           provoke warnings when this option is used.  The only difference
           between -Wswitch and this option is that this option gives a
           warning about an omitted enumeration code even if there is a
           "default" label.

       -Wsync-nand (C and C++ only)
           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch"
           built-in functions are used.  These functions changed semantics in
           GCC 4.4.

       -Wtrigraphs
           Warn if any trigraphs are encountered that might change the meaning
           of the program (trigraphs within comments are not warned about).
           This warning is enabled by -Wall.

       -Wunused-but-set-parameter
           Warn whenever a function parameter is assigned to, but otherwise
           unused (aside from its declaration).

           To suppress this warning use the unused attribute.

           This warning is also enabled by -Wunused together with -Wextra.

       -Wunused-but-set-variable
           Warn whenever a local variable is assigned to, but otherwise unused
           (aside from its declaration).  This warning is enabled by -Wall.

           To suppress this warning use the unused attribute.

           This warning is also enabled by -Wunused, which is enabled by
           -Wall.

       -Wunused-function
           Warn whenever a static function is declared but not defined or a
           non-inline static function is unused.  This warning is enabled by
           -Wall.

       -Wunused-label
           Warn whenever a label is declared but not used.  This warning is
           enabled by -Wall.

           To suppress this warning use the unused attribute.

       -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
           Warn when a typedef locally defined in a function is not used.
           This warning is enabled by -Wall.

       -Wunused-parameter
           Warn whenever a function parameter is unused aside from its
           declaration.

           To suppress this warning use the unused attribute.

       -Wno-unused-result
           Do not warn if a caller of a function marked with attribute
           "warn_unused_result" does not use its return value. The default is
           -Wunused-result.

       -Wunused-variable
           Warn whenever a local variable or non-constant static variable is
           unused aside from its declaration.  This warning is enabled by
           -Wall.

           To suppress this warning use the unused attribute.

       -Wunused-value
           Warn whenever a statement computes a result that is explicitly not
           used. To suppress this warning cast the unused expression to void.
           This includes an expression-statement or the left-hand side of a
           comma expression that contains no side effects. For example, an
           expression such as x[i,j] causes a warning, while x[(void)i,j] does
           not.

           This warning is enabled by -Wall.

       -Wunused
           All the above -Wunused options combined.

           In order to get a warning about an unused function parameter, you
           must either specify -Wextra -Wunused (note that -Wall implies
           -Wunused), or separately specify -Wunused-parameter.

       -Wuninitialized
           Warn if an automatic variable is used without first being
           initialized or if a variable may be clobbered by a "setjmp" call.
           In C++, warn if a non-static reference or non-static const member
           appears in a class without constructors.

           If you want to warn about code that uses the uninitialized value of
           the variable in its own initializer, use the -Winit-self option.

           These warnings occur for individual uninitialized or clobbered
           elements of structure, union or array variables as well as for
           variables that are uninitialized or clobbered as a whole.  They do
           not occur for variables or elements declared "volatile".  Because
           these warnings depend on optimization, the exact variables or
           elements for which there are warnings depends on the precise
           optimization options and version of GCC used.

           Note that there may be no warning about a variable that is used
           only to compute a value that itself is never used, because such
           computations may be deleted by data flow analysis before the
           warnings are printed.

       -Wmaybe-uninitialized
           For an automatic variable, if there exists a path from the function
           entry to a use of the variable that is initialized, but there exist
           some other paths for which the variable is not initialized, the
           compiler emits a warning if it cannot prove the uninitialized paths
           are not executed at run time. These warnings are made optional
           because GCC is not smart enough to see all the reasons why the code
           might be correct in spite of appearing to have an error.  Here is
           one example of how this can happen:

                   {
                     int x;
                     switch (y)
                       {
                       case 1: x = 1;
                         break;
                       case 2: x = 4;
                         break;
                       case 3: x = 5;
                       }
                     foo (x);
                   }

           If the value of "y" is always 1, 2 or 3, then "x" is always
           initialized, but GCC doesn't know this. To suppress the warning,
           you need to provide a default case with assert(0) or similar code.

           This option also warns when a non-volatile automatic variable might
           be changed by a call to "longjmp".  These warnings as well are
           possible only in optimizing compilation.

           The compiler sees only the calls to "setjmp".  It cannot know where
           "longjmp" will be called; in fact, a signal handler could call it
           at any point in the code.  As a result, you may get a warning even
           when there is in fact no problem because "longjmp" cannot in fact
           be called at the place that would cause a problem.

           Some spurious warnings can be avoided if you declare all the
           functions you use that never return as "noreturn".

           This warning is enabled by -Wall or -Wextra.

       -Wunknown-pragmas
           Warn when a "#pragma" directive is encountered that is not
           understood by GCC.  If this command-line option is used, warnings
           are even issued for unknown pragmas in system header files.  This
           is not the case if the warnings are only enabled by the -Wall
           command-line option.

       -Wno-pragmas
           Do not warn about misuses of pragmas, such as incorrect parameters,
           invalid syntax, or conflicts between pragmas.  See also
           -Wunknown-pragmas.

       -Wstrict-aliasing
           This option is only active when -fstrict-aliasing is active.  It
           warns about code that might break the strict aliasing rules that
           the compiler is using for optimization.  The warning does not catch
           all cases, but does attempt to catch the more common pitfalls.  It
           is included in -Wall.  It is equivalent to -Wstrict-aliasing=3

       -Wstrict-aliasing=n
           This option is only active when -fstrict-aliasing is active.  It
           warns about code that might break the strict aliasing rules that
           the compiler is using for optimization.  Higher levels correspond
           to higher accuracy (fewer false positives).  Higher levels also
           correspond to more effort, similar to the way -O works.
           -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3.

           Level 1: Most aggressive, quick, least accurate.  Possibly useful
           when higher levels do not warn but -fstrict-aliasing still breaks
           the code, as it has very few false negatives.  However, it has many
           false positives.  Warns for all pointer conversions between
           possibly incompatible types, even if never dereferenced.  Runs in
           the front end only.

           Level 2: Aggressive, quick, not too precise.  May still have many
           false positives (not as many as level 1 though), and few false
           negatives (but possibly more than level 1).  Unlike level 1, it
           only warns when an address is taken.  Warns about incomplete types.
           Runs in the front end only.

           Level 3 (default for -Wstrict-aliasing): Should have very few false
           positives and few false negatives.  Slightly slower than levels 1
           or 2 when optimization is enabled.  Takes care of the common
           pun+dereference pattern in the front end: "*(int*)&some_float".  If
           optimization is enabled, it also runs in the back end, where it
           deals with multiple statement cases using flow-sensitive points-to
           information.  Only warns when the converted pointer is
           dereferenced.  Does not warn about incomplete types.

       -Wstrict-overflow
       -Wstrict-overflow=n
           This option is only active when -fstrict-overflow is active.  It
           warns about cases where the compiler optimizes based on the
           assumption that signed overflow does not occur.  Note that it does
           not warn about all cases where the code might overflow: it only
           warns about cases where the compiler implements some optimization.
           Thus this warning depends on the optimization level.

           An optimization that assumes that signed overflow does not occur is
           perfectly safe if the values of the variables involved are such
           that overflow never does, in fact, occur.  Therefore this warning
           can easily give a false positive: a warning about code that is not
           actually a problem.  To help focus on important issues, several
           warning levels are defined.  No warnings are issued for the use of
           undefined signed overflow when estimating how many iterations a
           loop requires, in particular when determining whether a loop will
           be executed at all.

           -Wstrict-overflow=1
               Warn about cases that are both questionable and easy to avoid.
               For example,  with -fstrict-overflow, the compiler simplifies
               "x + 1 > x" to 1.  This level of -Wstrict-overflow is enabled
               by -Wall; higher levels are not, and must be explicitly
               requested.

           -Wstrict-overflow=2
               Also warn about other cases where a comparison is simplified to
               a constant.  For example: "abs (x) >= 0".  This can only be
               simplified when -fstrict-overflow is in effect, because "abs
               (INT_MIN)" overflows to "INT_MIN", which is less than zero.
               -Wstrict-overflow (with no level) is the same as
               -Wstrict-overflow=2.

           -Wstrict-overflow=3
               Also warn about other cases where a comparison is simplified.
               For example: "x + 1 > 1" is simplified to "x > 0".

           -Wstrict-overflow=4
               Also warn about other simplifications not covered by the above
               cases.  For example: "(x * 10) / 5" is simplified to "x * 2".

           -Wstrict-overflow=5
               Also warn about cases where the compiler reduces the magnitude
               of a constant involved in a comparison.  For example: "x + 2 >
               y" is simplified to "x + 1 >= y".  This is reported only at the
               highest warning level because this simplification applies to
               many comparisons, so this warning level gives a very large
               number of false positives.

       -Wsuggest-attribute=[pure|const|noreturn|format]
           Warn for cases where adding an attribute may be beneficial. The
           attributes currently supported are listed below.

           -Wsuggest-attribute=pure
           -Wsuggest-attribute=const
           -Wsuggest-attribute=noreturn
               Warn about functions that might be candidates for attributes
               "pure", "const" or "noreturn".  The compiler only warns for
               functions visible in other compilation units or (in the case of
               "pure" and "const") if it cannot prove that the function
               returns normally. A function returns normally if it doesn't
               contain an infinite loop or return abnormally by throwing,
               calling "abort()" or trapping.  This analysis requires option
               -fipa-pure-const, which is enabled by default at -O and higher.
               Higher optimization levels improve the accuracy of the
               analysis.

           -Wsuggest-attribute=format
           -Wmissing-format-attribute
               Warn about function pointers that might be candidates for
               "format" attributes.  Note these are only possible candidates,
               not absolute ones.  GCC guesses that function pointers with
               "format" attributes that are used in assignment,
               initialization, parameter passing or return statements should
               have a corresponding "format" attribute in the resulting type.
               I.e. the left-hand side of the assignment or initialization,
               the type of the parameter variable, or the return type of the
               containing function respectively should also have a "format"
               attribute to avoid the warning.

               GCC also warns about function definitions that might be
               candidates for "format" attributes.  Again, these are only
               possible candidates.  GCC guesses that "format" attributes
               might be appropriate for any function that calls a function
               like "vprintf" or "vscanf", but this might not always be the
               case, and some functions for which "format" attributes are
               appropriate may not be detected.

       -Warray-bounds
           This option is only active when -ftree-vrp is active (default for
           -O2 and above). It warns about subscripts to arrays that are always
           out of bounds. This warning is enabled by -Wall.

       -Wno-div-by-zero
           Do not warn about compile-time integer division by zero.  Floating-
           point division by zero is not warned about, as it can be a
           legitimate way of obtaining infinities and NaNs.

       -Wsystem-headers
           Print warning messages for constructs found in system header files.
           Warnings from system headers are normally suppressed, on the
           assumption that they usually do not indicate real problems and
           would only make the compiler output harder to read.  Using this
           command-line option tells GCC to emit warnings from system headers
           as if they occurred in user code.  However, note that using -Wall
           in conjunction with this option does not warn about unknown pragmas
           in system headers---for that, -Wunknown-pragmas must also be used.

       -Wtrampolines
            Warn about trampolines generated for pointers to nested functions.

            A trampoline is a small piece of data or code that is created at run
            time on the stack when the address of a nested function is taken, and
            is used to call the nested function indirectly.  For some targets, it
            is made up of data only and thus requires no special treatment.  But,
            for most targets, it is made up of code and thus requires the stack
            to be made executable in order for the program to work properly.

       -Wfloat-equal
           Warn if floating-point values are used in equality comparisons.

           The idea behind this is that sometimes it is convenient (for the
           programmer) to consider floating-point values as approximations to
           infinitely precise real numbers.  If you are doing this, then you
           need to compute (by analyzing the code, or in some other way) the
           maximum or likely maximum error that the computation introduces,
           and allow for it when performing comparisons (and when producing
           output, but that's a different problem).  In particular, instead of
           testing for equality, you should check to see whether the two
           values have ranges that overlap; and this is done with the
           relational operators, so equality comparisons are probably
           mistaken.

       -Wtraditional (C and Objective-C only)
           Warn about certain constructs that behave differently in
           traditional and ISO C.  Also warn about ISO C constructs that have
           no traditional C equivalent, and/or problematic constructs that
           should be avoided.

              Macro parameters that appear within string literals in the
               macro body.  In traditional C macro replacement takes place
               within string literals, but in ISO C it does not.

              In traditional C, some preprocessor directives did not exist.
               Traditional preprocessors only considered a line to be a
               directive if the # appeared in column 1 on the line.  Therefore
               -Wtraditional warns about directives that traditional C
               understands but ignores because the # does not appear as the
               first character on the line.  It also suggests you hide
               directives like #pragma not understood by traditional C by
               indenting them.  Some traditional implementations do not
               recognize #elif, so this option suggests avoiding it
               altogether.

              A function-like macro that appears without arguments.

              The unary plus operator.

              The U integer constant suffix, or the F or L floating-point
               constant suffixes.  (Traditional C does support the L suffix on
               integer constants.)  Note, these suffixes appear in macros
               defined in the system headers of most modern systems, e.g. the
               _MIN/_MAX macros in "<limits.h>".  Use of these macros in user
               code might normally lead to spurious warnings, however GCC's
               integrated preprocessor has enough context to avoid warning in
               these cases.

              A function declared external in one block and then used after
               the end of the block.

              A "switch" statement has an operand of type "long".

              A non-"static" function declaration follows a "static" one.
               This construct is not accepted by some traditional C compilers.

              The ISO type of an integer constant has a different width or
               signedness from its traditional type.  This warning is only
               issued if the base of the constant is ten.  I.e. hexadecimal or
               octal values, which typically represent bit patterns, are not
               warned about.

              Usage of ISO string concatenation is detected.

              Initialization of automatic aggregates.

              Identifier conflicts with labels.  Traditional C lacks a
               separate namespace for labels.

              Initialization of unions.  If the initializer is zero, the
               warning is omitted.  This is done under the assumption that the
               zero initializer in user code appears conditioned on e.g.
               "__STDC__" to avoid missing initializer warnings and relies on
               default initialization to zero in the traditional C case.

              Conversions by prototypes between fixed/floating-point values
               and vice versa.  The absence of these prototypes when compiling
               with traditional C causes serious problems.  This is a subset
               of the possible conversion warnings; for the full set use
               -Wtraditional-conversion.

              Use of ISO C style function definitions.  This warning
               intentionally is not issued for prototype declarations or
               variadic functions because these ISO C features appear in your
               code when using libiberty's traditional C compatibility macros,
               "PARAMS" and "VPARAMS".  This warning is also bypassed for
               nested functions because that feature is already a GCC
               extension and thus not relevant to traditional C compatibility.

       -Wtraditional-conversion (C and Objective-C only)
           Warn if a prototype causes a type conversion that is different from
           what would happen to the same argument in the absence of a
           prototype.  This includes conversions of fixed point to floating
           and vice versa, and conversions changing the width or signedness of
           a fixed-point argument except when the same as the default
           promotion.

       -Wdeclaration-after-statement (C and Objective-C only)
           Warn when a declaration is found after a statement in a block.
           This construct, known from C++, was introduced with ISO C99 and is
           by default allowed in GCC.  It is not supported by ISO C90 and was
           not supported by GCC versions before GCC 3.0.

       -Wundef
           Warn if an undefined identifier is evaluated in an #if directive.

       -Wno-endif-labels
           Do not warn whenever an #else or an #endif are followed by text.

       -Wshadow
           Warn whenever a local variable or type declaration shadows another
           variable, parameter, type, or class member (in C++), or whenever a
           built-in function is shadowed. Note that in C++, the compiler warns
           if a local variable shadows an explicit typedef, but not if it
           shadows a struct/class/enum.

       -Wlarger-than=len
           Warn whenever an object of larger than len bytes is defined.

       -Wframe-larger-than=len
           Warn if the size of a function frame is larger than len bytes.  The
           computation done to determine the stack frame size is approximate
           and not conservative.  The actual requirements may be somewhat
           greater than len even if you do not get a warning.  In addition,
           any space allocated via "alloca", variable-length arrays, or
           related constructs is not included by the compiler when determining
           whether or not to issue a warning.

       -Wno-free-nonheap-object
           Do not warn when attempting to free an object that was not
           allocated on the heap.

       -Wstack-usage=len
           Warn if the stack usage of a function might be larger than len
           bytes.  The computation done to determine the stack usage is
           conservative.  Any space allocated via "alloca", variable-length
           arrays, or related constructs is included by the compiler when
           determining whether or not to issue a warning.

           The message is in keeping with the output of -fstack-usage.

              If the stack usage is fully static but exceeds the specified
               amount, it's:

                         warning: stack usage is 1120 bytes

              If the stack usage is (partly) dynamic but bounded, it's:

                         warning: stack usage might be 1648 bytes

              If the stack usage is (partly) dynamic and not bounded, it's:

                         warning: stack usage might be unbounded

       -Wunsafe-loop-optimizations
           Warn if the loop cannot be optimized because the compiler cannot
           assume anything on the bounds of the loop indices.  With
           -funsafe-loop-optimizations warn if the compiler makes such
           assumptions.

       -Wno-pedantic-ms-format (MinGW targets only)
           When used in combination with -Wformat and -pedantic without GNU
           extensions, this option disables the warnings about non-ISO
           "printf" / "scanf" format width specifiers "I32", "I64", and "I"
           used on Windows targets, which depend on the MS runtime.

       -Wpointer-arith
           Warn about anything that depends on the "size of" a function type
           or of "void".  GNU C assigns these types a size of 1, for
           convenience in calculations with "void *" pointers and pointers to
           functions.  In C++, warn also when an arithmetic operation involves
           "NULL".  This warning is also enabled by -Wpedantic.

       -Wtype-limits
           Warn if a comparison is always true or always false due to the
           limited range of the data type, but do not warn for constant
           expressions.  For example, warn if an unsigned variable is compared
           against zero with < or >=.  This warning is also enabled by
           -Wextra.

       -Wbad-function-cast (C and Objective-C only)
           Warn whenever a function call is cast to a non-matching type.  For
           example, warn if "int malloc()" is cast to "anything *".

       -Wc++-compat (C and Objective-C only)
           Warn about ISO C constructs that are outside of the common subset
           of ISO C and ISO C++, e.g. request for implicit conversion from
           "void *" to a pointer to non-"void" type.

       -Wc++11-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++
           1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are
           keywords in ISO C++ 2011.  This warning turns on -Wnarrowing and is
           enabled by -Wall.

       -Wcast-qual
           Warn whenever a pointer is cast so as to remove a type qualifier
           from the target type.  For example, warn if a "const char *" is
           cast to an ordinary "char *".

           Also warn when making a cast that introduces a type qualifier in an
           unsafe way.  For example, casting "char **" to "const char **" is
           unsafe, as in this example:

                     /* p is char ** value.  */
                     const char **q = (const char **) p;
                     /* Assignment of readonly string to const char * is OK.  */
                     *q = "string";
                     /* Now char** pointer points to read-only memory.  */
                     **p = 'b';

       -Wcast-align
           Warn whenever a pointer is cast such that the required alignment of
           the target is increased.  For example, warn if a "char *" is cast
           to an "int *" on machines where integers can only be accessed at
           two- or four-byte boundaries.

       -Wwrite-strings
           When compiling C, give string constants the type "const
           char[length]" so that copying the address of one into a non-"const"
           "char *" pointer produces a warning.  These warnings help you find
           at compile time code that can try to write into a string constant,
           but only if you have been very careful about using "const" in
           declarations and prototypes.  Otherwise, it is just a nuisance.
           This is why we did not make -Wall request these warnings.

           When compiling C++, warn about the deprecated conversion from
           string literals to "char *".  This warning is enabled by default
           for C++ programs.

       -Wclobbered
           Warn for variables that might be changed by longjmp or vfork.  This
           warning is also enabled by -Wextra.

       -Wconversion
           Warn for implicit conversions that may alter a value. This includes
           conversions between real and integer, like "abs (x)" when "x" is
           "double"; conversions between signed and unsigned, like "unsigned
           ui = -1"; and conversions to smaller types, like "sqrtf (M_PI)". Do
           not warn for explicit casts like "abs ((int) x)" and "ui =
           (unsigned) -1", or if the value is not changed by the conversion
           like in "abs (2.0)".  Warnings about conversions between signed and
           unsigned integers can be disabled by using -Wno-sign-conversion.

           For C++, also warn for confusing overload resolution for user-
           defined conversions; and conversions that never use a type
           conversion operator: conversions to "void", the same type, a base
           class or a reference to them. Warnings about conversions between
           signed and unsigned integers are disabled by default in C++ unless
           -Wsign-conversion is explicitly enabled.

       -Wno-conversion-null (C++ and Objective-C++ only)
           Do not warn for conversions between "NULL" and non-pointer types.
           -Wconversion-null is enabled by default.

       -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
           Warn when a literal '0' is used as null pointer constant.  This can
           be useful to facilitate the conversion to "nullptr" in C++11.

       -Wuseless-cast (C++ and Objective-C++ only)
           Warn when an expression is casted to its own type.

       -Wempty-body
           Warn if an empty body occurs in an if, else or do while statement.
           This warning is also enabled by -Wextra.

       -Wenum-compare
           Warn about a comparison between values of different enumerated
           types.  In C++ enumeral mismatches in conditional expressions are
           also diagnosed and the warning is enabled by default.  In C this
           warning is enabled by -Wall.

       -Wjump-misses-init (C, Objective-C only)
           Warn if a "goto" statement or a "switch" statement jumps forward
           across the initialization of a variable, or jumps backward to a
           label after the variable has been initialized.  This only warns
           about variables that are initialized when they are declared.  This
           warning is only supported for C and Objective-C; in C++ this sort
           of branch is an error in any case.

           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled
           with the -Wno-jump-misses-init option.

       -Wsign-compare
           Warn when a comparison between signed and unsigned values could
           produce an incorrect result when the signed value is converted to
           unsigned.  This warning is also enabled by -Wextra; to get the
           other warnings of -Wextra without this warning, use -Wextra
           -Wno-sign-compare.

       -Wsign-conversion
           Warn for implicit conversions that may change the sign of an
           integer value, like assigning a signed integer expression to an
           unsigned integer variable. An explicit cast silences the warning.
           In C, this option is enabled also by -Wconversion.

       -Wsizeof-pointer-memaccess
           Warn for suspicious length parameters to certain string and memory
           built-in functions if the argument uses "sizeof".  This warning
           warns e.g.  about "memset (ptr, 0, sizeof (ptr));" if "ptr" is not
           an array, but a pointer, and suggests a possible fix, or about
           "memcpy (&foo, ptr, sizeof (&foo));".  This warning is enabled by
           -Wall.

       -Waddress
           Warn about suspicious uses of memory addresses. These include using
           the address of a function in a conditional expression, such as
           "void func(void); if (func)", and comparisons against the memory
           address of a string literal, such as "if (x == "abc")".  Such uses
           typically indicate a programmer error: the address of a function
           always evaluates to true, so their use in a conditional usually
           indicate that the programmer forgot the parentheses in a function
           call; and comparisons against string literals result in unspecified
           behavior and are not portable in C, so they usually indicate that
           the programmer intended to use "strcmp".  This warning is enabled
           by -Wall.

       -Wlogical-op
           Warn about suspicious uses of logical operators in expressions.
           This includes using logical operators in contexts where a bit-wise
           operator is likely to be expected.

       -Waggregate-return
           Warn if any functions that return structures or unions are defined
           or called.  (In languages where you can return an array, this also
           elicits a warning.)

       -Wno-aggressive-loop-optimizations
           Warn if in a loop with constant number of iterations the compiler
           detects undefined behavior in some statement during one or more of
           the iterations.

       -Wno-attributes
           Do not warn if an unexpected "__attribute__" is used, such as
           unrecognized attributes, function attributes applied to variables,
           etc.  This does not stop errors for incorrect use of supported
           attributes.

       -Wno-builtin-macro-redefined
           Do not warn if certain built-in macros are redefined.  This
           suppresses warnings for redefinition of "__TIMESTAMP__",
           "__TIME__", "__DATE__", "__FILE__", and "__BASE_FILE__".

       -Wstrict-prototypes (C and Objective-C only)
           Warn if a function is declared or defined without specifying the
           argument types.  (An old-style function definition is permitted
           without a warning if preceded by a declaration that specifies the
           argument types.)

       -Wold-style-declaration (C and Objective-C only)
           Warn for obsolescent usages, according to the C Standard, in a
           declaration. For example, warn if storage-class specifiers like
           "static" are not the first things in a declaration.  This warning
           is also enabled by -Wextra.

       -Wold-style-definition (C and Objective-C only)
           Warn if an old-style function definition is used.  A warning is
           given even if there is a previous prototype.

       -Wmissing-parameter-type (C and Objective-C only)
           A function parameter is declared without a type specifier in
           K&R-style functions:

                   void foo(bar) { }

           This warning is also enabled by -Wextra.

       -Wmissing-prototypes (C and Objective-C only)
           Warn if a global function is defined without a previous prototype
           declaration.  This warning is issued even if the definition itself
           provides a prototype.  Use this option to detect global functions
           that do not have a matching prototype declaration in a header file.
           This option is not valid for C++ because all function declarations
           provide prototypes and a non-matching declaration will declare an
           overload rather than conflict with an earlier declaration.  Use
           -Wmissing-declarations to detect missing declarations in C++.

       -Wmissing-declarations
           Warn if a global function is defined without a previous
           declaration.  Do so even if the definition itself provides a
           prototype.  Use this option to detect global functions that are not
           declared in header files.  In C, no warnings are issued for
           functions with previous non-prototype declarations; use
           -Wmissing-prototype to detect missing prototypes.  In C++, no
           warnings are issued for function templates, or for inline
           functions, or for functions in anonymous namespaces.

       -Wmissing-field-initializers
           Warn if a structure's initializer has some fields missing.  For
           example, the following code causes such a warning, because "x.h" is
           implicitly zero:

                   struct s { int f, g, h; };
                   struct s x = { 3, 4 };

           This option does not warn about designated initializers, so the
           following modification does not trigger a warning:

                   struct s { int f, g, h; };
                   struct s x = { .f = 3, .g = 4 };

           This warning is included in -Wextra.  To get other -Wextra warnings
           without this one, use -Wextra -Wno-missing-field-initializers.

       -Wno-multichar
           Do not warn if a multicharacter constant ('FOOF') is used.  Usually
           they indicate a typo in the user's code, as they have
           implementation-defined values, and should not be used in portable
           code.

       -Wnormalized=<none|id|nfc|nfkc>
           In ISO C and ISO C++, two identifiers are different if they are
           different sequences of characters.  However, sometimes when
           characters outside the basic ASCII character set are used, you can
           have two different character sequences that look the same.  To
           avoid confusion, the ISO 10646 standard sets out some normalization
           rules which when applied ensure that two sequences that look the
           same are turned into the same sequence.  GCC can warn you if you
           are using identifiers that have not been normalized; this option
           controls that warning.

           There are four levels of warning supported by GCC.  The default is
           -Wnormalized=nfc, which warns about any identifier that is not in
           the ISO 10646 "C" normalized form, NFC.  NFC is the recommended
           form for most uses.

           Unfortunately, there are some characters allowed in identifiers by
           ISO C and ISO C++ that, when turned into NFC, are not allowed in
           identifiers.  That is, there's no way to use these symbols in
           portable ISO C or C++ and have all your identifiers in NFC.
           -Wnormalized=id suppresses the warning for these characters.  It is
           hoped that future versions of the standards involved will correct
           this, which is why this option is not the default.

           You can switch the warning off for all characters by writing
           -Wnormalized=none.  You should only do this if you are using some
           other normalization scheme (like "D"), because otherwise you can
           easily create bugs that are literally impossible to see.

           Some characters in ISO 10646 have distinct meanings but look
           identical in some fonts or display methodologies, especially once
           formatting has been applied.  For instance "\u207F", "SUPERSCRIPT
           LATIN SMALL LETTER N", displays just like a regular "n" that has
           been placed in a superscript.  ISO 10646 defines the NFKC
           normalization scheme to convert all these into a standard form as
           well, and GCC warns if your code is not in NFKC if you use
           -Wnormalized=nfkc.  This warning is comparable to warning about
           every identifier that contains the letter O because it might be
           confused with the digit 0, and so is not the default, but may be
           useful as a local coding convention if the programming environment
           cannot be fixed to display these characters distinctly.

       -Wno-deprecated
           Do not warn about usage of deprecated features.

       -Wno-deprecated-declarations
           Do not warn about uses of functions, variables, and types marked as
           deprecated by using the "deprecated" attribute.

       -Wno-overflow
           Do not warn about compile-time overflow in constant expressions.

       -Woverride-init (C and Objective-C only)
           Warn if an initialized field without side effects is overridden
           when using designated initializers.

           This warning is included in -Wextra.  To get other -Wextra warnings
           without this one, use -Wextra -Wno-override-init.

       -Wpacked
           Warn if a structure is given the packed attribute, but the packed
           attribute has no effect on the layout or size of the structure.
           Such structures may be mis-aligned for little benefit.  For
           instance, in this code, the variable "f.x" in "struct bar" is
           misaligned even though "struct bar" does not itself have the packed
           attribute:

                   struct foo {
                     int x;
                     char a, b, c, d;
                   } __attribute__((packed));
                   struct bar {
                     char z;
                     struct foo f;
                   };

       -Wpacked-bitfield-compat
           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on
           bit-fields of type "char".  This has been fixed in GCC 4.4 but the
           change can lead to differences in the structure layout.  GCC
           informs you when the offset of such a field has changed in GCC 4.4.
           For example there is no longer a 4-bit padding between field "a"
           and "b" in this structure:

                   struct foo
                   {
                     char a:4;
                     char b:8;
                   } __attribute__ ((packed));

           This warning is enabled by default.  Use
           -Wno-packed-bitfield-compat to disable this warning.

       -Wpadded
           Warn if padding is included in a structure, either to align an
           element of the structure or to align the whole structure.
           Sometimes when this happens it is possible to rearrange the fields
           of the structure to reduce the padding and so make the structure
           smaller.

       -Wredundant-decls
           Warn if anything is declared more than once in the same scope, even
           in cases where multiple declaration is valid and changes nothing.

       -Wnested-externs (C and Objective-C only)
           Warn if an "extern" declaration is encountered within a function.

       -Wno-inherited-variadic-ctor
           Suppress warnings about use of C++11 inheriting constructors when
           the base class inherited from has a C variadic constructor; the
           warning is on by default because the ellipsis is not inherited.

       -Winline
           Warn if a function that is declared as inline cannot be inlined.
           Even with this option, the compiler does not warn about failures to
           inline functions declared in system headers.

           The compiler uses a variety of heuristics to determine whether or
           not to inline a function.  For example, the compiler takes into
           account the size of the function being inlined and the amount of
           inlining that has already been done in the current function.
           Therefore, seemingly insignificant changes in the source program
           can cause the warnings produced by -Winline to appear or disappear.

       -Wno-invalid-offsetof (C++ and Objective-C++ only)
           Suppress warnings from applying the offsetof macro to a non-POD
           type.  According to the 1998 ISO C++ standard, applying offsetof to
           a non-POD type is undefined.  In existing C++ implementations,
           however, offsetof typically gives meaningful results even when
           applied to certain kinds of non-POD types (such as a simple struct
           that fails to be a POD type only by virtue of having a
           constructor).  This flag is for users who are aware that they are
           writing nonportable code and who have deliberately chosen to ignore
           the warning about it.

           The restrictions on offsetof may be relaxed in a future version of
           the C++ standard.

       -Wno-int-to-pointer-cast
           Suppress warnings from casts to pointer type of an integer of a
           different size. In C++, casting to a pointer type of smaller size
           is an error. Wint-to-pointer-cast is enabled by default.

       -Wno-pointer-to-int-cast (C and Objective-C only)
           Suppress warnings from casts from a pointer to an integer type of a
           different size.

       -Winvalid-pch
           Warn if a precompiled header is found in the search path but can't
           be used.

       -Wlong-long
           Warn if long long type is used.  This is enabled by either
           -Wpedantic or -Wtraditional in ISO C90 and C++98 modes.  To inhibit
           the warning messages, use -Wno-long-long.

       -Wvariadic-macros
           Warn if variadic macros are used in pedantic ISO C90 mode, or the
           GNU alternate syntax when in pedantic ISO C99 mode.  This is
           default.  To inhibit the warning messages, use
           -Wno-variadic-macros.

       -Wvarargs
           Warn upon questionable usage of the macros used to handle variable
           arguments like va_start.  This is default.  To inhibit the warning
           messages, use -Wno-varargs.

       -Wvector-operation-performance
           Warn if vector operation is not implemented via SIMD capabilities
           of the architecture.  Mainly useful for the performance tuning.
           Vector operation can be implemented "piecewise", which means that
           the scalar operation is performed on every vector element; "in
           parallel", which means that the vector operation is implemented
           using scalars of wider type, which normally is more performance
           efficient; and "as a single scalar", which means that vector fits
           into a scalar type.

       -Wno-virtual-move-assign
           Suppress warnings about inheriting from a virtual base with a non-
           trivial C++11 move assignment operator.  This is dangerous because
           if the virtual base is reachable along more than one path, it will
           be moved multiple times, which can mean both objects end up in the
           moved-from state.  If the move assignment operator is written to
           avoid moving from a moved-from object, this warning can be
           disabled.

       -Wvla
           Warn if variable length array is used in the code.  -Wno-vla
           prevents the -Wpedantic warning of the variable length array.

       -Wvolatile-register-var
           Warn if a register variable is declared volatile.  The volatile
           modifier does not inhibit all optimizations that may eliminate
           reads and/or writes to register variables.  This warning is enabled
           by -Wall.

       -Wdisabled-optimization
           Warn if a requested optimization pass is disabled.  This warning
           does not generally indicate that there is anything wrong with your
           code; it merely indicates that GCC's optimizers are unable to
           handle the code effectively.  Often, the problem is that your code
           is too big or too complex; GCC refuses to optimize programs when
           the optimization itself is likely to take inordinate amounts of
           time.

       -Wpointer-sign (C and Objective-C only)
           Warn for pointer argument passing or assignment with different
           signedness.  This option is only supported for C and Objective-C.
           It is implied by -Wall and by -Wpedantic, which can be disabled
           with -Wno-pointer-sign.

       -Wstack-protector
           This option is only active when -fstack-protector is active.  It
           warns about functions that are not protected against stack
           smashing.

       -Wno-mudflap
           Suppress warnings about constructs that cannot be instrumented by
           -fmudflap.

       -Woverlength-strings
           Warn about string constants that are longer than the "minimum
           maximum" length specified in the C standard.  Modern compilers
           generally allow string constants that are much longer than the
           standard's minimum limit, but very portable programs should avoid
           using longer strings.

           The limit applies after string constant concatenation, and does not
           count the trailing NUL.  In C90, the limit was 509 characters; in
           C99, it was raised to 4095.  C++98 does not specify a normative
           minimum maximum, so we do not diagnose overlength strings in C++.

           This option is implied by -Wpedantic, and can be disabled with
           -Wno-overlength-strings.

       -Wunsuffixed-float-constants (C and Objective-C only)
           Issue a warning for any floating constant that does not have a
           suffix.  When used together with -Wsystem-headers it warns about
           such constants in system header files.  This can be useful when
           preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma from
           the decimal floating-point extension to C99.

   Options for Debugging Your Program or GCC
       GCC has various special options that are used for debugging either your
       program or GCC:

       -g  Produce debugging information in the operating system's native
           format (stabs, COFF, XCOFF, or DWARF 2).  GDB can work with this
           debugging information.

           On most systems that use stabs format, -g enables use of extra
           debugging information that only GDB can use; this extra information
           makes debugging work better in GDB but probably makes other
           debuggers crash or refuse to read the program.  If you want to
           control for certain whether to generate the extra information, use
           -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).

           GCC allows you to use -g with -O.  The shortcuts taken by optimized
           code may occasionally produce surprising results: some variables
           you declared may not exist at all; flow of control may briefly move
           where you did not expect it; some statements may not be executed
           because they compute constant results or their values are already
           at hand; some statements may execute in different places because
           they have been moved out of loops.

           Nevertheless it proves possible to debug optimized output.  This
           makes it reasonable to use the optimizer for programs that might
           have bugs.

           The following options are useful when GCC is generated with the
           capability for more than one debugging format.

       -gsplit-dwarf
           Separate as much dwarf debugging information as possible into a
           separate output file with the extension .dwo.  This option allows
           the build system to avoid linking files with debug information.  To
           be useful, this option requires a debugger capable of reading .dwo
           files.

       -ggdb
           Produce debugging information for use by GDB.  This means to use
           the most expressive format available (DWARF 2, stabs, or the native
           format if neither of those are supported), including GDB extensions
           if at all possible.

       -gpubnames
           Generate dwarf .debug_pubnames and .debug_pubtypes sections.

       -gstabs
           Produce debugging information in stabs format (if that is
           supported), without GDB extensions.  This is the format used by DBX
           on most BSD systems.  On MIPS, Alpha and System V Release 4 systems
           this option produces stabs debugging output that is not understood
           by DBX or SDB.  On System V Release 4 systems this option requires
           the GNU assembler.

       -feliminate-unused-debug-symbols
           Produce debugging information in stabs format (if that is
           supported), for only symbols that are actually used.

       -femit-class-debug-always
           Instead of emitting debugging information for a C++ class in only
           one object file, emit it in all object files using the class.  This
           option should be used only with debuggers that are unable to handle
           the way GCC normally emits debugging information for classes
           because using this option increases the size of debugging
           information by as much as a factor of two.

       -fdebug-types-section
           When using DWARF Version 4 or higher, type DIEs can be put into
           their own ".debug_types" section instead of making them part of the
           ".debug_info" section.  It is more efficient to put them in a
           separate comdat sections since the linker can then remove
           duplicates.  But not all DWARF consumers support ".debug_types"
           sections yet and on some objects ".debug_types" produces larger
           instead of smaller debugging information.

       -gstabs+
           Produce debugging information in stabs format (if that is
           supported), using GNU extensions understood only by the GNU
           debugger (GDB).  The use of these extensions is likely to make
           other debuggers crash or refuse to read the program.

       -gcoff
           Produce debugging information in COFF format (if that is
           supported).  This is the format used by SDB on most System V
           systems prior to System V Release 4.

       -gxcoff
           Produce debugging information in XCOFF format (if that is
           supported).  This is the format used by the DBX debugger on IBM
           RS/6000 systems.

       -gxcoff+
           Produce debugging information in XCOFF format (if that is
           supported), using GNU extensions understood only by the GNU
           debugger (GDB).  The use of these extensions is likely to make
           other debuggers crash or refuse to read the program, and may cause
           assemblers other than the GNU assembler (GAS) to fail with an
           error.

       -gdwarf-version
           Produce debugging information in DWARF format (if that is
           supported).  The value of version may be either 2, 3 or 4; the
           default version for most targets is 4.

           Note that with DWARF Version 2, some ports require and always use
           some non-conflicting DWARF 3 extensions in the unwind tables.

           Version 4 may require GDB 7.0 and -fvar-tracking-assignments for
           maximum benefit.

       -grecord-gcc-switches
           This switch causes the command-line options used to invoke the
           compiler that may affect code generation to be appended to the
           DW_AT_producer attribute in DWARF debugging information.  The
           options are concatenated with spaces separating them from each
           other and from the compiler version.  See also
           -frecord-gcc-switches for another way of storing compiler options
           into the object file.  This is the default.

       -gno-record-gcc-switches
           Disallow appending command-line options to the DW_AT_producer
           attribute in DWARF debugging information.

       -gstrict-dwarf
           Disallow using extensions of later DWARF standard version than
           selected with -gdwarf-version.  On most targets using non-
           conflicting DWARF extensions from later standard versions is
           allowed.

       -gno-strict-dwarf
           Allow using extensions of later DWARF standard version than
           selected with -gdwarf-version.

       -gvms
           Produce debugging information in Alpha/VMS debug format (if that is
           supported).  This is the format used by DEBUG on Alpha/VMS systems.

       -glevel
       -ggdblevel
       -gstabslevel
       -gcofflevel
       -gxcofflevel
       -gvmslevel
           Request debugging information and also use level to specify how
           much information.  The default level is 2.

           Level 0 produces no debug information at all.  Thus, -g0 negates
           -g.

           Level 1 produces minimal information, enough for making backtraces
           in parts of the program that you don't plan to debug.  This
           includes descriptions of functions and external variables, but no
           information about local variables and no line numbers.

           Level 3 includes extra information, such as all the macro
           definitions present in the program.  Some debuggers support macro
           expansion when you use -g3.

           -gdwarf-2 does not accept a concatenated debug level, because GCC
           used to support an option -gdwarf that meant to generate debug
           information in version 1 of the DWARF format (which is very
           different from version 2), and it would have been too confusing.
           That debug format is long obsolete, but the option cannot be
           changed now.  Instead use an additional -glevel option to change
           the debug level for DWARF.

       -gtoggle
           Turn off generation of debug info, if leaving out this option
           generates it, or turn it on at level 2 otherwise.  The position of
           this argument in the command line does not matter; it takes effect
           after all other options are processed, and it does so only once, no
           matter how many times it is given.  This is mainly intended to be
           used with -fcompare-debug.

       -fsanitize=address
           Enable AddressSanitizer, a fast memory error detector.  Memory
           access instructions will be instrumented to detect out-of-bounds
           and use-after-free bugs.  See
           <http://code.google.com/p/address-sanitizer/> for more details.

       -fsanitize=thread
           Enable ThreadSanitizer, a fast data race detector.  Memory access
           instructions will be instrumented to detect data race bugs.  See
           <http://code.google.com/p/data-race-test/wiki/ThreadSanitizer> for
           more details.

       -fdump-final-insns[=file]
           Dump the final internal representation (RTL) to file.  If the
           optional argument is omitted (or if file is "."), the name of the
           dump file is determined by appending ".gkd" to the compilation
           output file name.

       -fcompare-debug[=opts]
           If no error occurs during compilation, run the compiler a second
           time, adding opts and -fcompare-debug-second to the arguments
           passed to the second compilation.  Dump the final internal
           representation in both compilations, and print an error if they
           differ.

           If the equal sign is omitted, the default -gtoggle is used.

           The environment variable GCC_COMPARE_DEBUG, if defined, non-empty
           and nonzero, implicitly enables -fcompare-debug.  If
           GCC_COMPARE_DEBUG is defined to a string starting with a dash, then
           it is used for opts, otherwise the default -gtoggle is used.

           -fcompare-debug=, with the equal sign but without opts, is
           equivalent to -fno-compare-debug, which disables the dumping of the
           final representation and the second compilation, preventing even
           GCC_COMPARE_DEBUG from taking effect.

           To verify full coverage during -fcompare-debug testing, set
           GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC
           rejects as an invalid option in any actual compilation (rather than
           preprocessing, assembly or linking).  To get just a warning,
           setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden
           will do.

       -fcompare-debug-second
           This option is implicitly passed to the compiler for the second
           compilation requested by -fcompare-debug, along with options to
           silence warnings, and omitting other options that would cause side-
           effect compiler outputs to files or to the standard output.  Dump
           files and preserved temporary files are renamed so as to contain
           the ".gk" additional extension during the second compilation, to
           avoid overwriting those generated by the first.

           When this option is passed to the compiler driver, it causes the
           first compilation to be skipped, which makes it useful for little
           other than debugging the compiler proper.

       -feliminate-dwarf2-dups
           Compress DWARF 2 debugging information by eliminating duplicated
           information about each symbol.  This option only makes sense when
           generating DWARF 2 debugging information with -gdwarf-2.

       -femit-struct-debug-baseonly
           Emit debug information for struct-like types only when the base
           name of the compilation source file matches the base name of file
           in which the struct is defined.

           This option substantially reduces the size of debugging
           information, but at significant potential loss in type information
           to the debugger.  See -femit-struct-debug-reduced for a less
           aggressive option.  See -femit-struct-debug-detailed for more
           detailed control.

           This option works only with DWARF 2.

       -femit-struct-debug-reduced
           Emit debug information for struct-like types only when the base
           name of the compilation source file matches the base name of file
           in which the type is defined, unless the struct is a template or
           defined in a system header.

           This option significantly reduces the size of debugging
           information, with some potential loss in type information to the
           debugger.  See -femit-struct-debug-baseonly for a more aggressive
           option.  See -femit-struct-debug-detailed for more detailed
           control.

           This option works only with DWARF 2.

       -femit-struct-debug-detailed[=spec-list]
           Specify the struct-like types for which the compiler generates
           debug information.  The intent is to reduce duplicate struct debug
           information between different object files within the same program.

           This option is a detailed version of -femit-struct-debug-reduced
           and -femit-struct-debug-baseonly, which serves for most needs.

           A specification has the
           syntax[dir:|ind:][ord:|gen:](any|sys|base|none)

           The optional first word limits the specification to structs that
           are used directly (dir:) or used indirectly (ind:).  A struct type
           is used directly when it is the type of a variable, member.
           Indirect uses arise through pointers to structs.  That is, when use
           of an incomplete struct is valid, the use is indirect.  An example
           is struct one direct; struct two * indirect;.

           The optional second word limits the specification to ordinary
           structs (ord:) or generic structs (gen:).  Generic structs are a
           bit complicated to explain.  For C++, these are non-explicit
           specializations of template classes, or non-template classes within
           the above.  Other programming languages have generics, but
           -femit-struct-debug-detailed does not yet implement them.

           The third word specifies the source files for those structs for
           which the compiler should emit debug information.  The values none
           and any have the normal meaning.  The value base means that the
           base of name of the file in which the type declaration appears must
           match the base of the name of the main compilation file.  In
           practice, this means that when compiling foo.c, debug information
           is generated for types declared in that file and foo.h, but not
           other header files.  The value sys means those types satisfying
           base or declared in system or compiler headers.

           You may need to experiment to determine the best settings for your
           application.

           The default is -femit-struct-debug-detailed=all.

           This option works only with DWARF 2.

       -fno-merge-debug-strings
           Direct the linker to not merge together strings in the debugging
           information that are identical in different object files.  Merging
           is not supported by all assemblers or linkers.  Merging decreases
           the size of the debug information in the output file at the cost of
           increasing link processing time.  Merging is enabled by default.

       -fdebug-prefix-map=old=new
           When compiling files in directory old, record debugging information
           describing them as in new instead.

       -fno-dwarf2-cfi-asm
           Emit DWARF 2 unwind info as compiler generated ".eh_frame" section
           instead of using GAS ".cfi_*" directives.

       -p  Generate extra code to write profile information suitable for the
           analysis program prof.  You must use this option when compiling the
           source files you want data about, and you must also use it when
           linking.

       -pg Generate extra code to write profile information suitable for the
           analysis program gprof.  You must use this option when compiling
           the source files you want data about, and you must also use it when
           linking.

       -Q  Makes the compiler print out each function name as it is compiled,
           and print some statistics about each pass when it finishes.

       -ftime-report
           Makes the compiler print some statistics about the time consumed by
           each pass when it finishes.

       -fmem-report
           Makes the compiler print some statistics about permanent memory
           allocation when it finishes.

       -fmem-report-wpa
           Makes the compiler print some statistics about permanent memory
           allocation for the WPA phase only.

       -fpre-ipa-mem-report
       -fpost-ipa-mem-report
           Makes the compiler print some statistics about permanent memory
           allocation before or after interprocedural optimization.

       -fprofile-report
           Makes the compiler print some statistics about consistency of the
           (estimated) profile and effect of individual passes.

       -fstack-usage
           Makes the compiler output stack usage information for the program,
           on a per-function basis.  The filename for the dump is made by
           appending .su to the auxname.  auxname is generated from the name
           of the output file, if explicitly specified and it is not an
           executable, otherwise it is the basename of the source file.  An
           entry is made up of three fields:

              The name of the function.

              A number of bytes.

              One or more qualifiers: "static", "dynamic", "bounded".

           The qualifier "static" means that the function manipulates the
           stack statically: a fixed number of bytes are allocated for the
           frame on function entry and released on function exit; no stack
           adjustments are otherwise made in the function.  The second field
           is this fixed number of bytes.

           The qualifier "dynamic" means that the function manipulates the
           stack dynamically: in addition to the static allocation described
           above, stack adjustments are made in the body of the function, for
           example to push/pop arguments around function calls.  If the
           qualifier "bounded" is also present, the amount of these
           adjustments is bounded at compile time and the second field is an
           upper bound of the total amount of stack used by the function.  If
           it is not present, the amount of these adjustments is not bounded
           at compile time and the second field only represents the bounded
           part.

       -fprofile-arcs
           Add code so that program flow arcs are instrumented.  During
           execution the program records how many times each branch and call
           is executed and how many times it is taken or returns.  When the
           compiled program exits it saves this data to a file called
           auxname.gcda for each source file.  The data may be used for
           profile-directed optimizations (-fbranch-probabilities), or for
           test coverage analysis (-ftest-coverage).  Each object file's
           auxname is generated from the name of the output file, if
           explicitly specified and it is not the final executable, otherwise
           it is the basename of the source file.  In both cases any suffix is
           removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda
           for output file specified as -o dir/foo.o).

       --coverage
           This option is used to compile and link code instrumented for
           coverage analysis.  The option is a synonym for -fprofile-arcs
           -ftest-coverage (when compiling) and -lgcov (when linking).  See
           the documentation for those options for more details.

              Compile the source files with -fprofile-arcs plus optimization
               and code generation options.  For test coverage analysis, use
               the additional -ftest-coverage option.  You do not need to
               profile every source file in a program.

              Link your object files with -lgcov or -fprofile-arcs (the
               latter implies the former).

              Run the program on a representative workload to generate the
               arc profile information.  This may be repeated any number of
               times.  You can run concurrent instances of your program, and
               provided that the file system supports locking, the data files
               will be correctly updated.  Also "fork" calls are detected and
               correctly handled (double counting will not happen).

              For profile-directed optimizations, compile the source files
               again with the same optimization and code generation options
               plus -fbranch-probabilities.

              For test coverage analysis, use gcov to produce human readable
               information from the .gcno and .gcda files.  Refer to the gcov
               documentation for further information.

           With -fprofile-arcs, for each function of your program GCC creates
           a program flow graph, then finds a spanning tree for the graph.
           Only arcs that are not on the spanning tree have to be
           instrumented: the compiler adds code to count the number of times
           that these arcs are executed.  When an arc is the only exit or only
           entrance to a block, the instrumentation code can be added to the
           block; otherwise, a new basic block must be created to hold the
           instrumentation code.

       -ftest-coverage
           Produce a notes file that the gcov code-coverage utility can use to
           show program coverage.  Each source file's note file is called
           auxname.gcno.  Refer to the -fprofile-arcs option above for a
           description of auxname and instructions on how to generate test
           coverage data.  Coverage data matches the source files more closely
           if you do not optimize.

       -fdbg-cnt-list
           Print the name and the counter upper bound for all debug counters.

       -fdbg-cnt=counter-value-list
           Set the internal debug counter upper bound.  counter-value-list is
           a comma-separated list of name:value pairs which sets the upper
           bound of each debug counter name to value.  All debug counters have
           the initial upper bound of "UINT_MAX"; thus "dbg_cnt()" returns
           true always unless the upper bound is set by this option.  For
           example, with -fdbg-cnt=dce:10,tail_call:0, "dbg_cnt(dce)" returns
           true only for first 10 invocations.

       -fenable-kind-pass
       -fdisable-kind-pass=range-list
           This is a set of options that are used to explicitly disable/enable
           optimization passes.  These options are intended for use for
           debugging GCC.  Compiler users should use regular options for
           enabling/disabling passes instead.

           -fdisable-ipa-pass
               Disable IPA pass pass. pass is the pass name.  If the same pass
               is statically invoked in the compiler multiple times, the pass
               name should be appended with a sequential number starting from
               1.

           -fdisable-rtl-pass
           -fdisable-rtl-pass=range-list
               Disable RTL pass pass.  pass is the pass name.  If the same
               pass is statically invoked in the compiler multiple times, the
               pass name should be appended with a sequential number starting
               from 1.  range-list is a comma-separated list of function
               ranges or assembler names.  Each range is a number pair
               separated by a colon.  The range is inclusive in both ends.  If
               the range is trivial, the number pair can be simplified as a
               single number.  If the function's call graph node's uid falls
               within one of the specified ranges, the pass is disabled for
               that function.  The uid is shown in the function header of a
               dump file, and the pass names can be dumped by using option
               -fdump-passes.

           -fdisable-tree-pass
           -fdisable-tree-pass=range-list
               Disable tree pass pass.  See -fdisable-rtl for the description
               of option arguments.

           -fenable-ipa-pass
               Enable IPA pass pass.  pass is the pass name.  If the same pass
               is statically invoked in the compiler multiple times, the pass
               name should be appended with a sequential number starting from
               1.

           -fenable-rtl-pass
           -fenable-rtl-pass=range-list
               Enable RTL pass pass.  See -fdisable-rtl for option argument
               description and examples.

           -fenable-tree-pass
           -fenable-tree-pass=range-list
               Enable tree pass pass.  See -fdisable-rtl for the description
               of option arguments.

           Here are some examples showing uses of these options.

                   # disable ccp1 for all functions
                      -fdisable-tree-ccp1
                   # disable complete unroll for function whose cgraph node uid is 1
                      -fenable-tree-cunroll=1
                   # disable gcse2 for functions at the following ranges [1,1],
                   # [300,400], and [400,1000]
                   # disable gcse2 for functions foo and foo2
                      -fdisable-rtl-gcse2=foo,foo2
                   # disable early inlining
                      -fdisable-tree-einline
                   # disable ipa inlining
                      -fdisable-ipa-inline
                   # enable tree full unroll
                      -fenable-tree-unroll

       -dletters
       -fdump-rtl-pass
       -fdump-rtl-pass=filename
           Says to make debugging dumps during compilation at times specified
           by letters.  This is used for debugging the RTL-based passes of the
           compiler.  The file names for most of the dumps are made by
           appending a pass number and a word to the dumpname, and the files
           are created in the directory of the output file. In case of
           =filename option, the dump is output on the given file instead of
           the pass numbered dump files. Note that the pass number is computed
           statically as passes get registered into the pass manager.  Thus
           the numbering is not related to the dynamic order of execution of
           passes.  In particular, a pass installed by a plugin could have a
           number over 200 even if it executed quite early.  dumpname is
           generated from the name of the output file, if explicitly specified
           and it is not an executable, otherwise it is the basename of the
           source file. These switches may have different effects when -E is
           used for preprocessing.

           Debug dumps can be enabled with a -fdump-rtl switch or some -d
           option letters.  Here are the possible letters for use in pass and
           letters, and their meanings:

           -fdump-rtl-alignments
               Dump after branch alignments have been computed.

           -fdump-rtl-asmcons
               Dump after fixing rtl statements that have unsatisfied in/out
               constraints.

           -fdump-rtl-auto_inc_dec
               Dump after auto-inc-dec discovery.  This pass is only run on
               architectures that have auto inc or auto dec instructions.

           -fdump-rtl-barriers
               Dump after cleaning up the barrier instructions.

           -fdump-rtl-bbpart
               Dump after partitioning hot and cold basic blocks.

           -fdump-rtl-bbro
               Dump after block reordering.

           -fdump-rtl-btl1
           -fdump-rtl-btl2
               -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the
               two branch target load optimization passes.

           -fdump-rtl-bypass
               Dump after jump bypassing and control flow optimizations.

           -fdump-rtl-combine
               Dump after the RTL instruction combination pass.

           -fdump-rtl-compgotos
               Dump after duplicating the computed gotos.

           -fdump-rtl-ce1
           -fdump-rtl-ce2
           -fdump-rtl-ce3
               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable
               dumping after the three if conversion passes.

           -fdump-rtl-cprop_hardreg
               Dump after hard register copy propagation.

           -fdump-rtl-csa
               Dump after combining stack adjustments.

           -fdump-rtl-cse1
           -fdump-rtl-cse2
               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the
               two common subexpression elimination passes.

           -fdump-rtl-dce
               Dump after the standalone dead code elimination passes.

           -fdump-rtl-dbr
               Dump after delayed branch scheduling.

           -fdump-rtl-dce1
           -fdump-rtl-dce2
               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the
               two dead store elimination passes.

           -fdump-rtl-eh
               Dump after finalization of EH handling code.

           -fdump-rtl-eh_ranges
               Dump after conversion of EH handling range regions.

           -fdump-rtl-expand
               Dump after RTL generation.

           -fdump-rtl-fwprop1
           -fdump-rtl-fwprop2
               -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after
               the two forward propagation passes.

           -fdump-rtl-gcse1
           -fdump-rtl-gcse2
               -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after
               global common subexpression elimination.

           -fdump-rtl-init-regs
               Dump after the initialization of the registers.

           -fdump-rtl-initvals
               Dump after the computation of the initial value sets.

           -fdump-rtl-into_cfglayout
               Dump after converting to cfglayout mode.

           -fdump-rtl-ira
               Dump after iterated register allocation.

           -fdump-rtl-jump
               Dump after the second jump optimization.

           -fdump-rtl-loop2
               -fdump-rtl-loop2 enables dumping after the rtl loop
               optimization passes.

           -fdump-rtl-mach
               Dump after performing the machine dependent reorganization
               pass, if that pass exists.

           -fdump-rtl-mode_sw
               Dump after removing redundant mode switches.

           -fdump-rtl-rnreg
               Dump after register renumbering.

           -fdump-rtl-outof_cfglayout
               Dump after converting from cfglayout mode.

           -fdump-rtl-peephole2
               Dump after the peephole pass.

           -fdump-rtl-postreload
               Dump after post-reload optimizations.

           -fdump-rtl-pro_and_epilogue
               Dump after generating the function prologues and epilogues.

           -fdump-rtl-regmove
               Dump after the register move pass.

           -fdump-rtl-sched1
           -fdump-rtl-sched2
               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after
               the basic block scheduling passes.

           -fdump-rtl-see
               Dump after sign extension elimination.

           -fdump-rtl-seqabstr
               Dump after common sequence discovery.

           -fdump-rtl-shorten
               Dump after shortening branches.

           -fdump-rtl-sibling
               Dump after sibling call optimizations.

           -fdump-rtl-split1
           -fdump-rtl-split2
           -fdump-rtl-split3
           -fdump-rtl-split4
           -fdump-rtl-split5
               -fdump-rtl-split1, -fdump-rtl-split2, -fdump-rtl-split3,
               -fdump-rtl-split4 and -fdump-rtl-split5 enable dumping after
               five rounds of instruction splitting.

           -fdump-rtl-sms
               Dump after modulo scheduling.  This pass is only run on some
               architectures.

           -fdump-rtl-stack
               Dump after conversion from GCC's "flat register file" registers
               to the x87's stack-like registers.  This pass is only run on
               x86 variants.

           -fdump-rtl-subreg1
           -fdump-rtl-subreg2
               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after
               the two subreg expansion passes.

           -fdump-rtl-unshare
               Dump after all rtl has been unshared.

           -fdump-rtl-vartrack
               Dump after variable tracking.

           -fdump-rtl-vregs
               Dump after converting virtual registers to hard registers.

           -fdump-rtl-web
               Dump after live range splitting.

           -fdump-rtl-regclass
           -fdump-rtl-subregs_of_mode_init
           -fdump-rtl-subregs_of_mode_finish
           -fdump-rtl-dfinit
           -fdump-rtl-dfinish
               These dumps are defined but always produce empty files.

           -da
           -fdump-rtl-all
               Produce all the dumps listed above.

           -dA Annotate the assembler output with miscellaneous debugging
               information.

           -dD Dump all macro definitions, at the end of preprocessing, in
               addition to normal output.

           -dH Produce a core dump whenever an error occurs.

           -dp Annotate the assembler output with a comment indicating which
               pattern and alternative is used.  The length of each
               instruction is also printed.

           -dP Dump the RTL in the assembler output as a comment before each
               instruction.  Also turns on -dp annotation.

           -dx Just generate RTL for a function instead of compiling it.
               Usually used with -fdump-rtl-expand.

       -fdump-noaddr
           When doing debugging dumps, suppress address output.  This makes it
           more feasible to use diff on debugging dumps for compiler
           invocations with different compiler binaries and/or different text
           / bss / data / heap / stack / dso start locations.

       -fdump-unnumbered
           When doing debugging dumps, suppress instruction numbers and
           address output.  This makes it more feasible to use diff on
           debugging dumps for compiler invocations with different options, in
           particular with and without -g.

       -fdump-unnumbered-links
           When doing debugging dumps (see -d option above), suppress
           instruction numbers for the links to the previous and next
           instructions in a sequence.

       -fdump-translation-unit (C++ only)
       -fdump-translation-unit-options (C++ only)
           Dump a representation of the tree structure for the entire
           translation unit to a file.  The file name is made by appending .tu
           to the source file name, and the file is created in the same
           directory as the output file.  If the -options form is used,
           options controls the details of the dump as described for the
           -fdump-tree options.

       -fdump-class-hierarchy (C++ only)
       -fdump-class-hierarchy-options (C++ only)
           Dump a representation of each class's hierarchy and virtual
           function table layout to a file.  The file name is made by
           appending .class to the source file name, and the file is created
           in the same directory as the output file.  If the -options form is
           used, options controls the details of the dump as described for the
           -fdump-tree options.

       -fdump-ipa-switch
           Control the dumping at various stages of inter-procedural analysis
           language tree to a file.  The file name is generated by appending a
           switch specific suffix to the source file name, and the file is
           created in the same directory as the output file.  The following
           dumps are possible:

           all Enables all inter-procedural analysis dumps.

           cgraph
               Dumps information about call-graph optimization, unused
               function removal, and inlining decisions.

           inline
               Dump after function inlining.

       -fdump-passes
           Dump the list of optimization passes that are turned on and off by
           the current command-line options.

       -fdump-statistics-option
           Enable and control dumping of pass statistics in a separate file.
           The file name is generated by appending a suffix ending in
           .statistics to the source file name, and the file is created in the
           same directory as the output file.  If the -option form is used,
           -stats causes counters to be summed over the whole compilation unit
           while -details dumps every event as the passes generate them.  The
           default with no option is to sum counters for each function
           compiled.

       -fdump-tree-switch
       -fdump-tree-switch-options
       -fdump-tree-switch-options=filename
           Control the dumping at various stages of processing the
           intermediate language tree to a file.  The file name is generated
           by appending a switch-specific suffix to the source file name, and
           the file is created in the same directory as the output file. In
           case of =filename option, the dump is output on the given file
           instead of the auto named dump files.  If the -options form is
           used, options is a list of - separated options which control the
           details of the dump.  Not all options are applicable to all dumps;
           those that are not meaningful are ignored.  The following options
           are available

           address
               Print the address of each node.  Usually this is not meaningful
               as it changes according to the environment and source file.
               Its primary use is for tying up a dump file with a debug
               environment.

           asmname
               If "DECL_ASSEMBLER_NAME" has been set for a given decl, use
               that in the dump instead of "DECL_NAME".  Its primary use is
               ease of use working backward from mangled names in the assembly
               file.

           slim
               When dumping front-end intermediate representations, inhibit
               dumping of members of a scope or body of a function merely
               because that scope has been reached.  Only dump such items when
               they are directly reachable by some other path.

               When dumping pretty-printed trees, this option inhibits dumping
               the bodies of control structures.

               When dumping RTL, print the RTL in slim (condensed) form
               instead of the default LISP-like representation.

           raw Print a raw representation of the tree.  By default, trees are
               pretty-printed into a C-like representation.

           details
               Enable more detailed dumps (not honored by every dump option).
               Also include information from the optimization passes.

           stats
               Enable dumping various statistics about the pass (not honored
               by every dump option).

           blocks
               Enable showing basic block boundaries (disabled in raw dumps).

           graph
               For each of the other indicated dump files (-fdump-rtl-pass),
               dump a representation of the control flow graph suitable for
               viewing with GraphViz to file.passid.pass.dot.  Each function
               in the file is pretty-printed as a subgraph, so that GraphViz
               can render them all in a single plot.

               This option currently only works for RTL dumps, and the RTL is
               always dumped in slim form.

           vops
               Enable showing virtual operands for every statement.

           lineno
               Enable showing line numbers for statements.

           uid Enable showing the unique ID ("DECL_UID") for each variable.

           verbose
               Enable showing the tree dump for each statement.

           eh  Enable showing the EH region number holding each statement.

           scev
               Enable showing scalar evolution analysis details.

           optimized
               Enable showing optimization information (only available in
               certain passes).

           missed
               Enable showing missed optimization information (only available
               in certain passes).

           notes
               Enable other detailed optimization information (only available
               in certain passes).

           =filename
               Instead of an auto named dump file, output into the given file
               name. The file names stdout and stderr are treated specially
               and are considered already open standard streams. For example,

                       gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
                            -fdump-tree-pre=stderr file.c

               outputs vectorizer dump into foo.dump, while the PRE dump is
               output on to stderr. If two conflicting dump filenames are
               given for the same pass, then the latter option overrides the
               earlier one.

           all Turn on all options, except raw, slim, verbose and lineno.

           optall
               Turn on all optimization options, i.e., optimized, missed, and
               note.

           The following tree dumps are possible:

           original
               Dump before any tree based optimization, to file.original.

           optimized
               Dump after all tree based optimization, to file.optimized.

           gimple
               Dump each function before and after the gimplification pass to
               a file.  The file name is made by appending .gimple to the
               source file name.

           cfg Dump the control flow graph of each function to a file.  The
               file name is made by appending .cfg to the source file name.

           ch  Dump each function after copying loop headers.  The file name
               is made by appending .ch to the source file name.

           ssa Dump SSA related information to a file.  The file name is made
               by appending .ssa to the source file name.

           alias
               Dump aliasing information for each function.  The file name is
               made by appending .alias to the source file name.

           ccp Dump each function after CCP.  The file name is made by
               appending .ccp to the source file name.

           storeccp
               Dump each function after STORE-CCP.  The file name is made by
               appending .storeccp to the source file name.

           pre Dump trees after partial redundancy elimination.  The file name
               is made by appending .pre to the source file name.

           fre Dump trees after full redundancy elimination.  The file name is
               made by appending .fre to the source file name.

           copyprop
               Dump trees after copy propagation.  The file name is made by
               appending .copyprop to the source file name.

           store_copyprop
               Dump trees after store copy-propagation.  The file name is made
               by appending .store_copyprop to the source file name.

           dce Dump each function after dead code elimination.  The file name
               is made by appending .dce to the source file name.

           mudflap
               Dump each function after adding mudflap instrumentation.  The
               file name is made by appending .mudflap to the source file
               name.

           sra Dump each function after performing scalar replacement of
               aggregates.  The file name is made by appending .sra to the
               source file name.

           sink
               Dump each function after performing code sinking.  The file
               name is made by appending .sink to the source file name.

           dom Dump each function after applying dominator tree optimizations.
               The file name is made by appending .dom to the source file
               name.

           dse Dump each function after applying dead store elimination.  The
               file name is made by appending .dse to the source file name.

           phiopt
               Dump each function after optimizing PHI nodes into straightline
               code.  The file name is made by appending .phiopt to the source
               file name.

           forwprop
               Dump each function after forward propagating single use
               variables.  The file name is made by appending .forwprop to the
               source file name.

           copyrename
               Dump each function after applying the copy rename optimization.
               The file name is made by appending .copyrename to the source
               file name.

           nrv Dump each function after applying the named return value
               optimization on generic trees.  The file name is made by
               appending .nrv to the source file name.

           vect
               Dump each function after applying vectorization of loops.  The
               file name is made by appending .vect to the source file name.

           slp Dump each function after applying vectorization of basic
               blocks.  The file name is made by appending .slp to the source
               file name.

           vrp Dump each function after Value Range Propagation (VRP).  The
               file name is made by appending .vrp to the source file name.

           all Enable all the available tree dumps with the flags provided in
               this option.

       -fopt-info
       -fopt-info-options
       -fopt-info-options=filename
           Controls optimization dumps from various optimization passes. If
           the -options form is used, options is a list of - separated options
           to select the dump details and optimizations.  If options is not
           specified, it defaults to all for details and optall for
           optimization groups. If the filename is not specified, it defaults
           to stderr. Note that the output filename will be overwritten in
           case of multiple translation units. If a combined output from
           multiple translation units is desired, stderr should be used
           instead.

           The options can be divided into two groups, 1) options describing
           the verbosity of the dump, and 2) options describing which
           optimizations should be included. The options from both the groups
           can be freely mixed as they are non-overlapping. However, in case
           of any conflicts, the latter options override the earlier options
           on the command line. Though multiple -fopt-info options are
           accepted, only one of them can have =filename. If other filenames
           are provided then all but the first one are ignored.

           The dump verbosity has the following options

           optimized
               Print information when an optimization is successfully applied.
               It is up to a pass to decide which information is relevant. For
               example, the vectorizer passes print the source location of
               loops which got successfully vectorized.

           missed
               Print information about missed optimizations. Individual passes
               control which information to include in the output. For
               example,

                       gcc -O2 -ftree-vectorize -fopt-info-vec-missed

               will print information about missed optimization opportunities
               from vectorization passes on stderr.

           note
               Print verbose information about optimizations, such as certain
               transformations, more detailed messages about decisions etc.

           all Print detailed optimization information. This includes
               optimized, missed, and note.

           The second set of options describes a group of optimizations and
           may include one or more of the following.

           ipa Enable dumps from all interprocedural optimizations.

           loop
               Enable dumps from all loop optimizations.

           inline
               Enable dumps from all inlining optimizations.

           vec Enable dumps from all vectorization optimizations.

           For example,

                   gcc -O3 -fopt-info-missed=missed.all

           outputs missed optimization report from all the passes into
           missed.all.

           As another example,

                   gcc -O3 -fopt-info-inline-optimized-missed=inline.txt

           will output information about missed optimizations as well as
           optimized locations from all the inlining passes into inline.txt.

           If the filename is provided, then the dumps from all the applicable
           optimizations are concatenated into the filename.  Otherwise the
           dump is output onto stderr. If options is omitted, it defaults to
           all-optall, which means dump all available optimization info from
           all the passes. In the following example, all optimization info is
           output on to stderr.

                   gcc -O3 -fopt-info

           Note that -fopt-info-vec-missed behaves the same as
           -fopt-info-missed-vec.

           As another example, consider

                   gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt

           Here the two output filenames vec.miss and loop.opt are in conflict
           since only one output file is allowed. In this case, only the first
           option takes effect and the subsequent options are ignored. Thus
           only the vec.miss is produced which cotaints dumps from the
           vectorizer about missed opportunities.

       -ftree-vectorizer-verbose=n
           This option is deprecated and is implemented in terms of
           -fopt-info. Please use -fopt-info-kind form instead, where kind is
           one of the valid opt-info options. It prints additional
           optimization information.  For n=0 no diagnostic information is
           reported.  If n=1 the vectorizer reports each loop that got
           vectorized, and the total number of loops that got vectorized.  If
           n=2 the vectorizer reports locations which could not be vectorized
           and the reasons for those. For any higher verbosity levels all the
           analysis and transformation information from the vectorizer is
           reported.

           Note that the information output by -ftree-vectorizer-verbose
           option is sent to stderr. If the equivalent form
           -fopt-info-options=filename is used then the output is sent into
           filename instead.

       -frandom-seed=string
           This option provides a seed that GCC uses in place of random
           numbers in generating certain symbol names that have to be
           different in every compiled file.  It is also used to place unique
           stamps in coverage data files and the object files that produce
           them.  You can use the -frandom-seed option to produce reproducibly
           identical object files.

           The string should be different for every file you compile.

       -fsched-verbose=n
           On targets that use instruction scheduling, this option controls
           the amount of debugging output the scheduler prints.  This
           information is written to standard error, unless -fdump-rtl-sched1
           or -fdump-rtl-sched2 is specified, in which case it is output to
           the usual dump listing file, .sched1 or .sched2 respectively.
           However for n greater than nine, the output is always printed to
           standard error.

           For n greater than zero, -fsched-verbose outputs the same
           information as -fdump-rtl-sched1 and -fdump-rtl-sched2.  For n
           greater than one, it also output basic block probabilities,
           detailed ready list information and unit/insn info.  For n greater
           than two, it includes RTL at abort point, control-flow and regions
           info.  And for n over four, -fsched-verbose also includes
           dependence info.

       -save-temps
       -save-temps=cwd
           Store the usual "temporary" intermediate files permanently; place
           them in the current directory and name them based on the source
           file.  Thus, compiling foo.c with -c -save-temps produces files
           foo.i and foo.s, as well as foo.o.  This creates a preprocessed
           foo.i output file even though the compiler now normally uses an
           integrated preprocessor.

           When used in combination with the -x command-line option,
           -save-temps is sensible enough to avoid over writing an input
           source file with the same extension as an intermediate file.  The
           corresponding intermediate file may be obtained by renaming the
           source file before using -save-temps.

           If you invoke GCC in parallel, compiling several different source
           files that share a common base name in different subdirectories or
           the same source file compiled for multiple output destinations, it
           is likely that the different parallel compilers will interfere with
           each other, and overwrite the temporary files.  For instance:

                   gcc -save-temps -o outdir1/foo.o indir1/foo.c&
                   gcc -save-temps -o outdir2/foo.o indir2/foo.c&

           may result in foo.i and foo.o being written to simultaneously by
           both compilers.

       -save-temps=obj
           Store the usual "temporary" intermediate files permanently.  If the
           -o option is used, the temporary files are based on the object
           file.  If the -o option is not used, the -save-temps=obj switch
           behaves like -save-temps.

           For example:

                   gcc -save-temps=obj -c foo.c
                   gcc -save-temps=obj -c bar.c -o dir/xbar.o
                   gcc -save-temps=obj foobar.c -o dir2/yfoobar

           creates foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i,
           dir2/yfoobar.s, and dir2/yfoobar.o.

       -time[=file]
           Report the CPU time taken by each subprocess in the compilation
           sequence.  For C source files, this is the compiler proper and
           assembler (plus the linker if linking is done).

           Without the specification of an output file, the output looks like
           this:

                   # cc1 0.12 0.01
                   # as 0.00 0.01

           The first number on each line is the "user time", that is time
           spent executing the program itself.  The second number is "system
           time", time spent executing operating system routines on behalf of
           the program.  Both numbers are in seconds.

           With the specification of an output file, the output is appended to
           the named file, and it looks like this:

                   0.12 0.01 cc1 <options>
                   0.00 0.01 as <options>

           The "user time" and the "system time" are moved before the program
           name, and the options passed to the program are displayed, so that
           one can later tell what file was being compiled, and with which
           options.

       -fvar-tracking
           Run variable tracking pass.  It computes where variables are stored
           at each position in code.  Better debugging information is then
           generated (if the debugging information format supports this
           information).

           It is enabled by default when compiling with optimization (-Os, -O,
           -O2, ...), debugging information (-g) and the debug info format
           supports it.

       -fvar-tracking-assignments
           Annotate assignments to user variables early in the compilation and
           attempt to carry the annotations over throughout the compilation
           all the way to the end, in an attempt to improve debug information
           while optimizing.  Use of -gdwarf-4 is recommended along with it.

           It can be enabled even if var-tracking is disabled, in which case
           annotations are created and maintained, but discarded at the end.

       -fvar-tracking-assignments-toggle
           Toggle -fvar-tracking-assignments, in the same way that -gtoggle
           toggles -g.

       -print-file-name=library
           Print the full absolute name of the library file library that would
           be used when linking---and don't do anything else.  With this
           option, GCC does not compile or link anything; it just prints the
           file name.

       -print-multi-directory
           Print the directory name corresponding to the multilib selected by
           any other switches present in the command line.  This directory is
           supposed to exist in GCC_EXEC_PREFIX.

       -print-multi-lib
           Print the mapping from multilib directory names to compiler
           switches that enable them.  The directory name is separated from
           the switches by ;, and each switch starts with an @ instead of the
           -, without spaces between multiple switches.  This is supposed to
           ease shell processing.

       -print-multi-os-directory
           Print the path to OS libraries for the selected multilib, relative
           to some lib subdirectory.  If OS libraries are present in the lib
           subdirectory and no multilibs are used, this is usually just ., if
           OS libraries are present in libsuffix sibling directories this
           prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
           present in lib/subdir subdirectories it prints e.g. amd64, sparcv9
           or ev6.

       -print-multiarch
           Print the path to OS libraries for the selected multiarch, relative
           to some lib subdirectory.

       -print-prog-name=program
           Like -print-file-name, but searches for a program such as cpp.

       -print-libgcc-file-name
           Same as -print-file-name=libgcc.a.

           This is useful when you use -nostdlib or -nodefaultlibs but you do
           want to link with libgcc.a.  You can do:

                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`

       -print-search-dirs
           Print the name of the configured installation directory and a list
           of program and library directories gcc searches---and don't do
           anything else.

           This is useful when gcc prints the error message installation
           problem, cannot exec cpp0: No such file or directory.  To resolve
           this you either need to put cpp0 and the other compiler components
           where gcc expects to find them, or you can set the environment
           variable GCC_EXEC_PREFIX to the directory where you installed them.
           Don't forget the trailing /.

       -print-sysroot
           Print the target sysroot directory that is used during compilation.
           This is the target sysroot specified either at configure time or
           using the --sysroot option, possibly with an extra suffix that
           depends on compilation options.  If no target sysroot is specified,
           the option prints nothing.

       -print-sysroot-headers-suffix
           Print the suffix added to the target sysroot when searching for
           headers, or give an error if the compiler is not configured with
           such a suffix---and don't do anything else.

       -dumpmachine
           Print the compiler's target machine (for example,
           i686-pc-linux-gnu)---and don't do anything else.

       -dumpversion
           Print the compiler version (for example, 3.0)---and don't do
           anything else.

       -dumpspecs
           Print the compiler's built-in specs---and don't do anything else.
           (This is used when GCC itself is being built.)

       -fno-eliminate-unused-debug-types
           Normally, when producing DWARF 2 output, GCC avoids producing debug
           symbol output for types that are nowhere used in the source file
           being compiled.  Sometimes it is useful to have GCC emit debugging
           information for all types declared in a compilation unit,
           regardless of whether or not they are actually used in that
           compilation unit, for example if, in the debugger, you want to cast
           a value to a type that is not actually used in your program (but is
           declared).  More often, however, this results in a significant
           amount of wasted space.

   Options That Control Optimization
       These options control various sorts of optimizations.

       Without any optimization option, the compiler's goal is to reduce the
       cost of compilation and to make debugging produce the expected results.
       Statements are independent: if you stop the program with a breakpoint
       between statements, you can then assign a new value to any variable or
       change the program counter to any other statement in the function and
       get exactly the results you expect from the source code.

       Turning on optimization flags makes the compiler attempt to improve the
       performance and/or code size at the expense of compilation time and
       possibly the ability to debug the program.

       The compiler performs optimization based on the knowledge it has of the
       program.  Compiling multiple files at once to a single output file mode
       allows the compiler to use information gained from all of the files
       when compiling each of them.

       Not all optimizations are controlled directly by a flag.  Only
       optimizations that have a flag are listed in this section.

       Most optimizations are only enabled if an -O level is set on the
       command line.  Otherwise they are disabled, even if individual
       optimization flags are specified.

       Depending on the target and how GCC was configured, a slightly
       different set of optimizations may be enabled at each -O level than
       those listed here.  You can invoke GCC with -Q --help=optimizers to
       find out the exact set of optimizations that are enabled at each level.

       -O
       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a
           lot more memory for a large function.

           With -O, the compiler tries to reduce code size and execution time,
           without performing any optimizations that take a great deal of
           compilation time.

           -O turns on the following optimization flags:

           -fauto-inc-dec -fcompare-elim -fcprop-registers -fdce -fdefer-pop
           -fdelayed-branch -fdse -fguess-branch-probability -fif-conversion2
           -fif-conversion -fipa-pure-const -fipa-profile -fipa-reference
           -fmerge-constants -fsplit-wide-types -ftree-bit-ccp
           -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copyrename
           -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop
           -ftree-fre -ftree-phiprop -ftree-slsr -ftree-sra -ftree-pta
           -ftree-ter -funit-at-a-time

           -O also turns on -fomit-frame-pointer on machines where doing so
           does not interfere with debugging.

       -O2 Optimize even more.  GCC performs nearly all supported
           optimizations that do not involve a space-speed tradeoff.  As
           compared to -O, this option increases both compilation time and the
           performance of the generated code.

           -O2 turns on all optimization flags specified by -O.  It also turns
           on the following optimization flags: -fthread-jumps
           -falign-functions  -falign-jumps -falign-loops  -falign-labels
           -fcaller-saves -fcrossjumping -fcse-follow-jumps  -fcse-skip-blocks
           -fdelete-null-pointer-checks -fdevirtualize
           -fexpensive-optimizations -fgcse  -fgcse-lm -fhoist-adjacent-loads
           -finline-small-functions -findirect-inlining -fipa-sra
           -foptimize-sibling-calls -fpartial-inlining -fpeephole2 -fregmove
           -freorder-blocks  -freorder-functions -frerun-cse-after-loop
           -fsched-interblock  -fsched-spec -fschedule-insns
           -fschedule-insns2 -fstrict-aliasing -fstrict-overflow
           -ftree-switch-conversion -ftree-tail-merge -ftree-pre -ftree-vrp

           Please note the warning under -fgcse about invoking -O2 on programs
           that use computed gotos.

       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2
           and also turns on the -finline-functions, -funswitch-loops,
           -fpredictive-commoning, -fgcse-after-reload, -ftree-vectorize,
           -fvect-cost-model, -ftree-partial-pre and -fipa-cp-clone options.

       -O0 Reduce compilation time and make debugging produce the expected
           results.  This is the default.

       -Os Optimize for size.  -Os enables all -O2 optimizations that do not
           typically increase code size.  It also performs further
           optimizations designed to reduce code size.

           -Os disables the following optimization flags: -falign-functions
           -falign-jumps  -falign-loops -falign-labels  -freorder-blocks
           -freorder-blocks-and-partition -fprefetch-loop-arrays
           -ftree-vect-loop-version

       -Ofast
           Disregard strict standards compliance.  -Ofast enables all -O3
           optimizations.  It also enables optimizations that are not valid
           for all standard-compliant programs.  It turns on -ffast-math and
           the Fortran-specific -fno-protect-parens and -fstack-arrays.

       -Og Optimize debugging experience.  -Og enables optimizations that do
           not interfere with debugging. It should be the optimization level
           of choice for the standard edit-compile-debug cycle, offering a
           reasonable level of optimization while maintaining fast compilation
           and a good debugging experience.

           If you use multiple -O options, with or without level numbers, the
           last such option is the one that is effective.

       Options of the form -fflag specify machine-independent flags.  Most
       flags have both positive and negative forms; the negative form of -ffoo
       is -fno-foo.  In the table below, only one of the forms is listed---the
       one you typically use.  You can figure out the other form by either
       removing no- or adding it.

       The following options control specific optimizations.  They are either
       activated by -O options or are related to ones that are.  You can use
       the following flags in the rare cases when "fine-tuning" of
       optimizations to be performed is desired.

       -fno-default-inline
           Do not make member functions inline by default merely because they
           are defined inside the class scope (C++ only).  Otherwise, when you
           specify -O, member functions defined inside class scope are
           compiled inline by default; i.e., you don't need to add inline in
           front of the member function name.

       -fno-defer-pop
           Always pop the arguments to each function call as soon as that
           function returns.  For machines that must pop arguments after a
           function call, the compiler normally lets arguments accumulate on
           the stack for several function calls and pops them all at once.

           Disabled at levels -O, -O2, -O3, -Os.

       -fforward-propagate
           Perform a forward propagation pass on RTL.  The pass tries to
           combine two instructions and checks if the result can be
           simplified.  If loop unrolling is active, two passes are performed
           and the second is scheduled after loop unrolling.

           This option is enabled by default at optimization levels -O, -O2,
           -O3, -Os.

       -ffp-contract=style
           -ffp-contract=off disables floating-point expression contraction.
           -ffp-contract=fast enables floating-point expression contraction
           such as forming of fused multiply-add operations if the target has
           native support for them.  -ffp-contract=on enables floating-point
           expression contraction if allowed by the language standard.  This
           is currently not implemented and treated equal to
           -ffp-contract=off.

           The default is -ffp-contract=fast.

       -fomit-frame-pointer
           Don't keep the frame pointer in a register for functions that don't
           need one.  This avoids the instructions to save, set up and restore
           frame pointers; it also makes an extra register available in many
           functions.  It also makes debugging impossible on some machines.

           On some machines, such as the VAX, this flag has no effect, because
           the standard calling sequence automatically handles the frame
           pointer and nothing is saved by pretending it doesn't exist.  The
           machine-description macro "FRAME_POINTER_REQUIRED" controls whether
           a target machine supports this flag.

           Starting with GCC version 4.6, the default setting (when not
           optimizing for size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86
           targets has been changed to -fomit-frame-pointer.  The default can
           be reverted to -fno-omit-frame-pointer by configuring GCC with the
           --enable-frame-pointer configure option.

           Enabled at levels -O, -O2, -O3, -Os.

       -foptimize-sibling-calls
           Optimize sibling and tail recursive calls.

           Enabled at levels -O2, -O3, -Os.

       -fno-inline
           Do not expand any functions inline apart from those marked with the
           "always_inline" attribute.  This is the default when not
           optimizing.

           Single functions can be exempted from inlining by marking them with
           the "noinline" attribute.

       -finline-small-functions
           Integrate functions into their callers when their body is smaller
           than expected function call code (so overall size of program gets
           smaller).  The compiler heuristically decides which functions are
           simple enough to be worth integrating in this way.  This inlining
           applies to all functions, even those not declared inline.

           Enabled at level -O2.

       -findirect-inlining
           Inline also indirect calls that are discovered to be known at
           compile time thanks to previous inlining.  This option has any
           effect only when inlining itself is turned on by the
           -finline-functions or -finline-small-functions options.

           Enabled at level -O2.

       -finline-functions
           Consider all functions for inlining, even if they are not declared
           inline.  The compiler heuristically decides which functions are
           worth integrating in this way.

           If all calls to a given function are integrated, and the function
           is declared "static", then the function is normally not output as
           assembler code in its own right.

           Enabled at level -O3.

       -finline-functions-called-once
           Consider all "static" functions called once for inlining into their
           caller even if they are not marked "inline".  If a call to a given
           function is integrated, then the function is not output as
           assembler code in its own right.

           Enabled at levels -O1, -O2, -O3 and -Os.

       -fearly-inlining
           Inline functions marked by "always_inline" and functions whose body
           seems smaller than the function call overhead early before doing
           -fprofile-generate instrumentation and real inlining pass.  Doing
           so makes profiling significantly cheaper and usually inlining
           faster on programs having large chains of nested wrapper functions.

           Enabled by default.

       -fipa-sra
           Perform interprocedural scalar replacement of aggregates, removal
           of unused parameters and replacement of parameters passed by
           reference by parameters passed by value.

           Enabled at levels -O2, -O3 and -Os.

       -finline-limit=n
           By default, GCC limits the size of functions that can be inlined.
           This flag allows coarse control of this limit.  n is the size of
           functions that can be inlined in number of pseudo instructions.

           Inlining is actually controlled by a number of parameters, which
           may be specified individually by using --param name=value.  The
           -finline-limit=n option sets some of these parameters as follows:

           max-inline-insns-single
               is set to n/2.

           max-inline-insns-auto
               is set to n/2.

           See below for a documentation of the individual parameters
           controlling inlining and for the defaults of these parameters.

           Note: there may be no value to -finline-limit that results in
           default behavior.

           Note: pseudo instruction represents, in this particular context, an
           abstract measurement of function's size.  In no way does it
           represent a count of assembly instructions and as such its exact
           meaning might change from one release to an another.

       -fno-keep-inline-dllexport
           This is a more fine-grained version of -fkeep-inline-functions,
           which applies only to functions that are declared using the
           "dllexport" attribute or declspec

       -fkeep-inline-functions
           In C, emit "static" functions that are declared "inline" into the
           object file, even if the function has been inlined into all of its
           callers.  This switch does not affect functions using the "extern
           inline" extension in GNU C90.  In C++, emit any and all inline
           functions into the object file.

       -fkeep-static-consts
           Emit variables declared "static const" when optimization isn't
           turned on, even if the variables aren't referenced.

           GCC enables this option by default.  If you want to force the
           compiler to check if a variable is referenced, regardless of
           whether or not optimization is turned on, use the
           -fno-keep-static-consts option.

       -fmerge-constants
           Attempt to merge identical constants (string constants and
           floating-point constants) across compilation units.

           This option is the default for optimized compilation if the
           assembler and linker support it.  Use -fno-merge-constants to
           inhibit this behavior.

           Enabled at levels -O, -O2, -O3, -Os.

       -fmerge-all-constants
           Attempt to merge identical constants and identical variables.

           This option implies -fmerge-constants.  In addition to
           -fmerge-constants this considers e.g. even constant initialized
           arrays or initialized constant variables with integral or floating-
           point types.  Languages like C or C++ require each variable,
           including multiple instances of the same variable in recursive
           calls, to have distinct locations, so using this option results in
           non-conforming behavior.

       -fmodulo-sched
           Perform swing modulo scheduling immediately before the first
           scheduling pass.  This pass looks at innermost loops and reorders
           their instructions by overlapping different iterations.

       -fmodulo-sched-allow-regmoves
           Perform more aggressive SMS-based modulo scheduling with register
           moves allowed.  By setting this flag certain anti-dependences edges
           are deleted, which triggers the generation of reg-moves based on
           the life-range analysis.  This option is effective only with
           -fmodulo-sched enabled.

       -fno-branch-count-reg
           Do not use "decrement and branch" instructions on a count register,
           but instead generate a sequence of instructions that decrement a
           register, compare it against zero, then branch based upon the
           result.  This option is only meaningful on architectures that
           support such instructions, which include x86, PowerPC, IA-64 and
           S/390.

           The default is -fbranch-count-reg.

       -fno-function-cse
           Do not put function addresses in registers; make each instruction
           that calls a constant function contain the function's address
           explicitly.

           This option results in less efficient code, but some strange hacks
           that alter the assembler output may be confused by the
           optimizations performed when this option is not used.

           The default is -ffunction-cse

       -fno-zero-initialized-in-bss
           If the target supports a BSS section, GCC by default puts variables
           that are initialized to zero into BSS.  This can save space in the
           resulting code.

           This option turns off this behavior because some programs
           explicitly rely on variables going to the data section---e.g., so
           that the resulting executable can find the beginning of that
           section and/or make assumptions based on that.

           The default is -fzero-initialized-in-bss.

       -fmudflap -fmudflapth -fmudflapir
           For front-ends that support it (C and C++), instrument all risky
           pointer/array dereferencing operations, some standard library
           string/heap functions, and some other associated constructs with
           range/validity tests.  Modules so instrumented should be immune to
           buffer overflows, invalid heap use, and some other classes of C/C++
           programming errors.  The instrumentation relies on a separate
           runtime library (libmudflap), which is linked into a program if
           -fmudflap is given at link time.  Run-time behavior of the
           instrumented program is controlled by the MUDFLAP_OPTIONS
           environment variable.  See "env MUDFLAP_OPTIONS=-help a.out" for
           its options.

           Use -fmudflapth instead of -fmudflap to compile and to link if your
           program is multi-threaded.  Use -fmudflapir, in addition to
           -fmudflap or -fmudflapth, if instrumentation should ignore pointer
           reads.  This produces less instrumentation (and therefore faster
           execution) and still provides some protection against outright
           memory corrupting writes, but allows erroneously read data to
           propagate within a program.

       -fthread-jumps
           Perform optimizations that check to see if a jump branches to a
           location where another comparison subsumed by the first is found.
           If so, the first branch is redirected to either the destination of
           the second branch or a point immediately following it, depending on
           whether the condition is known to be true or false.

           Enabled at levels -O2, -O3, -Os.

       -fsplit-wide-types
           When using a type that occupies multiple registers, such as "long
           long" on a 32-bit system, split the registers apart and allocate
           them independently.  This normally generates better code for those
           types, but may make debugging more difficult.

           Enabled at levels -O, -O2, -O3, -Os.

       -fcse-follow-jumps
           In common subexpression elimination (CSE), scan through jump
           instructions when the target of the jump is not reached by any
           other path.  For example, when CSE encounters an "if" statement
           with an "else" clause, CSE follows the jump when the condition
           tested is false.

           Enabled at levels -O2, -O3, -Os.

       -fcse-skip-blocks
           This is similar to -fcse-follow-jumps, but causes CSE to follow
           jumps that conditionally skip over blocks.  When CSE encounters a
           simple "if" statement with no else clause, -fcse-skip-blocks causes
           CSE to follow the jump around the body of the "if".

           Enabled at levels -O2, -O3, -Os.

       -frerun-cse-after-loop
           Re-run common subexpression elimination after loop optimizations
           are performed.

           Enabled at levels -O2, -O3, -Os.

       -fgcse
           Perform a global common subexpression elimination pass.  This pass
           also performs global constant and copy propagation.

           Note: When compiling a program using computed gotos, a GCC
           extension, you may get better run-time performance if you disable
           the global common subexpression elimination pass by adding
           -fno-gcse to the command line.

           Enabled at levels -O2, -O3, -Os.

       -fgcse-lm
           When -fgcse-lm is enabled, global common subexpression elimination
           attempts to move loads that are only killed by stores into
           themselves.  This allows a loop containing a load/store sequence to
           be changed to a load outside the loop, and a copy/store within the
           loop.

           Enabled by default when -fgcse is enabled.

       -fgcse-sm
           When -fgcse-sm is enabled, a store motion pass is run after global
           common subexpression elimination.  This pass attempts to move
           stores out of loops.  When used in conjunction with -fgcse-lm,
           loops containing a load/store sequence can be changed to a load
           before the loop and a store after the loop.

           Not enabled at any optimization level.

       -fgcse-las
           When -fgcse-las is enabled, the global common subexpression
           elimination pass eliminates redundant loads that come after stores
           to the same memory location (both partial and full redundancies).

           Not enabled at any optimization level.

       -fgcse-after-reload
           When -fgcse-after-reload is enabled, a redundant load elimination
           pass is performed after reload.  The purpose of this pass is to
           clean up redundant spilling.

       -faggressive-loop-optimizations
           This option tells the loop optimizer to use language constraints to
           derive bounds for the number of iterations of a loop.  This assumes
           that loop code does not invoke undefined behavior by for example
           causing signed integer overflows or out-of-bound array accesses.
           The bounds for the number of iterations of a loop are used to guide
           loop unrolling and peeling and loop exit test optimizations.  This
           option is enabled by default.

       -funsafe-loop-optimizations
           This option tells the loop optimizer to assume that loop indices do
           not overflow, and that loops with nontrivial exit condition are not
           infinite.  This enables a wider range of loop optimizations even if
           the loop optimizer itself cannot prove that these assumptions are
           valid.  If you use -Wunsafe-loop-optimizations, the compiler warns
           you if it finds this kind of loop.

       -fcrossjumping
           Perform cross-jumping transformation.  This transformation unifies
           equivalent code and saves code size.  The resulting code may or may
           not perform better than without cross-jumping.

           Enabled at levels -O2, -O3, -Os.

       -fauto-inc-dec
           Combine increments or decrements of addresses with memory accesses.
           This pass is always skipped on architectures that do not have
           instructions to support this.  Enabled by default at -O and higher
           on architectures that support this.

       -fdce
           Perform dead code elimination (DCE) on RTL.  Enabled by default at
           -O and higher.

       -fdse
           Perform dead store elimination (DSE) on RTL.  Enabled by default at
           -O and higher.

       -fif-conversion
           Attempt to transform conditional jumps into branch-less
           equivalents.  This includes use of conditional moves, min, max, set
           flags and abs instructions, and some tricks doable by standard
           arithmetics.  The use of conditional execution on chips where it is
           available is controlled by "if-conversion2".

           Enabled at levels -O, -O2, -O3, -Os.

       -fif-conversion2
           Use conditional execution (where available) to transform
           conditional jumps into branch-less equivalents.

           Enabled at levels -O, -O2, -O3, -Os.

       -fdelete-null-pointer-checks
           Assume that programs cannot safely dereference null pointers, and
           that no code or data element resides there.  This enables simple
           constant folding optimizations at all optimization levels.  In
           addition, other optimization passes in GCC use this flag to control
           global dataflow analyses that eliminate useless checks for null
           pointers; these assume that if a pointer is checked after it has
           already been dereferenced, it cannot be null.

           Note however that in some environments this assumption is not true.
           Use -fno-delete-null-pointer-checks to disable this optimization
           for programs that depend on that behavior.

           Some targets, especially embedded ones, disable this option at all
           levels.  Otherwise it is enabled at all levels: -O0, -O1, -O2, -O3,
           -Os.  Passes that use the information are enabled independently at
           different optimization levels.

       -fdevirtualize
           Attempt to convert calls to virtual functions to direct calls.
           This is done both within a procedure and interprocedurally as part
           of indirect inlining ("-findirect-inlining") and interprocedural
           constant propagation (-fipa-cp).  Enabled at levels -O2, -O3, -Os.

       -fexpensive-optimizations
           Perform a number of minor optimizations that are relatively
           expensive.

           Enabled at levels -O2, -O3, -Os.

       -free
           Attempt to remove redundant extension instructions.  This is
           especially helpful for the x86-64 architecture, which implicitly
           zero-extends in 64-bit registers after writing to their lower
           32-bit half.

           Enabled for x86 at levels -O2, -O3.

       -foptimize-register-move
       -fregmove
           Attempt to reassign register numbers in move instructions and as
           operands of other simple instructions in order to maximize the
           amount of register tying.  This is especially helpful on machines
           with two-operand instructions.

           Note -fregmove and -foptimize-register-move are the same
           optimization.

           Enabled at levels -O2, -O3, -Os.

       -fira-algorithm=algorithm
           Use the specified coloring algorithm for the integrated register
           allocator.  The algorithm argument can be priority, which specifies
           Chow's priority coloring, or CB, which specifies Chaitin-Briggs
           coloring.  Chaitin-Briggs coloring is not implemented for all
           architectures, but for those targets that do support it, it is the
           default because it generates better code.

       -fira-region=region
           Use specified regions for the integrated register allocator.  The
           region argument should be one of the following:

           all Use all loops as register allocation regions.  This can give
               the best results for machines with a small and/or irregular
               register set.

           mixed
               Use all loops except for loops with small register pressure as
               the regions.  This value usually gives the best results in most
               cases and for most architectures, and is enabled by default
               when compiling with optimization for speed (-O, -O2, ...).

           one Use all functions as a single region.  This typically results
               in the smallest code size, and is enabled by default for -Os or
               -O0.

       -fira-hoist-pressure
           Use IRA to evaluate register pressure in the code hoisting pass for
           decisions to hoist expressions.  This option usually results in
           smaller code, but it can slow the compiler down.

           This option is enabled at level -Os for all targets.

       -fira-loop-pressure
           Use IRA to evaluate register pressure in loops for decisions to
           move loop invariants.  This option usually results in generation of
           faster and smaller code on machines with large register files (>=
           32 registers), but it can slow the compiler down.

           This option is enabled at level -O3 for some targets.

       -fno-ira-share-save-slots
           Disable sharing of stack slots used for saving call-used hard
           registers living through a call.  Each hard register gets a
           separate stack slot, and as a result function stack frames are
           larger.

       -fno-ira-share-spill-slots
           Disable sharing of stack slots allocated for pseudo-registers.
           Each pseudo-register that does not get a hard register gets a
           separate stack slot, and as a result function stack frames are
           larger.

       -fira-verbose=n
           Control the verbosity of the dump file for the integrated register
           allocator.  The default value is 5.  If the value n is greater or
           equal to 10, the dump output is sent to stderr using the same
           format as n minus 10.

       -fdelayed-branch
           If supported for the target machine, attempt to reorder
           instructions to exploit instruction slots available after delayed
           branch instructions.

           Enabled at levels -O, -O2, -O3, -Os.

       -fschedule-insns
           If supported for the target machine, attempt to reorder
           instructions to eliminate execution stalls due to required data
           being unavailable.  This helps machines that have slow floating
           point or memory load instructions by allowing other instructions to
           be issued until the result of the load or floating-point
           instruction is required.

           Enabled at levels -O2, -O3.

       -fschedule-insns2
           Similar to -fschedule-insns, but requests an additional pass of
           instruction scheduling after register allocation has been done.
           This is especially useful on machines with a relatively small
           number of registers and where memory load instructions take more
           than one cycle.

           Enabled at levels -O2, -O3, -Os.

       -fno-sched-interblock
           Don't schedule instructions across basic blocks.  This is normally
           enabled by default when scheduling before register allocation, i.e.
           with -fschedule-insns or at -O2 or higher.

       -fno-sched-spec
           Don't allow speculative motion of non-load instructions.  This is
           normally enabled by default when scheduling before register
           allocation, i.e.  with -fschedule-insns or at -O2 or higher.

       -fsched-pressure
           Enable register pressure sensitive insn scheduling before register
           allocation.  This only makes sense when scheduling before register
           allocation is enabled, i.e. with -fschedule-insns or at -O2 or
           higher.  Usage of this option can improve the generated code and
           decrease its size by preventing register pressure increase above
           the number of available hard registers and subsequent spills in
           register allocation.

       -fsched-spec-load
           Allow speculative motion of some load instructions.  This only
           makes sense when scheduling before register allocation, i.e. with
           -fschedule-insns or at -O2 or higher.

       -fsched-spec-load-dangerous
           Allow speculative motion of more load instructions.  This only
           makes sense when scheduling before register allocation, i.e. with
           -fschedule-insns or at -O2 or higher.

       -fsched-stalled-insns
       -fsched-stalled-insns=n
           Define how many insns (if any) can be moved prematurely from the
           queue of stalled insns into the ready list during the second
           scheduling pass.  -fno-sched-stalled-insns means that no insns are
           moved prematurely, -fsched-stalled-insns=0 means there is no limit
           on how many queued insns can be moved prematurely.
           -fsched-stalled-insns without a value is equivalent to
           -fsched-stalled-insns=1.

       -fsched-stalled-insns-dep
       -fsched-stalled-insns-dep=n
           Define how many insn groups (cycles) are examined for a dependency
           on a stalled insn that is a candidate for premature removal from
           the queue of stalled insns.  This has an effect only during the
           second scheduling pass, and only if -fsched-stalled-insns is used.
           -fno-sched-stalled-insns-dep is equivalent to
           -fsched-stalled-insns-dep=0.  -fsched-stalled-insns-dep without a
           value is equivalent to -fsched-stalled-insns-dep=1.

       -fsched2-use-superblocks
           When scheduling after register allocation, use superblock
           scheduling.  This allows motion across basic block boundaries,
           resulting in faster schedules.  This option is experimental, as not
           all machine descriptions used by GCC model the CPU closely enough
           to avoid unreliable results from the algorithm.

           This only makes sense when scheduling after register allocation,
           i.e. with -fschedule-insns2 or at -O2 or higher.

       -fsched-group-heuristic
           Enable the group heuristic in the scheduler.  This heuristic favors
           the instruction that belongs to a schedule group.  This is enabled
           by default when scheduling is enabled, i.e. with -fschedule-insns
           or -fschedule-insns2 or at -O2 or higher.

       -fsched-critical-path-heuristic
           Enable the critical-path heuristic in the scheduler.  This
           heuristic favors instructions on the critical path.  This is
           enabled by default when scheduling is enabled, i.e. with
           -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -fsched-spec-insn-heuristic
           Enable the speculative instruction heuristic in the scheduler.
           This heuristic favors speculative instructions with greater
           dependency weakness.  This is enabled by default when scheduling is
           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
           or higher.

       -fsched-rank-heuristic
           Enable the rank heuristic in the scheduler.  This heuristic favors
           the instruction belonging to a basic block with greater size or
           frequency.  This is enabled by default when scheduling is enabled,
           i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2 or
           higher.

       -fsched-last-insn-heuristic
           Enable the last-instruction heuristic in the scheduler.  This
           heuristic favors the instruction that is less dependent on the last
           instruction scheduled.  This is enabled by default when scheduling
           is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at
           -O2 or higher.

       -fsched-dep-count-heuristic
           Enable the dependent-count heuristic in the scheduler.  This
           heuristic favors the instruction that has more instructions
           depending on it.  This is enabled by default when scheduling is
           enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
           or higher.

       -freschedule-modulo-scheduled-loops
           Modulo scheduling is performed before traditional scheduling.  If a
           loop is modulo scheduled, later scheduling passes may change its
           schedule.  Use this option to control that behavior.

       -fselective-scheduling
           Schedule instructions using selective scheduling algorithm.
           Selective scheduling runs instead of the first scheduler pass.

       -fselective-scheduling2
           Schedule instructions using selective scheduling algorithm.
           Selective scheduling runs instead of the second scheduler pass.

       -fsel-sched-pipelining
           Enable software pipelining of innermost loops during selective
           scheduling.  This option has no effect unless one of
           -fselective-scheduling or -fselective-scheduling2 is turned on.

       -fsel-sched-pipelining-outer-loops
           When pipelining loops during selective scheduling, also pipeline
           outer loops.  This option has no effect unless
           -fsel-sched-pipelining is turned on.

       -fshrink-wrap
           Emit function prologues only before parts of the function that need
           it, rather than at the top of the function.  This flag is enabled
           by default at -O and higher.

       -fcaller-saves
           Enable allocation of values to registers that are clobbered by
           function calls, by emitting extra instructions to save and restore
           the registers around such calls.  Such allocation is done only when
           it seems to result in better code.

           This option is always enabled by default on certain machines,
           usually those which have no call-preserved registers to use
           instead.

           Enabled at levels -O2, -O3, -Os.

       -fcombine-stack-adjustments
           Tracks stack adjustments (pushes and pops) and stack memory
           references and then tries to find ways to combine them.

           Enabled by default at -O1 and higher.

       -fconserve-stack
           Attempt to minimize stack usage.  The compiler attempts to use less
           stack space, even if that makes the program slower.  This option
           implies setting the large-stack-frame parameter to 100 and the
           large-stack-frame-growth parameter to 400.

       -ftree-reassoc
           Perform reassociation on trees.  This flag is enabled by default at
           -O and higher.

       -ftree-pre
           Perform partial redundancy elimination (PRE) on trees.  This flag
           is enabled by default at -O2 and -O3.

       -ftree-partial-pre
           Make partial redundancy elimination (PRE) more aggressive.  This
           flag is enabled by default at -O3.

       -ftree-forwprop
           Perform forward propagation on trees.  This flag is enabled by
           default at -O and higher.

       -ftree-fre
           Perform full redundancy elimination (FRE) on trees.  The difference
           between FRE and PRE is that FRE only considers expressions that are
           computed on all paths leading to the redundant computation.  This
           analysis is faster than PRE, though it exposes fewer redundancies.
           This flag is enabled by default at -O and higher.

       -ftree-phiprop
           Perform hoisting of loads from conditional pointers on trees.  This
           pass is enabled by default at -O and higher.

       -fhoist-adjacent-loads
           Speculatively hoist loads from both branches of an if-then-else if
           the loads are from adjacent locations in the same structure and the
           target architecture has a conditional move instruction.  This flag
           is enabled by default at -O2 and higher.

       -ftree-copy-prop
           Perform copy propagation on trees.  This pass eliminates
           unnecessary copy operations.  This flag is enabled by default at -O
           and higher.

       -fipa-pure-const
           Discover which functions are pure or constant.  Enabled by default
           at -O and higher.

       -fipa-reference
           Discover which static variables do not escape the compilation unit.
           Enabled by default at -O and higher.

       -fipa-pta
           Perform interprocedural pointer analysis and interprocedural
           modification and reference analysis.  This option can cause
           excessive memory and compile-time usage on large compilation units.
           It is not enabled by default at any optimization level.

       -fipa-profile
           Perform interprocedural profile propagation.  The functions called
           only from cold functions are marked as cold. Also functions
           executed once (such as "cold", "noreturn", static constructors or
           destructors) are identified. Cold functions and loop less parts of
           functions executed once are then optimized for size.  Enabled by
           default at -O and higher.

       -fipa-cp
           Perform interprocedural constant propagation.  This optimization
           analyzes the program to determine when values passed to functions
           are constants and then optimizes accordingly.  This optimization
           can substantially increase performance if the application has
           constants passed to functions.  This flag is enabled by default at
           -O2, -Os and -O3.

       -fipa-cp-clone
           Perform function cloning to make interprocedural constant
           propagation stronger.  When enabled, interprocedural constant
           propagation performs function cloning when externally visible
           function can be called with constant arguments.  Because this
           optimization can create multiple copies of functions, it may
           significantly increase code size (see --param
           ipcp-unit-growth=value).  This flag is enabled by default at -O3.

       -ftree-sink
           Perform forward store motion  on trees.  This flag is enabled by
           default at -O and higher.

       -ftree-bit-ccp
           Perform sparse conditional bit constant propagation on trees and
           propagate pointer alignment information.  This pass only operates
           on local scalar variables and is enabled by default at -O and
           higher.  It requires that -ftree-ccp is enabled.

       -ftree-ccp
           Perform sparse conditional constant propagation (CCP) on trees.
           This pass only operates on local scalar variables and is enabled by
           default at -O and higher.

       -ftree-switch-conversion
           Perform conversion of simple initializations in a switch to
           initializations from a scalar array.  This flag is enabled by
           default at -O2 and higher.

       -ftree-tail-merge
           Look for identical code sequences.  When found, replace one with a
           jump to the other.  This optimization is known as tail merging or
           cross jumping.  This flag is enabled by default at -O2 and higher.
           The compilation time in this pass can be limited using max-tail-
           merge-comparisons parameter and max-tail-merge-iterations
           parameter.

       -ftree-dce
           Perform dead code elimination (DCE) on trees.  This flag is enabled
           by default at -O and higher.

       -ftree-builtin-call-dce
           Perform conditional dead code elimination (DCE) for calls to built-
           in functions that may set "errno" but are otherwise side-effect
           free.  This flag is enabled by default at -O2 and higher if -Os is
           not also specified.

       -ftree-dominator-opts
           Perform a variety of simple scalar cleanups (constant/copy
           propagation, redundancy elimination, range propagation and
           expression simplification) based on a dominator tree traversal.
           This also performs jump threading (to reduce jumps to jumps). This
           flag is enabled by default at -O and higher.

       -ftree-dse
           Perform dead store elimination (DSE) on trees.  A dead store is a
           store into a memory location that is later overwritten by another
           store without any intervening loads.  In this case the earlier
           store can be deleted.  This flag is enabled by default at -O and
           higher.

       -ftree-ch
           Perform loop header copying on trees.  This is beneficial since it
           increases effectiveness of code motion optimizations.  It also
           saves one jump.  This flag is enabled by default at -O and higher.
           It is not enabled for -Os, since it usually increases code size.

       -ftree-loop-optimize
           Perform loop optimizations on trees.  This flag is enabled by
           default at -O and higher.

       -ftree-loop-linear
           Perform loop interchange transformations on tree.  Same as
           -floop-interchange.  To use this code transformation, GCC has to be
           configured with --with-ppl and --with-cloog to enable the Graphite
           loop transformation infrastructure.

       -floop-interchange
           Perform loop interchange transformations on loops.  Interchanging
           two nested loops switches the inner and outer loops.  For example,
           given a loop like:

                   DO J = 1, M
                     DO I = 1, N
                       A(J, I) = A(J, I) * C
                     ENDDO
                   ENDDO

           loop interchange transforms the loop as if it were written:

                   DO I = 1, N
                     DO J = 1, M
                       A(J, I) = A(J, I) * C
                     ENDDO
                   ENDDO

           which can be beneficial when "N" is larger than the caches, because
           in Fortran, the elements of an array are stored in memory
           contiguously by column, and the original loop iterates over rows,
           potentially creating at each access a cache miss.  This
           optimization applies to all the languages supported by GCC and is
           not limited to Fortran.  To use this code transformation, GCC has
           to be configured with --with-ppl and --with-cloog to enable the
           Graphite loop transformation infrastructure.

       -floop-strip-mine
           Perform loop strip mining transformations on loops.  Strip mining
           splits a loop into two nested loops.  The outer loop has strides
           equal to the strip size and the inner loop has strides of the
           original loop within a strip.  The strip length can be changed
           using the loop-block-tile-size parameter.  For example, given a
           loop like:

                   DO I = 1, N
                     A(I) = A(I) + C
                   ENDDO

           loop strip mining transforms the loop as if it were written:

                   DO II = 1, N, 51
                     DO I = II, min (II + 50, N)
                       A(I) = A(I) + C
                     ENDDO
                   ENDDO

           This optimization applies to all the languages supported by GCC and
           is not limited to Fortran.  To use this code transformation, GCC
           has to be configured with --with-ppl and --with-cloog to enable the
           Graphite loop transformation infrastructure.

       -floop-block
           Perform loop blocking transformations on loops.  Blocking strip
           mines each loop in the loop nest such that the memory accesses of
           the element loops fit inside caches.  The strip length can be
           changed using the loop-block-tile-size parameter.  For example,
           given a loop like:

                   DO I = 1, N
                     DO J = 1, M
                       A(J, I) = B(I) + C(J)
                     ENDDO
                   ENDDO

           loop blocking transforms the loop as if it were written:

                   DO II = 1, N, 51
                     DO JJ = 1, M, 51
                       DO I = II, min (II + 50, N)
                         DO J = JJ, min (JJ + 50, M)
                           A(J, I) = B(I) + C(J)
                         ENDDO
                       ENDDO
                     ENDDO
                   ENDDO

           which can be beneficial when "M" is larger than the caches, because
           the innermost loop iterates over a smaller amount of data which can
           be kept in the caches.  This optimization applies to all the
           languages supported by GCC and is not limited to Fortran.  To use
           this code transformation, GCC has to be configured with --with-ppl
           and --with-cloog to enable the Graphite loop transformation
           infrastructure.

       -fgraphite-identity
           Enable the identity transformation for graphite.  For every SCoP we
           generate the polyhedral representation and transform it back to
           gimple.  Using -fgraphite-identity we can check the costs or
           benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.  Some
           minimal optimizations are also performed by the code generator
           CLooG, like index splitting and dead code elimination in loops.

       -floop-nest-optimize
           Enable the ISL based loop nest optimizer.  This is a generic loop
           nest optimizer based on the Pluto optimization algorithms.  It
           calculates a loop structure optimized for data-locality and
           parallelism.  This option is experimental.

       -floop-parallelize-all
           Use the Graphite data dependence analysis to identify loops that
           can be parallelized.  Parallelize all the loops that can be
           analyzed to not contain loop carried dependences without checking
           that it is profitable to parallelize the loops.

       -fcheck-data-deps
           Compare the results of several data dependence analyzers.  This
           option is used for debugging the data dependence analyzers.

       -ftree-loop-if-convert
           Attempt to transform conditional jumps in the innermost loops to
           branch-less equivalents.  The intent is to remove control-flow from
           the innermost loops in order to improve the ability of the
           vectorization pass to handle these loops.  This is enabled by
           default if vectorization is enabled.

       -ftree-loop-if-convert-stores
           Attempt to also if-convert conditional jumps containing memory
           writes.  This transformation can be unsafe for multi-threaded
           programs as it transforms conditional memory writes into
           unconditional memory writes.  For example,

                   for (i = 0; i < N; i++)
                     if (cond)
                       A[i] = expr;

           is transformed to

                   for (i = 0; i < N; i++)
                     A[i] = cond ? expr : A[i];

           potentially producing data races.

       -ftree-loop-distribution
           Perform loop distribution.  This flag can improve cache performance
           on big loop bodies and allow further loop optimizations, like
           parallelization or vectorization, to take place.  For example, the
           loop

                   DO I = 1, N
                     A(I) = B(I) + C
                     D(I) = E(I) * F
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = B(I) + C
                   ENDDO
                   DO I = 1, N
                      D(I) = E(I) * F
                   ENDDO

       -ftree-loop-distribute-patterns
           Perform loop distribution of patterns that can be code generated
           with calls to a library.  This flag is enabled by default at -O3.

           This pass distributes the initialization loops and generates a call
           to memset zero.  For example, the loop

                   DO I = 1, N
                     A(I) = 0
                     B(I) = A(I) + I
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = 0
                   ENDDO
                   DO I = 1, N
                      B(I) = A(I) + I
                   ENDDO

           and the initialization loop is transformed into a call to memset
           zero.

       -ftree-loop-im
           Perform loop invariant motion on trees.  This pass moves only
           invariants that are hard to handle at RTL level (function calls,
           operations that expand to nontrivial sequences of insns).  With
           -funswitch-loops it also moves operands of conditions that are
           invariant out of the loop, so that we can use just trivial
           invariantness analysis in loop unswitching.  The pass also includes
           store motion.

       -ftree-loop-ivcanon
           Create a canonical counter for number of iterations in loops for
           which determining number of iterations requires complicated
           analysis.  Later optimizations then may determine the number
           easily.  Useful especially in connection with unrolling.

       -fivopts
           Perform induction variable optimizations (strength reduction,
           induction variable merging and induction variable elimination) on
           trees.

       -ftree-parallelize-loops=n
           Parallelize loops, i.e., split their iteration space to run in n
           threads.  This is only possible for loops whose iterations are
           independent and can be arbitrarily reordered.  The optimization is
           only profitable on multiprocessor machines, for loops that are CPU-
           intensive, rather than constrained e.g. by memory bandwidth.  This
           option implies -pthread, and thus is only supported on targets that
           have support for -pthread.

       -ftree-pta
           Perform function-local points-to analysis on trees.  This flag is
           enabled by default at -O and higher.

       -ftree-sra
           Perform scalar replacement of aggregates.  This pass replaces
           structure references with scalars to prevent committing structures
           to memory too early.  This flag is enabled by default at -O and
           higher.

       -ftree-copyrename
           Perform copy renaming on trees.  This pass attempts to rename
           compiler temporaries to other variables at copy locations, usually
           resulting in variable names which more closely resemble the
           original variables.  This flag is enabled by default at -O and
           higher.

       -ftree-coalesce-inlined-vars
           Tell the copyrename pass (see -ftree-copyrename) to attempt to
           combine small user-defined variables too, but only if they were
           inlined from other functions.  It is a more limited form of
           -ftree-coalesce-vars.  This may harm debug information of such
           inlined variables, but it will keep variables of the inlined-into
           function apart from each other, such that they are more likely to
           contain the expected values in a debugging session.  This was the
           default in GCC versions older than 4.7.

       -ftree-coalesce-vars
           Tell the copyrename pass (see -ftree-copyrename) to attempt to
           combine small user-defined variables too, instead of just compiler
           temporaries.  This may severely limit the ability to debug an
           optimized program compiled with -fno-var-tracking-assignments.  In
           the negated form, this flag prevents SSA coalescing of user
           variables, including inlined ones.  This option is enabled by
           default.

       -ftree-ter
           Perform temporary expression replacement during the SSA->normal
           phase.  Single use/single def temporaries are replaced at their use
           location with their defining expression.  This results in non-
           GIMPLE code, but gives the expanders much more complex trees to
           work on resulting in better RTL generation.  This is enabled by
           default at -O and higher.

       -ftree-slsr
           Perform straight-line strength reduction on trees.  This recognizes
           related expressions involving multiplications and replaces them by
           less expensive calculations when possible.  This is enabled by
           default at -O and higher.

       -ftree-vectorize
           Perform loop vectorization on trees. This flag is enabled by
           default at -O3.

       -ftree-slp-vectorize
           Perform basic block vectorization on trees. This flag is enabled by
           default at -O3 and when -ftree-vectorize is enabled.

       -ftree-vect-loop-version
           Perform loop versioning when doing loop vectorization on trees.
           When a loop appears to be vectorizable except that data alignment
           or data dependence cannot be determined at compile time, then
           vectorized and non-vectorized versions of the loop are generated
           along with run-time checks for alignment or dependence to control
           which version is executed.  This option is enabled by default
           except at level -Os where it is disabled.

       -fvect-cost-model
           Enable cost model for vectorization.  This option is enabled by
           default at -O3.

       -ftree-vrp
           Perform Value Range Propagation on trees.  This is similar to the
           constant propagation pass, but instead of values, ranges of values
           are propagated.  This allows the optimizers to remove unnecessary
           range checks like array bound checks and null pointer checks.  This
           is enabled by default at -O2 and higher.  Null pointer check
           elimination is only done if -fdelete-null-pointer-checks is
           enabled.

       -ftracer
           Perform tail duplication to enlarge superblock size.  This
           transformation simplifies the control flow of the function allowing
           other optimizations to do a better job.

       -funroll-loops
           Unroll loops whose number of iterations can be determined at
           compile time or upon entry to the loop.  -funroll-loops implies
           -frerun-cse-after-loop.  This option makes code larger, and may or
           may not make it run faster.

       -funroll-all-loops
           Unroll all loops, even if their number of iterations is uncertain
           when the loop is entered.  This usually makes programs run more
           slowly.  -funroll-all-loops implies the same options as
           -funroll-loops,

       -fsplit-ivs-in-unroller
           Enables expression of values of induction variables in later
           iterations of the unrolled loop using the value in the first
           iteration.  This breaks long dependency chains, thus improving
           efficiency of the scheduling passes.

           A combination of -fweb and CSE is often sufficient to obtain the
           same effect.  However, that is not reliable in cases where the loop
           body is more complicated than a single basic block.  It also does
           not work at all on some architectures due to restrictions in the
           CSE pass.

           This optimization is enabled by default.

       -fvariable-expansion-in-unroller
           With this option, the compiler creates multiple copies of some
           local variables when unrolling a loop, which can result in superior
           code.

       -fpartial-inlining
           Inline parts of functions.  This option has any effect only when
           inlining itself is turned on by the -finline-functions or
           -finline-small-functions options.

           Enabled at level -O2.

       -fpredictive-commoning
           Perform predictive commoning optimization, i.e., reusing
           computations (especially memory loads and stores) performed in
           previous iterations of loops.

           This option is enabled at level -O3.

       -fprefetch-loop-arrays
           If supported by the target machine, generate instructions to
           prefetch memory to improve the performance of loops that access
           large arrays.

           This option may generate better or worse code; results are highly
           dependent on the structure of loops within the source code.

           Disabled at level -Os.

       -fno-peephole
       -fno-peephole2
           Disable any machine-specific peephole optimizations.  The
           difference between -fno-peephole and -fno-peephole2 is in how they
           are implemented in the compiler; some targets use one, some use the
           other, a few use both.

           -fpeephole is enabled by default.  -fpeephole2 enabled at levels
           -O2, -O3, -Os.

       -fno-guess-branch-probability
           Do not guess branch probabilities using heuristics.

           GCC uses heuristics to guess branch probabilities if they are not
           provided by profiling feedback (-fprofile-arcs).  These heuristics
           are based on the control flow graph.  If some branch probabilities
           are specified by __builtin_expect, then the heuristics are used to
           guess branch probabilities for the rest of the control flow graph,
           taking the __builtin_expect info into account.  The interactions
           between the heuristics and __builtin_expect can be complex, and in
           some cases, it may be useful to disable the heuristics so that the
           effects of __builtin_expect are easier to understand.

           The default is -fguess-branch-probability at levels -O, -O2, -O3,
           -Os.

       -freorder-blocks
           Reorder basic blocks in the compiled function in order to reduce
           number of taken branches and improve code locality.

           Enabled at levels -O2, -O3.

       -freorder-blocks-and-partition
           In addition to reordering basic blocks in the compiled function, in
           order to reduce number of taken branches, partitions hot and cold
           basic blocks into separate sections of the assembly and .o files,
           to improve paging and cache locality performance.

           This optimization is automatically turned off in the presence of
           exception handling, for linkonce sections, for functions with a
           user-defined section attribute and on any architecture that does
           not support named sections.

       -freorder-functions
           Reorder functions in the object file in order to improve code
           locality.  This is implemented by using special subsections
           ".text.hot" for most frequently executed functions and
           ".text.unlikely" for unlikely executed functions.  Reordering is
           done by the linker so object file format must support named
           sections and linker must place them in a reasonable way.

           Also profile feedback must be available to make this option
           effective.  See -fprofile-arcs for details.

           Enabled at levels -O2, -O3, -Os.

       -fstrict-aliasing
           Allow the compiler to assume the strictest aliasing rules
           applicable to the language being compiled.  For C (and C++), this
           activates optimizations based on the type of expressions.  In
           particular, an object of one type is assumed never to reside at the
           same address as an object of a different type, unless the types are
           almost the same.  For example, an "unsigned int" can alias an
           "int", but not a "void*" or a "double".  A character type may alias
           any other type.

           Pay special attention to code like this:

                   union a_union {
                     int i;
                     double d;
                   };

                   int f() {
                     union a_union t;
                     t.d = 3.0;
                     return t.i;
                   }

           The practice of reading from a different union member than the one
           most recently written to (called "type-punning") is common.  Even
           with -fstrict-aliasing, type-punning is allowed, provided the
           memory is accessed through the union type.  So, the code above
           works as expected.    However, this code might not:

                   int f() {
                     union a_union t;
                     int* ip;
                     t.d = 3.0;
                     ip = &t.i;
                     return *ip;
                   }

           Similarly, access by taking the address, casting the resulting
           pointer and dereferencing the result has undefined behavior, even
           if the cast uses a union type, e.g.:

                   int f() {
                     double d = 3.0;
                     return ((union a_union *) &d)->i;
                   }

           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.

       -fstrict-overflow
           Allow the compiler to assume strict signed overflow rules,
           depending on the language being compiled.  For C (and C++) this
           means that overflow when doing arithmetic with signed numbers is
           undefined, which means that the compiler may assume that it does
           not happen.  This permits various optimizations.  For example, the
           compiler assumes that an expression like "i + 10 > i" is always
           true for signed "i".  This assumption is only valid if signed
           overflow is undefined, as the expression is false if "i + 10"
           overflows when using twos complement arithmetic.  When this option
           is in effect any attempt to determine whether an operation on
           signed numbers overflows must be written carefully to not actually
           involve overflow.

           This option also allows the compiler to assume strict pointer
           semantics: given a pointer to an object, if adding an offset to
           that pointer does not produce a pointer to the same object, the
           addition is undefined.  This permits the compiler to conclude that
           "p + u > p" is always true for a pointer "p" and unsigned integer
           "u".  This assumption is only valid because pointer wraparound is
           undefined, as the expression is false if "p + u" overflows using
           twos complement arithmetic.

           See also the -fwrapv option.  Using -fwrapv means that integer
           signed overflow is fully defined: it wraps.  When -fwrapv is used,
           there is no difference between -fstrict-overflow and
           -fno-strict-overflow for integers.  With -fwrapv certain types of
           overflow are permitted.  For example, if the compiler gets an
           overflow when doing arithmetic on constants, the overflowed value
           can still be used with -fwrapv, but not otherwise.

           The -fstrict-overflow option is enabled at levels -O2, -O3, -Os.

       -falign-functions
       -falign-functions=n
           Align the start of functions to the next power-of-two greater than
           n, skipping up to n bytes.  For instance, -falign-functions=32
           aligns functions to the next 32-byte boundary, but
           -falign-functions=24 aligns to the next 32-byte boundary only if
           this can be done by skipping 23 bytes or less.

           -fno-align-functions and -falign-functions=1 are equivalent and
           mean that functions are not aligned.

           Some assemblers only support this flag when n is a power of two; in
           that case, it is rounded up.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -falign-labels
       -falign-labels=n
           Align all branch targets to a power-of-two boundary, skipping up to
           n bytes like -falign-functions.  This option can easily make code
           slower, because it must insert dummy operations for when the branch
           target is reached in the usual flow of the code.

           -fno-align-labels and -falign-labels=1 are equivalent and mean that
           labels are not aligned.

           If -falign-loops or -falign-jumps are applicable and are greater
           than this value, then their values are used instead.

           If n is not specified or is zero, use a machine-dependent default
           which is very likely to be 1, meaning no alignment.

           Enabled at levels -O2, -O3.

       -falign-loops
       -falign-loops=n
           Align loops to a power-of-two boundary, skipping up to n bytes like
           -falign-functions.  If the loops are executed many times, this
           makes up for any execution of the dummy operations.

           -fno-align-loops and -falign-loops=1 are equivalent and mean that
           loops are not aligned.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -falign-jumps
       -falign-jumps=n
           Align branch targets to a power-of-two boundary, for branch targets
           where the targets can only be reached by jumping, skipping up to n
           bytes like -falign-functions.  In this case, no dummy operations
           need be executed.

           -fno-align-jumps and -falign-jumps=1 are equivalent and mean that
           loops are not aligned.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -funit-at-a-time
           This option is left for compatibility reasons. -funit-at-a-time has
           no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder
           and -fno-section-anchors.

           Enabled by default.

       -fno-toplevel-reorder
           Do not reorder top-level functions, variables, and "asm"
           statements.  Output them in the same order that they appear in the
           input file.  When this option is used, unreferenced static
           variables are not removed.  This option is intended to support
           existing code that relies on a particular ordering.  For new code,
           it is better to use attributes.

           Enabled at level -O0.  When disabled explicitly, it also implies
           -fno-section-anchors, which is otherwise enabled at -O0 on some
           targets.

       -fweb
           Constructs webs as commonly used for register allocation purposes
           and assign each web individual pseudo register.  This allows the
           register allocation pass to operate on pseudos directly, but also
           strengthens several other optimization passes, such as CSE, loop
           optimizer and trivial dead code remover.  It can, however, make
           debugging impossible, since variables no longer stay in a "home
           register".

           Enabled by default with -funroll-loops.

       -fwhole-program
           Assume that the current compilation unit represents the whole
           program being compiled.  All public functions and variables with
           the exception of "main" and those merged by attribute
           "externally_visible" become static functions and in effect are
           optimized more aggressively by interprocedural optimizers.

           This option should not be used in combination with "-flto".
           Instead relying on a linker plugin should provide safer and more
           precise information.

       -flto[=n]
           This option runs the standard link-time optimizer.  When invoked
           with source code, it generates GIMPLE (one of GCC's internal
           representations) and writes it to special ELF sections in the
           object file.  When the object files are linked together, all the
           function bodies are read from these ELF sections and instantiated
           as if they had been part of the same translation unit.

           To use the link-time optimizer, -flto needs to be specified at
           compile time and during the final link.  For example:

                   gcc -c -O2 -flto foo.c
                   gcc -c -O2 -flto bar.c
                   gcc -o myprog -flto -O2 foo.o bar.o

           The first two invocations to GCC save a bytecode representation of
           GIMPLE into special ELF sections inside foo.o and bar.o.  The final
           invocation reads the GIMPLE bytecode from foo.o and bar.o, merges
           the two files into a single internal image, and compiles the result
           as usual.  Since both foo.o and bar.o are merged into a single
           image, this causes all the interprocedural analyses and
           optimizations in GCC to work across the two files as if they were a
           single one.  This means, for example, that the inliner is able to
           inline functions in bar.o into functions in foo.o and vice-versa.

           Another (simpler) way to enable link-time optimization is:

                   gcc -o myprog -flto -O2 foo.c bar.c

           The above generates bytecode for foo.c and bar.c, merges them
           together into a single GIMPLE representation and optimizes them as
           usual to produce myprog.

           The only important thing to keep in mind is that to enable link-
           time optimizations the -flto flag needs to be passed to both the
           compile and the link commands.

           To make whole program optimization effective, it is necessary to
           make certain whole program assumptions.  The compiler needs to know
           what functions and variables can be accessed by libraries and
           runtime outside of the link-time optimized unit.  When supported by
           the linker, the linker plugin (see -fuse-linker-plugin) passes
           information to the compiler about used and externally visible
           symbols.  When the linker plugin is not available, -fwhole-program
           should be used to allow the compiler to make these assumptions,
           which leads to more aggressive optimization decisions.

           Note that when a file is compiled with -flto, the generated object
           file is larger than a regular object file because it contains
           GIMPLE bytecodes and the usual final code.  This means that object
           files with LTO information can be linked as normal object files; if
           -flto is not passed to the linker, no interprocedural optimizations
           are applied.

           Additionally, the optimization flags used to compile individual
           files are not necessarily related to those used at link time.  For
           instance,

                   gcc -c -O0 -flto foo.c
                   gcc -c -O0 -flto bar.c
                   gcc -o myprog -flto -O3 foo.o bar.o

           This produces individual object files with unoptimized assembler
           code, but the resulting binary myprog is optimized at -O3.  If,
           instead, the final binary is generated without -flto, then myprog
           is not optimized.

           When producing the final binary with -flto, GCC only applies link-
           time optimizations to those files that contain bytecode.
           Therefore, you can mix and match object files and libraries with
           GIMPLE bytecodes and final object code.  GCC automatically selects
           which files to optimize in LTO mode and which files to link without
           further processing.

           There are some code generation flags preserved by GCC when
           generating bytecodes, as they need to be used during the final link
           stage.  Currently, the following options are saved into the GIMPLE
           bytecode files: -fPIC, -fcommon and all the -m target flags.

           At link time, these options are read in and reapplied.  Note that
           the current implementation makes no attempt to recognize
           conflicting values for these options.  If different files have
           conflicting option values (e.g., one file is compiled with -fPIC
           and another isn't), the compiler simply uses the last value read
           from the bytecode files.  It is recommended, then, that you compile
           all the files participating in the same link with the same options.

           If LTO encounters objects with C linkage declared with incompatible
           types in separate translation units to be linked together
           (undefined behavior according to ISO C99 6.2.7), a non-fatal
           diagnostic may be issued.  The behavior is still undefined at run
           time.

           Another feature of LTO is that it is possible to apply
           interprocedural optimizations on files written in different
           languages.  This requires support in the language front end.
           Currently, the C, C++ and Fortran front ends are capable of
           emitting GIMPLE bytecodes, so something like this should work:

                   gcc -c -flto foo.c
                   g++ -c -flto bar.cc
                   gfortran -c -flto baz.f90
                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran

           Notice that the final link is done with g++ to get the C++ runtime
           libraries and -lgfortran is added to get the Fortran runtime
           libraries.  In general, when mixing languages in LTO mode, you
           should use the same link command options as when mixing languages
           in a regular (non-LTO) compilation; all you need to add is -flto to
           all the compile and link commands.

           If object files containing GIMPLE bytecode are stored in a library
           archive, say libfoo.a, it is possible to extract and use them in an
           LTO link if you are using a linker with plugin support.  To enable
           this feature, use the flag -fuse-linker-plugin at link time:

                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo

           With the linker plugin enabled, the linker extracts the needed
           GIMPLE files from libfoo.a and passes them on to the running GCC to
           make them part of the aggregated GIMPLE image to be optimized.

           If you are not using a linker with plugin support and/or do not
           enable the linker plugin, then the objects inside libfoo.a are
           extracted and linked as usual, but they do not participate in the
           LTO optimization process.

           Link-time optimizations do not require the presence of the whole
           program to operate.  If the program does not require any symbols to
           be exported, it is possible to combine -flto and -fwhole-program to
           allow the interprocedural optimizers to use more aggressive
           assumptions which may lead to improved optimization opportunities.
           Use of -fwhole-program is not needed when linker plugin is active
           (see -fuse-linker-plugin).

           The current implementation of LTO makes no attempt to generate
           bytecode that is portable between different types of hosts.  The
           bytecode files are versioned and there is a strict version check,
           so bytecode files generated in one version of GCC will not work
           with an older/newer version of GCC.

           Link-time optimization does not work well with generation of
           debugging information.  Combining -flto with -g is currently
           experimental and expected to produce wrong results.

           If you specify the optional n, the optimization and code generation
           done at link time is executed in parallel using n parallel jobs by
           utilizing an installed make program.  The environment variable MAKE
           may be used to override the program used.  The default value for n
           is 1.

           You can also specify -flto=jobserver to use GNU make's job server
           mode to determine the number of parallel jobs. This is useful when
           the Makefile calling GCC is already executing in parallel.  You
           must prepend a + to the command recipe in the parent Makefile for
           this to work.  This option likely only works if MAKE is GNU make.

           This option is disabled by default.

       -flto-partition=alg
           Specify the partitioning algorithm used by the link-time optimizer.
           The value is either "1to1" to specify a partitioning mirroring the
           original source files or "balanced" to specify partitioning into
           equally sized chunks (whenever possible) or "max" to create new
           partition for every symbol where possible.  Specifying "none" as an
           algorithm disables partitioning and streaming completely.  The
           default value is "balanced". While "1to1" can be used as an
           workaround for various code ordering issues, the "max" partitioning
           is intended for internal testing only.

       -flto-compression-level=n
           This option specifies the level of compression used for
           intermediate language written to LTO object files, and is only
           meaningful in conjunction with LTO mode (-flto).  Valid values are
           0 (no compression) to 9 (maximum compression).  Values outside this
           range are clamped to either 0 or 9.  If the option is not given, a
           default balanced compression setting is used.

       -flto-report
           Prints a report with internal details on the workings of the link-
           time optimizer.  The contents of this report vary from version to
           version.  It is meant to be useful to GCC developers when
           processing object files in LTO mode (via -flto).

           Disabled by default.

       -fuse-linker-plugin
           Enables the use of a linker plugin during link-time optimization.
           This option relies on plugin support in the linker, which is
           available in gold or in GNU ld 2.21 or newer.

           This option enables the extraction of object files with GIMPLE
           bytecode out of library archives. This improves the quality of
           optimization by exposing more code to the link-time optimizer.
           This information specifies what symbols can be accessed externally
           (by non-LTO object or during dynamic linking).  Resulting code
           quality improvements on binaries (and shared libraries that use
           hidden visibility) are similar to "-fwhole-program".  See -flto for
           a description of the effect of this flag and how to use it.

           This option is enabled by default when LTO support in GCC is
           enabled and GCC was configured for use with a linker supporting
           plugins (GNU ld 2.21 or newer or gold).

       -ffat-lto-objects
           Fat LTO objects are object files that contain both the intermediate
           language and the object code. This makes them usable for both LTO
           linking and normal linking. This option is effective only when
           compiling with -flto and is ignored at link time.

           -fno-fat-lto-objects improves compilation time over plain LTO, but
           requires the complete toolchain to be aware of LTO. It requires a
           linker with linker plugin support for basic functionality.
           Additionally, nm, ar and ranlib need to support linker plugins to
           allow a full-featured build environment (capable of building static
           libraries etc).  GCC provides the gcc-ar, gcc-nm, gcc-ranlib
           wrappers to pass the right options to these tools. With non fat LTO
           makefiles need to be modified to use them.

           The default is -ffat-lto-objects but this default is intended to
           change in future releases when linker plugin enabled environments
           become more common.

       -fcompare-elim
           After register allocation and post-register allocation instruction
           splitting, identify arithmetic instructions that compute processor
           flags similar to a comparison operation based on that arithmetic.
           If possible, eliminate the explicit comparison operation.

           This pass only applies to certain targets that cannot explicitly
           represent the comparison operation before register allocation is
           complete.

           Enabled at levels -O, -O2, -O3, -Os.

       -fuse-ld=bfd
           Use the bfd linker instead of the default linker.

       -fuse-ld=gold
           Use the gold linker instead of the default linker.

       -fcprop-registers
           After register allocation and post-register allocation instruction
           splitting, perform a copy-propagation pass to try to reduce
           scheduling dependencies and occasionally eliminate the copy.

           Enabled at levels -O, -O2, -O3, -Os.

       -fprofile-correction
           Profiles collected using an instrumented binary for multi-threaded
           programs may be inconsistent due to missed counter updates. When
           this option is specified, GCC uses heuristics to correct or smooth
           out such inconsistencies. By default, GCC emits an error message
           when an inconsistent profile is detected.

       -fprofile-dir=path
           Set the directory to search for the profile data files in to path.
           This option affects only the profile data generated by
           -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by
           -fprofile-use and -fbranch-probabilities and its related options.
           Both absolute and relative paths can be used.  By default, GCC uses
           the current directory as path, thus the profile data file appears
           in the same directory as the object file.

       -fprofile-generate
       -fprofile-generate=path
           Enable options usually used for instrumenting application to
           produce profile useful for later recompilation with profile
           feedback based optimization.  You must use -fprofile-generate both
           when compiling and when linking your program.

           The following options are enabled: "-fprofile-arcs",
           "-fprofile-values", "-fvpt".

           If path is specified, GCC looks at the path to find the profile
           feedback data files. See -fprofile-dir.

       -fprofile-use
       -fprofile-use=path
           Enable profile feedback directed optimizations, and optimizations
           generally profitable only with profile feedback available.

           The following options are enabled: "-fbranch-probabilities",
           "-fvpt", "-funroll-loops", "-fpeel-loops", "-ftracer",
           "-ftree-vectorize", "ftree-loop-distribute-patterns"

           By default, GCC emits an error message if the feedback profiles do
           not match the source code.  This error can be turned into a warning
           by using -Wcoverage-mismatch.  Note this may result in poorly
           optimized code.

           If path is specified, GCC looks at the path to find the profile
           feedback data files. See -fprofile-dir.

       The following options control compiler behavior regarding floating-
       point arithmetic.  These options trade off between speed and
       correctness.  All must be specifically enabled.

       -ffloat-store
           Do not store floating-point variables in registers, and inhibit
           other options that might change whether a floating-point value is
           taken from a register or memory.

           This option prevents undesirable excess precision on machines such
           as the 68000 where the floating registers (of the 68881) keep more
           precision than a "double" is supposed to have.  Similarly for the
           x86 architecture.  For most programs, the excess precision does
           only good, but a few programs rely on the precise definition of
           IEEE floating point.  Use -ffloat-store for such programs, after
           modifying them to store all pertinent intermediate computations
           into variables.

       -fexcess-precision=style
           This option allows further control over excess precision on
           machines where floating-point registers have more precision than
           the IEEE "float" and "double" types and the processor does not
           support operations rounding to those types.  By default,
           -fexcess-precision=fast is in effect; this means that operations
           are carried out in the precision of the registers and that it is
           unpredictable when rounding to the types specified in the source
           code takes place.  When compiling C, if -fexcess-precision=standard
           is specified then excess precision follows the rules specified in
           ISO C99; in particular, both casts and assignments cause values to
           be rounded to their semantic types (whereas -ffloat-store only
           affects assignments).  This option is enabled by default for C if a
           strict conformance option such as -std=c99 is used.

           -fexcess-precision=standard is not implemented for languages other
           than C, and has no effect if -funsafe-math-optimizations or
           -ffast-math is specified.  On the x86, it also has no effect if
           -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case,
           IEEE semantics apply without excess precision, and in the latter,
           rounding is unpredictable.

       -ffast-math
           Sets -fno-math-errno, -funsafe-math-optimizations,
           -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans and
           -fcx-limited-range.

           This option causes the preprocessor macro "__FAST_MATH__" to be
           defined.

           This option is not turned on by any -O option besides -Ofast since
           it can result in incorrect output for programs that depend on an
           exact implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.

       -fno-math-errno
           Do not set "errno" after calling math functions that are executed
           with a single instruction, e.g., "sqrt".  A program that relies on
           IEEE exceptions for math error handling may want to use this flag
           for speed while maintaining IEEE arithmetic compatibility.

           This option is not turned on by any -O option since it can result
           in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.

           The default is -fmath-errno.

           On Darwin systems, the math library never sets "errno".  There is
           therefore no reason for the compiler to consider the possibility
           that it might, and -fno-math-errno is the default.

       -funsafe-math-optimizations
           Allow optimizations for floating-point arithmetic that (a) assume
           that arguments and results are valid and (b) may violate IEEE or
           ANSI standards.  When used at link-time, it may include libraries
           or startup files that change the default FPU control word or other
           similar optimizations.

           This option is not turned on by any -O option since it can result
           in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.  Enables
           -fno-signed-zeros, -fno-trapping-math, -fassociative-math and
           -freciprocal-math.

           The default is -fno-unsafe-math-optimizations.

       -fassociative-math
           Allow re-association of operands in series of floating-point
           operations.  This violates the ISO C and C++ language standard by
           possibly changing computation result.  NOTE: re-ordering may change
           the sign of zero as well as ignore NaNs and inhibit or create
           underflow or overflow (and thus cannot be used on code that relies
           on rounding behavior like "(x + 2**52) - 2**52".  May also reorder
           floating-point comparisons and thus may not be used when ordered
           comparisons are required.  This option requires that both
           -fno-signed-zeros and -fno-trapping-math be in effect.  Moreover,
           it doesn't make much sense with -frounding-math. For Fortran the
           option is automatically enabled when both -fno-signed-zeros and
           -fno-trapping-math are in effect.

           The default is -fno-associative-math.

       -freciprocal-math
           Allow the reciprocal of a value to be used instead of dividing by
           the value if this enables optimizations.  For example "x / y" can
           be replaced with "x * (1/y)", which is useful if "(1/y)" is subject
           to common subexpression elimination.  Note that this loses
           precision and increases the number of flops operating on the value.

           The default is -fno-reciprocal-math.

       -ffinite-math-only
           Allow optimizations for floating-point arithmetic that assume that
           arguments and results are not NaNs or +-Infs.

           This option is not turned on by any -O option since it can result
           in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions. It may, however, yield faster code for programs that do
           not require the guarantees of these specifications.

           The default is -fno-finite-math-only.

       -fno-signed-zeros
           Allow optimizations for floating-point arithmetic that ignore the
           signedness of zero.  IEEE arithmetic specifies the behavior of
           distinct +0.0 and -0.0 values, which then prohibits simplification
           of expressions such as x+0.0 or 0.0*x (even with
           -ffinite-math-only).  This option implies that the sign of a zero
           result isn't significant.

           The default is -fsigned-zeros.

       -fno-trapping-math
           Compile code assuming that floating-point operations cannot
           generate user-visible traps.  These traps include division by zero,
           overflow, underflow, inexact result and invalid operation.  This
           option requires that -fno-signaling-nans be in effect.  Setting
           this option may allow faster code if one relies on "non-stop" IEEE
           arithmetic, for example.

           This option should never be turned on by any -O option since it can
           result in incorrect output for programs that depend on an exact
           implementation of IEEE or ISO rules/specifications for math
           functions.

           The default is -ftrapping-math.

       -frounding-math
           Disable transformations and optimizations that assume default
           floating-point rounding behavior.  This is round-to-zero for all
           floating point to integer conversions, and round-to-nearest for all
           other arithmetic truncations.  This option should be specified for
           programs that change the FP rounding mode dynamically, or that may
           be executed with a non-default rounding mode.  This option disables
           constant folding of floating-point expressions at compile time
           (which may be affected by rounding mode) and arithmetic
           transformations that are unsafe in the presence of sign-dependent
           rounding modes.

           The default is -fno-rounding-math.

           This option is experimental and does not currently guarantee to
           disable all GCC optimizations that are affected by rounding mode.
           Future versions of GCC may provide finer control of this setting
           using C99's "FENV_ACCESS" pragma.  This command-line option will be
           used to specify the default state for "FENV_ACCESS".

       -fsignaling-nans
           Compile code assuming that IEEE signaling NaNs may generate user-
           visible traps during floating-point operations.  Setting this
           option disables optimizations that may change the number of
           exceptions visible with signaling NaNs.  This option implies
           -ftrapping-math.

           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be
           defined.

           The default is -fno-signaling-nans.

           This option is experimental and does not currently guarantee to
           disable all GCC optimizations that affect signaling NaN behavior.

       -fsingle-precision-constant
           Treat floating-point constants as single precision instead of
           implicitly converting them to double-precision constants.

       -fcx-limited-range
           When enabled, this option states that a range reduction step is not
           needed when performing complex division.  Also, there is no
           checking whether the result of a complex multiplication or division
           is "NaN + I*NaN", with an attempt to rescue the situation in that
           case.  The default is -fno-cx-limited-range, but is enabled by
           -ffast-math.

           This option controls the default setting of the ISO C99
           "CX_LIMITED_RANGE" pragma.  Nevertheless, the option applies to all
           languages.

       -fcx-fortran-rules
           Complex multiplication and division follow Fortran rules.  Range
           reduction is done as part of complex division, but there is no
           checking whether the result of a complex multiplication or division
           is "NaN + I*NaN", with an attempt to rescue the situation in that
           case.

           The default is -fno-cx-fortran-rules.

       The following options control optimizations that may improve
       performance, but are not enabled by any -O options.  This section
       includes experimental options that may produce broken code.

       -fbranch-probabilities
           After running a program compiled with -fprofile-arcs, you can
           compile it a second time using -fbranch-probabilities, to improve
           optimizations based on the number of times each branch was taken.
           When a program compiled with -fprofile-arcs exits, it saves arc
           execution counts to a file called sourcename.gcda for each source
           file.  The information in this data file is very dependent on the
           structure of the generated code, so you must use the same source
           code and the same optimization options for both compilations.

           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each
           JUMP_INSN and CALL_INSN.  These can be used to improve
           optimization.  Currently, they are only used in one place: in
           reorg.c, instead of guessing which path a branch is most likely to
           take, the REG_BR_PROB values are used to exactly determine which
           path is taken more often.

       -fprofile-values
           If combined with -fprofile-arcs, it adds code so that some data
           about values of expressions in the program is gathered.

           With -fbranch-probabilities, it reads back the data gathered from
           profiling values of expressions for usage in optimizations.

           Enabled with -fprofile-generate and -fprofile-use.

       -fvpt
           If combined with -fprofile-arcs, this option instructs the compiler
           to add code to gather information about values of expressions.

           With -fbranch-probabilities, it reads back the data gathered and
           actually performs the optimizations based on them.  Currently the
           optimizations include specialization of division operations using
           the knowledge about the value of the denominator.

       -frename-registers
           Attempt to avoid false dependencies in scheduled code by making use
           of registers left over after register allocation.  This
           optimization most benefits processors with lots of registers.
           Depending on the debug information format adopted by the target,
           however, it can make debugging impossible, since variables no
           longer stay in a "home register".

           Enabled by default with -funroll-loops and -fpeel-loops.

       -ftracer
           Perform tail duplication to enlarge superblock size.  This
           transformation simplifies the control flow of the function allowing
           other optimizations to do a better job.

           Enabled with -fprofile-use.

       -funroll-loops
           Unroll loops whose number of iterations can be determined at
           compile time or upon entry to the loop.  -funroll-loops implies
           -frerun-cse-after-loop, -fweb and -frename-registers.  It also
           turns on complete loop peeling (i.e. complete removal of loops with
           a small constant number of iterations).  This option makes code
           larger, and may or may not make it run faster.

           Enabled with -fprofile-use.

       -funroll-all-loops
           Unroll all loops, even if their number of iterations is uncertain
           when the loop is entered.  This usually makes programs run more
           slowly.  -funroll-all-loops implies the same options as
           -funroll-loops.

       -fpeel-loops
           Peels loops for which there is enough information that they do not
           roll much (from profile feedback).  It also turns on complete loop
           peeling (i.e. complete removal of loops with small constant number
           of iterations).

           Enabled with -fprofile-use.

       -fmove-loop-invariants
           Enables the loop invariant motion pass in the RTL loop optimizer.
           Enabled at level -O1

       -funswitch-loops
           Move branches with loop invariant conditions out of the loop, with
           duplicates of the loop on both branches (modified according to
           result of the condition).

       -ffunction-sections
       -fdata-sections
           Place each function or data item into its own section in the output
           file if the target supports arbitrary sections.  The name of the
           function or the name of the data item determines the section's name
           in the output file.

           Use these options on systems where the linker can perform
           optimizations to improve locality of reference in the instruction
           space.  Most systems using the ELF object format and SPARC
           processors running Solaris 2 have linkers with such optimizations.
           AIX may have these optimizations in the future.

           Only use these options when there are significant benefits from
           doing so.  When you specify these options, the assembler and linker
           create larger object and executable files and are also slower.  You
           cannot use "gprof" on all systems if you specify this option, and
           you may have problems with debugging if you specify both this
           option and -g.

       -fbranch-target-load-optimize
           Perform branch target register load optimization before prologue /
           epilogue threading.  The use of target registers can typically be
           exposed only during reload, thus hoisting loads out of loops and
           doing inter-block scheduling needs a separate optimization pass.

       -fbranch-target-load-optimize2
           Perform branch target register load optimization after prologue /
           epilogue threading.

       -fbtr-bb-exclusive
           When performing branch target register load optimization, don't
           reuse branch target registers within any basic block.

       -fstack-protector
           Emit extra code to check for buffer overflows, such as stack
           smashing attacks.  This is done by adding a guard variable to
           functions with vulnerable objects.  This includes functions that
           call "alloca", and functions with buffers larger than 8 bytes.  The
           guards are initialized when a function is entered and then checked
           when the function exits.  If a guard check fails, an error message
           is printed and the program exits.

       -fstack-protector-all
           Like -fstack-protector except that all functions are protected.

       -fsection-anchors
           Try to reduce the number of symbolic address calculations by using
           shared "anchor" symbols to address nearby objects.  This
           transformation can help to reduce the number of GOT entries and GOT
           accesses on some targets.

           For example, the implementation of the following function "foo":

                   static int a, b, c;
                   int foo (void) { return a + b + c; }

           usually calculates the addresses of all three variables, but if you
           compile it with -fsection-anchors, it accesses the variables from a
           common anchor point instead.  The effect is similar to the
           following pseudocode (which isn't valid C):

                   int foo (void)
                   {
                     register int *xr = &x;
                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
                   }

           Not all targets support this option.

       --param name=value
           In some places, GCC uses various constants to control the amount of
           optimization that is done.  For example, GCC does not inline
           functions that contain more than a certain number of instructions.
           You can control some of these constants on the command line using
           the --param option.

           The names of specific parameters, and the meaning of the values,
           are tied to the internals of the compiler, and are subject to
           change without notice in future releases.

           In each case, the value is an integer.  The allowable choices for
           name are:

           predictable-branch-outcome
               When branch is predicted to be taken with probability lower
               than this threshold (in percent), then it is considered well
               predictable. The default is 10.

           max-crossjump-edges
               The maximum number of incoming edges to consider for cross-
               jumping.  The algorithm used by -fcrossjumping is O(N^2) in the
               number of edges incoming to each block.  Increasing values mean
               more aggressive optimization, making the compilation time
               increase with probably small improvement in executable size.

           min-crossjump-insns
               The minimum number of instructions that must be matched at the
               end of two blocks before cross-jumping is performed on them.
               This value is ignored in the case where all instructions in the
               block being cross-jumped from are matched.  The default value
               is 5.

           max-grow-copy-bb-insns
               The maximum code size expansion factor when copying basic
               blocks instead of jumping.  The expansion is relative to a jump
               instruction.  The default value is 8.

           max-goto-duplication-insns
               The maximum number of instructions to duplicate to a block that
               jumps to a computed goto.  To avoid O(N^2) behavior in a number
               of passes, GCC factors computed gotos early in the compilation
               process, and unfactors them as late as possible.  Only computed
               jumps at the end of a basic blocks with no more than max-goto-
               duplication-insns are unfactored.  The default value is 8.

           max-delay-slot-insn-search
               The maximum number of instructions to consider when looking for
               an instruction to fill a delay slot.  If more than this
               arbitrary number of instructions are searched, the time savings
               from filling the delay slot are minimal, so stop searching.
               Increasing values mean more aggressive optimization, making the
               compilation time increase with probably small improvement in
               execution time.

           max-delay-slot-live-search
               When trying to fill delay slots, the maximum number of
               instructions to consider when searching for a block with valid
               live register information.  Increasing this arbitrarily chosen
               value means more aggressive optimization, increasing the
               compilation time.  This parameter should be removed when the
               delay slot code is rewritten to maintain the control-flow
               graph.

           max-gcse-memory
               The approximate maximum amount of memory that can be allocated
               in order to perform the global common subexpression elimination
               optimization.  If more memory than specified is required, the
               optimization is not done.

           max-gcse-insertion-ratio
               If the ratio of expression insertions to deletions is larger
               than this value for any expression, then RTL PRE inserts or
               removes the expression and thus leaves partially redundant
               computations in the instruction stream.  The default value is
               20.

           max-pending-list-length
               The maximum number of pending dependencies scheduling allows
               before flushing the current state and starting over.  Large
               functions with few branches or calls can create excessively
               large lists which needlessly consume memory and resources.

           max-modulo-backtrack-attempts
               The maximum number of backtrack attempts the scheduler should
               make when modulo scheduling a loop.  Larger values can
               exponentially increase compilation time.

           max-inline-insns-single
               Several parameters control the tree inliner used in GCC.  This
               number sets the maximum number of instructions (counted in
               GCC's internal representation) in a single function that the
               tree inliner considers for inlining.  This only affects
               functions declared inline and methods implemented in a class
               declaration (C++).  The default value is 400.

           max-inline-insns-auto
               When you use -finline-functions (included in -O3), a lot of
               functions that would otherwise not be considered for inlining
               by the compiler are investigated.  To those functions, a
               different (more restrictive) limit compared to functions
               declared inline can be applied.  The default value is 40.

           inline-min-speedup
               When estimated performance improvement of caller + callee
               runtime exceeds this threshold (in precent), the function can
               be inlined regardless the limit on --param max-inline-insns-
               single and --param max-inline-insns-auto.

           large-function-insns
               The limit specifying really large functions.  For functions
               larger than this limit after inlining, inlining is constrained
               by --param large-function-growth.  This parameter is useful
               primarily to avoid extreme compilation time caused by non-
               linear algorithms used by the back end.  The default value is
               2700.

           large-function-growth
               Specifies maximal growth of large function caused by inlining
               in percents.  The default value is 100 which limits large
               function growth to 2.0 times the original size.

           large-unit-insns
               The limit specifying large translation unit.  Growth caused by
               inlining of units larger than this limit is limited by --param
               inline-unit-growth.  For small units this might be too tight.
               For example, consider a unit consisting of function A that is
               inline and B that just calls A three times.  If B is small
               relative to A, the growth of unit is 300\% and yet such
               inlining is very sane.  For very large units consisting of
               small inlineable functions, however, the overall unit growth
               limit is needed to avoid exponential explosion of code size.
               Thus for smaller units, the size is increased to --param large-
               unit-insns before applying --param inline-unit-growth.  The
               default is 10000.

           inline-unit-growth
               Specifies maximal overall growth of the compilation unit caused
               by inlining.  The default value is 30 which limits unit growth
               to 1.3 times the original size.

           ipcp-unit-growth
               Specifies maximal overall growth of the compilation unit caused
               by interprocedural constant propagation.  The default value is
               10 which limits unit growth to 1.1 times the original size.

           large-stack-frame
               The limit specifying large stack frames.  While inlining the
               algorithm is trying to not grow past this limit too much.  The
               default value is 256 bytes.

           large-stack-frame-growth
               Specifies maximal growth of large stack frames caused by
               inlining in percents.  The default value is 1000 which limits
               large stack frame growth to 11 times the original size.

           max-inline-insns-recursive
           max-inline-insns-recursive-auto
               Specifies the maximum number of instructions an out-of-line
               copy of a self-recursive inline function can grow into by
               performing recursive inlining.

               For functions declared inline, --param max-inline-insns-
               recursive is taken into account.  For functions not declared
               inline, recursive inlining happens only when -finline-functions
               (included in -O3) is enabled and --param max-inline-insns-
               recursive-auto is used.  The default value is 450.

           max-inline-recursive-depth
           max-inline-recursive-depth-auto
               Specifies the maximum recursion depth used for recursive
               inlining.

               For functions declared inline, --param max-inline-recursive-
               depth is taken into account.  For functions not declared
               inline, recursive inlining happens only when -finline-functions
               (included in -O3) is enabled and --param max-inline-recursive-
               depth-auto is used.  The default value is 8.

           min-inline-recursive-probability
               Recursive inlining is profitable only for function having deep
               recursion in average and can hurt for function having little
               recursion depth by increasing the prologue size or complexity
               of function body to other optimizers.

               When profile feedback is available (see -fprofile-generate) the
               actual recursion depth can be guessed from probability that
               function recurses via a given call expression.  This parameter
               limits inlining only to call expressions whose probability
               exceeds the given threshold (in percents).  The default value
               is 10.

           early-inlining-insns
               Specify growth that the early inliner can make.  In effect it
               increases the amount of inlining for code having a large
               abstraction penalty.  The default value is 10.

           max-early-inliner-iterations
           max-early-inliner-iterations
               Limit of iterations of the early inliner.  This basically
               bounds the number of nested indirect calls the early inliner
               can resolve.  Deeper chains are still handled by late inlining.

           comdat-sharing-probability
           comdat-sharing-probability
               Probability (in percent) that C++ inline function with comdat
               visibility are shared across multiple compilation units.  The
               default value is 20.

           min-vect-loop-bound
               The minimum number of iterations under which loops are not
               vectorized when -ftree-vectorize is used.  The number of
               iterations after vectorization needs to be greater than the
               value specified by this option to allow vectorization.  The
               default value is 0.

           gcse-cost-distance-ratio
               Scaling factor in calculation of maximum distance an expression
               can be moved by GCSE optimizations.  This is currently
               supported only in the code hoisting pass.  The bigger the
               ratio, the more aggressive code hoisting is with simple
               expressions, i.e., the expressions that have cost less than
               gcse-unrestricted-cost.  Specifying 0 disables hoisting of
               simple expressions.  The default value is 10.

           gcse-unrestricted-cost
               Cost, roughly measured as the cost of a single typical machine
               instruction, at which GCSE optimizations do not constrain the
               distance an expression can travel.  This is currently supported
               only in the code hoisting pass.  The lesser the cost, the more
               aggressive code hoisting is.  Specifying 0 allows all
               expressions to travel unrestricted distances.  The default
               value is 3.

           max-hoist-depth
               The depth of search in the dominator tree for expressions to
               hoist.  This is used to avoid quadratic behavior in hoisting
               algorithm.  The value of 0 does not limit on the search, but
               may slow down compilation of huge functions.  The default value
               is 30.

           max-tail-merge-comparisons
               The maximum amount of similar bbs to compare a bb with.  This
               is used to avoid quadratic behavior in tree tail merging.  The
               default value is 10.

           max-tail-merge-iterations
               The maximum amount of iterations of the pass over the function.
               This is used to limit compilation time in tree tail merging.
               The default value is 2.

           max-unrolled-insns
               The maximum number of instructions that a loop may have to be
               unrolled.  If a loop is unrolled, this parameter also
               determines how many times the loop code is unrolled.

           max-average-unrolled-insns
               The maximum number of instructions biased by probabilities of
               their execution that a loop may have to be unrolled.  If a loop
               is unrolled, this parameter also determines how many times the
               loop code is unrolled.

           max-unroll-times
               The maximum number of unrollings of a single loop.

           max-peeled-insns
               The maximum number of instructions that a loop may have to be
               peeled.  If a loop is peeled, this parameter also determines
               how many times the loop code is peeled.

           max-peel-times
               The maximum number of peelings of a single loop.

           max-peel-branches
               The maximum number of branches on the hot path through the
               peeled sequence.

           max-completely-peeled-insns
               The maximum number of insns of a completely peeled loop.

           max-completely-peel-times
               The maximum number of iterations of a loop to be suitable for
               complete peeling.

           max-completely-peel-loop-nest-depth
               The maximum depth of a loop nest suitable for complete peeling.

           max-unswitch-insns
               The maximum number of insns of an unswitched loop.

           max-unswitch-level
               The maximum number of branches unswitched in a single loop.

           lim-expensive
               The minimum cost of an expensive expression in the loop
               invariant motion.

           iv-consider-all-candidates-bound
               Bound on number of candidates for induction variables, below
               which all candidates are considered for each use in induction
               variable optimizations.  If there are more candidates than
               this, only the most relevant ones are considered to avoid
               quadratic time complexity.

           iv-max-considered-uses
               The induction variable optimizations give up on loops that
               contain more induction variable uses.

           iv-always-prune-cand-set-bound
               If the number of candidates in the set is smaller than this
               value, always try to remove unnecessary ivs from the set when
               adding a new one.

           scev-max-expr-size
               Bound on size of expressions used in the scalar evolutions
               analyzer.  Large expressions slow the analyzer.

           scev-max-expr-complexity
               Bound on the complexity of the expressions in the scalar
               evolutions analyzer.  Complex expressions slow the analyzer.

           omega-max-vars
               The maximum number of variables in an Omega constraint system.
               The default value is 128.

           omega-max-geqs
               The maximum number of inequalities in an Omega constraint
               system.  The default value is 256.

           omega-max-eqs
               The maximum number of equalities in an Omega constraint system.
               The default value is 128.

           omega-max-wild-cards
               The maximum number of wildcard variables that the Omega solver
               is able to insert.  The default value is 18.

           omega-hash-table-size
               The size of the hash table in the Omega solver.  The default
               value is 550.

           omega-max-keys
               The maximal number of keys used by the Omega solver.  The
               default value is 500.

           omega-eliminate-redundant-constraints
               When set to 1, use expensive methods to eliminate all redundant
               constraints.  The default value is 0.

           vect-max-version-for-alignment-checks
               The maximum number of run-time checks that can be performed
               when doing loop versioning for alignment in the vectorizer.
               See option -ftree-vect-loop-version for more information.

           vect-max-version-for-alias-checks
               The maximum number of run-time checks that can be performed
               when doing loop versioning for alias in the vectorizer.  See
               option -ftree-vect-loop-version for more information.

           max-iterations-to-track
               The maximum number of iterations of a loop the brute-force
               algorithm for analysis of the number of iterations of the loop
               tries to evaluate.

           hot-bb-count-ws-permille
               A basic block profile count is considered hot if it contributes
               to the given permillage (i.e. 0...1000) of the entire profiled
               execution.

           hot-bb-frequency-fraction
               Select fraction of the entry block frequency of executions of
               basic block in function given basic block needs to have to be
               considered hot.

           max-predicted-iterations
               The maximum number of loop iterations we predict statically.
               This is useful in cases where a function contains a single loop
               with known bound and another loop with unknown bound.  The
               known number of iterations is predicted correctly, while the
               unknown number of iterations average to roughly 10.  This means
               that the loop without bounds appears artificially cold relative
               to the other one.

           align-threshold
               Select fraction of the maximal frequency of executions of a
               basic block in a function to align the basic block.

           align-loop-iterations
               A loop expected to iterate at least the selected number of
               iterations is aligned.

           tracer-dynamic-coverage
           tracer-dynamic-coverage-feedback
               This value is used to limit superblock formation once the given
               percentage of executed instructions is covered.  This limits
               unnecessary code size expansion.

               The tracer-dynamic-coverage-feedback is used only when profile
               feedback is available.  The real profiles (as opposed to
               statically estimated ones) are much less balanced allowing the
               threshold to be larger value.

           tracer-max-code-growth
               Stop tail duplication once code growth has reached given
               percentage.  This is a rather artificial limit, as most of the
               duplicates are eliminated later in cross jumping, so it may be
               set to much higher values than is the desired code growth.

           tracer-min-branch-ratio
               Stop reverse growth when the reverse probability of best edge
               is less than this threshold (in percent).

           tracer-min-branch-ratio
           tracer-min-branch-ratio-feedback
               Stop forward growth if the best edge has probability lower than
               this threshold.

               Similarly to tracer-dynamic-coverage two values are present,
               one for compilation for profile feedback and one for
               compilation without.  The value for compilation with profile
               feedback needs to be more conservative (higher) in order to
               make tracer effective.

           max-cse-path-length
               The maximum number of basic blocks on path that CSE considers.
               The default is 10.

           max-cse-insns
               The maximum number of instructions CSE processes before
               flushing.  The default is 1000.

           ggc-min-expand
               GCC uses a garbage collector to manage its own memory
               allocation.  This parameter specifies the minimum percentage by
               which the garbage collector's heap should be allowed to expand
               between collections.  Tuning this may improve compilation
               speed; it has no effect on code generation.

               The default is 30% + 70% * (RAM/1GB) with an upper bound of
               100% when RAM >= 1GB.  If "getrlimit" is available, the notion
               of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or
               "RLIMIT_AS".  If GCC is not able to calculate RAM on a
               particular platform, the lower bound of 30% is used.  Setting
               this parameter and ggc-min-heapsize to zero causes a full
               collection to occur at every opportunity.  This is extremely
               slow, but can be useful for debugging.

           ggc-min-heapsize
               Minimum size of the garbage collector's heap before it begins
               bothering to collect garbage.  The first collection occurs
               after the heap expands by ggc-min-expand% beyond ggc-min-
               heapsize.  Again, tuning this may improve compilation speed,
               and has no effect on code generation.

               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
               that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
               exceeded, but with a lower bound of 4096 (four megabytes) and
               an upper bound of 131072 (128 megabytes).  If GCC is not able
               to calculate RAM on a particular platform, the lower bound is
               used.  Setting this parameter very large effectively disables
               garbage collection.  Setting this parameter and ggc-min-expand
               to zero causes a full collection to occur at every opportunity.

           max-reload-search-insns
               The maximum number of instruction reload should look backward
               for equivalent register.  Increasing values mean more
               aggressive optimization, making the compilation time increase
               with probably slightly better performance.  The default value
               is 100.

           max-cselib-memory-locations
               The maximum number of memory locations cselib should take into
               account.  Increasing values mean more aggressive optimization,
               making the compilation time increase with probably slightly
               better performance.  The default value is 500.

           reorder-blocks-duplicate
           reorder-blocks-duplicate-feedback
               Used by the basic block reordering pass to decide whether to
               use unconditional branch or duplicate the code on its
               destination.  Code is duplicated when its estimated size is
               smaller than this value multiplied by the estimated size of
               unconditional jump in the hot spots of the program.

               The reorder-block-duplicate-feedback is used only when profile
               feedback is available.  It may be set to higher values than
               reorder-block-duplicate since information about the hot spots
               is more accurate.

           max-sched-ready-insns
               The maximum number of instructions ready to be issued the
               scheduler should consider at any given time during the first
               scheduling pass.  Increasing values mean more thorough
               searches, making the compilation time increase with probably
               little benefit.  The default value is 100.

           max-sched-region-blocks
               The maximum number of blocks in a region to be considered for
               interblock scheduling.  The default value is 10.

           max-pipeline-region-blocks
               The maximum number of blocks in a region to be considered for
               pipelining in the selective scheduler.  The default value is
               15.

           max-sched-region-insns
               The maximum number of insns in a region to be considered for
               interblock scheduling.  The default value is 100.

           max-pipeline-region-insns
               The maximum number of insns in a region to be considered for
               pipelining in the selective scheduler.  The default value is
               200.

           min-spec-prob
               The minimum probability (in percents) of reaching a source
               block for interblock speculative scheduling.  The default value
               is 40.

           max-sched-extend-regions-iters
               The maximum number of iterations through CFG to extend regions.
               A value of 0 (the default) disables region extensions.

           max-sched-insn-conflict-delay
               The maximum conflict delay for an insn to be considered for
               speculative motion.  The default value is 3.

           sched-spec-prob-cutoff
               The minimal probability of speculation success (in percents),
               so that speculative insns are scheduled.  The default value is
               40.

           sched-spec-state-edge-prob-cutoff
               The minimum probability an edge must have for the scheduler to
               save its state across it.  The default value is 10.

           sched-mem-true-dep-cost
               Minimal distance (in CPU cycles) between store and load
               targeting same memory locations.  The default value is 1.

           selsched-max-lookahead
               The maximum size of the lookahead window of selective
               scheduling.  It is a depth of search for available
               instructions.  The default value is 50.

           selsched-max-sched-times
               The maximum number of times that an instruction is scheduled
               during selective scheduling.  This is the limit on the number
               of iterations through which the instruction may be pipelined.
               The default value is 2.

           selsched-max-insns-to-rename
               The maximum number of best instructions in the ready list that
               are considered for renaming in the selective scheduler.  The
               default value is 2.

           sms-min-sc
               The minimum value of stage count that swing modulo scheduler
               generates.  The default value is 2.

           max-last-value-rtl
               The maximum size measured as number of RTLs that can be
               recorded in an expression in combiner for a pseudo register as
               last known value of that register.  The default is 10000.

           integer-share-limit
               Small integer constants can use a shared data structure,
               reducing the compiler's memory usage and increasing its speed.
               This sets the maximum value of a shared integer constant.  The
               default value is 256.

           ssp-buffer-size
               The minimum size of buffers (i.e. arrays) that receive stack
               smashing protection when -fstack-protection is used.

           max-jump-thread-duplication-stmts
               Maximum number of statements allowed in a block that needs to
               be duplicated when threading jumps.

           max-fields-for-field-sensitive
               Maximum number of fields in a structure treated in a field
               sensitive manner during pointer analysis.  The default is zero
               for -O0 and -O1, and 100 for -Os, -O2, and -O3.

           prefetch-latency
               Estimate on average number of instructions that are executed
               before prefetch finishes.  The distance prefetched ahead is
               proportional to this constant.  Increasing this number may also
               lead to less streams being prefetched (see simultaneous-
               prefetches).

           simultaneous-prefetches
               Maximum number of prefetches that can run at the same time.

           l1-cache-line-size
               The size of cache line in L1 cache, in bytes.

           l1-cache-size
               The size of L1 cache, in kilobytes.

           l2-cache-size
               The size of L2 cache, in kilobytes.

           min-insn-to-prefetch-ratio
               The minimum ratio between the number of instructions and the
               number of prefetches to enable prefetching in a loop.

           prefetch-min-insn-to-mem-ratio
               The minimum ratio between the number of instructions and the
               number of memory references to enable prefetching in a loop.

           use-canonical-types
               Whether the compiler should use the "canonical" type system.
               By default, this should always be 1, which uses a more
               efficient internal mechanism for comparing types in C++ and
               Objective-C++.  However, if bugs in the canonical type system
               are causing compilation failures, set this value to 0 to
               disable canonical types.

           switch-conversion-max-branch-ratio
               Switch initialization conversion refuses to create arrays that
               are bigger than switch-conversion-max-branch-ratio times the
               number of branches in the switch.

           max-partial-antic-length
               Maximum length of the partial antic set computed during the
               tree partial redundancy elimination optimization (-ftree-pre)
               when optimizing at -O3 and above.  For some sorts of source
               code the enhanced partial redundancy elimination optimization
               can run away, consuming all of the memory available on the host
               machine.  This parameter sets a limit on the length of the sets
               that are computed, which prevents the runaway behavior.
               Setting a value of 0 for this parameter allows an unlimited set
               length.

           sccvn-max-scc-size
               Maximum size of a strongly connected component (SCC) during
               SCCVN processing.  If this limit is hit, SCCVN processing for
               the whole function is not done and optimizations depending on
               it are disabled.  The default maximum SCC size is 10000.

           sccvn-max-alias-queries-per-access
               Maximum number of alias-oracle queries we perform when looking
               for redundancies for loads and stores.  If this limit is hit
               the search is aborted and the load or store is not considered
               redundant.  The number of queries is algorithmically limited to
               the number of stores on all paths from the load to the function
               entry.  The default maxmimum number of queries is 1000.

           ira-max-loops-num
               IRA uses regional register allocation by default.  If a
               function contains more loops than the number given by this
               parameter, only at most the given number of the most
               frequently-executed loops form regions for regional register
               allocation.  The default value of the parameter is 100.

           ira-max-conflict-table-size
               Although IRA uses a sophisticated algorithm to compress the
               conflict table, the table can still require excessive amounts
               of memory for huge functions.  If the conflict table for a
               function could be more than the size in MB given by this
               parameter, the register allocator instead uses a faster,
               simpler, and lower-quality algorithm that does not require
               building a pseudo-register conflict table.  The default value
               of the parameter is 2000.

           ira-loop-reserved-regs
               IRA can be used to evaluate more accurate register pressure in
               loops for decisions to move loop invariants (see -O3).  The
               number of available registers reserved for some other purposes
               is given by this parameter.  The default value of the parameter
               is 2, which is the minimal number of registers needed by
               typical instructions.  This value is the best found from
               numerous experiments.

           loop-invariant-max-bbs-in-loop
               Loop invariant motion can be very expensive, both in
               compilation time and in amount of needed compile-time memory,
               with very large loops.  Loops with more basic blocks than this
               parameter won't have loop invariant motion optimization
               performed on them.  The default value of the parameter is 1000
               for -O1 and 10000 for -O2 and above.

           loop-max-datarefs-for-datadeps
               Building data dapendencies is expensive for very large loops.
               This parameter limits the number of data references in loops
               that are considered for data dependence analysis.  These large
               loops are no handled by the optimizations using loop data
               dependencies.  The default value is 1000.

           max-vartrack-size
               Sets a maximum number of hash table slots to use during
               variable tracking dataflow analysis of any function.  If this
               limit is exceeded with variable tracking at assignments
               enabled, analysis for that function is retried without it,
               after removing all debug insns from the function.  If the limit
               is exceeded even without debug insns, var tracking analysis is
               completely disabled for the function.  Setting the parameter to
               zero makes it unlimited.

           max-vartrack-expr-depth
               Sets a maximum number of recursion levels when attempting to
               map variable names or debug temporaries to value expressions.
               This trades compilation time for more complete debug
               information.  If this is set too low, value expressions that
               are available and could be represented in debug information may
               end up not being used; setting this higher may enable the
               compiler to find more complex debug expressions, but compile
               time and memory use may grow.  The default is 12.

           min-nondebug-insn-uid
               Use uids starting at this parameter for nondebug insns.  The
               range below the parameter is reserved exclusively for debug
               insns created by -fvar-tracking-assignments, but debug insns
               may get (non-overlapping) uids above it if the reserved range
               is exhausted.

           ipa-sra-ptr-growth-factor
               IPA-SRA replaces a pointer to an aggregate with one or more new
               parameters only when their cumulative size is less or equal to
               ipa-sra-ptr-growth-factor times the size of the original
               pointer parameter.

           tm-max-aggregate-size
               When making copies of thread-local variables in a transaction,
               this parameter specifies the size in bytes after which
               variables are saved with the logging functions as opposed to
               save/restore code sequence pairs.  This option only applies
               when using -fgnu-tm.

           graphite-max-nb-scop-params
               To avoid exponential effects in the Graphite loop transforms,
               the number of parameters in a Static Control Part (SCoP) is
               bounded.  The default value is 10 parameters.  A variable whose
               value is unknown at compilation time and defined outside a SCoP
               is a parameter of the SCoP.

           graphite-max-bbs-per-function
               To avoid exponential effects in the detection of SCoPs, the
               size of the functions analyzed by Graphite is bounded.  The
               default value is 100 basic blocks.

           loop-block-tile-size
               Loop blocking or strip mining transforms, enabled with
               -floop-block or -floop-strip-mine, strip mine each loop in the
               loop nest by a given number of iterations.  The strip length
               can be changed using the loop-block-tile-size parameter.  The
               default value is 51 iterations.

           ipa-cp-value-list-size
               IPA-CP attempts to track all possible values and types passed
               to a function's parameter in order to propagate them and
               perform devirtualization.  ipa-cp-value-list-size is the
               maximum number of values and types it stores per one formal
               parameter of a function.

           lto-partitions
               Specify desired number of partitions produced during WHOPR
               compilation.  The number of partitions should exceed the number
               of CPUs used for compilation.  The default value is 32.

           lto-minpartition
               Size of minimal partition for WHOPR (in estimated
               instructions).  This prevents expenses of splitting very small
               programs into too many partitions.

           cxx-max-namespaces-for-diagnostic-help
               The maximum number of namespaces to consult for suggestions
               when C++ name lookup fails for an identifier.  The default is
               1000.

           sink-frequency-threshold
               The maximum relative execution frequency (in percents) of the
               target block relative to a statement's original block to allow
               statement sinking of a statement.  Larger numbers result in
               more aggressive statement sinking.  The default value is 75.  A
               small positive adjustment is applied for statements with memory
               operands as those are even more profitable so sink.

           max-stores-to-sink
               The maximum number of conditional stores paires that can be
               sunk.  Set to 0 if either vectorization (-ftree-vectorize) or
               if-conversion (-ftree-loop-if-convert) is disabled.  The
               default is 2.

           allow-load-data-races
               Allow optimizers to introduce new data races on loads.  Set to
               1 to allow, otherwise to 0.  This option is enabled by default
               unless implicitly set by the -fmemory-model= option.

           allow-store-data-races
               Allow optimizers to introduce new data races on stores.  Set to
               1 to allow, otherwise to 0.  This option is enabled by default
               unless implicitly set by the -fmemory-model= option.

           allow-packed-load-data-races
               Allow optimizers to introduce new data races on packed data
               loads.  Set to 1 to allow, otherwise to 0.  This option is
               enabled by default unless implicitly set by the -fmemory-model=
               option.

           allow-packed-store-data-races
               Allow optimizers to introduce new data races on packed data
               stores.  Set to 1 to allow, otherwise to 0.  This option is
               enabled by default unless implicitly set by the -fmemory-model=
               option.

           case-values-threshold
               The smallest number of different values for which it is best to
               use a jump-table instead of a tree of conditional branches.  If
               the value is 0, use the default for the machine.  The default
               is 0.

           tree-reassoc-width
               Set the maximum number of instructions executed in parallel in
               reassociated tree. This parameter overrides target dependent
               heuristics used by default if has non zero value.

           sched-pressure-algorithm
               Choose between the two available implementations of
               -fsched-pressure.  Algorithm 1 is the original implementation
               and is the more likely to prevent instructions from being
               reordered.  Algorithm 2 was designed to be a compromise between
               the relatively conservative approach taken by algorithm 1 and
               the rather aggressive approach taken by the default scheduler.
               It relies more heavily on having a regular register file and
               accurate register pressure classes.  See haifa-sched.c in the
               GCC sources for more details.

               The default choice depends on the target.

           max-slsr-cand-scan
               Set the maximum number of existing candidates that will be
               considered when seeking a basis for a new straight-line
               strength reduction candidate.

   Options Controlling the Preprocessor
       These options control the C preprocessor, which is run on each C source
       file before actual compilation.

       If you use the -E option, nothing is done except preprocessing.  Some
       of these options make sense only together with -E because they cause
       the preprocessor output to be unsuitable for actual compilation.

       -Wp,option
           You can use -Wp,option to bypass the compiler driver and pass
           option directly through to the preprocessor.  If option contains
           commas, it is split into multiple options at the commas.  However,
           many options are modified, translated or interpreted by the
           compiler driver before being passed to the preprocessor, and -Wp
           forcibly bypasses this phase.  The preprocessor's direct interface
           is undocumented and subject to change, so whenever possible you
           should avoid using -Wp and let the driver handle the options
           instead.

       -Xpreprocessor option
           Pass option as an option to the preprocessor.  You can use this to
           supply system-specific preprocessor options that GCC does not
           recognize.

           If you want to pass an option that takes an argument, you must use
           -Xpreprocessor twice, once for the option and once for the
           argument.

       -no-integrated-cpp
           Perform preprocessing as a separate pass before compilation.  By
           default, GCC performs preprocessing as an integrated part of input
           tokenization and parsing.  If this option is provided, the
           appropriate language front end (cc1, cc1plus, or cc1obj for C, C++,
           and Objective-C, respectively) is instead invoked twice, once for
           preprocessing only and once for actual compilation of the
           preprocessed input.  This option may be useful in conjunction with
           the -B or -wrapper options to specify an alternate preprocessor or
           perform additional processing of the program source between normal
           preprocessing and compilation.

       -D name
           Predefine name as a macro, with definition 1.

       -D name=definition
           The contents of definition are tokenized and processed as if they
           appeared during translation phase three in a #define directive.  In
           particular, the definition will be truncated by embedded newline
           characters.

           If you are invoking the preprocessor from a shell or shell-like
           program you may need to use the shell's quoting syntax to protect
           characters such as spaces that have a meaning in the shell syntax.

           If you wish to define a function-like macro on the command line,
           write its argument list with surrounding parentheses before the
           equals sign (if any).  Parentheses are meaningful to most shells,
           so you will need to quote the option.  With sh and csh,
           -D'name(args...)=definition' works.

           -D and -U options are processed in the order they are given on the
           command line.  All -imacros file and -include file options are
           processed after all -D and -U options.

       -U name
           Cancel any previous definition of name, either built in or provided
           with a -D option.

       -undef
           Do not predefine any system-specific or GCC-specific macros.  The
           standard predefined macros remain defined.

       -I dir
           Add the directory dir to the list of directories to be searched for
           header files.  Directories named by -I are searched before the
           standard system include directories.  If the directory dir is a
           standard system include directory, the option is ignored to ensure
           that the default search order for system directories and the
           special treatment of system headers are not defeated .  If dir
           begins with "=", then the "=" will be replaced by the sysroot
           prefix; see --sysroot and -isysroot.

       -o file
           Write output to file.  This is the same as specifying file as the
           second non-option argument to cpp.  gcc has a different
           interpretation of a second non-option argument, so you must use -o
           to specify the output file.

       -Wall
           Turns on all optional warnings which are desirable for normal code.
           At present this is -Wcomment, -Wtrigraphs, -Wmultichar and a
           warning about integer promotion causing a change of sign in "#if"
           expressions.  Note that many of the preprocessor's warnings are on
           by default and have no options to control them.

       -Wcomment
       -Wcomments
           Warn whenever a comment-start sequence /* appears in a /* comment,
           or whenever a backslash-newline appears in a // comment.  (Both
           forms have the same effect.)

       -Wtrigraphs
           Most trigraphs in comments cannot affect the meaning of the
           program.  However, a trigraph that would form an escaped newline
           (??/ at the end of a line) can, by changing where the comment
           begins or ends.  Therefore, only trigraphs that would form escaped
           newlines produce warnings inside a comment.

           This option is implied by -Wall.  If -Wall is not given, this
           option is still enabled unless trigraphs are enabled.  To get
           trigraph conversion without warnings, but get the other -Wall
           warnings, use -trigraphs -Wall -Wno-trigraphs.

       -Wtraditional
           Warn about certain constructs that behave differently in
           traditional and ISO C.  Also warn about ISO C constructs that have
           no traditional C equivalent, and problematic constructs which
           should be avoided.

       -Wundef
           Warn whenever an identifier which is not a macro is encountered in
           an #if directive, outside of defined.  Such identifiers are
           replaced with zero.

       -Wunused-macros
           Warn about macros defined in the main file that are unused.  A
           macro is used if it is expanded or tested for existence at least
           once.  The preprocessor will also warn if the macro has not been
           used at the time it is redefined or undefined.

           Built-in macros, macros defined on the command line, and macros
           defined in include files are not warned about.

           Note: If a macro is actually used, but only used in skipped
           conditional blocks, then CPP will report it as unused.  To avoid
           the warning in such a case, you might improve the scope of the
           macro's definition by, for example, moving it into the first
           skipped block.  Alternatively, you could provide a dummy use with
           something like:

                   #if defined the_macro_causing_the_warning
                   #endif

       -Wendif-labels
           Warn whenever an #else or an #endif are followed by text.  This
           usually happens in code of the form

                   #if FOO
                   ...
                   #else FOO
                   ...
                   #endif FOO

           The second and third "FOO" should be in comments, but often are not
           in older programs.  This warning is on by default.

       -Werror
           Make all warnings into hard errors.  Source code which triggers
           warnings will be rejected.

       -Wsystem-headers
           Issue warnings for code in system headers.  These are normally
           unhelpful in finding bugs in your own code, therefore suppressed.
           If you are responsible for the system library, you may want to see
           them.

       -w  Suppress all warnings, including those which GNU CPP issues by
           default.

       -pedantic
           Issue all the mandatory diagnostics listed in the C standard.  Some
           of them are left out by default, since they trigger frequently on
           harmless code.

       -pedantic-errors
           Issue all the mandatory diagnostics, and make all mandatory
           diagnostics into errors.  This includes mandatory diagnostics that
           GCC issues without -pedantic but treats as warnings.

       -M  Instead of outputting the result of preprocessing, output a rule
           suitable for make describing the dependencies of the main source
           file.  The preprocessor outputs one make rule containing the object
           file name for that source file, a colon, and the names of all the
           included files, including those coming from -include or -imacros
           command line options.

           Unless specified explicitly (with -MT or -MQ), the object file name
           consists of the name of the source file with any suffix replaced
           with object file suffix and with any leading directory parts
           removed.  If there are many included files then the rule is split
           into several lines using \-newline.  The rule has no commands.

           This option does not suppress the preprocessor's debug output, such
           as -dM.  To avoid mixing such debug output with the dependency
           rules you should explicitly specify the dependency output file with
           -MF, or use an environment variable like DEPENDENCIES_OUTPUT.
           Debug output will still be sent to the regular output stream as
           normal.

           Passing -M to the driver implies -E, and suppresses warnings with
           an implicit -w.

       -MM Like -M but do not mention header files that are found in system
           header directories, nor header files that are included, directly or
           indirectly, from such a header.

           This implies that the choice of angle brackets or double quotes in
           an #include directive does not in itself determine whether that
           header will appear in -MM dependency output.  This is a slight
           change in semantics from GCC versions 3.0 and earlier.

       -MF file
           When used with -M or -MM, specifies a file to write the
           dependencies to.  If no -MF switch is given the preprocessor sends
           the rules to the same place it would have sent preprocessed output.

           When used with the driver options -MD or -MMD, -MF overrides the
           default dependency output file.

       -MG In conjunction with an option such as -M requesting dependency
           generation, -MG assumes missing header files are generated files
           and adds them to the dependency list without raising an error.  The
           dependency filename is taken directly from the "#include" directive
           without prepending any path.  -MG also suppresses preprocessed
           output, as a missing header file renders this useless.

           This feature is used in automatic updating of makefiles.

       -MP This option instructs CPP to add a phony target for each dependency
           other than the main file, causing each to depend on nothing.  These
           dummy rules work around errors make gives if you remove header
           files without updating the Makefile to match.

           This is typical output:

                   test.o: test.c test.h

                   test.h:

       -MT target
           Change the target of the rule emitted by dependency generation.  By
           default CPP takes the name of the main input file, deletes any
           directory components and any file suffix such as .c, and appends
           the platform's usual object suffix.  The result is the target.

           An -MT option will set the target to be exactly the string you
           specify.  If you want multiple targets, you can specify them as a
           single argument to -MT, or use multiple -MT options.

           For example, -MT '$(objpfx)foo.o' might give

                   $(objpfx)foo.o: foo.c

       -MQ target
           Same as -MT, but it quotes any characters which are special to
           Make.  -MQ '$(objpfx)foo.o' gives

                   $$(objpfx)foo.o: foo.c

           The default target is automatically quoted, as if it were given
           with -MQ.

       -MD -MD is equivalent to -M -MF file, except that -E is not implied.
           The driver determines file based on whether an -o option is given.
           If it is, the driver uses its argument but with a suffix of .d,
           otherwise it takes the name of the input file, removes any
           directory components and suffix, and applies a .d suffix.

           If -MD is used in conjunction with -E, any -o switch is understood
           to specify the dependency output file, but if used without -E, each
           -o is understood to specify a target object file.

           Since -E is not implied, -MD can be used to generate a dependency
           output file as a side-effect of the compilation process.

       -MMD
           Like -MD except mention only user header files, not system header
           files.

       -fpch-deps
           When using precompiled headers, this flag will cause the
           dependency-output flags to also list the files from the precompiled
           header's dependencies.  If not specified only the precompiled
           header would be listed and not the files that were used to create
           it because those files are not consulted when a precompiled header
           is used.

       -fpch-preprocess
           This option allows use of a precompiled header together with -E.
           It inserts a special "#pragma", "#pragma GCC pch_preprocess
           "filename"" in the output to mark the place where the precompiled
           header was found, and its filename.  When -fpreprocessed is in use,
           GCC recognizes this "#pragma" and loads the PCH.

           This option is off by default, because the resulting preprocessed
           output is only really suitable as input to GCC.  It is switched on
           by -save-temps.

           You should not write this "#pragma" in your own code, but it is
           safe to edit the filename if the PCH file is available in a
           different location.  The filename may be absolute or it may be
           relative to GCC's current directory.

       -x c
       -x c++
       -x objective-c
       -x assembler-with-cpp
           Specify the source language: C, C++, Objective-C, or assembly.
           This has nothing to do with standards conformance or extensions; it
           merely selects which base syntax to expect.  If you give none of
           these options, cpp will deduce the language from the extension of
           the source file: .c, .cc, .m, or .S.  Some other common extensions
           for C++ and assembly are also recognized.  If cpp does not
           recognize the extension, it will treat the file as C; this is the
           most generic mode.

           Note: Previous versions of cpp accepted a -lang option which
           selected both the language and the standards conformance level.
           This option has been removed, because it conflicts with the -l
           option.

       -std=standard
       -ansi
           Specify the standard to which the code should conform.  Currently
           CPP knows about C and C++ standards; others may be added in the
           future.

           standard may be one of:

           "c90"
           "c89"
           "iso9899:1990"
               The ISO C standard from 1990.  c90 is the customary shorthand
               for this version of the standard.

               The -ansi option is equivalent to -std=c90.

           "iso9899:199409"
               The 1990 C standard, as amended in 1994.

           "iso9899:1999"
           "c99"
           "iso9899:199x"
           "c9x"
               The revised ISO C standard, published in December 1999.  Before
               publication, this was known as C9X.

           "iso9899:2011"
           "c11"
           "c1x"
               The revised ISO C standard, published in December 2011.  Before
               publication, this was known as C1X.

           "gnu90"
           "gnu89"
               The 1990 C standard plus GNU extensions.  This is the default.

           "gnu99"
           "gnu9x"
               The 1999 C standard plus GNU extensions.

           "gnu11"
           "gnu1x"
               The 2011 C standard plus GNU extensions.

           "c++98"
               The 1998 ISO C++ standard plus amendments.

           "gnu++98"
               The same as -std=c++98 plus GNU extensions.  This is the
               default for C++ code.

       -I- Split the include path.  Any directories specified with -I options
           before -I- are searched only for headers requested with
           "#include "file""; they are not searched for "#include <file>".  If
           additional directories are specified with -I options after the -I-,
           those directories are searched for all #include directives.

           In addition, -I- inhibits the use of the directory of the current
           file directory as the first search directory for "#include "file"".
           This option has been deprecated.

       -nostdinc
           Do not search the standard system directories for header files.
           Only the directories you have specified with -I options (and the
           directory of the current file, if appropriate) are searched.

       -nostdinc++
           Do not search for header files in the C++-specific standard
           directories, but do still search the other standard directories.
           (This option is used when building the C++ library.)

       -include file
           Process file as if "#include "file"" appeared as the first line of
           the primary source file.  However, the first directory searched for
           file is the preprocessor's working directory instead of the
           directory containing the main source file.  If not found there, it
           is searched for in the remainder of the "#include "..."" search
           chain as normal.

           If multiple -include options are given, the files are included in
           the order they appear on the command line.

       -imacros file
           Exactly like -include, except that any output produced by scanning
           file is thrown away.  Macros it defines remain defined.  This
           allows you to acquire all the macros from a header without also
           processing its declarations.

           All files specified by -imacros are processed before all files
           specified by -include.

       -idirafter dir
           Search dir for header files, but do it after all directories
           specified with -I and the standard system directories have been
           exhausted.  dir is treated as a system include directory.  If dir
           begins with "=", then the "=" will be replaced by the sysroot
           prefix; see --sysroot and -isysroot.

       -iprefix prefix
           Specify prefix as the prefix for subsequent -iwithprefix options.
           If the prefix represents a directory, you should include the final
           /.

       -iwithprefix dir
       -iwithprefixbefore dir
           Append dir to the prefix specified previously with -iprefix, and
           add the resulting directory to the include search path.
           -iwithprefixbefore puts it in the same place -I would; -iwithprefix
           puts it where -idirafter would.

       -isysroot dir
           This option is like the --sysroot option, but applies only to
           header files (except for Darwin targets, where it applies to both
           header files and libraries).  See the --sysroot option for more
           information.

       -imultilib dir
           Use dir as a subdirectory of the directory containing target-
           specific C++ headers.

       -isystem dir
           Search dir for header files, after all directories specified by -I
           but before the standard system directories.  Mark it as a system
           directory, so that it gets the same special treatment as is applied
           to the standard system directories.  If dir begins with "=", then
           the "=" will be replaced by the sysroot prefix; see --sysroot and
           -isysroot.

       -cxx-isystem dir
           Search dir for C++ header files, after all directories specified by
           -I but before the standard system directories.  Mark it as a system
           directory, so that it gets the same special treatment as is applied
           to the standard system directories.

       -iquote dir
           Search dir only for header files requested with "#include "file"";
           they are not searched for "#include <file>", before all directories
           specified by -I and before the standard system directories.  If dir
           begins with "=", then the "=" will be replaced by the sysroot
           prefix; see --sysroot and -isysroot.

       -fdirectives-only
           When preprocessing, handle directives, but do not expand macros.

           The option's behavior depends on the -E and -fpreprocessed options.

           With -E, preprocessing is limited to the handling of directives
           such as "#define", "#ifdef", and "#error".  Other preprocessor
           operations, such as macro expansion and trigraph conversion are not
           performed.  In addition, the -dD option is implicitly enabled.

           With -fpreprocessed, predefinition of command line and most builtin
           macros is disabled.  Macros such as "__LINE__", which are
           contextually dependent, are handled normally.  This enables
           compilation of files previously preprocessed with "-E
           -fdirectives-only".

           With both -E and -fpreprocessed, the rules for -fpreprocessed take
           precedence.  This enables full preprocessing of files previously
           preprocessed with "-E -fdirectives-only".

       -iremap src:dst
           Replace the prefix src in __FILE__ with dst at expansion time.
           This option can be specified more than once.  Processing stops at
           the first match.

       -fdollars-in-identifiers
           Accept $ in identifiers.

       -fextended-identifiers
           Accept universal character names in identifiers.  This option is
           experimental; in a future version of GCC, it will be enabled by
           default for C99 and C++.

       -fno-canonical-system-headers
           When preprocessing, do not shorten system header paths with
           canonicalization.

       -fpreprocessed
           Indicate to the preprocessor that the input file has already been
           preprocessed.  This suppresses things like macro expansion,
           trigraph conversion, escaped newline splicing, and processing of
           most directives.  The preprocessor still recognizes and removes
           comments, so that you can pass a file preprocessed with -C to the
           compiler without problems.  In this mode the integrated
           preprocessor is little more than a tokenizer for the front ends.

           -fpreprocessed is implicit if the input file has one of the
           extensions .i, .ii or .mi.  These are the extensions that GCC uses
           for preprocessed files created by -save-temps.

       -ftabstop=width
           Set the distance between tab stops.  This helps the preprocessor
           report correct column numbers in warnings or errors, even if tabs
           appear on the line.  If the value is less than 1 or greater than
           100, the option is ignored.  The default is 8.

       -fdebug-cpp
           This option is only useful for debugging GCC.  When used with -E,
           dumps debugging information about location maps.  Every token in
           the output is preceded by the dump of the map its location belongs
           to.  The dump of the map holding the location of a token would be:

                   {"P":F</file/path>;"F":F</includer/path>;"L":<line_num>;"C":<col_num>;"S":<system_header_p>;"M":<map_address>;"E":<macro_expansion_p>,"loc":<location>}

           When used without -E, this option has no effect.

       -ftrack-macro-expansion[=level]
           Track locations of tokens across macro expansions. This allows the
           compiler to emit diagnostic about the current macro expansion stack
           when a compilation error occurs in a macro expansion. Using this
           option makes the preprocessor and the compiler consume more memory.
           The level parameter can be used to choose the level of precision of
           token location tracking thus decreasing the memory consumption if
           necessary. Value 0 of level de-activates this option just as if no
           -ftrack-macro-expansion was present on the command line. Value 1
           tracks tokens locations in a degraded mode for the sake of minimal
           memory overhead. In this mode all tokens resulting from the
           expansion of an argument of a function-like macro have the same
           location. Value 2 tracks tokens locations completely. This value is
           the most memory hungry.  When this option is given no argument, the
           default parameter value is 2.

           Note that -ftrack-macro-expansion=2 is activated by default.

       -fexec-charset=charset
           Set the execution character set, used for string and character
           constants.  The default is UTF-8.  charset can be any encoding
           supported by the system's "iconv" library routine.

       -fwide-exec-charset=charset
           Set the wide execution character set, used for wide string and
           character constants.  The default is UTF-32 or UTF-16, whichever
           corresponds to the width of "wchar_t".  As with -fexec-charset,
           charset can be any encoding supported by the system's "iconv"
           library routine; however, you will have problems with encodings
           that do not fit exactly in "wchar_t".

       -finput-charset=charset
           Set the input character set, used for translation from the
           character set of the input file to the source character set used by
           GCC.  If the locale does not specify, or GCC cannot get this
           information from the locale, the default is UTF-8.  This can be
           overridden by either the locale or this command line option.
           Currently the command line option takes precedence if there's a
           conflict.  charset can be any encoding supported by the system's
           "iconv" library routine.

       -fworking-directory
           Enable generation of linemarkers in the preprocessor output that
           will let the compiler know the current working directory at the
           time of preprocessing.  When this option is enabled, the
           preprocessor will emit, after the initial linemarker, a second
           linemarker with the current working directory followed by two
           slashes.  GCC will use this directory, when it's present in the
           preprocessed input, as the directory emitted as the current working
           directory in some debugging information formats.  This option is
           implicitly enabled if debugging information is enabled, but this
           can be inhibited with the negated form -fno-working-directory.  If
           the -P flag is present in the command line, this option has no
           effect, since no "#line" directives are emitted whatsoever.

       -fno-show-column
           Do not print column numbers in diagnostics.  This may be necessary
           if diagnostics are being scanned by a program that does not
           understand the column numbers, such as dejagnu.

       -A predicate=answer
           Make an assertion with the predicate predicate and answer answer.
           This form is preferred to the older form -A predicate(answer),
           which is still supported, because it does not use shell special
           characters.

       -A -predicate=answer
           Cancel an assertion with the predicate predicate and answer answer.

       -dCHARS
           CHARS is a sequence of one or more of the following characters, and
           must not be preceded by a space.  Other characters are interpreted
           by the compiler proper, or reserved for future versions of GCC, and
           so are silently ignored.  If you specify characters whose behavior
           conflicts, the result is undefined.

           M   Instead of the normal output, generate a list of #define
               directives for all the macros defined during the execution of
               the preprocessor, including predefined macros.  This gives you
               a way of finding out what is predefined in your version of the
               preprocessor.  Assuming you have no file foo.h, the command

                       touch foo.h; cpp -dM foo.h

               will show all the predefined macros.

               If you use -dM without the -E option, -dM is interpreted as a
               synonym for -fdump-rtl-mach.

           D   Like M except in two respects: it does not include the
               predefined macros, and it outputs both the #define directives
               and the result of preprocessing.  Both kinds of output go to
               the standard output file.

           N   Like D, but emit only the macro names, not their expansions.

           I   Output #include directives in addition to the result of
               preprocessing.

           U   Like D except that only macros that are expanded, or whose
               definedness is tested in preprocessor directives, are output;
               the output is delayed until the use or test of the macro; and
               #undef directives are also output for macros tested but
               undefined at the time.

       -P  Inhibit generation of linemarkers in the output from the
           preprocessor.  This might be useful when running the preprocessor
           on something that is not C code, and will be sent to a program
           which might be confused by the linemarkers.

       -C  Do not discard comments.  All comments are passed through to the
           output file, except for comments in processed directives, which are
           deleted along with the directive.

           You should be prepared for side effects when using -C; it causes
           the preprocessor to treat comments as tokens in their own right.
           For example, comments appearing at the start of what would be a
           directive line have the effect of turning that line into an
           ordinary source line, since the first token on the line is no
           longer a #.

       -CC Do not discard comments, including during macro expansion.  This is
           like -C, except that comments contained within macros are also
           passed through to the output file where the macro is expanded.

           In addition to the side-effects of the -C option, the -CC option
           causes all C++-style comments inside a macro to be converted to
           C-style comments.  This is to prevent later use of that macro from
           inadvertently commenting out the remainder of the source line.

           The -CC option is generally used to support lint comments.

       -traditional-cpp
           Try to imitate the behavior of old-fashioned C preprocessors, as
           opposed to ISO C preprocessors.

       -trigraphs
           Process trigraph sequences.  These are three-character sequences,
           all starting with ??, that are defined by ISO C to stand for single
           characters.  For example, ??/ stands for \, so '??/n' is a
           character constant for a newline.  By default, GCC ignores
           trigraphs, but in standard-conforming modes it converts them.  See
           the -std and -ansi options.

           The nine trigraphs and their replacements are

                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
                   Replacement:      [    ]    {    }    #    \    ^    |    ~

       -remap
           Enable special code to work around file systems which only permit
           very short file names, such as MS-DOS.

       --help
       --target-help
           Print text describing all the command line options instead of
           preprocessing anything.

       -v  Verbose mode.  Print out GNU CPP's version number at the beginning
           of execution, and report the final form of the include path.

       -H  Print the name of each header file used, in addition to other
           normal activities.  Each name is indented to show how deep in the
           #include stack it is.  Precompiled header files are also printed,
           even if they are found to be invalid; an invalid precompiled header
           file is printed with ...x and a valid one with ...! .

       -version
       --version
           Print out GNU CPP's version number.  With one dash, proceed to
           preprocess as normal.  With two dashes, exit immediately.

   Passing Options to the Assembler
       You can pass options to the assembler.

       -Wa,option
           Pass option as an option to the assembler.  If option contains
           commas, it is split into multiple options at the commas.

       -Xassembler option
           Pass option as an option to the assembler.  You can use this to
           supply system-specific assembler options that GCC does not
           recognize.

           If you want to pass an option that takes an argument, you must use
           -Xassembler twice, once for the option and once for the argument.

   Options for Linking
       These options come into play when the compiler links object files into
       an executable output file.  They are meaningless if the compiler is not
       doing a link step.

       object-file-name
           A file name that does not end in a special recognized suffix is
           considered to name an object file or library.  (Object files are
           distinguished from libraries by the linker according to the file
           contents.)  If linking is done, these object files are used as
           input to the linker.

       -c
       -S
       -E  If any of these options is used, then the linker is not run, and
           object file names should not be used as arguments.

       -llibrary
       -l library
           Search the library named library when linking.  (The second
           alternative with the library as a separate argument is only for
           POSIX compliance and is not recommended.)

           It makes a difference where in the command you write this option;
           the linker searches and processes libraries and object files in the
           order they are specified.  Thus, foo.o -lz bar.o searches library z
           after file foo.o but before bar.o.  If bar.o refers to functions in
           z, those functions may not be loaded.

           The linker searches a standard list of directories for the library,
           which is actually a file named liblibrary.a.  The linker then uses
           this file as if it had been specified precisely by name.

           The directories searched include several standard system
           directories plus any that you specify with -L.

           Normally the files found this way are library files---archive files
           whose members are object files.  The linker handles an archive file
           by scanning through it for members which define symbols that have
           so far been referenced but not defined.  But if the file that is
           found is an ordinary object file, it is linked in the usual
           fashion.  The only difference between using an -l option and
           specifying a file name is that -l surrounds library with lib and .a
           and searches several directories.

       -lobjc
           You need this special case of the -l option in order to link an
           Objective-C or Objective-C++ program.

       -nostartfiles
           Do not use the standard system startup files when linking.  The
           standard system libraries are used normally, unless -nostdlib or
           -nodefaultlibs is used.

       -nodefaultlibs
           Do not use the standard system libraries when linking.  Only the
           libraries you specify are passed to the linker, and options
           specifying linkage of the system libraries, such as
           "-static-libgcc" or "-shared-libgcc", are ignored.  The standard
           startup files are used normally, unless -nostartfiles is used.

           The compiler may generate calls to "memcmp", "memset", "memcpy" and
           "memmove".  These entries are usually resolved by entries in libc.
           These entry points should be supplied through some other mechanism
           when this option is specified.

       -nostdlib
           Do not use the standard system startup files or libraries when
           linking.  No startup files and only the libraries you specify are
           passed to the linker, and options specifying linkage of the system
           libraries, such as "-static-libgcc" or "-shared-libgcc", are
           ignored.

           The compiler may generate calls to "memcmp", "memset", "memcpy" and
           "memmove".  These entries are usually resolved by entries in libc.
           These entry points should be supplied through some other mechanism
           when this option is specified.

           One of the standard libraries bypassed by -nostdlib and
           -nodefaultlibs is libgcc.a, a library of internal subroutines which
           GCC uses to overcome shortcomings of particular machines, or
           special needs for some languages.

           In most cases, you need libgcc.a even when you want to avoid other
           standard libraries.  In other words, when you specify -nostdlib or
           -nodefaultlibs you should usually specify -lgcc as well.  This
           ensures that you have no unresolved references to internal GCC
           library subroutines.  (An example of such an internal subroutine is
           __main, used to ensure C++ constructors are called.)

       -pie
           Produce a position independent executable on targets that support
           it.  For predictable results, you must also specify the same set of
           options used for compilation (-fpie, -fPIE, or model suboptions)
           when you specify this linker option.

       -rdynamic
           Pass the flag -export-dynamic to the ELF linker, on targets that
           support it. This instructs the linker to add all symbols, not only
           used ones, to the dynamic symbol table. This option is needed for
           some uses of "dlopen" or to allow obtaining backtraces from within
           a program.

       -s  Remove all symbol table and relocation information from the
           executable.

       -static
           On systems that support dynamic linking, this prevents linking with
           the shared libraries.  On other systems, this option has no effect.

       -shared
           Produce a shared object which can then be linked with other objects
           to form an executable.  Not all systems support this option.  For
           predictable results, you must also specify the same set of options
           used for compilation (-fpic, -fPIC, or model suboptions) when you
           specify this linker option.[1]

       -shared-libgcc
       -static-libgcc
           On systems that provide libgcc as a shared library, these options
           force the use of either the shared or static version, respectively.
           If no shared version of libgcc was built when the compiler was
           configured, these options have no effect.

           There are several situations in which an application should use the
           shared libgcc instead of the static version.  The most common of
           these is when the application wishes to throw and catch exceptions
           across different shared libraries.  In that case, each of the
           libraries as well as the application itself should use the shared
           libgcc.

           Therefore, the G++ and GCJ drivers automatically add -shared-libgcc
           whenever you build a shared library or a main executable, because
           C++ and Java programs typically use exceptions, so this is the
           right thing to do.

           If, instead, you use the GCC driver to create shared libraries, you
           may find that they are not always linked with the shared libgcc.
           If GCC finds, at its configuration time, that you have a non-GNU
           linker or a GNU linker that does not support option --eh-frame-hdr,
           it links the shared version of libgcc into shared libraries by
           default.  Otherwise, it takes advantage of the linker and optimizes
           away the linking with the shared version of libgcc, linking with
           the static version of libgcc by default.  This allows exceptions to
           propagate through such shared libraries, without incurring
           relocation costs at library load time.

           However, if a library or main executable is supposed to throw or
           catch exceptions, you must link it using the G++ or GCJ driver, as
           appropriate for the languages used in the program, or using the
           option -shared-libgcc, such that it is linked with the shared
           libgcc.

       -static-libasan
           When the -fsanitize=address option is used to link a program, the
           GCC driver automatically links against libasan.  If libasan is
           available as a shared library, and the -static option is not used,
           then this links against the shared version of libasan.  The
           -static-libasan option directs the GCC driver to link libasan
           statically, without necessarily linking other libraries statically.

       -static-libtsan
           When the -fsanitize=thread option is used to link a program, the
           GCC driver automatically links against libtsan.  If libtsan is
           available as a shared library, and the -static option is not used,
           then this links against the shared version of libtsan.  The
           -static-libtsan option directs the GCC driver to link libtsan
           statically, without necessarily linking other libraries statically.

       -static-libstdc++
           When the g++ program is used to link a C++ program, it normally
           automatically links against libstdc++.  If libstdc++ is available
           as a shared library, and the -static option is not used, then this
           links against the shared version of libstdc++.  That is normally
           fine.  However, it is sometimes useful to freeze the version of
           libstdc++ used by the program without going all the way to a fully
           static link.  The -static-libstdc++ option directs the g++ driver
           to link libstdc++ statically, without necessarily linking other
           libraries statically.

       -symbolic
           Bind references to global symbols when building a shared object.
           Warn about any unresolved references (unless overridden by the link
           editor option -Xlinker -z -Xlinker defs).  Only a few systems
           support this option.

       -T script
           Use script as the linker script.  This option is supported by most
           systems using the GNU linker.  On some targets, such as bare-board
           targets without an operating system, the -T option may be required
           when linking to avoid references to undefined symbols.

       -Xlinker option
           Pass option as an option to the linker.  You can use this to supply
           system-specific linker options that GCC does not recognize.

           If you want to pass an option that takes a separate argument, you
           must use -Xlinker twice, once for the option and once for the
           argument.  For example, to pass -assert definitions, you must write
           -Xlinker -assert -Xlinker definitions.  It does not work to write
           -Xlinker "-assert definitions", because this passes the entire
           string as a single argument, which is not what the linker expects.

           When using the GNU linker, it is usually more convenient to pass
           arguments to linker options using the option=value syntax than as
           separate arguments.  For example, you can specify -Xlinker
           -Map=output.map rather than -Xlinker -Map -Xlinker output.map.
           Other linkers may not support this syntax for command-line options.

       -Wl,option
           Pass option as an option to the linker.  If option contains commas,
           it is split into multiple options at the commas.  You can use this
           syntax to pass an argument to the option.  For example,
           -Wl,-Map,output.map passes -Map output.map to the linker.  When
           using the GNU linker, you can also get the same effect with
           -Wl,-Map=output.map.

       -u symbol
           Pretend the symbol symbol is undefined, to force linking of library
           modules to define it.  You can use -u multiple times with different
           symbols to force loading of additional library modules.

   Options for Directory Search
       These options specify directories to search for header files, for
       libraries and for parts of the compiler:

       -Idir
           Add the directory dir to the head of the list of directories to be
           searched for header files.  This can be used to override a system
           header file, substituting your own version, since these directories
           are searched before the system header file directories.  However,
           you should not use this option to add directories that contain
           vendor-supplied system header files (use -isystem for that).  If
           you use more than one -I option, the directories are scanned in
           left-to-right order; the standard system directories come after.

           If a standard system include directory, or a directory specified
           with -isystem, is also specified with -I, the -I option is ignored.
           The directory is still searched but as a system directory at its
           normal position in the system include chain.  This is to ensure
           that GCC's procedure to fix buggy system headers and the ordering
           for the "include_next" directive are not inadvertently changed.  If
           you really need to change the search order for system directories,
           use the -nostdinc and/or -isystem options.

       -iplugindir=dir
           Set the directory to search for plugins that are passed by
           -fplugin=name instead of -fplugin=path/name.so.  This option is not
           meant to be used by the user, but only passed by the driver.

       -iquotedir
           Add the directory dir to the head of the list of directories to be
           searched for header files only for the case of #include "file";
           they are not searched for #include <file>, otherwise just like -I.

       -iremap src:dst
           Replace the prefix src in __FILE__ with dst at expansion time.
           This option can be specified more than once.  Processing stops at
           the first match.

       -Ldir
           Add directory dir to the list of directories to be searched for -l.

       -Bprefix
           This option specifies where to find the executables, libraries,
           include files, and data files of the compiler itself.

           The compiler driver program runs one or more of the subprograms
           cpp, cc1, as and ld.  It tries prefix as a prefix for each program
           it tries to run, both with and without machine/version/.

           For each subprogram to be run, the compiler driver first tries the
           -B prefix, if any.  If that name is not found, or if -B is not
           specified, the driver tries two standard prefixes, /usr/lib/gcc/
           and /usr/local/lib/gcc/.  If neither of those results in a file
           name that is found, the unmodified program name is searched for
           using the directories specified in your PATH environment variable.

           The compiler checks to see if the path provided by the -B refers to
           a directory, and if necessary it adds a directory separator
           character at the end of the path.

           -B prefixes that effectively specify directory names also apply to
           libraries in the linker, because the compiler translates these
           options into -L options for the linker.  They also apply to
           includes files in the preprocessor, because the compiler translates
           these options into -isystem options for the preprocessor.  In this
           case, the compiler appends include to the prefix.

           The runtime support file libgcc.a can also be searched for using
           the -B prefix, if needed.  If it is not found there, the two
           standard prefixes above are tried, and that is all.  The file is
           left out of the link if it is not found by those means.

           Another way to specify a prefix much like the -B prefix is to use
           the environment variable GCC_EXEC_PREFIX.

           As a special kludge, if the path provided by -B is [dir/]stageN/,
           where N is a number in the range 0 to 9, then it is replaced by
           [dir/]include.  This is to help with boot-strapping the compiler.

       -specs=file
           Process file after the compiler reads in the standard specs file,
           in order to override the defaults which the gcc driver program uses
           when determining what switches to pass to cc1, cc1plus, as, ld,
           etc.  More than one -specs=file can be specified on the command
           line, and they are processed in order, from left to right.

       --sysroot=dir
           Use dir as the logical root directory for headers and libraries.
           For example, if the compiler normally searches for headers in
           /usr/include and libraries in /usr/lib, it instead searches
           dir/usr/include and dir/usr/lib.

           If you use both this option and the -isysroot option, then the
           --sysroot option applies to libraries, but the -isysroot option
           applies to header files.

           The GNU linker (beginning with version 2.16) has the necessary
           support for this option.  If your linker does not support this
           option, the header file aspect of --sysroot still works, but the
           library aspect does not.

       --no-sysroot-suffix
           For some targets, a suffix is added to the root directory specified
           with --sysroot, depending on the other options used, so that
           headers may for example be found in dir/suffix/usr/include instead
           of dir/usr/include.  This option disables the addition of such a
           suffix.

       -I- This option has been deprecated.  Please use -iquote instead for -I
           directories before the -I- and remove the -I-.  Any directories you
           specify with -I options before the -I- option are searched only for
           the case of #include "file"; they are not searched for #include
           <file>.

           If additional directories are specified with -I options after the
           -I-, these directories are searched for all #include directives.
           (Ordinarily all -I directories are used this way.)

           In addition, the -I- option inhibits the use of the current
           directory (where the current input file came from) as the first
           search directory for #include "file".  There is no way to override
           this effect of -I-.  With -I. you can specify searching the
           directory that is current when the compiler is invoked.  That is
           not exactly the same as what the preprocessor does by default, but
           it is often satisfactory.

           -I- does not inhibit the use of the standard system directories for
           header files.  Thus, -I- and -nostdinc are independent.

   Specifying Target Machine and Compiler Version
       The usual way to run GCC is to run the executable called gcc, or
       machine-gcc when cross-compiling, or machine-gcc-version to run a
       version other than the one that was installed last.

   Hardware Models and Configurations
       Each target machine types can have its own special options, starting
       with -m, to choose among various hardware models or
       configurations---for example, 68010 vs 68020, floating coprocessor or
       none.  A single installed version of the compiler can compile for any
       model or configuration, according to the options specified.

       Some configurations of the compiler also support additional special
       options, usually for compatibility with other compilers on the same
       platform.

       AArch64 Options

       These options are defined for AArch64 implementations:

       -mbig-endian
           Generate big-endian code.  This is the default when GCC is
           configured for an aarch64_be-*-* target.

       -mgeneral-regs-only
           Generate code which uses only the general registers.

       -mlittle-endian
           Generate little-endian code.  This is the default when GCC is
           configured for an aarch64-*-* but not an aarch64_be-*-* target.

       -mcmodel=tiny
           Generate code for the tiny code model.  The program and its
           statically defined symbols must be within 1GB of each other.
           Pointers are 64 bits.  Programs can be statically or dynamically
           linked.  This model is not fully implemented and mostly treated as
           small.

       -mcmodel=small
           Generate code for the small code model.  The program and its
           statically defined symbols must be within 4GB of each other.
           Pointers are 64 bits.  Programs can be statically or dynamically
           linked.  This is the default code model.

       -mcmodel=large
           Generate code for the large code model.  This makes no assumptions
           about addresses and sizes of sections.  Pointers are 64 bits.
           Programs can be statically linked only.

       -mstrict-align
           Do not assume that unaligned memory references will be handled by
           the system.

       -momit-leaf-frame-pointer
       -mno-omit-leaf-frame-pointer
           Omit or keep the frame pointer in leaf functions.  The former
           behaviour is the default.

       -mtls-dialect=desc
           Use TLS descriptors as the thread-local storage mechanism for
           dynamic accesses of TLS variables.  This is the default.

       -mtls-dialect=traditional
           Use traditional TLS as the thread-local storage mechanism for
           dynamic accesses of TLS variables.

       -march=name
           Specify the name of the target architecture, optionally suffixed by
           one or more feature modifiers.  This option has the form
           -march=arch{+[no]feature}*, where the only value for arch is
           armv8-a.  The possible values for feature are documented in the
           sub-section below.

           Where conflicting feature modifiers are specified, the right-most
           feature is used.

           GCC uses this name to determine what kind of instructions it can
           emit when generating assembly code.  This option can be used in
           conjunction with or instead of the -mcpu= option.

       -mcpu=name
           Specify the name of the target processor, optionally suffixed by
           one or more feature modifiers.  This option has the form
           -mcpu=cpu{+[no]feature}*, where the possible values for cpu are
           generic, large.  The possible values for feature are documented in
           the sub-section below.

           Where conflicting feature modifiers are specified, the right-most
           feature is used.

           GCC uses this name to determine what kind of instructions it can
           emit when generating assembly code.

       -mtune=name
           Specify the name of the processor to tune the performance for.  The
           code will be tuned as if the target processor were of the type
           specified in this option, but still using instructions compatible
           with the target processor specified by a -mcpu= option.  This
           option cannot be suffixed by feature modifiers.

       -march and -mcpu feature modifiers

       Feature modifiers used with -march and -mcpu can be one the following:

       crypto
           Enable Crypto extension.  This implies Advanced SIMD is enabled.

       fp  Enable floating-point instructions.

       simd
           Enable Advanced SIMD instructions.  This implies floating-point
           instructions are enabled.  This is the default for all current
           possible values for options -march and -mcpu=.

       Adapteva Epiphany Options

       These -m options are defined for Adapteva Epiphany:

       -mhalf-reg-file
           Don't allocate any register in the range "r32"..."r63".  That
           allows code to run on hardware variants that lack these registers.

       -mprefer-short-insn-regs
           Preferrentially allocate registers that allow short instruction
           generation.  This can result in increased instruction count, so
           this may either reduce or increase overall code size.

       -mbranch-cost=num
           Set the cost of branches to roughly num "simple" instructions.
           This cost is only a heuristic and is not guaranteed to produce
           consistent results across releases.

       -mcmove
           Enable the generation of conditional moves.

       -mnops=num
           Emit num NOPs before every other generated instruction.

       -mno-soft-cmpsf
           For single-precision floating-point comparisons, emit an "fsub"
           instruction and test the flags.  This is faster than a software
           comparison, but can get incorrect results in the presence of NaNs,
           or when two different small numbers are compared such that their
           difference is calculated as zero.  The default is -msoft-cmpsf,
           which uses slower, but IEEE-compliant, software comparisons.

       -mstack-offset=num
           Set the offset between the top of the stack and the stack pointer.
           E.g., a value of 8 means that the eight bytes in the range
           "sp+0...sp+7" can be used by leaf functions without stack
           allocation.  Values other than 8 or 16 are untested and unlikely to
           work.  Note also that this option changes the ABI; compiling a
           program with a different stack offset than the libraries have been
           compiled with generally does not work.  This option can be useful
           if you want to evaluate if a different stack offset would give you
           better code, but to actually use a different stack offset to build
           working programs, it is recommended to configure the toolchain with
           the appropriate --with-stack-offset=num option.

       -mno-round-nearest
           Make the scheduler assume that the rounding mode has been set to
           truncating.  The default is -mround-nearest.

       -mlong-calls
           If not otherwise specified by an attribute, assume all calls might
           be beyond the offset range of the "b" / "bl" instructions, and
           therefore load the function address into a register before
           performing a (otherwise direct) call.  This is the default.

       -mshort-calls
           If not otherwise specified by an attribute, assume all direct calls
           are in the range of the "b" / "bl" instructions, so use these
           instructions for direct calls.  The default is -mlong-calls.

       -msmall16
           Assume addresses can be loaded as 16-bit unsigned values.  This
           does not apply to function addresses for which -mlong-calls
           semantics are in effect.

       -mfp-mode=mode
           Set the prevailing mode of the floating-point unit.  This
           determines the floating-point mode that is provided and expected at
           function call and return time.  Making this mode match the mode you
           predominantly need at function start can make your programs smaller
           and faster by avoiding unnecessary mode switches.

           mode can be set to one the following values:

           caller
               Any mode at function entry is valid, and retained or restored
               when the function returns, and when it calls other functions.
               This mode is useful for compiling libraries or other
               compilation units you might want to incorporate into different
               programs with different prevailing FPU modes, and the
               convenience of being able to use a single object file outweighs
               the size and speed overhead for any extra mode switching that
               might be needed, compared with what would be needed with a more
               specific choice of prevailing FPU mode.

           truncate
               This is the mode used for floating-point calculations with
               truncating (i.e. round towards zero) rounding mode.  That
               includes conversion from floating point to integer.

           round-nearest
               This is the mode used for floating-point calculations with
               round-to-nearest-or-even rounding mode.

           int This is the mode used to perform integer calculations in the
               FPU, e.g.  integer multiply, or integer multiply-and-
               accumulate.

           The default is -mfp-mode=caller

       -mnosplit-lohi
       -mno-postinc
       -mno-postmodify
           Code generation tweaks that disable, respectively, splitting of
           32-bit loads, generation of post-increment addresses, and
           generation of post-modify addresses.  The defaults are msplit-lohi,
           -mpost-inc, and -mpost-modify.

       -mnovect-double
           Change the preferred SIMD mode to SImode.  The default is
           -mvect-double, which uses DImode as preferred SIMD mode.

       -max-vect-align=num
           The maximum alignment for SIMD vector mode types.  num may be 4 or
           8.  The default is 8.  Note that this is an ABI change, even though
           many library function interfaces are unaffected if they don't use
           SIMD vector modes in places that affect size and/or alignment of
           relevant types.

       -msplit-vecmove-early
           Split vector moves into single word moves before reload.  In theory
           this can give better register allocation, but so far the reverse
           seems to be generally the case.

       -m1reg-reg
           Specify a register to hold the constant -1, which makes loading
           small negative constants and certain bitmasks faster.  Allowable
           values for reg are r43 and r63, which specify use of that register
           as a fixed register, and none, which means that no register is used
           for this purpose.  The default is -m1reg-none.

       ARM Options

       These -m options are defined for Advanced RISC Machines (ARM)
       architectures:

       -mabi=name
           Generate code for the specified ABI.  Permissible values are: apcs-
           gnu, atpcs, aapcs, aapcs-linux and iwmmxt.

       -mapcs-frame
           Generate a stack frame that is compliant with the ARM Procedure
           Call Standard for all functions, even if this is not strictly
           necessary for correct execution of the code.  Specifying
           -fomit-frame-pointer with this option causes the stack frames not
           to be generated for leaf functions.  The default is
           -mno-apcs-frame.

       -mapcs
           This is a synonym for -mapcs-frame.

       -mthumb-interwork
           Generate code that supports calling between the ARM and Thumb
           instruction sets.  Without this option, on pre-v5 architectures,
           the two instruction sets cannot be reliably used inside one
           program.  The default is -mno-thumb-interwork, since slightly
           larger code is generated when -mthumb-interwork is specified.  In
           AAPCS configurations this option is meaningless.

       -mno-sched-prolog
           Prevent the reordering of instructions in the function prologue, or
           the merging of those instruction with the instructions in the
           function's body.  This means that all functions start with a
           recognizable set of instructions (or in fact one of a choice from a
           small set of different function prologues), and this information
           can be used to locate the start of functions inside an executable
           piece of code.  The default is -msched-prolog.

       -mfloat-abi=name
           Specifies which floating-point ABI to use.  Permissible values are:
           soft, softfp and hard.

           Specifying soft causes GCC to generate output containing library
           calls for floating-point operations.  softfp allows the generation
           of code using hardware floating-point instructions, but still uses
           the soft-float calling conventions.  hard allows generation of
           floating-point instructions and uses FPU-specific calling
           conventions.

           The default depends on the specific target configuration.  Note
           that the hard-float and soft-float ABIs are not link-compatible;
           you must compile your entire program with the same ABI, and link
           with a compatible set of libraries.

       -mlittle-endian
           Generate code for a processor running in little-endian mode.  This
           is the default for all standard configurations.

       -mbig-endian
           Generate code for a processor running in big-endian mode; the
           default is to compile code for a little-endian processor.

       -mwords-little-endian
           This option only applies when generating code for big-endian
           processors.  Generate code for a little-endian word order but a
           big-endian byte order.  That is, a byte order of the form 32107654.
           Note: this option should only be used if you require compatibility
           with code for big-endian ARM processors generated by versions of
           the compiler prior to 2.8.  This option is now deprecated.

       -mcpu=name
           This specifies the name of the target ARM processor.  GCC uses this
           name to determine what kind of instructions it can emit when
           generating assembly code.  Permissible names are: arm2, arm250,
           arm3, arm6, arm60, arm600, arm610, arm620, arm7, arm7m, arm7d,
           arm7dm, arm7di, arm7dmi, arm70, arm700, arm700i, arm710, arm710c,
           arm7100, arm720, arm7500, arm7500fe, arm7tdmi, arm7tdmi-s, arm710t,
           arm720t, arm740t, strongarm, strongarm110, strongarm1100,
           strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t,
           arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi,
           arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e,
           arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s,
           arm1156t2f-s, arm1176jz-s, arm1176jzf-s, cortex-a5, cortex-a7,
           cortex-a8, cortex-a9, cortex-a15, cortex-r4, cortex-r4f, cortex-r5,
           cortex-m4, cortex-m3, cortex-m1, cortex-m0, cortex-m0plus,
           marvell-pj4, xscale, iwmmxt, iwmmxt2, ep9312, fa526, fa626,
           fa606te, fa626te, fmp626, fa726te.

           -mcpu=generic-arch is also permissible, and is equivalent to
           -march=arch -mtune=generic-arch.  See -mtune for more information.

           -mcpu=native causes the compiler to auto-detect the CPU of the
           build computer.  At present, this feature is only supported on
           Linux, and not all architectures are recognized.  If the auto-
           detect is unsuccessful the option has no effect.

       -mtune=name
           This option is very similar to the -mcpu= option, except that
           instead of specifying the actual target processor type, and hence
           restricting which instructions can be used, it specifies that GCC
           should tune the performance of the code as if the target were of
           the type specified in this option, but still choosing the
           instructions it generates based on the CPU specified by a -mcpu=
           option.  For some ARM implementations better performance can be
           obtained by using this option.

           -mtune=generic-arch specifies that GCC should tune the performance
           for a blend of processors within architecture arch.  The aim is to
           generate code that run well on the current most popular processors,
           balancing between optimizations that benefit some CPUs in the
           range, and avoiding performance pitfalls of other CPUs.  The
           effects of this option may change in future GCC versions as CPU
           models come and go.

           -mtune=native causes the compiler to auto-detect the CPU of the
           build computer.  At present, this feature is only supported on
           Linux, and not all architectures are recognized.  If the auto-
           detect is unsuccessful the option has no effect.

       -march=name
           This specifies the name of the target ARM architecture.  GCC uses
           this name to determine what kind of instructions it can emit when
           generating assembly code.  This option can be used in conjunction
           with or instead of the -mcpu= option.  Permissible names are:
           armv2, armv2a, armv3, armv3m, armv4, armv4t, armv5, armv5t, armv5e,
           armv5te, armv6, armv6j, armv6t2, armv6z, armv6zk, armv6-m, armv7,
           armv7-a, armv7-r, armv7-m, armv8-a, iwmmxt, iwmmxt2, ep9312.

           -march=native causes the compiler to auto-detect the architecture
           of the build computer.  At present, this feature is only supported
           on Linux, and not all architectures are recognized.  If the auto-
           detect is unsuccessful the option has no effect.

       -mfpu=name
           This specifies what floating-point hardware (or hardware emulation)
           is available on the target.  Permissible names are: vfp, vfpv3,
           vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd, vfpv3xd-fp16, neon,
           neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16, neon-vfpv4, fp-armv8,
           neon-fp-armv8, and crypto-neon-fp-armv8.

           If -msoft-float is specified this specifies the format of floating-
           point values.

           If the selected floating-point hardware includes the NEON extension
           (e.g. -mfpu=neon), note that floating-point operations are not
           generated by GCC's auto-vectorization pass unless
           -funsafe-math-optimizations is also specified.  This is because
           NEON hardware does not fully implement the IEEE 754 standard for
           floating-point arithmetic (in particular denormal values are
           treated as zero), so the use of NEON instructions may lead to a
           loss of precision.

       -mfp16-format=name
           Specify the format of the "__fp16" half-precision floating-point
           type.  Permissible names are none, ieee, and alternative; the
           default is none, in which case the "__fp16" type is not defined.

       -mstructure-size-boundary=n
           The sizes of all structures and unions are rounded up to a multiple
           of the number of bits set by this option.  Permissible values are
           8, 32 and 64.  The default value varies for different toolchains.
           For the COFF targeted toolchain the default value is 8.  A value of
           64 is only allowed if the underlying ABI supports it.

           Specifying a larger number can produce faster, more efficient code,
           but can also increase the size of the program.  Different values
           are potentially incompatible.  Code compiled with one value cannot
           necessarily expect to work with code or libraries compiled with
           another value, if they exchange information using structures or
           unions.

       -mabort-on-noreturn
           Generate a call to the function "abort" at the end of a "noreturn"
           function.  It is executed if the function tries to return.

       -mlong-calls
       -mno-long-calls
           Tells the compiler to perform function calls by first loading the
           address of the function into a register and then performing a
           subroutine call on this register.  This switch is needed if the
           target function lies outside of the 64-megabyte addressing range of
           the offset-based version of subroutine call instruction.

           Even if this switch is enabled, not all function calls are turned
           into long calls.  The heuristic is that static functions, functions
           that have the short-call attribute, functions that are inside the
           scope of a #pragma no_long_calls directive, and functions whose
           definitions have already been compiled within the current
           compilation unit are not turned into long calls.  The exceptions to
           this rule are that weak function definitions, functions with the
           long-call attribute or the section attribute, and functions that
           are within the scope of a #pragma long_calls directive are always
           turned into long calls.

           This feature is not enabled by default.  Specifying -mno-long-calls
           restores the default behavior, as does placing the function calls
           within the scope of a #pragma long_calls_off directive.  Note these
           switches have no effect on how the compiler generates code to
           handle function calls via function pointers.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather
           than loading it in the prologue for each function.  The runtime
           system is responsible for initializing this register with an
           appropriate value before execution begins.

       -mpic-register=reg
           Specify the register to be used for PIC addressing.  For standard
           PIC base case, the default will be any suitable register determined
           by compiler.  For single PIC base case, the default is R9 if target
           is EABI based or stack-checking is enabled, otherwise the default
           is R10.

       -mpoke-function-name
           Write the name of each function into the text section, directly
           preceding the function prologue.  The generated code is similar to
           this:

                        t0
                            .ascii "arm_poke_function_name", 0
                            .align
                        t1
                            .word 0xff000000 + (t1 - t0)
                        arm_poke_function_name
                            mov     ip, sp
                            stmfd   sp!, {fp, ip, lr, pc}
                            sub     fp, ip, #4

           When performing a stack backtrace, code can inspect the value of
           "pc" stored at "fp + 0".  If the trace function then looks at
           location "pc - 12" and the top 8 bits are set, then we know that
           there is a function name embedded immediately preceding this
           location and has length "((pc[-3]) & 0xff000000)".

       -mthumb
       -marm
           Select between generating code that executes in ARM and Thumb
           states.  The default for most configurations is to generate code
           that executes in ARM state, but the default can be changed by
           configuring GCC with the --with-mode=state configure option.

       -mtpcs-frame
           Generate a stack frame that is compliant with the Thumb Procedure
           Call Standard for all non-leaf functions.  (A leaf function is one
           that does not call any other functions.)  The default is
           -mno-tpcs-frame.

       -mtpcs-leaf-frame
           Generate a stack frame that is compliant with the Thumb Procedure
           Call Standard for all leaf functions.  (A leaf function is one that
           does not call any other functions.)  The default is
           -mno-apcs-leaf-frame.

       -mcallee-super-interworking
           Gives all externally visible functions in the file being compiled
           an ARM instruction set header which switches to Thumb mode before
           executing the rest of the function.  This allows these functions to
           be called from non-interworking code.  This option is not valid in
           AAPCS configurations because interworking is enabled by default.

       -mcaller-super-interworking
           Allows calls via function pointers (including virtual functions) to
           execute correctly regardless of whether the target code has been
           compiled for interworking or not.  There is a small overhead in the
           cost of executing a function pointer if this option is enabled.
           This option is not valid in AAPCS configurations because
           interworking is enabled by default.

       -mtp=name
           Specify the access model for the thread local storage pointer.  The
           valid models are soft, which generates calls to "__aeabi_read_tp",
           cp15, which fetches the thread pointer from "cp15" directly
           (supported in the arm6k architecture), and auto, which uses the
           best available method for the selected processor.  The default
           setting is auto.

       -mtls-dialect=dialect
           Specify the dialect to use for accessing thread local storage.  Two
           dialects are supported---gnu and gnu2.  The gnu dialect selects the
           original GNU scheme for supporting local and global dynamic TLS
           models.  The gnu2 dialect selects the GNU descriptor scheme, which
           provides better performance for shared libraries.  The GNU
           descriptor scheme is compatible with the original scheme, but does
           require new assembler, linker and library support.  Initial and
           local exec TLS models are unaffected by this option and always use
           the original scheme.

       -mword-relocations
           Only generate absolute relocations on word-sized values (i.e.
           R_ARM_ABS32).  This is enabled by default on targets (uClinux,
           SymbianOS) where the runtime loader imposes this restriction, and
           when -fpic or -fPIC is specified.

       -mfix-cortex-m3-ldrd
           Some Cortex-M3 cores can cause data corruption when "ldrd"
           instructions with overlapping destination and base registers are
           used.  This option avoids generating these instructions.  This
           option is enabled by default when -mcpu=cortex-m3 is specified.

       -munaligned-access
       -mno-unaligned-access
           Enables (or disables) reading and writing of 16- and 32- bit values
           from addresses that are not 16- or 32- bit aligned.  By default
           unaligned access is disabled for all pre-ARMv6 and all ARMv6-M
           architectures, and enabled for all other architectures.  If
           unaligned access is not enabled then words in packed data
           structures will be accessed a byte at a time.

           The ARM attribute "Tag_CPU_unaligned_access" will be set in the
           generated object file to either true or false, depending upon the
           setting of this option.  If unaligned access is enabled then the
           preprocessor symbol "__ARM_FEATURE_UNALIGNED" will also be defined.

       AVR Options

       These options are defined for AVR implementations:

       -mmcu=mcu
           Specify Atmel AVR instruction set architectures (ISA) or MCU type.

           The default for this option is@tie{}"avr2".

           GCC supports the following AVR devices and ISAs:

           "avr2"
               "Classic" devices with up to 8@tie{}KiB of program memory.
               mcu@tie{}= "attiny22", "attiny26", "at90c8534", "at90s2313",
               "at90s2323", "at90s2333", "at90s2343", "at90s4414",
               "at90s4433", "at90s4434", "at90s8515", "at90s8535".

           "avr25"
               "Classic" devices with up to 8@tie{}KiB of program memory and
               with the "MOVW" instruction.  mcu@tie{}= "ata5272", "ata6289",
               "attiny13", "attiny13a", "attiny2313", "attiny2313a",
               "attiny24", "attiny24a", "attiny25", "attiny261", "attiny261a",
               "attiny43u", "attiny4313", "attiny44", "attiny44a", "attiny45",
               "attiny461", "attiny461a", "attiny48", "attiny84", "attiny84a",
               "attiny85", "attiny861", "attiny861a", "attiny87", "attiny88",
               "at86rf401".

           "avr3"
               "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of
               program memory.  mcu@tie{}= "at43usb355", "at76c711".

           "avr31"
               "Classic" devices with 128@tie{}KiB of program memory.
               mcu@tie{}= "atmega103", "at43usb320".

           "avr35"
               "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of program
               memory and with the "MOVW" instruction.  mcu@tie{}= "ata5505",
               "atmega16u2", "atmega32u2", "atmega8u2", "attiny1634",
               "attiny167", "at90usb162", "at90usb82".

           "avr4"
               "Enhanced" devices with up to 8@tie{}KiB of program memory.
               mcu@tie{}= "ata6285", "ata6286", "atmega48", "atmega48a",
               "atmega48p", "atmega48pa", "atmega8", "atmega8a", "atmega8hva",
               "atmega8515", "atmega8535", "atmega88", "atmega88a",
               "atmega88p", "atmega88pa", "at90pwm1", "at90pwm2", "at90pwm2b",
               "at90pwm3", "at90pwm3b", "at90pwm81".

           "avr5"
               "Enhanced" devices with 16@tie{}KiB up to 64@tie{}KiB of
               program memory.  mcu@tie{}= "ata5790", "ata5790n", "ata5795",
               "atmega16", "atmega16a", "atmega16hva", "atmega16hva2",
               "atmega16hvb", "atmega16hvbrevb", "atmega16m1", "atmega16u4",
               "atmega161", "atmega162", "atmega163", "atmega164a",
               "atmega164p", "atmega164pa", "atmega165", "atmega165a",
               "atmega165p", "atmega165pa", "atmega168", "atmega168a",
               "atmega168p", "atmega168pa", "atmega169", "atmega169a",
               "atmega169p", "atmega169pa", "atmega26hvg", "atmega32",
               "atmega32a", "atmega32c1", "atmega32hvb", "atmega32hvbrevb",
               "atmega32m1", "atmega32u4", "atmega32u6", "atmega323",
               "atmega324a", "atmega324p", "atmega324pa", "atmega325",
               "atmega325a", "atmega325p", "atmega3250", "atmega3250a",
               "atmega3250p", "atmega3250pa", "atmega328", "atmega328p",
               "atmega329", "atmega329a", "atmega329p", "atmega329pa",
               "atmega3290", "atmega3290a", "atmega3290p", "atmega3290pa",
               "atmega406", "atmega48hvf", "atmega64", "atmega64a",
               "atmega64c1", "atmega64hve", "atmega64m1", "atmega64rfa2",
               "atmega64rfr2", "atmega640", "atmega644", "atmega644a",
               "atmega644p", "atmega644pa", "atmega645", "atmega645a",
               "atmega645p", "atmega6450", "atmega6450a", "atmega6450p",
               "atmega649", "atmega649a", "atmega649p", "atmega6490",
               "atmega6490a", "atmega6490p", "at90can32", "at90can64",
               "at90pwm161", "at90pwm216", "at90pwm316", "at90scr100",
               "at90usb646", "at90usb647", "at94k", "m3000".

           "avr51"
               "Enhanced" devices with 128@tie{}KiB of program memory.
               mcu@tie{}= "atmega128", "atmega128a", "atmega128rfa1",
               "atmega1280", "atmega1281", "atmega1284", "atmega1284p",
               "at90can128", "at90usb1286", "at90usb1287".

           "avr6"
               "Enhanced" devices with 3-byte PC, i.e. with more than
               128@tie{}KiB of program memory.  mcu@tie{}= "atmega2560",
               "atmega2561".

           "avrxmega2"
               "XMEGA" devices with more than 8@tie{}KiB and up to 64@tie{}KiB
               of program memory.  mcu@tie{}= "atmxt112sl", "atmxt224",
               "atmxt224e", "atmxt336s", "atxmega16a4", "atxmega16a4u",
               "atxmega16c4", "atxmega16d4", "atxmega16x1", "atxmega32a4",
               "atxmega32a4u", "atxmega32c4", "atxmega32d4", "atxmega32e5",
               "atxmega32x1".

           "avrxmega4"
               "XMEGA" devices with more than 64@tie{}KiB and up to
               128@tie{}KiB of program memory.  mcu@tie{}= "atxmega64a3",
               "atxmega64a3u", "atxmega64a4u", "atxmega64b1", "atxmega64b3",
               "atxmega64c3", "atxmega64d3", "atxmega64d4".

           "avrxmega5"
               "XMEGA" devices with more than 64@tie{}KiB and up to
               128@tie{}KiB of program memory and more than 64@tie{}KiB of
               RAM.  mcu@tie{}= "atxmega64a1", "atxmega64a1u".

           "avrxmega6"
               "XMEGA" devices with more than 128@tie{}KiB of program memory.
               mcu@tie{}= "atmxt540s", "atmxt540sreva", "atxmega128a3",
               "atxmega128a3u", "atxmega128b1", "atxmega128b3",
               "atxmega128c3", "atxmega128d3", "atxmega128d4", "atxmega192a3",
               "atxmega192a3u", "atxmega192c3", "atxmega192d3",
               "atxmega256a3", "atxmega256a3b", "atxmega256a3bu",
               "atxmega256a3u", "atxmega256c3", "atxmega256d3",
               "atxmega384c3", "atxmega384d3".

           "avrxmega7"
               "XMEGA" devices with more than 128@tie{}KiB of program memory
               and more than 64@tie{}KiB of RAM.  mcu@tie{}= "atxmega128a1",
               "atxmega128a1u", "atxmega128a4u".

           "avr1"
               This ISA is implemented by the minimal AVR core and supported
               for assembler only.  mcu@tie{}= "attiny11", "attiny12",
               "attiny15", "attiny28", "at90s1200".

       -maccumulate-args
           Accumulate outgoing function arguments and acquire/release the
           needed stack space for outgoing function arguments once in function
           prologue/epilogue.  Without this option, outgoing arguments are
           pushed before calling a function and popped afterwards.

           Popping the arguments after the function call can be expensive on
           AVR so that accumulating the stack space might lead to smaller
           executables because arguments need not to be removed from the stack
           after such a function call.

           This option can lead to reduced code size for functions that
           perform several calls to functions that get their arguments on the
           stack like calls to printf-like functions.

       -mbranch-cost=cost
           Set the branch costs for conditional branch instructions to cost.
           Reasonable values for cost are small, non-negative integers. The
           default branch cost is 0.

       -mcall-prologues
           Functions prologues/epilogues are expanded as calls to appropriate
           subroutines.  Code size is smaller.

       -mint8
           Assume "int" to be 8-bit integer.  This affects the sizes of all
           types: a "char" is 1 byte, an "int" is 1 byte, a "long" is 2 bytes,
           and "long long" is 4 bytes.  Please note that this option does not
           conform to the C standards, but it results in smaller code size.

       -mno-interrupts
           Generated code is not compatible with hardware interrupts.  Code
           size is smaller.

       -mrelax
           Try to replace "CALL" resp. "JMP" instruction by the shorter
           "RCALL" resp. "RJMP" instruction if applicable.  Setting "-mrelax"
           just adds the "--relax" option to the linker command line when the
           linker is called.

           Jump relaxing is performed by the linker because jump offsets are
           not known before code is located. Therefore, the assembler code
           generated by the compiler is the same, but the instructions in the
           executable may differ from instructions in the assembler code.

           Relaxing must be turned on if linker stubs are needed, see the
           section on "EIND" and linker stubs below.

       -msp8
           Treat the stack pointer register as an 8-bit register, i.e. assume
           the high byte of the stack pointer is zero.  In general, you don't
           need to set this option by hand.

           This option is used internally by the compiler to select and build
           multilibs for architectures "avr2" and "avr25".  These
           architectures mix devices with and without "SPH".  For any setting
           other than "-mmcu=avr2" or "-mmcu=avr25" the compiler driver will
           add or remove this option from the compiler proper's command line,
           because the compiler then knows if the device or architecture has
           an 8-bit stack pointer and thus no "SPH" register or not.

       -mstrict-X
           Use address register "X" in a way proposed by the hardware.  This
           means that "X" is only used in indirect, post-increment or pre-
           decrement addressing.

           Without this option, the "X" register may be used in the same way
           as "Y" or "Z" which then is emulated by additional instructions.
           For example, loading a value with "X+const" addressing with a small
           non-negative "const < 64" to a register Rn is performed as

                   adiw r26, const   ; X += const
                   ld   <Rn>, X        ; <Rn> = *X
                   sbiw r26, const   ; X -= const

       -mtiny-stack
           Only change the lower 8@tie{}bits of the stack pointer.

       -Waddr-space-convert
           Warn about conversions between address spaces in the case where the
           resulting address space is not contained in the incoming address
           space.

       "EIND" and Devices with more than 128 Ki Bytes of Flash

       Pointers in the implementation are 16@tie{}bits wide.  The address of a
       function or label is represented as word address so that indirect jumps
       and calls can target any code address in the range of 64@tie{}Ki words.

       In order to facilitate indirect jump on devices with more than
       128@tie{}Ki bytes of program memory space, there is a special function
       register called "EIND" that serves as most significant part of the
       target address when "EICALL" or "EIJMP" instructions are used.

       Indirect jumps and calls on these devices are handled as follows by the
       compiler and are subject to some limitations:

          The compiler never sets "EIND".

          The compiler uses "EIND" implicitely in "EICALL"/"EIJMP"
           instructions or might read "EIND" directly in order to emulate an
           indirect call/jump by means of a "RET" instruction.

          The compiler assumes that "EIND" never changes during the startup
           code or during the application. In particular, "EIND" is not
           saved/restored in function or interrupt service routine
           prologue/epilogue.

          For indirect calls to functions and computed goto, the linker
           generates stubs. Stubs are jump pads sometimes also called
           trampolines. Thus, the indirect call/jump jumps to such a stub.
           The stub contains a direct jump to the desired address.

          Linker relaxation must be turned on so that the linker will
           generate the stubs correctly an all situaltion. See the compiler
           option "-mrelax" and the linler option "--relax".  There are corner
           cases where the linker is supposed to generate stubs but aborts
           without relaxation and without a helpful error message.

          The default linker script is arranged for code with "EIND = 0".  If
           code is supposed to work for a setup with "EIND != 0", a custom
           linker script has to be used in order to place the sections whose
           name start with ".trampolines" into the segment where "EIND" points
           to.

          The startup code from libgcc never sets "EIND".  Notice that
           startup code is a blend of code from libgcc and AVR-LibC.  For the
           impact of AVR-LibC on "EIND", see the AVR-LibC user manual
           ("http://nongnu.org/avr-libc/user-manual/").

          It is legitimate for user-specific startup code to set up "EIND"
           early, for example by means of initialization code located in
           section ".init3". Such code runs prior to general startup code that
           initializes RAM and calls constructors, but after the bit of
           startup code from AVR-LibC that sets "EIND" to the segment where
           the vector table is located.

                   #include <avr/io.h>

                   static void
                   __attribute__((section(".init3"),naked,used,no_instrument_function))
                   init3_set_eind (void)
                   {
                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
                   }

           The "__trampolines_start" symbol is defined in the linker script.

          Stubs are generated automatically by the linker if the following
           two conditions are met:

           -<The address of a label is taken by means of the "gs" modifier>
               (short for generate stubs) like so:

                       LDI r24, lo8(gs(<func>))
                       LDI r25, hi8(gs(<func>))

           -<The final location of that label is in a code segment>
               outside the segment where the stubs are located.

          The compiler emits such "gs" modifiers for code labels in the
           following situations:

           -<Taking address of a function or code label.>
           -<Computed goto.>
           -<If prologue-save function is used, see -mcall-prologues>
               command-line option.

           -<Switch/case dispatch tables. If you do not want such dispatch>
               tables you can specify the -fno-jump-tables command-line
               option.

           -<C and C++ constructors/destructors called during
           startup/shutdown.>
           -<If the tools hit a "gs()" modifier explained above.>
          Jumping to non-symbolic addresses like so is not supported:

                   int main (void)
                   {
                       /* Call function at word address 0x2 */
                       return ((int(*)(void)) 0x2)();
                   }

           Instead, a stub has to be set up, i.e. the function has to be
           called through a symbol ("func_4" in the example):

                   int main (void)
                   {
                       extern int func_4 (void);

                       /* Call function at byte address 0x4 */
                       return func_4();
                   }

           and the application be linked with "-Wl,--defsym,func_4=0x4".
           Alternatively, "func_4" can be defined in the linker script.

       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function
       Registers

       Some AVR devices support memories larger than the 64@tie{}KiB range
       that can be accessed with 16-bit pointers.  To access memory locations
       outside this 64@tie{}KiB range, the contentent of a "RAMP" register is
       used as high part of the address: The "X", "Y", "Z" address register is
       concatenated with the "RAMPX", "RAMPY", "RAMPZ" special function
       register, respectively, to get a wide address. Similarly, "RAMPD" is
       used together with direct addressing.

          The startup code initializes the "RAMP" special function registers
           with zero.

          If a AVR Named Address Spaces,named address space other than
           generic or "__flash" is used, then "RAMPZ" is set as needed before
           the operation.

          If the device supports RAM larger than 64@tie{KiB} and the compiler
           needs to change "RAMPZ" to accomplish an operation, "RAMPZ" is
           reset to zero after the operation.

          If the device comes with a specific "RAMP" register, the ISR
           prologue/epilogue saves/restores that SFR and initializes it with
           zero in case the ISR code might (implicitly) use it.

          RAM larger than 64@tie{KiB} is not supported by GCC for AVR
           targets.  If you use inline assembler to read from locations
           outside the 16-bit address range and change one of the "RAMP"
           registers, you must reset it to zero after the access.

       AVR Built-in Macros

       GCC defines several built-in macros so that the user code can test for
       the presence or absence of features.  Almost any of the following
       built-in macros are deduced from device capabilities and thus triggered
       by the "-mmcu=" command-line option.

       For even more AVR-specific built-in macros see AVR Named Address Spaces
       and AVR Built-in Functions.

       "__AVR_ARCH__"
           Build-in macro that resolves to a decimal number that identifies
           the architecture and depends on the "-mmcu=mcu" option.  Possible
           values are:

           2, 25, 3, 31, 35, 4, 5, 51, 6, 102, 104, 105, 106, 107

           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5",
           "avr51", "avr6", "avrxmega2", "avrxmega4", "avrxmega5",
           "avrxmega6", "avrxmega7", respectively.  If mcu specifies a device,
           this built-in macro is set accordingly. For example, with
           "-mmcu=atmega8" the macro will be defined to 4.

       "__AVR_Device__"
           Setting "-mmcu=device" defines this built-in macro which reflects
           the device's name. For example, "-mmcu=atmega8" defines the built-
           in macro "__AVR_ATmega8__", "-mmcu=attiny261a" defines
           "__AVR_ATtiny261A__", etc.

           The built-in macros' names follow the scheme "__AVR_Device__" where
           Device is the device name as from the AVR user manual. The
           difference between Device in the built-in macro and device in
           "-mmcu=device" is that the latter is always lowercase.

           If device is not a device but only a core architecture like
           "avr51", this macro will not be defined.

       "__AVR_XMEGA__"
           The device / architecture belongs to the XMEGA family of devices.

       "__AVR_HAVE_ELPM__"
           The device has the the "ELPM" instruction.

       "__AVR_HAVE_ELPMX__"
           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.

       "__AVR_HAVE_MOVW__"
           The device has the "MOVW" instruction to perform 16-bit register-
           register moves.

       "__AVR_HAVE_LPMX__"
           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.

       "__AVR_HAVE_MUL__"
           The device has a hardware multiplier.

       "__AVR_HAVE_JMP_CALL__"
           The device has the "JMP" and "CALL" instructions.  This is the case
           for devices with at least 16@tie{}KiB of program memory.

       "__AVR_HAVE_EIJMP_EICALL__"
       "__AVR_3_BYTE_PC__"
           The device has the "EIJMP" and "EICALL" instructions.  This is the
           case for devices with more than 128@tie{}KiB of program memory.
           This also means that the program counter (PC) is 3@tie{}bytes wide.

       "__AVR_2_BYTE_PC__"
           The program counter (PC) is 2@tie{}bytes wide. This is the case for
           devices with up to 128@tie{}KiB of program memory.

       "__AVR_HAVE_8BIT_SP__"
       "__AVR_HAVE_16BIT_SP__"
           The stack pointer (SP) register is treated as 8-bit respectively
           16-bit register by the compiler.  The definition of these macros is
           affected by "-mtiny-stack".

       "__AVR_HAVE_SPH__"
       "__AVR_SP8__"
           The device has the SPH (high part of stack pointer) special
           function register or has an 8-bit stack pointer, respectively.  The
           definition of these macros is affected by "-mmcu=" and in the cases
           of "-mmcu=avr2" and "-mmcu=avr25" also by "-msp8".

       "__AVR_HAVE_RAMPD__"
       "__AVR_HAVE_RAMPX__"
       "__AVR_HAVE_RAMPY__"
       "__AVR_HAVE_RAMPZ__"
           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special
           function register, respectively.

       "__NO_INTERRUPTS__"
           This macro reflects the "-mno-interrupts" command line option.

       "__AVR_ERRATA_SKIP__"
       "__AVR_ERRATA_SKIP_JMP_CALL__"
           Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
           instructions because of a hardware erratum.  Skip instructions are
           "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".  The second macro is
           only defined if "__AVR_HAVE_JMP_CALL__" is also set.

       "__AVR_SFR_OFFSET__=offset"
           Instructions that can address I/O special function registers
           directly like "IN", "OUT", "SBI", etc. may use a different address
           as if addressed by an instruction to access RAM like "LD" or "STS".
           This offset depends on the device architecture and has to be
           subtracted from the RAM address in order to get the respective
           I/O@tie{}address.

       "__WITH_AVRLIBC__"
           The compiler is configured to be used together with AVR-Libc.  See
           the "--with-avrlibc" configure option.

       Blackfin Options

       -mcpu=cpu[-sirevision]
           Specifies the name of the target Blackfin processor.  Currently,
           cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524,
           bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537,
           bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m,
           bf547m, bf548m, bf549m, bf561, bf592.

           The optional sirevision specifies the silicon revision of the
           target Blackfin processor.  Any workarounds available for the
           targeted silicon revision are enabled.  If sirevision is none, no
           workarounds are enabled.  If sirevision is any, all workarounds for
           the targeted processor are enabled.  The "__SILICON_REVISION__"
           macro is defined to two hexadecimal digits representing the major
           and minor numbers in the silicon revision.  If sirevision is none,
           the "__SILICON_REVISION__" is not defined.  If sirevision is any,
           the "__SILICON_REVISION__" is defined to be 0xffff.  If this
           optional sirevision is not used, GCC assumes the latest known
           silicon revision of the targeted Blackfin processor.

           GCC defines a preprocessor macro for the specified cpu.  For the
           bfin-elf toolchain, this option causes the hardware BSP provided by
           libgloss to be linked in if -msim is not given.

           Without this option, bf532 is used as the processor by default.

           Note that support for bf561 is incomplete.  For bf561, only the
           preprocessor macro is defined.

       -msim
           Specifies that the program will be run on the simulator.  This
           causes the simulator BSP provided by libgloss to be linked in.
           This option has effect only for bfin-elf toolchain.  Certain other
           options, such as -mid-shared-library and -mfdpic, imply -msim.

       -momit-leaf-frame-pointer
           Don't keep the frame pointer in a register for leaf functions.
           This avoids the instructions to save, set up and restore frame
           pointers and makes an extra register available in leaf functions.
           The option -fomit-frame-pointer removes the frame pointer for all
           functions, which might make debugging harder.

       -mspecld-anomaly
           When enabled, the compiler ensures that the generated code does not
           contain speculative loads after jump instructions. If this option
           is used, "__WORKAROUND_SPECULATIVE_LOADS" is defined.

       -mno-specld-anomaly
           Don't generate extra code to prevent speculative loads from
           occurring.

       -mcsync-anomaly
           When enabled, the compiler ensures that the generated code does not
           contain CSYNC or SSYNC instructions too soon after conditional
           branches.  If this option is used, "__WORKAROUND_SPECULATIVE_SYNCS"
           is defined.

       -mno-csync-anomaly
           Don't generate extra code to prevent CSYNC or SSYNC instructions
           from occurring too soon after a conditional branch.

       -mlow-64k
           When enabled, the compiler is free to take advantage of the
           knowledge that the entire program fits into the low 64k of memory.

       -mno-low-64k
           Assume that the program is arbitrarily large.  This is the default.

       -mstack-check-l1
           Do stack checking using information placed into L1 scratchpad
           memory by the uClinux kernel.

       -mid-shared-library
           Generate code that supports shared libraries via the library ID
           method.  This allows for execute in place and shared libraries in
           an environment without virtual memory management.  This option
           implies -fPIC.  With a bfin-elf target, this option implies -msim.

       -mno-id-shared-library
           Generate code that doesn't assume ID-based shared libraries are
           being used.  This is the default.

       -mleaf-id-shared-library
           Generate code that supports shared libraries via the library ID
           method, but assumes that this library or executable won't link
           against any other ID shared libraries.  That allows the compiler to
           use faster code for jumps and calls.

       -mno-leaf-id-shared-library
           Do not assume that the code being compiled won't link against any
           ID shared libraries.  Slower code is generated for jump and call
           insns.

       -mshared-library-id=n
           Specifies the identification number of the ID-based shared library
           being compiled.  Specifying a value of 0 generates more compact
           code; specifying other values forces the allocation of that number
           to the current library but is no more space- or time-efficient than
           omitting this option.

       -msep-data
           Generate code that allows the data segment to be located in a
           different area of memory from the text segment.  This allows for
           execute in place in an environment without virtual memory
           management by eliminating relocations against the text section.

       -mno-sep-data
           Generate code that assumes that the data segment follows the text
           segment.  This is the default.

       -mlong-calls
       -mno-long-calls
           Tells the compiler to perform function calls by first loading the
           address of the function into a register and then performing a
           subroutine call on this register.  This switch is needed if the
           target function lies outside of the 24-bit addressing range of the
           offset-based version of subroutine call instruction.

           This feature is not enabled by default.  Specifying -mno-long-calls
           restores the default behavior.  Note these switches have no effect
           on how the compiler generates code to handle function calls via
           function pointers.

       -mfast-fp
           Link with the fast floating-point library. This library relaxes
           some of the IEEE floating-point standard's rules for checking
           inputs against Not-a-Number (NAN), in the interest of performance.

       -minline-plt
           Enable inlining of PLT entries in function calls to functions that
           are not known to bind locally.  It has no effect without -mfdpic.

       -mmulticore
           Build a standalone application for multicore Blackfin processors.
           This option causes proper start files and link scripts supporting
           multicore to be used, and defines the macro "__BFIN_MULTICORE".  It
           can only be used with -mcpu=bf561[-sirevision].

           This option can be used with -mcorea or -mcoreb, which selects the
           one-application-per-core programming model.  Without -mcorea or
           -mcoreb, the single-application/dual-core programming model is
           used. In this model, the main function of Core B should be named as
           "coreb_main".

           If this option is not used, the single-core application programming
           model is used.

       -mcorea
           Build a standalone application for Core A of BF561 when using the
           one-application-per-core programming model. Proper start files and
           link scripts are used to support Core A, and the macro
           "__BFIN_COREA" is defined.  This option can only be used in
           conjunction with -mmulticore.

       -mcoreb
           Build a standalone application for Core B of BF561 when using the
           one-application-per-core programming model. Proper start files and
           link scripts are used to support Core B, and the macro
           "__BFIN_COREB" is defined. When this option is used, "coreb_main"
           should be used instead of "main".  This option can only be used in
           conjunction with -mmulticore.

       -msdram
           Build a standalone application for SDRAM. Proper start files and
           link scripts are used to put the application into SDRAM, and the
           macro "__BFIN_SDRAM" is defined.  The loader should initialize
           SDRAM before loading the application.

       -micplb
           Assume that ICPLBs are enabled at run time.  This has an effect on
           certain anomaly workarounds.  For Linux targets, the default is to
           assume ICPLBs are enabled; for standalone applications the default
           is off.

       C6X Options

       -march=name
           This specifies the name of the target architecture.  GCC uses this
           name to determine what kind of instructions it can emit when
           generating assembly code.  Permissible names are: c62x, c64x,
           c64x+, c67x, c67x+, c674x.

       -mbig-endian
           Generate code for a big-endian target.

       -mlittle-endian
           Generate code for a little-endian target.  This is the default.

       -msim
           Choose startup files and linker script suitable for the simulator.

       -msdata=default
           Put small global and static data in the .neardata section, which is
           pointed to by register "B14".  Put small uninitialized global and
           static data in the .bss section, which is adjacent to the .neardata
           section.  Put small read-only data into the .rodata section.  The
           corresponding sections used for large pieces of data are .fardata,
           .far and .const.

       -msdata=all
           Put all data, not just small objects, into the sections reserved
           for small data, and use addressing relative to the "B14" register
           to access them.

       -msdata=none
           Make no use of the sections reserved for small data, and use
           absolute addresses to access all data.  Put all initialized global
           and static data in the .fardata section, and all uninitialized data
           in the .far section.  Put all constant data into the .const
           section.

       CRIS Options

       These options are defined specifically for the CRIS ports.

       -march=architecture-type
       -mcpu=architecture-type
           Generate code for the specified architecture.  The choices for
           architecture-type are v3, v8 and v10 for respectively ETRAX 4,
           ETRAX 100, and ETRAX 100 LX.  Default is v0 except for cris-axis-
           linux-gnu, where the default is v10.

       -mtune=architecture-type
           Tune to architecture-type everything applicable about the generated
           code, except for the ABI and the set of available instructions.
           The choices for architecture-type are the same as for
           -march=architecture-type.

       -mmax-stack-frame=n
           Warn when the stack frame of a function exceeds n bytes.

       -metrax4
       -metrax100
           The options -metrax4 and -metrax100 are synonyms for -march=v3 and
           -march=v8 respectively.

       -mmul-bug-workaround
       -mno-mul-bug-workaround
           Work around a bug in the "muls" and "mulu" instructions for CPU
           models where it applies.  This option is active by default.

       -mpdebug
           Enable CRIS-specific verbose debug-related information in the
           assembly code.  This option also has the effect of turning off the
           #NO_APP formatted-code indicator to the assembler at the beginning
           of the assembly file.

       -mcc-init
           Do not use condition-code results from previous instruction; always
           emit compare and test instructions before use of condition codes.

       -mno-side-effects
           Do not emit instructions with side effects in addressing modes
           other than post-increment.

       -mstack-align
       -mno-stack-align
       -mdata-align
       -mno-data-align
       -mconst-align
       -mno-const-align
           These options (no- options) arrange (eliminate arrangements) for
           the stack frame, individual data and constants to be aligned for
           the maximum single data access size for the chosen CPU model.  The
           default is to arrange for 32-bit alignment.  ABI details such as
           structure layout are not affected by these options.

       -m32-bit
       -m16-bit
       -m8-bit
           Similar to the stack- data- and const-align options above, these
           options arrange for stack frame, writable data and constants to all
           be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
           alignment.

       -mno-prologue-epilogue
       -mprologue-epilogue
           With -mno-prologue-epilogue, the normal function prologue and
           epilogue which set up the stack frame are omitted and no return
           instructions or return sequences are generated in the code.  Use
           this option only together with visual inspection of the compiled
           code: no warnings or errors are generated when call-saved registers
           must be saved, or storage for local variables needs to be
           allocated.

       -mno-gotplt
       -mgotplt
           With -fpic and -fPIC, don't generate (do generate) instruction
           sequences that load addresses for functions from the PLT part of
           the GOT rather than (traditional on other architectures) calls to
           the PLT.  The default is -mgotplt.

       -melf
           Legacy no-op option only recognized with the cris-axis-elf and
           cris-axis-linux-gnu targets.

       -mlinux
           Legacy no-op option only recognized with the cris-axis-linux-gnu
           target.

       -sim
           This option, recognized for the cris-axis-elf, arranges to link
           with input-output functions from a simulator library.  Code,
           initialized data and zero-initialized data are allocated
           consecutively.

       -sim2
           Like -sim, but pass linker options to locate initialized data at
           0x40000000 and zero-initialized data at 0x80000000.

       CR16 Options

       These options are defined specifically for the CR16 ports.

       -mmac
           Enable the use of multiply-accumulate instructions. Disabled by
           default.

       -mcr16cplus
       -mcr16c
           Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
           is default.

       -msim
           Links the library libsim.a which is in compatible with simulator.
           Applicable to ELF compiler only.

       -mint32
           Choose integer type as 32-bit wide.

       -mbit-ops
           Generates "sbit"/"cbit" instructions for bit manipulations.

       -mdata-model=model
           Choose a data model. The choices for model are near, far or medium.
           medium is default.  However, far is not valid with -mcr16c, as the
           CR16C architecture does not support the far data model.

       Darwin Options

       These options are defined for all architectures running the Darwin
       operating system.

       FSF GCC on Darwin does not create "fat" object files; it creates an
       object file for the single architecture that GCC was built to target.
       Apple's GCC on Darwin does create "fat" files if multiple -arch options
       are used; it does so by running the compiler or linker multiple times
       and joining the results together with lipo.

       The subtype of the file created (like ppc7400 or ppc970 or i686) is
       determined by the flags that specify the ISA that GCC is targeting,
       like -mcpu or -march.  The -force_cpusubtype_ALL option can be used to
       override this.

       The Darwin tools vary in their behavior when presented with an ISA
       mismatch.  The assembler, as, only permits instructions to be used that
       are valid for the subtype of the file it is generating, so you cannot
       put 64-bit instructions in a ppc750 object file.  The linker for shared
       libraries, /usr/bin/libtool, fails and prints an error if asked to
       create a shared library with a less restrictive subtype than its input
       files (for instance, trying to put a ppc970 object file in a ppc7400
       library).  The linker for executables, ld, quietly gives the executable
       the most restrictive subtype of any of its input files.

       -Fdir
           Add the framework directory dir to the head of the list of
           directories to be searched for header files.  These directories are
           interleaved with those specified by -I options and are scanned in a
           left-to-right order.

           A framework directory is a directory with frameworks in it.  A
           framework is a directory with a Headers and/or PrivateHeaders
           directory contained directly in it that ends in .framework.  The
           name of a framework is the name of this directory excluding the
           .framework.  Headers associated with the framework are found in one
           of those two directories, with Headers being searched first.  A
           subframework is a framework directory that is in a framework's
           Frameworks directory.  Includes of subframework headers can only
           appear in a header of a framework that contains the subframework,
           or in a sibling subframework header.  Two subframeworks are
           siblings if they occur in the same framework.  A subframework
           should not have the same name as a framework; a warning is issued
           if this is violated.  Currently a subframework cannot have
           subframeworks; in the future, the mechanism may be extended to
           support this.  The standard frameworks can be found in
           /System/Library/Frameworks and /Library/Frameworks.  An example
           include looks like "#include <Framework/header.h>", where Framework
           denotes the name of the framework and header.h is found in the
           PrivateHeaders or Headers directory.

       -iframeworkdir
           Like -F except the directory is a treated as a system directory.
           The main difference between this -iframework and -F is that with
           -iframework the compiler does not warn about constructs contained
           within header files found via dir.  This option is valid only for
           the C family of languages.

       -gused
           Emit debugging information for symbols that are used.  For stabs
           debugging format, this enables -feliminate-unused-debug-symbols.
           This is by default ON.

       -gfull
           Emit debugging information for all symbols and types.

       -mmacosx-version-min=version
           The earliest version of MacOS X that this executable will run on is
           version.  Typical values of version include 10.1, 10.2, and 10.3.9.

           If the compiler was built to use the system's headers by default,
           then the default for this option is the system version on which the
           compiler is running, otherwise the default is to make choices that
           are compatible with as many systems and code bases as possible.

       -mkernel
           Enable kernel development mode.  The -mkernel option sets -static,
           -fno-common, -fno-cxa-atexit, -fno-exceptions,
           -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti
           where applicable.  This mode also sets -mno-altivec, -msoft-float,
           -fno-builtin and -mlong-branch for PowerPC targets.

       -mone-byte-bool
           Override the defaults for bool so that sizeof(bool)==1.  By default
           sizeof(bool) is 4 when compiling for Darwin/PowerPC and 1 when
           compiling for Darwin/x86, so this option has no effect on x86.

           Warning: The -mone-byte-bool switch causes GCC to generate code
           that is not binary compatible with code generated without that
           switch.  Using this switch may require recompiling all other
           modules in a program, including system libraries.  Use this switch
           to conform to a non-default data model.

       -mfix-and-continue
       -ffix-and-continue
       -findirect-data
           Generate code suitable for fast turnaround development, such as to
           allow GDB to dynamically load ".o" files into already-running
           programs.  -findirect-data and -ffix-and-continue are provided for
           backwards compatibility.

       -all_load
           Loads all members of static archive libraries.  See man ld(1) for
           more information.

       -arch_errors_fatal
           Cause the errors having to do with files that have the wrong
           architecture to be fatal.

       -bind_at_load
           Causes the output file to be marked such that the dynamic linker
           will bind all undefined references when the file is loaded or
           launched.

       -bundle
           Produce a Mach-o bundle format file.  See man ld(1) for more
           information.

       -bundle_loader executable
           This option specifies the executable that will load the build
           output file being linked.  See man ld(1) for more information.

       -dynamiclib
           When passed this option, GCC produces a dynamic library instead of
           an executable when linking, using the Darwin libtool command.

       -force_cpusubtype_ALL
           This causes GCC's output file to have the ALL subtype, instead of
           one controlled by the -mcpu or -march option.

       -allowable_client  client_name
       -client_name
       -compatibility_version
       -current_version
       -dead_strip
       -dependency-file
       -dylib_file
       -dylinker_install_name
       -dynamic
       -exported_symbols_list
       -filelist
       -flat_namespace
       -force_flat_namespace
       -headerpad_max_install_names
       -image_base
       -init
       -install_name
       -keep_private_externs
       -multi_module
       -multiply_defined
       -multiply_defined_unused
       -noall_load
       -no_dead_strip_inits_and_terms
       -nofixprebinding
       -nomultidefs
       -noprebind
       -noseglinkedit
       -pagezero_size
       -prebind
       -prebind_all_twolevel_modules
       -private_bundle
       -read_only_relocs
       -sectalign
       -sectobjectsymbols
       -whyload
       -seg1addr
       -sectcreate
       -sectobjectsymbols
       -sectorder
       -segaddr
       -segs_read_only_addr
       -segs_read_write_addr
       -seg_addr_table
       -seg_addr_table_filename
       -seglinkedit
       -segprot
       -segs_read_only_addr
       -segs_read_write_addr
       -single_module
       -static
       -sub_library
       -sub_umbrella
       -twolevel_namespace
       -umbrella
       -undefined
       -unexported_symbols_list
       -weak_reference_mismatches
       -whatsloaded
           These options are passed to the Darwin linker.  The Darwin linker
           man page describes them in detail.

       DEC Alpha Options

       These -m options are defined for the DEC Alpha implementations:

       -mno-soft-float
       -msoft-float
           Use (do not use) the hardware floating-point instructions for
           floating-point operations.  When -msoft-float is specified,
           functions in libgcc.a are used to perform floating-point
           operations.  Unless they are replaced by routines that emulate the
           floating-point operations, or compiled in such a way as to call
           such emulations routines, these routines issue floating-point
           operations.   If you are compiling for an Alpha without floating-
           point operations, you must ensure that the library is built so as
           not to call them.

           Note that Alpha implementations without floating-point operations
           are required to have floating-point registers.

       -mfp-reg
       -mno-fp-regs
           Generate code that uses (does not use) the floating-point register
           set.  -mno-fp-regs implies -msoft-float.  If the floating-point
           register set is not used, floating-point operands are passed in
           integer registers as if they were integers and floating-point
           results are passed in $0 instead of $f0.  This is a non-standard
           calling sequence, so any function with a floating-point argument or
           return value called by code compiled with -mno-fp-regs must also be
           compiled with that option.

           A typical use of this option is building a kernel that does not
           use, and hence need not save and restore, any floating-point
           registers.

       -mieee
           The Alpha architecture implements floating-point hardware optimized
           for maximum performance.  It is mostly compliant with the IEEE
           floating-point standard.  However, for full compliance, software
           assistance is required.  This option generates code fully IEEE-
           compliant code except that the inexact-flag is not maintained (see
           below).  If this option is turned on, the preprocessor macro
           "_IEEE_FP" is defined during compilation.  The resulting code is
           less efficient but is able to correctly support denormalized
           numbers and exceptional IEEE values such as not-a-number and
           plus/minus infinity.  Other Alpha compilers call this option
           -ieee_with_no_inexact.

       -mieee-with-inexact
           This is like -mieee except the generated code also maintains the
           IEEE inexact-flag.  Turning on this option causes the generated
           code to implement fully-compliant IEEE math.  In addition to
           "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro.
           On some Alpha implementations the resulting code may execute
           significantly slower than the code generated by default.  Since
           there is very little code that depends on the inexact-flag, you
           should normally not specify this option.  Other Alpha compilers
           call this option -ieee_with_inexact.

       -mfp-trap-mode=trap-mode
           This option controls what floating-point related traps are enabled.
           Other Alpha compilers call this option -fptm trap-mode.  The trap
           mode can be set to one of four values:

           n   This is the default (normal) setting.  The only traps that are
               enabled are the ones that cannot be disabled in software (e.g.,
               division by zero trap).

           u   In addition to the traps enabled by n, underflow traps are
               enabled as well.

           su  Like u, but the instructions are marked to be safe for software
               completion (see Alpha architecture manual for details).

           sui Like su, but inexact traps are enabled as well.

       -mfp-rounding-mode=rounding-mode
           Selects the IEEE rounding mode.  Other Alpha compilers call this
           option -fprm rounding-mode.  The rounding-mode can be one of:

           n   Normal IEEE rounding mode.  Floating-point numbers are rounded
               towards the nearest machine number or towards the even machine
               number in case of a tie.

           m   Round towards minus infinity.

           c   Chopped rounding mode.  Floating-point numbers are rounded
               towards zero.

           d   Dynamic rounding mode.  A field in the floating-point control
               register (fpcr, see Alpha architecture reference manual)
               controls the rounding mode in effect.  The C library
               initializes this register for rounding towards plus infinity.
               Thus, unless your program modifies the fpcr, d corresponds to
               round towards plus infinity.

       -mtrap-precision=trap-precision
           In the Alpha architecture, floating-point traps are imprecise.
           This means without software assistance it is impossible to recover
           from a floating trap and program execution normally needs to be
           terminated.  GCC can generate code that can assist operating system
           trap handlers in determining the exact location that caused a
           floating-point trap.  Depending on the requirements of an
           application, different levels of precisions can be selected:

           p   Program precision.  This option is the default and means a trap
               handler can only identify which program caused a floating-point
               exception.

           f   Function precision.  The trap handler can determine the
               function that caused a floating-point exception.

           i   Instruction precision.  The trap handler can determine the
               exact instruction that caused a floating-point exception.

           Other Alpha compilers provide the equivalent options called
           -scope_safe and -resumption_safe.

       -mieee-conformant
           This option marks the generated code as IEEE conformant.  You must
           not use this option unless you also specify -mtrap-precision=i and
           either -mfp-trap-mode=su or -mfp-trap-mode=sui.  Its only effect is
           to emit the line .eflag 48 in the function prologue of the
           generated assembly file.

       -mbuild-constants
           Normally GCC examines a 32- or 64-bit integer constant to see if it
           can construct it from smaller constants in two or three
           instructions.  If it cannot, it outputs the constant as a literal
           and generates code to load it from the data segment at run time.

           Use this option to require GCC to construct all integer constants
           using code, even if it takes more instructions (the maximum is
           six).

           You typically use this option to build a shared library dynamic
           loader.  Itself a shared library, it must relocate itself in memory
           before it can find the variables and constants in its own data
           segment.

       -mbwx
       -mno-bwx
       -mcix
       -mno-cix
       -mfix
       -mno-fix
       -mmax
       -mno-max
           Indicate whether GCC should generate code to use the optional BWX,
           CIX, FIX and MAX instruction sets.  The default is to use the
           instruction sets supported by the CPU type specified via -mcpu=
           option or that of the CPU on which GCC was built if none is
           specified.

       -mfloat-vax
       -mfloat-ieee
           Generate code that uses (does not use) VAX F and G floating-point
           arithmetic instead of IEEE single and double precision.

       -mexplicit-relocs
       -mno-explicit-relocs
           Older Alpha assemblers provided no way to generate symbol
           relocations except via assembler macros.  Use of these macros does
           not allow optimal instruction scheduling.  GNU binutils as of
           version 2.12 supports a new syntax that allows the compiler to
           explicitly mark which relocations should apply to which
           instructions.  This option is mostly useful for debugging, as GCC
           detects the capabilities of the assembler when it is built and sets
           the default accordingly.

       -msmall-data
       -mlarge-data
           When -mexplicit-relocs is in effect, static data is accessed via
           gp-relative relocations.  When -msmall-data is used, objects 8
           bytes long or smaller are placed in a small data area (the ".sdata"
           and ".sbss" sections) and are accessed via 16-bit relocations off
           of the $gp register.  This limits the size of the small data area
           to 64KB, but allows the variables to be directly accessed via a
           single instruction.

           The default is -mlarge-data.  With this option the data area is
           limited to just below 2GB.  Programs that require more than 2GB of
           data must use "malloc" or "mmap" to allocate the data in the heap
           instead of in the program's data segment.

           When generating code for shared libraries, -fpic implies
           -msmall-data and -fPIC implies -mlarge-data.

       -msmall-text
       -mlarge-text
           When -msmall-text is used, the compiler assumes that the code of
           the entire program (or shared library) fits in 4MB, and is thus
           reachable with a branch instruction.  When -msmall-data is used,
           the compiler can assume that all local symbols share the same $gp
           value, and thus reduce the number of instructions required for a
           function call from 4 to 1.

           The default is -mlarge-text.

       -mcpu=cpu_type
           Set the instruction set and instruction scheduling parameters for
           machine type cpu_type.  You can specify either the EV style name or
           the corresponding chip number.  GCC supports scheduling parameters
           for the EV4, EV5 and EV6 family of processors and chooses the
           default values for the instruction set from the processor you
           specify.  If you do not specify a processor type, GCC defaults to
           the processor on which the compiler was built.

           Supported values for cpu_type are

           ev4
           ev45
           21064
               Schedules as an EV4 and has no instruction set extensions.

           ev5
           21164
               Schedules as an EV5 and has no instruction set extensions.

           ev56
           21164a
               Schedules as an EV5 and supports the BWX extension.

           pca56
           21164pc
           21164PC
               Schedules as an EV5 and supports the BWX and MAX extensions.

           ev6
           21264
               Schedules as an EV6 and supports the BWX, FIX, and MAX
               extensions.

           ev67
           21264a
               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
               extensions.

           Native toolchains also support the value native, which selects the
           best architecture option for the host processor.  -mcpu=native has
           no effect if GCC does not recognize the processor.

       -mtune=cpu_type
           Set only the instruction scheduling parameters for machine type
           cpu_type.  The instruction set is not changed.

           Native toolchains also support the value native, which selects the
           best architecture option for the host processor.  -mtune=native has
           no effect if GCC does not recognize the processor.

       -mmemory-latency=time
           Sets the latency the scheduler should assume for typical memory
           references as seen by the application.  This number is highly
           dependent on the memory access patterns used by the application and
           the size of the external cache on the machine.

           Valid options for time are

           number
               A decimal number representing clock cycles.

           L1
           L2
           L3
           main
               The compiler contains estimates of the number of clock cycles
               for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
               (also called Dcache, Scache, and Bcache), as well as to main
               memory.  Note that L3 is only valid for EV5.

       FR30 Options

       These options are defined specifically for the FR30 port.

       -msmall-model
           Use the small address space model.  This can produce smaller code,
           but it does assume that all symbolic values and addresses fit into
           a 20-bit range.

       -mno-lsim
           Assume that runtime support has been provided and so there is no
           need to include the simulator library (libsim.a) on the linker
           command line.

       FRV Options

       -mgpr-32
           Only use the first 32 general-purpose registers.

       -mgpr-64
           Use all 64 general-purpose registers.

       -mfpr-32
           Use only the first 32 floating-point registers.

       -mfpr-64
           Use all 64 floating-point registers.

       -mhard-float
           Use hardware instructions for floating-point operations.

       -msoft-float
           Use library routines for floating-point operations.

       -malloc-cc
           Dynamically allocate condition code registers.

       -mfixed-cc
           Do not try to dynamically allocate condition code registers, only
           use "icc0" and "fcc0".

       -mdword
           Change ABI to use double word insns.

       -mno-dword
           Do not use double word instructions.

       -mdouble
           Use floating-point double instructions.

       -mno-double
           Do not use floating-point double instructions.

       -mmedia
           Use media instructions.

       -mno-media
           Do not use media instructions.

       -mmuladd
           Use multiply and add/subtract instructions.

       -mno-muladd
           Do not use multiply and add/subtract instructions.

       -mfdpic
           Select the FDPIC ABI, which uses function descriptors to represent
           pointers to functions.  Without any PIC/PIE-related options, it
           implies -fPIE.  With -fpic or -fpie, it assumes GOT entries and
           small data are within a 12-bit range from the GOT base address;
           with -fPIC or -fPIE, GOT offsets are computed with 32 bits.  With a
           bfin-elf target, this option implies -msim.

       -minline-plt
           Enable inlining of PLT entries in function calls to functions that
           are not known to bind locally.  It has no effect without -mfdpic.
           It's enabled by default if optimizing for speed and compiling for
           shared libraries (i.e., -fPIC or -fpic), or when an optimization
           option such as -O3 or above is present in the command line.

       -mTLS
           Assume a large TLS segment when generating thread-local code.

       -mtls
           Do not assume a large TLS segment when generating thread-local
           code.

       -mgprel-ro
           Enable the use of "GPREL" relocations in the FDPIC ABI for data
           that is known to be in read-only sections.  It's enabled by
           default, except for -fpic or -fpie: even though it may help make
           the global offset table smaller, it trades 1 instruction for 4.
           With -fPIC or -fPIE, it trades 3 instructions for 4, one of which
           may be shared by multiple symbols, and it avoids the need for a GOT
           entry for the referenced symbol, so it's more likely to be a win.
           If it is not, -mno-gprel-ro can be used to disable it.

       -multilib-library-pic
           Link with the (library, not FD) pic libraries.  It's implied by
           -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic.  You
           should never have to use it explicitly.

       -mlinked-fp
           Follow the EABI requirement of always creating a frame pointer
           whenever a stack frame is allocated.  This option is enabled by
           default and can be disabled with -mno-linked-fp.

       -mlong-calls
           Use indirect addressing to call functions outside the current
           compilation unit.  This allows the functions to be placed anywhere
           within the 32-bit address space.

       -malign-labels
           Try to align labels to an 8-byte boundary by inserting NOPs into
           the previous packet.  This option only has an effect when VLIW
           packing is enabled.  It doesn't create new packets; it merely adds
           NOPs to existing ones.

       -mlibrary-pic
           Generate position-independent EABI code.

       -macc-4
           Use only the first four media accumulator registers.

       -macc-8
           Use all eight media accumulator registers.

       -mpack
           Pack VLIW instructions.

       -mno-pack
           Do not pack VLIW instructions.

       -mno-eflags
           Do not mark ABI switches in e_flags.

       -mcond-move
           Enable the use of conditional-move instructions (default).

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mno-cond-move
           Disable the use of conditional-move instructions.

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mscc
           Enable the use of conditional set instructions (default).

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mno-scc
           Disable the use of conditional set instructions.

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mcond-exec
           Enable the use of conditional execution (default).

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mno-cond-exec
           Disable the use of conditional execution.

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mvliw-branch
           Run a pass to pack branches into VLIW instructions (default).

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mno-vliw-branch
           Do not run a pass to pack branches into VLIW instructions.

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mmulti-cond-exec
           Enable optimization of "&&" and "||" in conditional execution
           (default).

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mno-multi-cond-exec
           Disable optimization of "&&" and "||" in conditional execution.

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mnested-cond-exec
           Enable nested conditional execution optimizations (default).

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -mno-nested-cond-exec
           Disable nested conditional execution optimizations.

           This switch is mainly for debugging the compiler and will likely be
           removed in a future version.

       -moptimize-membar
           This switch removes redundant "membar" instructions from the
           compiler-generated code.  It is enabled by default.

       -mno-optimize-membar
           This switch disables the automatic removal of redundant "membar"
           instructions from the generated code.

       -mtomcat-stats
           Cause gas to print out tomcat statistics.

       -mcpu=cpu
           Select the processor type for which to generate code.  Possible
           values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300
           and simple.

       GNU/Linux Options

       These -m options are defined for GNU/Linux targets:

       -mglibc
           Use the GNU C library.  This is the default except on
           *-*-linux-*uclibc* and *-*-linux-*android* targets.

       -muclibc
           Use uClibc C library.  This is the default on *-*-linux-*uclibc*
           targets.

       -mbionic
           Use Bionic C library.  This is the default on *-*-linux-*android*
           targets.

       -mandroid
           Compile code compatible with Android platform.  This is the default
           on *-*-linux-*android* targets.

           When compiling, this option enables -mbionic, -fPIC,
           -fno-exceptions and -fno-rtti by default.  When linking, this
           option makes the GCC driver pass Android-specific options to the
           linker.  Finally, this option causes the preprocessor macro
           "__ANDROID__" to be defined.

       -tno-android-cc
           Disable compilation effects of -mandroid, i.e., do not enable
           -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default.

       -tno-android-ld
           Disable linking effects of -mandroid, i.e., pass standard Linux
           linking options to the linker.

       H8/300 Options

       These -m options are defined for the H8/300 implementations:

       -mrelax
           Shorten some address references at link time, when possible; uses
           the linker option -relax.

       -mh Generate code for the H8/300H.

       -ms Generate code for the H8S.

       -mn Generate code for the H8S and H8/300H in the normal mode.  This
           switch must be used either with -mh or -ms.

       -ms2600
           Generate code for the H8S/2600.  This switch must be used with -ms.

       -mexr
           Extended registers are stored on stack before execution of function
           with monitor attribute. Default option is -mexr.  This option is
           valid only for H8S targets.

       -mno-exr
           Extended registers are not stored on stack before execution of
           function with monitor attribute. Default option is -mno-exr.  This
           option is valid only for H8S targets.

       -mint32
           Make "int" data 32 bits by default.

       -malign-300
           On the H8/300H and H8S, use the same alignment rules as for the
           H8/300.  The default for the H8/300H and H8S is to align longs and
           floats on 4-byte boundaries.  -malign-300 causes them to be aligned
           on 2-byte boundaries.  This option has no effect on the H8/300.

       HPPA Options

       These -m options are defined for the HPPA family of computers:

       -march=architecture-type
           Generate code for the specified architecture.  The choices for
           architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for
           PA 2.0 processors.  Refer to /usr/lib/sched.models on an HP-UX
           system to determine the proper architecture option for your
           machine.  Code compiled for lower numbered architectures runs on
           higher numbered architectures, but not the other way around.

       -mpa-risc-1-0
       -mpa-risc-1-1
       -mpa-risc-2-0
           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.

       -mbig-switch
           Generate code suitable for big switch tables.  Use this option only
           if the assembler/linker complain about out-of-range branches within
           a switch table.

       -mjump-in-delay
           Fill delay slots of function calls with unconditional jump
           instructions by modifying the return pointer for the function call
           to be the target of the conditional jump.

       -mdisable-fpregs
           Prevent floating-point registers from being used in any manner.
           This is necessary for compiling kernels that perform lazy context
           switching of floating-point registers.  If you use this option and
           attempt to perform floating-point operations, the compiler aborts.

       -mdisable-indexing
           Prevent the compiler from using indexing address modes.  This
           avoids some rather obscure problems when compiling MIG generated
           code under MACH.

       -mno-space-regs
           Generate code that assumes the target has no space registers.  This
           allows GCC to generate faster indirect calls and use unscaled index
           address modes.

           Such code is suitable for level 0 PA systems and kernels.

       -mfast-indirect-calls
           Generate code that assumes calls never cross space boundaries.
           This allows GCC to emit code that performs faster indirect calls.

           This option does not work in the presence of shared libraries or
           nested functions.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.
           A fixed register is one that the register allocator cannot use.
           This is useful when compiling kernel code.  A register range is
           specified as two registers separated by a dash.  Multiple register
           ranges can be specified separated by a comma.

       -mlong-load-store
           Generate 3-instruction load and store sequences as sometimes
           required by the HP-UX 10 linker.  This is equivalent to the +k
           option to the HP compilers.

       -mportable-runtime
           Use the portable calling conventions proposed by HP for ELF
           systems.

       -mgas
           Enable the use of assembler directives only GAS understands.

       -mschedule=cpu-type
           Schedule code according to the constraints for the machine type
           cpu-type.  The choices for cpu-type are 700 7100, 7100LC, 7200,
           7300 and 8000.  Refer to /usr/lib/sched.models on an HP-UX system
           to determine the proper scheduling option for your machine.  The
           default scheduling is 8000.

       -mlinker-opt
           Enable the optimization pass in the HP-UX linker.  Note this makes
           symbolic debugging impossible.  It also triggers a bug in the HP-UX
           8 and HP-UX 9 linkers in which they give bogus error messages when
           linking some programs.

       -msoft-float
           Generate output containing library calls for floating point.
           Warning: the requisite libraries are not available for all HPPA
           targets.  Normally the facilities of the machine's usual C compiler
           are used, but this cannot be done directly in cross-compilation.
           You must make your own arrangements to provide suitable library
           functions for cross-compilation.

           -msoft-float changes the calling convention in the output file;
           therefore, it is only useful if you compile all of a program with
           this option.  In particular, you need to compile libgcc.a, the
           library that comes with GCC, with -msoft-float in order for this to
           work.

       -msio
           Generate the predefine, "_SIO", for server IO.  The default is
           -mwsio.  This generates the predefines, "__hp9000s700",
           "__hp9000s700__" and "_WSIO", for workstation IO.  These options
           are available under HP-UX and HI-UX.

       -mgnu-ld
           Use options specific to GNU ld.  This passes -shared to ld when
           building a shared library.  It is the default when GCC is
           configured, explicitly or implicitly, with the GNU linker.  This
           option does not affect which ld is called; it only changes what
           parameters are passed to that ld.  The ld that is called is
           determined by the --with-ld configure option, GCC's program search
           path, and finally by the user's PATH.  The linker used by GCC can
           be printed using which `gcc -print-prog-name=ld`.  This option is
           only available on the 64-bit HP-UX GCC, i.e. configured with
           hppa*64*-*-hpux*.

       -mhp-ld
           Use options specific to HP ld.  This passes -b to ld when building
           a shared library and passes +Accept TypeMismatch to ld on all
           links.  It is the default when GCC is configured, explicitly or
           implicitly, with the HP linker.  This option does not affect which
           ld is called; it only changes what parameters are passed to that
           ld.  The ld that is called is determined by the --with-ld configure
           option, GCC's program search path, and finally by the user's PATH.
           The linker used by GCC can be printed using which `gcc
           -print-prog-name=ld`.  This option is only available on the 64-bit
           HP-UX GCC, i.e. configured with hppa*64*-*-hpux*.

       -mlong-calls
           Generate code that uses long call sequences.  This ensures that a
           call is always able to reach linker generated stubs.  The default
           is to generate long calls only when the distance from the call site
           to the beginning of the function or translation unit, as the case
           may be, exceeds a predefined limit set by the branch type being
           used.  The limits for normal calls are 7,600,000 and 240,000 bytes,
           respectively for the PA 2.0 and PA 1.X architectures.  Sibcalls are
           always limited at 240,000 bytes.

           Distances are measured from the beginning of functions when using
           the -ffunction-sections option, or when using the -mgas and
           -mno-portable-runtime options together under HP-UX with the SOM
           linker.

           It is normally not desirable to use this option as it degrades
           performance.  However, it may be useful in large applications,
           particularly when partial linking is used to build the application.

           The types of long calls used depends on the capabilities of the
           assembler and linker, and the type of code being generated.  The
           impact on systems that support long absolute calls, and long pic
           symbol-difference or pc-relative calls should be relatively small.
           However, an indirect call is used on 32-bit ELF systems in pic code
           and it is quite long.

       -munix=unix-std
           Generate compiler predefines and select a startfile for the
           specified UNIX standard.  The choices for unix-std are 93, 95 and
           98.  93 is supported on all HP-UX versions.  95 is available on HP-
           UX 10.10 and later.  98 is available on HP-UX 11.11 and later.  The
           default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to
           11.00, and 98 for HP-UX 11.11 and later.

           -munix=93 provides the same predefines as GCC 3.3 and 3.4.
           -munix=95 provides additional predefines for "XOPEN_UNIX" and
           "_XOPEN_SOURCE_EXTENDED", and the startfile unix95.o.  -munix=98
           provides additional predefines for "_XOPEN_UNIX",
           "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and
           "_INCLUDE_XOPEN_SOURCE_500", and the startfile unix98.o.

           It is important to note that this option changes the interfaces for
           various library routines.  It also affects the operational behavior
           of the C library.  Thus, extreme care is needed in using this
           option.

           Library code that is intended to operate with more than one UNIX
           standard must test, set and restore the variable
           __xpg4_extended_mask as appropriate.  Most GNU software doesn't
           provide this capability.

       -nolibdld
           Suppress the generation of link options to search libdld.sl when
           the -static option is specified on HP-UX 10 and later.

       -static
           The HP-UX implementation of setlocale in libc has a dependency on
           libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
           when the -static option is specified, special link options are
           needed to resolve this dependency.

           On HP-UX 10 and later, the GCC driver adds the necessary options to
           link with libdld.sl when the -static option is specified.  This
           causes the resulting binary to be dynamic.  On the 64-bit port, the
           linkers generate dynamic binaries by default in any case.  The
           -nolibdld option can be used to prevent the GCC driver from adding
           these link options.

       -threads
           Add support for multithreading with the dce thread library under
           HP-UX.  This option sets flags for both the preprocessor and
           linker.

       Intel 386 and AMD x86-64 Options

       These -m options are defined for the i386 and x86-64 family of
       computers:

       -march=cpu-type
           Generate instructions for the machine type cpu-type.  In contrast
           to -mtune=cpu-type, which merely tunes the generated code for the
           specified cpu-type, -march=cpu-type allows GCC to generate code
           that may not run at all on processors other than the one indicated.
           Specifying -march=cpu-type implies -mtune=cpu-type.

           The choices for cpu-type are:

           native
               This selects the CPU to generate code for at compilation time
               by determining the processor type of the compiling machine.
               Using -march=native enables all instruction subsets supported
               by the local machine (hence the result might not run on
               different machines).  Using -mtune=native produces code
               optimized for the local machine under the constraints of the
               selected instruction set.

           i386
               Original Intel i386 CPU.

           i486
               Intel i486 CPU.  (No scheduling is implemented for this chip.)

           i586
           pentium
               Intel Pentium CPU with no MMX support.

           pentium-mmx
               Intel Pentium MMX CPU, based on Pentium core with MMX
               instruction set support.

           pentiumpro
               Intel Pentium Pro CPU.

           i686
               When used with -march, the Pentium Pro instruction set is used,
               so the code runs on all i686 family chips.  When used with
               -mtune, it has the same meaning as generic.

           pentium2
               Intel Pentium II CPU, based on Pentium Pro core with MMX
               instruction set support.

           pentium3
           pentium3m
               Intel Pentium III CPU, based on Pentium Pro core with MMX and
               SSE instruction set support.

           pentium-m
               Intel Pentium M; low-power version of Intel Pentium III CPU
               with MMX, SSE and SSE2 instruction set support.  Used by
               Centrino notebooks.

           pentium4
           pentium4m
               Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set
               support.

           prescott
               Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and
               SSE3 instruction set support.

           nocona
               Improved version of Intel Pentium 4 CPU with 64-bit extensions,
               MMX, SSE, SSE2 and SSE3 instruction set support.

           core2
               Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
               and SSSE3 instruction set support.

           corei7
               Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
               SSSE3, SSE4.1 and SSE4.2 instruction set support.

           corei7-avx
               Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
               SSSE3, SSE4.1, SSE4.2, AVX, AES and PCLMUL instruction set
               support.

           core-avx-i
               Intel Core CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3,
               SSSE3, SSE4.1, SSE4.2, AVX, AES, PCLMUL, FSGSBASE, RDRND and
               F16C instruction set support.

           core-avx2
               Intel Core CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2,
               SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2, AES, PCLMUL, FSGSBASE,
               RDRND, FMA, BMI, BMI2 and F16C instruction set support.

           atom
               Intel Atom CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2,
               SSE3 and SSSE3 instruction set support.

           k6  AMD K6 CPU with MMX instruction set support.

           k6-2
           k6-3
               Improved versions of AMD K6 CPU with MMX and 3DNow! instruction
               set support.

           athlon
           athlon-tbird
               AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE
               prefetch instructions support.

           athlon-4
           athlon-xp
           athlon-mp
               Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and
               full SSE instruction set support.

           k8
           opteron
           athlon64
           athlon-fx
               Processors based on the AMD K8 core with x86-64 instruction set
               support, including the AMD Opteron, Athlon 64, and Athlon 64 FX
               processors.  (This supersets MMX, SSE, SSE2, 3DNow!, enhanced
               3DNow! and 64-bit instruction set extensions.)

           k8-sse3
           opteron-sse3
           athlon64-sse3
               Improved versions of AMD K8 cores with SSE3 instruction set
               support.

           amdfam10
           barcelona
               CPUs based on AMD Family 10h cores with x86-64 instruction set
               support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!,
               enhanced 3DNow!, ABM and 64-bit instruction set extensions.)

           bdver1
               CPUs based on AMD Family 15h cores with x86-64 instruction set
               support.  (This supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL,
               CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM
               and 64-bit instruction set extensions.)

           bdver2
               AMD Family 15h core based CPUs with x86-64 instruction set
               support.  (This supersets BMI, TBM, F16C, FMA, AVX, XOP, LWP,
               AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
               SSE4.2, ABM and 64-bit instruction set extensions.)

           bdver3
               AMD Family 15h core based CPUs with x86-64 instruction set
               support.  (This supersets BMI, TBM, F16C, FMA, AVX, XOP, LWP,
               AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
               SSE4.2, ABM and 64-bit instruction set extensions.

           btver1
               CPUs based on AMD Family 14h cores with x86-64 instruction set
               support.  (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A,
               CX16, ABM and 64-bit instruction set extensions.)

           btver2
               CPUs based on AMD Family 16h cores with x86-64 instruction set
               support. This includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES,
               SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX
               and 64-bit instruction set extensions.

           winchip-c6
               IDT WinChip C6 CPU, dealt in same way as i486 with additional
               MMX instruction set support.

           winchip2
               IDT WinChip 2 CPU, dealt in same way as i486 with additional
               MMX and 3DNow!  instruction set support.

           c3  VIA C3 CPU with MMX and 3DNow! instruction set support.  (No
               scheduling is implemented for this chip.)

           c3-2
               VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set
               support.  (No scheduling is implemented for this chip.)

           geode
               AMD Geode embedded processor with MMX and 3DNow! instruction
               set support.

       -mtune=cpu-type
           Tune to cpu-type everything applicable about the generated code,
           except for the ABI and the set of available instructions.  While
           picking a specific cpu-type schedules things appropriately for that
           particular chip, the compiler does not generate any code that
           cannot run on the default machine type unless you use a -march=cpu-
           type option.  For example, if GCC is configured for
           i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned
           for Pentium 4 but still runs on i686 machines.

           The choices for cpu-type are the same as for -march.  In addition,
           -mtune supports an extra choice for cpu-type:

           generic
               Produce code optimized for the most common IA32/AMD64/EM64T
               processors.  If you know the CPU on which your code will run,
               then you should use the corresponding -mtune or -march option
               instead of -mtune=generic.  But, if you do not know exactly
               what CPU users of your application will have, then you should
               use this option.

               As new processors are deployed in the marketplace, the behavior
               of this option will change.  Therefore, if you upgrade to a
               newer version of GCC, code generation controlled by this option
               will change to reflect the processors that are most common at
               the time that version of GCC is released.

               There is no -march=generic option because -march indicates the
               instruction set the compiler can use, and there is no generic
               instruction set applicable to all processors.  In contrast,
               -mtune indicates the processor (or, in this case, collection of
               processors) for which the code is optimized.

       -mcpu=cpu-type
           A deprecated synonym for -mtune.

       -mfpmath=unit
           Generate floating-point arithmetic for selected unit unit.  The
           choices for unit are:

           387 Use the standard 387 floating-point coprocessor present on the
               majority of chips and emulated otherwise.  Code compiled with
               this option runs almost everywhere.  The temporary results are
               computed in 80-bit precision instead of the precision specified
               by the type, resulting in slightly different results compared
               to most of other chips.  See -ffloat-store for more detailed
               description.

               This is the default choice for i386 compiler.

           sse Use scalar floating-point instructions present in the SSE
               instruction set.  This instruction set is supported by Pentium
               III and newer chips, and in the AMD line by Athlon-4, Athlon XP
               and Athlon MP chips.  The earlier version of the SSE
               instruction set supports only single-precision arithmetic, thus
               the double and extended-precision arithmetic are still done
               using 387.  A later version, present only in Pentium 4 and AMD
               x86-64 chips, supports double-precision arithmetic too.

               For the i386 compiler, you must use -march=cpu-type, -msse or
               -msse2 switches to enable SSE extensions and make this option
               effective.  For the x86-64 compiler, these extensions are
               enabled by default.

               The resulting code should be considerably faster in the
               majority of cases and avoid the numerical instability problems
               of 387 code, but may break some existing code that expects
               temporaries to be 80 bits.

               This is the default choice for the x86-64 compiler.

           sse,387
           sse+387
           both
               Attempt to utilize both instruction sets at once.  This
               effectively doubles the amount of available registers, and on
               chips with separate execution units for 387 and SSE the
               execution resources too.  Use this option with care, as it is
               still experimental, because the GCC register allocator does not
               model separate functional units well, resulting in unstable
               performance.

       -masm=dialect
           Output assembly instructions using selected dialect.  Supported
           choices are intel or att (the default).  Darwin does not support
           intel.

       -mieee-fp
       -mno-ieee-fp
           Control whether or not the compiler uses IEEE floating-point
           comparisons.  These correctly handle the case where the result of a
           comparison is unordered.

       -msoft-float
           Generate output containing library calls for floating point.

           Warning: the requisite libraries are not part of GCC.  Normally the
           facilities of the machine's usual C compiler are used, but this
           can't be done directly in cross-compilation.  You must make your
           own arrangements to provide suitable library functions for cross-
           compilation.

           On machines where a function returns floating-point results in the
           80387 register stack, some floating-point opcodes may be emitted
           even if -msoft-float is used.

       -mno-fp-ret-in-387
           Do not use the FPU registers for return values of functions.

           The usual calling convention has functions return values of types
           "float" and "double" in an FPU register, even if there is no FPU.
           The idea is that the operating system should emulate an FPU.

           The option -mno-fp-ret-in-387 causes such values to be returned in
           ordinary CPU registers instead.

       -mno-fancy-math-387
           Some 387 emulators do not support the "sin", "cos" and "sqrt"
           instructions for the 387.  Specify this option to avoid generating
           those instructions.  This option is the default on FreeBSD, OpenBSD
           and NetBSD.  This option is overridden when -march indicates that
           the target CPU always has an FPU and so the instruction does not
           need emulation.  These instructions are not generated unless you
           also use the -funsafe-math-optimizations switch.

       -malign-double
       -mno-align-double
           Control whether GCC aligns "double", "long double", and "long long"
           variables on a two-word boundary or a one-word boundary.  Aligning
           "double" variables on a two-word boundary produces code that runs
           somewhat faster on a Pentium at the expense of more memory.

           On x86-64, -malign-double is enabled by default.

           Warning: if you use the -malign-double switch, structures
           containing the above types are aligned differently than the
           published application binary interface specifications for the 386
           and are not binary compatible with structures in code compiled
           without that switch.

       -m96bit-long-double
       -m128bit-long-double
           These switches control the size of "long double" type.  The i386
           application binary interface specifies the size to be 96 bits, so
           -m96bit-long-double is the default in 32-bit mode.

           Modern architectures (Pentium and newer) prefer "long double" to be
           aligned to an 8- or 16-byte boundary.  In arrays or structures
           conforming to the ABI, this is not possible.  So specifying
           -m128bit-long-double aligns "long double" to a 16-byte boundary by
           padding the "long double" with an additional 32-bit zero.

           In the x86-64 compiler, -m128bit-long-double is the default choice
           as its ABI specifies that "long double" is aligned on 16-byte
           boundary.

           Notice that neither of these options enable any extra precision
           over the x87 standard of 80 bits for a "long double".

           Warning: if you override the default value for your target ABI,
           this changes the size of structures and arrays containing "long
           double" variables, as well as modifying the function calling
           convention for functions taking "long double".  Hence they are not
           binary-compatible with code compiled without that switch.

       -mlong-double-64
       -mlong-double-80
           These switches control the size of "long double" type. A size of 64
           bits makes the "long double" type equivalent to the "double" type.
           This is the default for Bionic C library.

           Warning: if you override the default value for your target ABI,
           this changes the size of structures and arrays containing "long
           double" variables, as well as modifying the function calling
           convention for functions taking "long double".  Hence they are not
           binary-compatible with code compiled without that switch.

       -mlarge-data-threshold=threshold
           When -mcmodel=medium is specified, data objects larger than
           threshold are placed in the large data section.  This value must be
           the same across all objects linked into the binary, and defaults to
           65535.

       -mrtd
           Use a different function-calling convention, in which functions
           that take a fixed number of arguments return with the "ret num"
           instruction, which pops their arguments while returning.  This
           saves one instruction in the caller since there is no need to pop
           the arguments there.

           You can specify that an individual function is called with this
           calling sequence with the function attribute stdcall.  You can also
           override the -mrtd option by using the function attribute cdecl.

           Warning: this calling convention is incompatible with the one
           normally used on Unix, so you cannot use it if you need to call
           libraries compiled with the Unix compiler.

           Also, you must provide function prototypes for all functions that
           take variable numbers of arguments (including "printf"); otherwise
           incorrect code is generated for calls to those functions.

           In addition, seriously incorrect code results if you call a
           function with too many arguments.  (Normally, extra arguments are
           harmlessly ignored.)

       -mregparm=num
           Control how many registers are used to pass integer arguments.  By
           default, no registers are used to pass arguments, and at most 3
           registers can be used.  You can control this behavior for a
           specific function by using the function attribute regparm.

           Warning: if you use this switch, and num is nonzero, then you must
           build all modules with the same value, including any libraries.
           This includes the system libraries and startup modules.

       -msseregparm
           Use SSE register passing conventions for float and double arguments
           and return values.  You can control this behavior for a specific
           function by using the function attribute sseregparm.

           Warning: if you use this switch then you must build all modules
           with the same value, including any libraries.  This includes the
           system libraries and startup modules.

       -mvect8-ret-in-mem
           Return 8-byte vectors in memory instead of MMX registers.  This is
           the default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of
           the Sun Studio compilers until version 12.  Later compiler versions
           (starting with Studio 12 Update@tie{}1) follow the ABI used by
           other x86 targets, which is the default on Solaris@tie{}10 and
           later.  Only use this option if you need to remain compatible with
           existing code produced by those previous compiler versions or older
           versions of GCC.

       -mpc32
       -mpc64
       -mpc80
           Set 80387 floating-point precision to 32, 64 or 80 bits.  When
           -mpc32 is specified, the significands of results of floating-point
           operations are rounded to 24 bits (single precision); -mpc64 rounds
           the significands of results of floating-point operations to 53 bits
           (double precision) and -mpc80 rounds the significands of results of
           floating-point operations to 64 bits (extended double precision),
           which is the default.  When this option is used, floating-point
           operations in higher precisions are not available to the programmer
           without setting the FPU control word explicitly.

           Setting the rounding of floating-point operations to less than the
           default 80 bits can speed some programs by 2% or more.  Note that
           some mathematical libraries assume that extended-precision (80-bit)
           floating-point operations are enabled by default; routines in such
           libraries could suffer significant loss of accuracy, typically
           through so-called "catastrophic cancellation", when this option is
           used to set the precision to less than extended precision.

       -mstackrealign
           Realign the stack at entry.  On the Intel x86, the -mstackrealign
           option generates an alternate prologue and epilogue that realigns
           the run-time stack if necessary.  This supports mixing legacy codes
           that keep 4-byte stack alignment with modern codes that keep
           16-byte stack alignment for SSE compatibility.  See also the
           attribute "force_align_arg_pointer", applicable to individual
           functions.

       -mpreferred-stack-boundary=num
           Attempt to keep the stack boundary aligned to a 2 raised to num
           byte boundary.  If -mpreferred-stack-boundary is not specified, the
           default is 4 (16 bytes or 128 bits).

           Warning: When generating code for the x86-64 architecture with SSE
           extensions disabled, -mpreferred-stack-boundary=3 can be used to
           keep the stack boundary aligned to 8 byte boundary.  Since x86-64
           ABI require 16 byte stack alignment, this is ABI incompatible and
           intended to be used in controlled environment where stack space is
           important limitation.  This option will lead to wrong code when
           functions compiled with 16 byte stack alignment (such as functions
           from a standard library) are called with misaligned stack.  In this
           case, SSE instructions may lead to misaligned memory access traps.
           In addition, variable arguments will be handled incorrectly for 16
           byte aligned objects (including x87 long double and __int128),
           leading to wrong results.  You must build all modules with
           -mpreferred-stack-boundary=3, including any libraries.  This
           includes the system libraries and startup modules.

       -mincoming-stack-boundary=num
           Assume the incoming stack is aligned to a 2 raised to num byte
           boundary.  If -mincoming-stack-boundary is not specified, the one
           specified by -mpreferred-stack-boundary is used.

           On Pentium and Pentium Pro, "double" and "long double" values
           should be aligned to an 8-byte boundary (see -malign-double) or
           suffer significant run time performance penalties.  On Pentium III,
           the Streaming SIMD Extension (SSE) data type "__m128" may not work
           properly if it is not 16-byte aligned.

           To ensure proper alignment of this values on the stack, the stack
           boundary must be as aligned as that required by any value stored on
           the stack.  Further, every function must be generated such that it
           keeps the stack aligned.  Thus calling a function compiled with a
           higher preferred stack boundary from a function compiled with a
           lower preferred stack boundary most likely misaligns the stack.  It
           is recommended that libraries that use callbacks always use the
           default setting.

           This extra alignment does consume extra stack space, and generally
           increases code size.  Code that is sensitive to stack space usage,
           such as embedded systems and operating system kernels, may want to
           reduce the preferred alignment to -mpreferred-stack-boundary=2.

       -mmmx
       -mno-mmx
       -msse
       -mno-sse
       -msse2
       -mno-sse2
       -msse3
       -mno-sse3
       -mssse3
       -mno-ssse3
       -msse4.1
       -mno-sse4.1
       -msse4.2
       -mno-sse4.2
       -msse4
       -mno-sse4
       -mavx
       -mno-avx
       -mavx2
       -mno-avx2
       -maes
       -mno-aes
       -mpclmul
       -mno-pclmul
       -mfsgsbase
       -mno-fsgsbase
       -mrdrnd
       -mno-rdrnd
       -mf16c
       -mno-f16c
       -mfma
       -mno-fma
       -msse4a
       -mno-sse4a
       -mfma4
       -mno-fma4
       -mxop
       -mno-xop
       -mlwp
       -mno-lwp
       -m3dnow
       -mno-3dnow
       -mpopcnt
       -mno-popcnt
       -mabm
       -mno-abm
       -mbmi
       -mbmi2
       -mno-bmi
       -mno-bmi2
       -mlzcnt
       -mno-lzcnt
       -mrtm
       -mtbm
       -mno-tbm
           These switches enable or disable the use of instructions in the
           MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AES, PCLMUL,
           FSGSBASE, RDRND, F16C, FMA, SSE4A, FMA4, XOP, LWP, ABM, BMI, BMI2,
           LZCNT, RTM or 3DNow!  extended instruction sets.  These extensions
           are also available as built-in functions: see X86 Built-in
           Functions, for details of the functions enabled and disabled by
           these switches.

           To generate SSE/SSE2 instructions automatically from floating-point
           code (as opposed to 387 instructions), see -mfpmath=sse.

           GCC depresses SSEx instructions when -mavx is used. Instead, it
           generates new AVX instructions or AVX equivalence for all SSEx
           instructions when needed.

           These options enable GCC to use these extended instructions in
           generated code, even without -mfpmath=sse.  Applications that
           perform run-time CPU detection must compile separate files for each
           supported architecture, using the appropriate flags.  In
           particular, the file containing the CPU detection code should be
           compiled without these options.

       -mcld
           This option instructs GCC to emit a "cld" instruction in the
           prologue of functions that use string instructions.  String
           instructions depend on the DF flag to select between autoincrement
           or autodecrement mode.  While the ABI specifies the DF flag to be
           cleared on function entry, some operating systems violate this
           specification by not clearing the DF flag in their exception
           dispatchers.  The exception handler can be invoked with the DF flag
           set, which leads to wrong direction mode when string instructions
           are used.  This option can be enabled by default on 32-bit x86
           targets by configuring GCC with the --enable-cld configure option.
           Generation of "cld" instructions can be suppressed with the
           -mno-cld compiler option in this case.

       -mvzeroupper
           This option instructs GCC to emit a "vzeroupper" instruction before
           a transfer of control flow out of the function to minimize the AVX
           to SSE transition penalty as well as remove unnecessary "zeroupper"
           intrinsics.

       -mprefer-avx128
           This option instructs GCC to use 128-bit AVX instructions instead
           of 256-bit AVX instructions in the auto-vectorizer.

       -mcx16
           This option enables GCC to generate "CMPXCHG16B" instructions.
           "CMPXCHG16B" allows for atomic operations on 128-bit double
           quadword (or oword) data types.  This is useful for high-resolution
           counters that can be updated by multiple processors (or cores).
           This instruction is generated as part of atomic built-in functions:
           see __sync Builtins or __atomic Builtins for details.

       -msahf
           This option enables generation of "SAHF" instructions in 64-bit
           code.  Early Intel Pentium 4 CPUs with Intel 64 support, prior to
           the introduction of Pentium 4 G1 step in December 2005, lacked the
           "LAHF" and "SAHF" instructions which were supported by AMD64.
           These are load and store instructions, respectively, for certain
           status flags.  In 64-bit mode, the "SAHF" instruction is used to
           optimize "fmod", "drem", and "remainder" built-in functions; see
           Other Builtins for details.

       -mmovbe
           This option enables use of the "movbe" instruction to implement
           "__builtin_bswap32" and "__builtin_bswap64".

       -mcrc32
           This option enables built-in functions "__builtin_ia32_crc32qi",
           "__builtin_ia32_crc32hi", "__builtin_ia32_crc32si" and
           "__builtin_ia32_crc32di" to generate the "crc32" machine
           instruction.

       -mrecip
           This option enables use of "RCPSS" and "RSQRTSS" instructions (and
           their vectorized variants "RCPPS" and "RSQRTPS") with an additional
           Newton-Raphson step to increase precision instead of "DIVSS" and
           "SQRTSS" (and their vectorized variants) for single-precision
           floating-point arguments.  These instructions are generated only
           when -funsafe-math-optimizations is enabled together with
           -finite-math-only and -fno-trapping-math.  Note that while the
           throughput of the sequence is higher than the throughput of the
           non-reciprocal instruction, the precision of the sequence can be
           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
           0.99999994).

           Note that GCC implements "1.0f/sqrtf(x)" in terms of "RSQRTSS" (or
           "RSQRTPS") already with -ffast-math (or the above option
           combination), and doesn't need -mrecip.

           Also note that GCC emits the above sequence with additional Newton-
           Raphson step for vectorized single-float division and vectorized
           "sqrtf(x)" already with -ffast-math (or the above option
           combination), and doesn't need -mrecip.

       -mrecip=opt
           This option controls which reciprocal estimate instructions may be
           used.  opt is a comma-separated list of options, which may be
           preceded by a ! to invert the option:

           all Enable all estimate instructions.

           default
               Enable the default instructions, equivalent to -mrecip.

           none
               Disable all estimate instructions, equivalent to -mno-recip.

           div Enable the approximation for scalar division.

           vec-div
               Enable the approximation for vectorized division.

           sqrt
               Enable the approximation for scalar square root.

           vec-sqrt
               Enable the approximation for vectorized square root.

           So, for example, -mrecip=all,!sqrt enables all of the reciprocal
           approximations, except for square root.

       -mveclibabi=type
           Specifies the ABI type to use for vectorizing intrinsics using an
           external library.  Supported values for type are svml for the Intel
           short vector math library and acml for the AMD math core library.
           To use this option, both -ftree-vectorize and
           -funsafe-math-optimizations have to be enabled, and an SVML or ACML
           ABI-compatible library must be specified at link time.

           GCC currently emits calls to "vmldExp2", "vmldLn2", "vmldLog102",
           "vmldLog102", "vmldPow2", "vmldTanh2", "vmldTan2", "vmldAtan2",
           "vmldAtanh2", "vmldCbrt2", "vmldSinh2", "vmldSin2", "vmldAsinh2",
           "vmldAsin2", "vmldCosh2", "vmldCos2", "vmldAcosh2", "vmldAcos2",
           "vmlsExp4", "vmlsLn4", "vmlsLog104", "vmlsLog104", "vmlsPow4",
           "vmlsTanh4", "vmlsTan4", "vmlsAtan4", "vmlsAtanh4", "vmlsCbrt4",
           "vmlsSinh4", "vmlsSin4", "vmlsAsinh4", "vmlsAsin4", "vmlsCosh4",
           "vmlsCos4", "vmlsAcosh4" and "vmlsAcos4" for corresponding function
           type when -mveclibabi=svml is used, and "__vrd2_sin", "__vrd2_cos",
           "__vrd2_exp", "__vrd2_log", "__vrd2_log2", "__vrd2_log10",
           "__vrs4_sinf", "__vrs4_cosf", "__vrs4_expf", "__vrs4_logf",
           "__vrs4_log2f", "__vrs4_log10f" and "__vrs4_powf" for the
           corresponding function type when -mveclibabi=acml is used.

       -mabi=name
           Generate code for the specified calling convention.  Permissible
           values are sysv for the ABI used on GNU/Linux and other systems,
           and ms for the Microsoft ABI.  The default is to use the Microsoft
           ABI when targeting Microsoft Windows and the SysV ABI on all other
           systems.  You can control this behavior for a specific function by
           using the function attribute ms_abi/sysv_abi.

       -mtls-dialect=type
           Generate code to access thread-local storage using the gnu or gnu2
           conventions.  gnu is the conservative default; gnu2 is more
           efficient, but it may add compile- and run-time requirements that
           cannot be satisfied on all systems.

       -mpush-args
       -mno-push-args
           Use PUSH operations to store outgoing parameters.  This method is
           shorter and usually equally fast as method using SUB/MOV operations
           and is enabled by default.  In some cases disabling it may improve
           performance because of improved scheduling and reduced
           dependencies.

       -maccumulate-outgoing-args
           If enabled, the maximum amount of space required for outgoing
           arguments is computed in the function prologue.  This is faster on
           most modern CPUs because of reduced dependencies, improved
           scheduling and reduced stack usage when the preferred stack
           boundary is not equal to 2.  The drawback is a notable increase in
           code size.  This switch implies -mno-push-args.

       -mthreads
           Support thread-safe exception handling on MinGW.  Programs that
           rely on thread-safe exception handling must compile and link all
           code with the -mthreads option.  When compiling, -mthreads defines
           "-D_MT"; when linking, it links in a special thread helper library
           -lmingwthrd which cleans up per-thread exception-handling data.

       -mno-align-stringops
           Do not align the destination of inlined string operations.  This
           switch reduces code size and improves performance in case the
           destination is already aligned, but GCC doesn't know about it.

       -minline-all-stringops
           By default GCC inlines string operations only when the destination
           is known to be aligned to least a 4-byte boundary.  This enables
           more inlining and increases code size, but may improve performance
           of code that depends on fast "memcpy", "strlen", and "memset" for
           short lengths.

       -minline-stringops-dynamically
           For string operations of unknown size, use run-time checks with
           inline code for small blocks and a library call for large blocks.

       -mstringop-strategy=alg
           Override the internal decision heuristic for the particular
           algorithm to use for inlining string operations.  The allowed
           values for alg are:

           rep_byte
           rep_4byte
           rep_8byte
               Expand using i386 "rep" prefix of the specified size.

           byte_loop
           loop
           unrolled_loop
               Expand into an inline loop.

           libcall
               Always use a library call.

       -momit-leaf-frame-pointer
           Don't keep the frame pointer in a register for leaf functions.
           This avoids the instructions to save, set up, and restore frame
           pointers and makes an extra register available in leaf functions.
           The option -fomit-leaf-frame-pointer removes the frame pointer for
           leaf functions, which might make debugging harder.

       -mtls-direct-seg-refs
       -mno-tls-direct-seg-refs
           Controls whether TLS variables may be accessed with offsets from
           the TLS segment register (%gs for 32-bit, %fs for 64-bit), or
           whether the thread base pointer must be added.  Whether or not this
           is valid depends on the operating system, and whether it maps the
           segment to cover the entire TLS area.

           For systems that use the GNU C Library, the default is on.

       -msse2avx
       -mno-sse2avx
           Specify that the assembler should encode SSE instructions with VEX
           prefix.  The option -mavx turns this on by default.

       -mfentry
       -mno-fentry
           If profiling is active (-pg), put the profiling counter call before
           the prologue.  Note: On x86 architectures the attribute
           "ms_hook_prologue" isn't possible at the moment for -mfentry and
           -pg.

       -m8bit-idiv
       -mno-8bit-idiv
           On some processors, like Intel Atom, 8-bit unsigned integer divide
           is much faster than 32-bit/64-bit integer divide.  This option
           generates a run-time check.  If both dividend and divisor are
           within range of 0 to 255, 8-bit unsigned integer divide is used
           instead of 32-bit/64-bit integer divide.

       -mavx256-split-unaligned-load
       -mavx256-split-unaligned-store
           Split 32-byte AVX unaligned load and store.

       These -m switches are supported in addition to the above on x86-64
       processors in 64-bit environments.

       -m32
       -m64
       -mx32
           Generate code for a 32-bit or 64-bit environment.  The -m32 option
           sets "int", "long", and pointer types to 32 bits, and generates
           code that runs on any i386 system.

           The -m64 option sets "int" to 32 bits and "long" and pointer types
           to 64 bits, and generates code for the x86-64 architecture.  For
           Darwin only the -m64 option also turns off the -fno-pic and
           -mdynamic-no-pic options.

           The -mx32 option sets "int", "long", and pointer types to 32 bits,
           and generates code for the x86-64 architecture.

       -mno-red-zone
           Do not use a so-called "red zone" for x86-64 code.  The red zone is
           mandated by the x86-64 ABI; it is a 128-byte area beyond the
           location of the stack pointer that is not modified by signal or
           interrupt handlers and therefore can be used for temporary data
           without adjusting the stack pointer.  The flag -mno-red-zone
           disables this red zone.

       -mcmodel=small
           Generate code for the small code model: the program and its symbols
           must be linked in the lower 2 GB of the address space.  Pointers
           are 64 bits.  Programs can be statically or dynamically linked.
           This is the default code model.

       -mcmodel=kernel
           Generate code for the kernel code model.  The kernel runs in the
           negative 2 GB of the address space.  This model has to be used for
           Linux kernel code.

       -mcmodel=medium
           Generate code for the medium model: the program is linked in the
           lower 2 GB of the address space.  Small symbols are also placed
           there.  Symbols with sizes larger than -mlarge-data-threshold are
           put into large data or BSS sections and can be located above 2GB.
           Programs can be statically or dynamically linked.

       -mcmodel=large
           Generate code for the large model.  This model makes no assumptions
           about addresses and sizes of sections.

       -maddress-mode=long
           Generate code for long address mode.  This is only supported for
           64-bit and x32 environments.  It is the default address mode for
           64-bit environments.

       -maddress-mode=short
           Generate code for short address mode.  This is only supported for
           32-bit and x32 environments.  It is the default address mode for
           32-bit and x32 environments.

       i386 and x86-64 Windows Options

       These additional options are available for Microsoft Windows targets:

       -mconsole
           This option specifies that a console application is to be
           generated, by instructing the linker to set the PE header subsystem
           type required for console applications.  This option is available
           for Cygwin and MinGW targets and is enabled by default on those
           targets.

       -mdll
           This option is available for Cygwin and MinGW targets.  It
           specifies that a DLL---a dynamic link library---is to be generated,
           enabling the selection of the required runtime startup object and
           entry point.

       -mnop-fun-dllimport
           This option is available for Cygwin and MinGW targets.  It
           specifies that the "dllimport" attribute should be ignored.

       -mthread
           This option is available for MinGW targets. It specifies that
           MinGW-specific thread support is to be used.

       -municode
           This option is available for MinGW-w64 targets.  It causes the
           "UNICODE" preprocessor macro to be predefined, and chooses Unicode-
           capable runtime startup code.

       -mwin32
           This option is available for Cygwin and MinGW targets.  It
           specifies that the typical Microsoft Windows predefined macros are
           to be set in the pre-processor, but does not influence the choice
           of runtime library/startup code.

       -mwindows
           This option is available for Cygwin and MinGW targets.  It
           specifies that a GUI application is to be generated by instructing
           the linker to set the PE header subsystem type appropriately.

       -fno-set-stack-executable
           This option is available for MinGW targets. It specifies that the
           executable flag for the stack used by nested functions isn't set.
           This is necessary for binaries running in kernel mode of Microsoft
           Windows, as there the User32 API, which is used to set executable
           privileges, isn't available.

       -fwritable-relocated-rdata
           This option is available for MinGW and Cygwin targets.  It
           specifies that relocated-data in read-only section is put into
           .data section.  This is a necessary for older runtimes not
           supporting modification of .rdata sections for pseudo-relocation.

       -mpe-aligned-commons
           This option is available for Cygwin and MinGW targets.  It
           specifies that the GNU extension to the PE file format that permits
           the correct alignment of COMMON variables should be used when
           generating code.  It is enabled by default if GCC detects that the
           target assembler found during configuration supports the feature.

       See also under i386 and x86-64 Options for standard options.

       IA-64 Options

       These are the -m options defined for the Intel IA-64 architecture.

       -mbig-endian
           Generate code for a big-endian target.  This is the default for HP-
           UX.

       -mlittle-endian
           Generate code for a little-endian target.  This is the default for
           AIX5 and GNU/Linux.

       -mgnu-as
       -mno-gnu-as
           Generate (or don't) code for the GNU assembler.  This is the
           default.

       -mgnu-ld
       -mno-gnu-ld
           Generate (or don't) code for the GNU linker.  This is the default.

       -mno-pic
           Generate code that does not use a global pointer register.  The
           result is not position independent code, and violates the IA-64
           ABI.

       -mvolatile-asm-stop
       -mno-volatile-asm-stop
           Generate (or don't) a stop bit immediately before and after
           volatile asm statements.

       -mregister-names
       -mno-register-names
           Generate (or don't) in, loc, and out register names for the stacked
           registers.  This may make assembler output more readable.

       -mno-sdata
       -msdata
           Disable (or enable) optimizations that use the small data section.
           This may be useful for working around optimizer bugs.

       -mconstant-gp
           Generate code that uses a single constant global pointer value.
           This is useful when compiling kernel code.

       -mauto-pic
           Generate code that is self-relocatable.  This implies
           -mconstant-gp.  This is useful when compiling firmware code.

       -minline-float-divide-min-latency
           Generate code for inline divides of floating-point values using the
           minimum latency algorithm.

       -minline-float-divide-max-throughput
           Generate code for inline divides of floating-point values using the
           maximum throughput algorithm.

       -mno-inline-float-divide
           Do not generate inline code for divides of floating-point values.

       -minline-int-divide-min-latency
           Generate code for inline divides of integer values using the
           minimum latency algorithm.

       -minline-int-divide-max-throughput
           Generate code for inline divides of integer values using the
           maximum throughput algorithm.

       -mno-inline-int-divide
           Do not generate inline code for divides of integer values.

       -minline-sqrt-min-latency
           Generate code for inline square roots using the minimum latency
           algorithm.

       -minline-sqrt-max-throughput
           Generate code for inline square roots using the maximum throughput
           algorithm.

       -mno-inline-sqrt
           Do not generate inline code for "sqrt".

       -mfused-madd
       -mno-fused-madd
           Do (don't) generate code that uses the fused multiply/add or
           multiply/subtract instructions.  The default is to use these
           instructions.

       -mno-dwarf2-asm
       -mdwarf2-asm
           Don't (or do) generate assembler code for the DWARF 2 line number
           debugging info.  This may be useful when not using the GNU
           assembler.

       -mearly-stop-bits
       -mno-early-stop-bits
           Allow stop bits to be placed earlier than immediately preceding the
           instruction that triggered the stop bit.  This can improve
           instruction scheduling, but does not always do so.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.
           A fixed register is one that the register allocator cannot use.
           This is useful when compiling kernel code.  A register range is
           specified as two registers separated by a dash.  Multiple register
           ranges can be specified separated by a comma.

       -mtls-size=tls-size
           Specify bit size of immediate TLS offsets.  Valid values are 14,
           22, and 64.

       -mtune=cpu-type
           Tune the instruction scheduling for a particular CPU, Valid values
           are itanium, itanium1, merced, itanium2, and mckinley.

       -milp32
       -mlp64
           Generate code for a 32-bit or 64-bit environment.  The 32-bit
           environment sets int, long and pointer to 32 bits.  The 64-bit
           environment sets int to 32 bits and long and pointer to 64 bits.
           These are HP-UX specific flags.

       -mno-sched-br-data-spec
       -msched-br-data-spec
           (Dis/En)able data speculative scheduling before reload.  This
           results in generation of "ld.a" instructions and the corresponding
           check instructions ("ld.c" / "chk.a").  The default is 'disable'.

       -msched-ar-data-spec
       -mno-sched-ar-data-spec
           (En/Dis)able data speculative scheduling after reload.  This
           results in generation of "ld.a" instructions and the corresponding
           check instructions ("ld.c" / "chk.a").  The default is 'enable'.

       -mno-sched-control-spec
       -msched-control-spec
           (Dis/En)able control speculative scheduling.  This feature is
           available only during region scheduling (i.e. before reload).  This
           results in generation of the "ld.s" instructions and the
           corresponding check instructions "chk.s".  The default is
           'disable'.

       -msched-br-in-data-spec
       -mno-sched-br-in-data-spec
           (En/Dis)able speculative scheduling of the instructions that are
           dependent on the data speculative loads before reload.  This is
           effective only with -msched-br-data-spec enabled.  The default is
           'enable'.

       -msched-ar-in-data-spec
       -mno-sched-ar-in-data-spec
           (En/Dis)able speculative scheduling of the instructions that are
           dependent on the data speculative loads after reload.  This is
           effective only with -msched-ar-data-spec enabled.  The default is
           'enable'.

       -msched-in-control-spec
       -mno-sched-in-control-spec
           (En/Dis)able speculative scheduling of the instructions that are
           dependent on the control speculative loads.  This is effective only
           with -msched-control-spec enabled.  The default is 'enable'.

       -mno-sched-prefer-non-data-spec-insns
       -msched-prefer-non-data-spec-insns
           If enabled, data-speculative instructions are chosen for schedule
           only if there are no other choices at the moment.  This makes the
           use of the data speculation much more conservative.  The default is
           'disable'.

       -mno-sched-prefer-non-control-spec-insns
       -msched-prefer-non-control-spec-insns
           If enabled, control-speculative instructions are chosen for
           schedule only if there are no other choices at the moment.  This
           makes the use of the control speculation much more conservative.
           The default is 'disable'.

       -mno-sched-count-spec-in-critical-path
       -msched-count-spec-in-critical-path
           If enabled, speculative dependencies are considered during
           computation of the instructions priorities.  This makes the use of
           the speculation a bit more conservative.  The default is 'disable'.

       -msched-spec-ldc
           Use a simple data speculation check.  This option is on by default.

       -msched-control-spec-ldc
           Use a simple check for control speculation.  This option is on by
           default.

       -msched-stop-bits-after-every-cycle
           Place a stop bit after every cycle when scheduling.  This option is
           on by default.

       -msched-fp-mem-deps-zero-cost
           Assume that floating-point stores and loads are not likely to cause
           a conflict when placed into the same instruction group.  This
           option is disabled by default.

       -msel-sched-dont-check-control-spec
           Generate checks for control speculation in selective scheduling.
           This flag is disabled by default.

       -msched-max-memory-insns=max-insns
           Limit on the number of memory insns per instruction group, giving
           lower priority to subsequent memory insns attempting to schedule in
           the same instruction group. Frequently useful to prevent cache bank
           conflicts.  The default value is 1.

       -msched-max-memory-insns-hard-limit
           Makes the limit specified by msched-max-memory-insns a hard limit,
           disallowing more than that number in an instruction group.
           Otherwise, the limit is "soft", meaning that non-memory operations
           are preferred when the limit is reached, but memory operations may
           still be scheduled.

       LM32 Options

       These -m options are defined for the LatticeMico32 architecture:

       -mbarrel-shift-enabled
           Enable barrel-shift instructions.

       -mdivide-enabled
           Enable divide and modulus instructions.

       -mmultiply-enabled
           Enable multiply instructions.

       -msign-extend-enabled
           Enable sign extend instructions.

       -muser-enabled
           Enable user-defined instructions.

       M32C Options

       -mcpu=name
           Select the CPU for which code is generated.  name may be one of r8c
           for the R8C/Tiny series, m16c for the M16C (up to /60) series,
           m32cm for the M16C/80 series, or m32c for the M32C/80 series.

       -msim
           Specifies that the program will be run on the simulator.  This
           causes an alternate runtime library to be linked in which supports,
           for example, file I/O.  You must not use this option when
           generating programs that will run on real hardware; you must
           provide your own runtime library for whatever I/O functions are
           needed.

       -memregs=number
           Specifies the number of memory-based pseudo-registers GCC uses
           during code generation.  These pseudo-registers are used like real
           registers, so there is a tradeoff between GCC's ability to fit the
           code into available registers, and the performance penalty of using
           memory instead of registers.  Note that all modules in a program
           must be compiled with the same value for this option.  Because of
           that, you must not use this option with GCC's default runtime
           libraries.

       M32R/D Options

       These -m options are defined for Renesas M32R/D architectures:

       -m32r2
           Generate code for the M32R/2.

       -m32rx
           Generate code for the M32R/X.

       -m32r
           Generate code for the M32R.  This is the default.

       -mmodel=small
           Assume all objects live in the lower 16MB of memory (so that their
           addresses can be loaded with the "ld24" instruction), and assume
           all subroutines are reachable with the "bl" instruction.  This is
           the default.

           The addressability of a particular object can be set with the
           "model" attribute.

       -mmodel=medium
           Assume objects may be anywhere in the 32-bit address space (the
           compiler generates "seth/add3" instructions to load their
           addresses), and assume all subroutines are reachable with the "bl"
           instruction.

       -mmodel=large
           Assume objects may be anywhere in the 32-bit address space (the
           compiler generates "seth/add3" instructions to load their
           addresses), and assume subroutines may not be reachable with the
           "bl" instruction (the compiler generates the much slower
           "seth/add3/jl" instruction sequence).

       -msdata=none
           Disable use of the small data area.  Variables are put into one of
           .data, .bss, or .rodata (unless the "section" attribute has been
           specified).  This is the default.

           The small data area consists of sections .sdata and .sbss.  Objects
           may be explicitly put in the small data area with the "section"
           attribute using one of these sections.

       -msdata=sdata
           Put small global and static data in the small data area, but do not
           generate special code to reference them.

       -msdata=use
           Put small global and static data in the small data area, and
           generate special instructions to reference them.

       -G num
           Put global and static objects less than or equal to num bytes into
           the small data or BSS sections instead of the normal data or BSS
           sections.  The default value of num is 8.  The -msdata option must
           be set to one of sdata or use for this option to have any effect.

           All modules should be compiled with the same -G num value.
           Compiling with different values of num may or may not work; if it
           doesn't the linker gives an error message---incorrect code is not
           generated.

       -mdebug
           Makes the M32R-specific code in the compiler display some
           statistics that might help in debugging programs.

       -malign-loops
           Align all loops to a 32-byte boundary.

       -mno-align-loops
           Do not enforce a 32-byte alignment for loops.  This is the default.

       -missue-rate=number
           Issue number instructions per cycle.  number can only be 1 or 2.

       -mbranch-cost=number
           number can only be 1 or 2.  If it is 1 then branches are preferred
           over conditional code, if it is 2, then the opposite applies.

       -mflush-trap=number
           Specifies the trap number to use to flush the cache.  The default
           is 12.  Valid numbers are between 0 and 15 inclusive.

       -mno-flush-trap
           Specifies that the cache cannot be flushed by using a trap.

       -mflush-func=name
           Specifies the name of the operating system function to call to
           flush the cache.  The default is _flush_cache, but a function call
           is only used if a trap is not available.

       -mno-flush-func
           Indicates that there is no OS function for flushing the cache.

       M680x0 Options

       These are the -m options defined for M680x0 and ColdFire processors.
       The default settings depend on which architecture was selected when the
       compiler was configured; the defaults for the most common choices are
       given below.

       -march=arch
           Generate code for a specific M680x0 or ColdFire instruction set
           architecture.  Permissible values of arch for M680x0 architectures
           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  ColdFire
           architectures are selected according to Freescale's ISA
           classification and the permissible values are: isaa, isaaplus, isab
           and isac.

           GCC defines a macro __mcfarch__ whenever it is generating code for
           a ColdFire target.  The arch in this macro is one of the -march
           arguments given above.

           When used together, -march and -mtune select code that runs on a
           family of similar processors but that is optimized for a particular
           microarchitecture.

       -mcpu=cpu
           Generate code for a specific M680x0 or ColdFire processor.  The
           M680x0 cpus are: 68000, 68010, 68020, 68030, 68040, 68060, 68302,
           68332 and cpu32.  The ColdFire cpus are given by the table below,
           which also classifies the CPUs into families:

           Family : -mcpu arguments
           51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm
           5206 : 5202 5204 5206
           5206e : 5206e
           5208 : 5207 5208
           5211a : 5210a 5211a
           5213 : 5211 5212 5213
           5216 : 5214 5216
           52235 : 52230 52231 52232 52233 52234 52235
           5225 : 5224 5225
           52259 : 52252 52254 52255 52256 52258 52259
           5235 : 5232 5233 5234 5235 523x
           5249 : 5249
           5250 : 5250
           5271 : 5270 5271
           5272 : 5272
           5275 : 5274 5275
           5282 : 5280 5281 5282 528x
           53017 : 53011 53012 53013 53014 53015 53016 53017
           5307 : 5307
           5329 : 5327 5328 5329 532x
           5373 : 5372 5373 537x
           5407 : 5407
           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484
           5485

           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.
           Other combinations of -mcpu and -march are rejected.

           GCC defines the macro __mcf_cpu_cpu when ColdFire target cpu is
           selected.  It also defines __mcf_family_family, where the value of
           family is given by the table above.

       -mtune=tune
           Tune the code for a particular microarchitecture within the
           constraints set by -march and -mcpu.  The M680x0 microarchitectures
           are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32.  The
           ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.

           You can also use -mtune=68020-40 for code that needs to run
           relatively well on 68020, 68030 and 68040 targets.  -mtune=68020-60
           is similar but includes 68060 targets as well.  These two options
           select the same tuning decisions as -m68020-40 and -m68020-60
           respectively.

           GCC defines the macros __mcarch and __mcarch__ when tuning for
           680x0 architecture arch.  It also defines mcarch unless either
           -ansi or a non-GNU -std option is used.  If GCC is tuning for a
           range of architectures, as selected by -mtune=68020-40 or
           -mtune=68020-60, it defines the macros for every architecture in
           the range.

           GCC also defines the macro __muarch__ when tuning for ColdFire
           microarchitecture uarch, where uarch is one of the arguments given
           above.

       -m68000
       -mc68000
           Generate output for a 68000.  This is the default when the compiler
           is configured for 68000-based systems.  It is equivalent to
           -march=68000.

           Use this option for microcontrollers with a 68000 or EC000 core,
           including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.

       -m68010
           Generate output for a 68010.  This is the default when the compiler
           is configured for 68010-based systems.  It is equivalent to
           -march=68010.

       -m68020
       -mc68020
           Generate output for a 68020.  This is the default when the compiler
           is configured for 68020-based systems.  It is equivalent to
           -march=68020.

       -m68030
           Generate output for a 68030.  This is the default when the compiler
           is configured for 68030-based systems.  It is equivalent to
           -march=68030.

       -m68040
           Generate output for a 68040.  This is the default when the compiler
           is configured for 68040-based systems.  It is equivalent to
           -march=68040.

           This option inhibits the use of 68881/68882 instructions that have
           to be emulated by software on the 68040.  Use this option if your
           68040 does not have code to emulate those instructions.

       -m68060
           Generate output for a 68060.  This is the default when the compiler
           is configured for 68060-based systems.  It is equivalent to
           -march=68060.

           This option inhibits the use of 68020 and 68881/68882 instructions
           that have to be emulated by software on the 68060.  Use this option
           if your 68060 does not have code to emulate those instructions.

       -mcpu32
           Generate output for a CPU32.  This is the default when the compiler
           is configured for CPU32-based systems.  It is equivalent to
           -march=cpu32.

           Use this option for microcontrollers with a CPU32 or CPU32+ core,
           including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
           68341, 68349 and 68360.

       -m5200
           Generate output for a 520X ColdFire CPU.  This is the default when
           the compiler is configured for 520X-based systems.  It is
           equivalent to -mcpu=5206, and is now deprecated in favor of that
           option.

           Use this option for microcontroller with a 5200 core, including the
           MCF5202, MCF5203, MCF5204 and MCF5206.

       -m5206e
           Generate output for a 5206e ColdFire CPU.  The option is now
           deprecated in favor of the equivalent -mcpu=5206e.

       -m528x
           Generate output for a member of the ColdFire 528X family.  The
           option is now deprecated in favor of the equivalent -mcpu=528x.

       -m5307
           Generate output for a ColdFire 5307 CPU.  The option is now
           deprecated in favor of the equivalent -mcpu=5307.

       -m5407
           Generate output for a ColdFire 5407 CPU.  The option is now
           deprecated in favor of the equivalent -mcpu=5407.

       -mcfv4e
           Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
           This includes use of hardware floating-point instructions.  The
           option is equivalent to -mcpu=547x, and is now deprecated in favor
           of that option.

       -m68020-40
           Generate output for a 68040, without using any of the new
           instructions.  This results in code that can run relatively
           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
           generated code does use the 68881 instructions that are emulated on
           the 68040.

           The option is equivalent to -march=68020 -mtune=68020-40.

       -m68020-60
           Generate output for a 68060, without using any of the new
           instructions.  This results in code that can run relatively
           efficiently on either a 68020/68881 or a 68030 or a 68040.  The
           generated code does use the 68881 instructions that are emulated on
           the 68060.

           The option is equivalent to -march=68020 -mtune=68020-60.

       -mhard-float
       -m68881
           Generate floating-point instructions.  This is the default for
           68020 and above, and for ColdFire devices that have an FPU.  It
           defines the macro __HAVE_68881__ on M680x0 targets and __mcffpu__
           on ColdFire targets.

       -msoft-float
           Do not generate floating-point instructions; use library calls
           instead.  This is the default for 68000, 68010, and 68832 targets.
           It is also the default for ColdFire devices that have no FPU.

       -mdiv
       -mno-div
           Generate (do not generate) ColdFire hardware divide and remainder
           instructions.  If -march is used without -mcpu, the default is "on"
           for ColdFire architectures and "off" for M680x0 architectures.
           Otherwise, the default is taken from the target CPU (either the
           default CPU, or the one specified by -mcpu).  For example, the
           default is "off" for -mcpu=5206 and "on" for -mcpu=5206e.

           GCC defines the macro __mcfhwdiv__ when this option is enabled.

       -mshort
           Consider type "int" to be 16 bits wide, like "short int".
           Additionally, parameters passed on the stack are also aligned to a
           16-bit boundary even on targets whose API mandates promotion to
           32-bit.

       -mno-short
           Do not consider type "int" to be 16 bits wide.  This is the
           default.

       -mnobitfield
       -mno-bitfield
           Do not use the bit-field instructions.  The -m68000, -mcpu32 and
           -m5200 options imply -mnobitfield.

       -mbitfield
           Do use the bit-field instructions.  The -m68020 option implies
           -mbitfield.  This is the default if you use a configuration
           designed for a 68020.

       -mrtd
           Use a different function-calling convention, in which functions
           that take a fixed number of arguments return with the "rtd"
           instruction, which pops their arguments while returning.  This
           saves one instruction in the caller since there is no need to pop
           the arguments there.

           This calling convention is incompatible with the one normally used
           on Unix, so you cannot use it if you need to call libraries
           compiled with the Unix compiler.

           Also, you must provide function prototypes for all functions that
           take variable numbers of arguments (including "printf"); otherwise
           incorrect code is generated for calls to those functions.

           In addition, seriously incorrect code results if you call a
           function with too many arguments.  (Normally, extra arguments are
           harmlessly ignored.)

           The "rtd" instruction is supported by the 68010, 68020, 68030,
           68040, 68060 and CPU32 processors, but not by the 68000 or 5200.

       -mno-rtd
           Do not use the calling conventions selected by -mrtd.  This is the
           default.

       -malign-int
       -mno-align-int
           Control whether GCC aligns "int", "long", "long long", "float",
           "double", and "long double" variables on a 32-bit boundary
           (-malign-int) or a 16-bit boundary (-mno-align-int).  Aligning
           variables on 32-bit boundaries produces code that runs somewhat
           faster on processors with 32-bit busses at the expense of more
           memory.

           Warning: if you use the -malign-int switch, GCC aligns structures
           containing the above types differently than most published
           application binary interface specifications for the m68k.

       -mpcrel
           Use the pc-relative addressing mode of the 68000 directly, instead
           of using a global offset table.  At present, this option implies
           -fpic, allowing at most a 16-bit offset for pc-relative addressing.
           -fPIC is not presently supported with -mpcrel, though this could be
           supported for 68020 and higher processors.

       -mno-strict-align
       -mstrict-align
           Do not (do) assume that unaligned memory references are handled by
           the system.

       -msep-data
           Generate code that allows the data segment to be located in a
           different area of memory from the text segment.  This allows for
           execute-in-place in an environment without virtual memory
           management.  This option implies -fPIC.

       -mno-sep-data
           Generate code that assumes that the data segment follows the text
           segment.  This is the default.

       -mid-shared-library
           Generate code that supports shared libraries via the library ID
           method.  This allows for execute-in-place and shared libraries in
           an environment without virtual memory management.  This option
           implies -fPIC.

       -mno-id-shared-library
           Generate code that doesn't assume ID-based shared libraries are
           being used.  This is the default.

       -mshared-library-id=n
           Specifies the identification number of the ID-based shared library
           being compiled.  Specifying a value of 0 generates more compact
           code; specifying other values forces the allocation of that number
           to the current library, but is no more space- or time-efficient
           than omitting this option.

       -mxgot
       -mno-xgot
           When generating position-independent code for ColdFire, generate
           code that works if the GOT has more than 8192 entries.  This code
           is larger and slower than code generated without this option.  On
           M680x0 processors, this option is not needed; -fPIC suffices.

           GCC normally uses a single instruction to load values from the GOT.
           While this is relatively efficient, it only works if the GOT is
           smaller than about 64k.  Anything larger causes the linker to
           report an error such as:

                   relocation truncated to fit: R_68K_GOT16O foobar

           If this happens, you should recompile your code with -mxgot.  It
           should then work with very large GOTs.  However, code generated
           with -mxgot is less efficient, since it takes 4 instructions to
           fetch the value of a global symbol.

           Note that some linkers, including newer versions of the GNU linker,
           can create multiple GOTs and sort GOT entries.  If you have such a
           linker, you should only need to use -mxgot when compiling a single
           object file that accesses more than 8192 GOT entries.  Very few do.

           These options have no effect unless GCC is generating position-
           independent code.

       MCore Options

       These are the -m options defined for the Motorola M*Core processors.

       -mhardlit
       -mno-hardlit
           Inline constants into the code stream if it can be done in two
           instructions or less.

       -mdiv
       -mno-div
           Use the divide instruction.  (Enabled by default).

       -mrelax-immediate
       -mno-relax-immediate
           Allow arbitrary-sized immediates in bit operations.

       -mwide-bitfields
       -mno-wide-bitfields
           Always treat bit-fields as "int"-sized.

       -m4byte-functions
       -mno-4byte-functions
           Force all functions to be aligned to a 4-byte boundary.

       -mcallgraph-data
       -mno-callgraph-data
           Emit callgraph information.

       -mslow-bytes
       -mno-slow-bytes
           Prefer word access when reading byte quantities.

       -mlittle-endian
       -mbig-endian
           Generate code for a little-endian target.

       -m210
       -m340
           Generate code for the 210 processor.

       -mno-lsim
           Assume that runtime support has been provided and so omit the
           simulator library (libsim.a) from the linker command line.

       -mstack-increment=size
           Set the maximum amount for a single stack increment operation.
           Large values can increase the speed of programs that contain
           functions that need a large amount of stack space, but they can
           also trigger a segmentation fault if the stack is extended too
           much.  The default value is 0x1000.

       MeP Options

       -mabsdiff
           Enables the "abs" instruction, which is the absolute difference
           between two registers.

       -mall-opts
           Enables all the optional instructions---average, multiply, divide,
           bit operations, leading zero, absolute difference, min/max, clip,
           and saturation.

       -maverage
           Enables the "ave" instruction, which computes the average of two
           registers.

       -mbased=n
           Variables of size n bytes or smaller are placed in the ".based"
           section by default.  Based variables use the $tp register as a base
           register, and there is a 128-byte limit to the ".based" section.

       -mbitops
           Enables the bit operation instructions---bit test ("btstm"), set
           ("bsetm"), clear ("bclrm"), invert ("bnotm"), and test-and-set
           ("tas").

       -mc=name
           Selects which section constant data is placed in.  name may be
           "tiny", "near", or "far".

       -mclip
           Enables the "clip" instruction.  Note that "-mclip" is not useful
           unless you also provide "-mminmax".

       -mconfig=name
           Selects one of the built-in core configurations.  Each MeP chip has
           one or more modules in it; each module has a core CPU and a variety
           of coprocessors, optional instructions, and peripherals.  The
           "MeP-Integrator" tool, not part of GCC, provides these
           configurations through this option; using this option is the same
           as using all the corresponding command-line options.  The default
           configuration is "default".

       -mcop
           Enables the coprocessor instructions.  By default, this is a 32-bit
           coprocessor.  Note that the coprocessor is normally enabled via the
           "-mconfig=" option.

       -mcop32
           Enables the 32-bit coprocessor's instructions.

       -mcop64
           Enables the 64-bit coprocessor's instructions.

       -mivc2
           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.

       -mdc
           Causes constant variables to be placed in the ".near" section.

       -mdiv
           Enables the "div" and "divu" instructions.

       -meb
           Generate big-endian code.

       -mel
           Generate little-endian code.

       -mio-volatile
           Tells the compiler that any variable marked with the "io" attribute
           is to be considered volatile.

       -ml Causes variables to be assigned to the ".far" section by default.

       -mleadz
           Enables the "leadz" (leading zero) instruction.

       -mm Causes variables to be assigned to the ".near" section by default.

       -mminmax
           Enables the "min" and "max" instructions.

       -mmult
           Enables the multiplication and multiply-accumulate instructions.

       -mno-opts
           Disables all the optional instructions enabled by "-mall-opts".

       -mrepeat
           Enables the "repeat" and "erepeat" instructions, used for low-
           overhead looping.

       -ms Causes all variables to default to the ".tiny" section.  Note that
           there is a 65536-byte limit to this section.  Accesses to these
           variables use the %gp base register.

       -msatur
           Enables the saturation instructions.  Note that the compiler does
           not currently generate these itself, but this option is included
           for compatibility with other tools, like "as".

       -msdram
           Link the SDRAM-based runtime instead of the default ROM-based
           runtime.

       -msim
           Link the simulator runtime libraries.

       -msimnovec
           Link the simulator runtime libraries, excluding built-in support
           for reset and exception vectors and tables.

       -mtf
           Causes all functions to default to the ".far" section.  Without
           this option, functions default to the ".near" section.

       -mtiny=n
           Variables that are n bytes or smaller are allocated to the ".tiny"
           section.  These variables use the $gp base register.  The default
           for this option is 4, but note that there's a 65536-byte limit to
           the ".tiny" section.

       MicroBlaze Options

       -msoft-float
           Use software emulation for floating point (default).

       -mhard-float
           Use hardware floating-point instructions.

       -mmemcpy
           Do not optimize block moves, use "memcpy".

       -mno-clearbss
           This option is deprecated.  Use -fno-zero-initialized-in-bss
           instead.

       -mcpu=cpu-type
           Use features of, and schedule code for, the given CPU.  Supported
           values are in the format vX.YY.Z, where X is a major version, YY is
           the minor version, and Z is compatibility code.  Example values are
           v3.00.a, v4.00.b, v5.00.a, v5.00.b, v5.00.b, v6.00.a.

       -mxl-soft-mul
           Use software multiply emulation (default).

       -mxl-soft-div
           Use software emulation for divides (default).

       -mxl-barrel-shift
           Use the hardware barrel shifter.

       -mxl-pattern-compare
           Use pattern compare instructions.

       -msmall-divides
           Use table lookup optimization for small signed integer divisions.

       -mxl-stack-check
           This option is deprecated.  Use -fstack-check instead.

       -mxl-gp-opt
           Use GP-relative ".sdata"/".sbss" sections.

       -mxl-multiply-high
           Use multiply high instructions for high part of 32x32 multiply.

       -mxl-float-convert
           Use hardware floating-point conversion instructions.

       -mxl-float-sqrt
           Use hardware floating-point square root instruction.

       -mbig-endian
           Generate code for a big-endian target.

       -mlittle-endian
           Generate code for a little-endian target.

       -mxl-reorder
           Use reorder instructions (swap and byte reversed load/store).

       -mxl-mode-app-model
           Select application model app-model.  Valid models are

           executable
               normal executable (default), uses startup code crt0.o.

           xmdstub
               for use with Xilinx Microprocessor Debugger (XMD) based
               software intrusive debug agent called xmdstub. This uses
               startup file crt1.o and sets the start address of the program
               to 0x800.

           bootstrap
               for applications that are loaded using a bootloader.  This
               model uses startup file crt2.o which does not contain a
               processor reset vector handler. This is suitable for
               transferring control on a processor reset to the bootloader
               rather than the application.

           novectors
               for applications that do not require any of the MicroBlaze
               vectors. This option may be useful for applications running
               within a monitoring application. This model uses crt3.o as a
               startup file.

           Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-
           model.

       MIPS Options

       -EB Generate big-endian code.

       -EL Generate little-endian code.  This is the default for mips*el-*-*
           configurations.

       -march=arch
           Generate code that runs on arch, which can be the name of a generic
           MIPS ISA, or the name of a particular processor.  The ISA names
           are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips64 and
           mips64r2.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec,
           4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec,
           24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1,
           74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, loongson2e,
           loongson2f, loongson3a, m4k, octeon, octeon+, octeon2, orion,
           r2000, r3000, r3900, r4000, r4400, r4600, r4650, r4700, r6000,
           r8000, rm7000, rm9000, r10000, r12000, r14000, r16000, sb1,
           sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400,
           vr5500, xlr and xlp.  The special value from-abi selects the most
           compatible architecture for the selected ABI (that is, mips1 for
           32-bit ABIs and mips3 for 64-bit ABIs).

           The native Linux/GNU toolchain also supports the value native,
           which selects the best architecture option for the host processor.
           -march=native has no effect if GCC does not recognize the
           processor.

           In processor names, a final 000 can be abbreviated as k (for
           example, -march=r2k).  Prefixes are optional, and vr may be written
           r.

           Names of the form nf2_1 refer to processors with FPUs clocked at
           half the rate of the core, names of the form nf1_1 refer to
           processors with FPUs clocked at the same rate as the core, and
           names of the form nf3_2 refer to processors with FPUs clocked a
           ratio of 3:2 with respect to the core.  For compatibility reasons,
           nf is accepted as a synonym for nf2_1 while nx and bfx are accepted
           as synonyms for nf1_1.

           GCC defines two macros based on the value of this option.  The
           first is _MIPS_ARCH, which gives the name of target architecture,
           as a string.  The second has the form _MIPS_ARCH_foo, where foo is
           the capitalized value of _MIPS_ARCH.  For example, -march=r2000
           sets _MIPS_ARCH to "r2000" and defines the macro _MIPS_ARCH_R2000.

           Note that the _MIPS_ARCH macro uses the processor names given
           above.  In other words, it has the full prefix and does not
           abbreviate 000 as k.  In the case of from-abi, the macro names the
           resolved architecture (either "mips1" or "mips3").  It names the
           default architecture when no -march option is given.

       -mtune=arch
           Optimize for arch.  Among other things, this option controls the
           way instructions are scheduled, and the perceived cost of
           arithmetic operations.  The list of arch values is the same as for
           -march.

           When this option is not used, GCC optimizes for the processor
           specified by -march.  By using -march and -mtune together, it is
           possible to generate code that runs on a family of processors, but
           optimize the code for one particular member of that family.

           -mtune defines the macros _MIPS_TUNE and _MIPS_TUNE_foo, which work
           in the same way as the -march ones described above.

       -mips1
           Equivalent to -march=mips1.

       -mips2
           Equivalent to -march=mips2.

       -mips3
           Equivalent to -march=mips3.

       -mips4
           Equivalent to -march=mips4.

       -mips32
           Equivalent to -march=mips32.

       -mips32r2
           Equivalent to -march=mips32r2.

       -mips64
           Equivalent to -march=mips64.

       -mips64r2
           Equivalent to -march=mips64r2.

       -mips16
       -mno-mips16
           Generate (do not generate) MIPS16 code.  If GCC is targeting a
           MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE.

           MIPS16 code generation can also be controlled on a per-function
           basis by means of "mips16" and "nomips16" attributes.

       -mflip-mips16
           Generate MIPS16 code on alternating functions.  This option is
           provided for regression testing of mixed MIPS16/non-MIPS16 code
           generation, and is not intended for ordinary use in compiling user
           code.

       -minterlink-mips16
       -mno-interlink-mips16
           Require (do not require) that non-MIPS16 code be link-compatible
           with MIPS16 code.

           For example, non-MIPS16 code cannot jump directly to MIPS16 code;
           it must either use a call or an indirect jump.  -minterlink-mips16
           therefore disables direct jumps unless GCC knows that the target of
           the jump is not MIPS16.

       -mabi=32
       -mabi=o64
       -mabi=n32
       -mabi=64
       -mabi=eabi
           Generate code for the given ABI.

           Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
           generates 64-bit code when you select a 64-bit architecture, but
           you can use -mgp32 to get 32-bit code instead.

           For information about the O64 ABI, see
           <http://gcc.gnu.org/projects/mipso64-abi.html>.

           GCC supports a variant of the o32 ABI in which floating-point
           registers are 64 rather than 32 bits wide.  You can select this
           combination with -mabi=32 -mfp64.  This ABI relies on the "mthc1"
           and "mfhc1" instructions and is therefore only supported for
           MIPS32R2 processors.

           The register assignments for arguments and return values remain the
           same, but each scalar value is passed in a single 64-bit register
           rather than a pair of 32-bit registers.  For example, scalar
           floating-point values are returned in $f0 only, not a $f0/$f1 pair.
           The set of call-saved registers also remains the same, but all 64
           bits are saved.

       -mabicalls
       -mno-abicalls
           Generate (do not generate) code that is suitable for SVR4-style
           dynamic objects.  -mabicalls is the default for SVR4-based systems.

       -mshared
       -mno-shared
           Generate (do not generate) code that is fully position-independent,
           and that can therefore be linked into shared libraries.  This
           option only affects -mabicalls.

           All -mabicalls code has traditionally been position-independent,
           regardless of options like -fPIC and -fpic.  However, as an
           extension, the GNU toolchain allows executables to use absolute
           accesses for locally-binding symbols.  It can also use shorter GP
           initialization sequences and generate direct calls to locally-
           defined functions.  This mode is selected by -mno-shared.

           -mno-shared depends on binutils 2.16 or higher and generates
           objects that can only be linked by the GNU linker.  However, the
           option does not affect the ABI of the final executable; it only
           affects the ABI of relocatable objects.  Using -mno-shared
           generally makes executables both smaller and quicker.

           -mshared is the default.

       -mplt
       -mno-plt
           Assume (do not assume) that the static and dynamic linkers support
           PLTs and copy relocations.  This option only affects -mno-shared
           -mabicalls.  For the n64 ABI, this option has no effect without
           -msym32.

           You can make -mplt the default by configuring GCC with
           --with-mips-plt.  The default is -mno-plt otherwise.

       -mxgot
       -mno-xgot
           Lift (do not lift) the usual restrictions on the size of the global
           offset table.

           GCC normally uses a single instruction to load values from the GOT.
           While this is relatively efficient, it only works if the GOT is
           smaller than about 64k.  Anything larger causes the linker to
           report an error such as:

                   relocation truncated to fit: R_MIPS_GOT16 foobar

           If this happens, you should recompile your code with -mxgot.  This
           works with very large GOTs, although the code is also less
           efficient, since it takes three instructions to fetch the value of
           a global symbol.

           Note that some linkers can create multiple GOTs.  If you have such
           a linker, you should only need to use -mxgot when a single object
           file accesses more than 64k's worth of GOT entries.  Very few do.

           These options have no effect unless GCC is generating position
           independent code.

       -mgp32
           Assume that general-purpose registers are 32 bits wide.

       -mgp64
           Assume that general-purpose registers are 64 bits wide.

       -mfp32
           Assume that floating-point registers are 32 bits wide.

       -mfp64
           Assume that floating-point registers are 64 bits wide.

       -mhard-float
           Use floating-point coprocessor instructions.

       -msoft-float
           Do not use floating-point coprocessor instructions.  Implement
           floating-point calculations using library calls instead.

       -mno-float
           Equivalent to -msoft-float, but additionally asserts that the
           program being compiled does not perform any floating-point
           operations.  This option is presently supported only by some bare-
           metal MIPS configurations, where it may select a special set of
           libraries that lack all floating-point support (including, for
           example, the floating-point "printf" formats).  If code compiled
           with "-mno-float" accidentally contains floating-point operations,
           it is likely to suffer a link-time or run-time failure.

       -msingle-float
           Assume that the floating-point coprocessor only supports single-
           precision operations.

       -mdouble-float
           Assume that the floating-point coprocessor supports double-
           precision operations.  This is the default.

       -mllsc
       -mno-llsc
           Use (do not use) ll, sc, and sync instructions to implement atomic
           memory built-in functions.  When neither option is specified, GCC
           uses the instructions if the target architecture supports them.

           -mllsc is useful if the runtime environment can emulate the
           instructions and -mno-llsc can be useful when compiling for
           nonstandard ISAs.  You can make either option the default by
           configuring GCC with --with-llsc and --without-llsc respectively.
           --with-llsc is the default for some configurations; see the
           installation documentation for details.

       -mdsp
       -mno-dsp
           Use (do not use) revision 1 of the MIPS DSP ASE.
             This option defines the preprocessor macro __mips_dsp.  It also
           defines __mips_dsp_rev to 1.

       -mdspr2
       -mno-dspr2
           Use (do not use) revision 2 of the MIPS DSP ASE.
             This option defines the preprocessor macros __mips_dsp and
           __mips_dspr2.  It also defines __mips_dsp_rev to 2.

       -msmartmips
       -mno-smartmips
           Use (do not use) the MIPS SmartMIPS ASE.

       -mpaired-single
       -mno-paired-single
           Use (do not use) paired-single floating-point instructions.
             This option requires hardware floating-point support to be
           enabled.

       -mdmx
       -mno-mdmx
           Use (do not use) MIPS Digital Media Extension instructions.  This
           option can only be used when generating 64-bit code and requires
           hardware floating-point support to be enabled.

       -mips3d
       -mno-mips3d
           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies
           -mpaired-single.

       -mmt
       -mno-mt
           Use (do not use) MT Multithreading instructions.

       -mmcu
       -mno-mcu
           Use (do not use) the MIPS MCU ASE instructions.

       -mlong64
           Force "long" types to be 64 bits wide.  See -mlong32 for an
           explanation of the default and the way that the pointer size is
           determined.

       -mlong32
           Force "long", "int", and pointer types to be 32 bits wide.

           The default size of "int"s, "long"s and pointers depends on the
           ABI.  All the supported ABIs use 32-bit "int"s.  The n64 ABI uses
           64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
           "long"s.  Pointers are the same size as "long"s, or the same size
           as integer registers, whichever is smaller.

       -msym32
       -mno-sym32
           Assume (do not assume) that all symbols have 32-bit values,
           regardless of the selected ABI.  This option is useful in
           combination with -mabi=64 and -mno-abicalls because it allows GCC
           to generate shorter and faster references to symbolic addresses.

       -G num
           Put definitions of externally-visible data in a small data section
           if that data is no bigger than num bytes.  GCC can then generate
           more efficient accesses to the data; see -mgpopt for details.

           The default -G option depends on the configuration.

       -mlocal-sdata
       -mno-local-sdata
           Extend (do not extend) the -G behavior to local data too, such as
           to static variables in C.  -mlocal-sdata is the default for all
           configurations.

           If the linker complains that an application is using too much small
           data, you might want to try rebuilding the less performance-
           critical parts with -mno-local-sdata.  You might also want to build
           large libraries with -mno-local-sdata, so that the libraries leave
           more room for the main program.

       -mextern-sdata
       -mno-extern-sdata
           Assume (do not assume) that externally-defined data is in a small
           data section if the size of that data is within the -G limit.
           -mextern-sdata is the default for all configurations.

           If you compile a module Mod with -mextern-sdata -G num -mgpopt, and
           Mod references a variable Var that is no bigger than num bytes, you
           must make sure that Var is placed in a small data section.  If Var
           is defined by another module, you must either compile that module
           with a high-enough -G setting or attach a "section" attribute to
           Var's definition.  If Var is common, you must link the application
           with a high-enough -G setting.

           The easiest way of satisfying these restrictions is to compile and
           link every module with the same -G option.  However, you may wish
           to build a library that supports several different small data
           limits.  You can do this by compiling the library with the highest
           supported -G setting and additionally using -mno-extern-sdata to
           stop the library from making assumptions about externally-defined
           data.

       -mgpopt
       -mno-gpopt
           Use (do not use) GP-relative accesses for symbols that are known to
           be in a small data section; see -G, -mlocal-sdata and
           -mextern-sdata.  -mgpopt is the default for all configurations.

           -mno-gpopt is useful for cases where the $gp register might not
           hold the value of "_gp".  For example, if the code is part of a
           library that might be used in a boot monitor, programs that call
           boot monitor routines pass an unknown value in $gp.  (In such
           situations, the boot monitor itself is usually compiled with -G0.)

           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.

       -membedded-data
       -mno-embedded-data
           Allocate variables to the read-only data section first if possible,
           then next in the small data section if possible, otherwise in data.
           This gives slightly slower code than the default, but reduces the
           amount of RAM required when executing, and thus may be preferred
           for some embedded systems.

       -muninit-const-in-rodata
       -mno-uninit-const-in-rodata
           Put uninitialized "const" variables in the read-only data section.
           This option is only meaningful in conjunction with -membedded-data.

       -mcode-readable=setting
           Specify whether GCC may generate code that reads from executable
           sections.  There are three possible settings:

           -mcode-readable=yes
               Instructions may freely access executable sections.  This is
               the default setting.

           -mcode-readable=pcrel
               MIPS16 PC-relative load instructions can access executable
               sections, but other instructions must not do so.  This option
               is useful on 4KSc and 4KSd processors when the code TLBs have
               the Read Inhibit bit set.  It is also useful on processors that
               can be configured to have a dual instruction/data SRAM
               interface and that, like the M4K, automatically redirect PC-
               relative loads to the instruction RAM.

           -mcode-readable=no
               Instructions must not access executable sections.  This option
               can be useful on targets that are configured to have a dual
               instruction/data SRAM interface but that (unlike the M4K) do
               not automatically redirect PC-relative loads to the instruction
               RAM.

       -msplit-addresses
       -mno-split-addresses
           Enable (disable) use of the "%hi()" and "%lo()" assembler
           relocation operators.  This option has been superseded by
           -mexplicit-relocs but is retained for backwards compatibility.

       -mexplicit-relocs
       -mno-explicit-relocs
           Use (do not use) assembler relocation operators when dealing with
           symbolic addresses.  The alternative, selected by
           -mno-explicit-relocs, is to use assembler macros instead.

           -mexplicit-relocs is the default if GCC was configured to use an
           assembler that supports relocation operators.

       -mcheck-zero-division
       -mno-check-zero-division
           Trap (do not trap) on integer division by zero.

           The default is -mcheck-zero-division.

       -mdivide-traps
       -mdivide-breaks
           MIPS systems check for division by zero by generating either a
           conditional trap or a break instruction.  Using traps results in
           smaller code, but is only supported on MIPS II and later.  Also,
           some versions of the Linux kernel have a bug that prevents trap
           from generating the proper signal ("SIGFPE").  Use -mdivide-traps
           to allow conditional traps on architectures that support them and
           -mdivide-breaks to force the use of breaks.

           The default is usually -mdivide-traps, but this can be overridden
           at configure time using --with-divide=breaks.  Divide-by-zero
           checks can be completely disabled using -mno-check-zero-division.

       -mmemcpy
       -mno-memcpy
           Force (do not force) the use of "memcpy()" for non-trivial block
           moves.  The default is -mno-memcpy, which allows GCC to inline most
           constant-sized copies.

       -mlong-calls
       -mno-long-calls
           Disable (do not disable) use of the "jal" instruction.  Calling
           functions using "jal" is more efficient but requires the caller and
           callee to be in the same 256 megabyte segment.

           This option has no effect on abicalls code.  The default is
           -mno-long-calls.

       -mmad
       -mno-mad
           Enable (disable) use of the "mad", "madu" and "mul" instructions,
           as provided by the R4650 ISA.

       -mfused-madd
       -mno-fused-madd
           Enable (disable) use of the floating-point multiply-accumulate
           instructions, when they are available.  The default is
           -mfused-madd.

           On the R8000 CPU when multiply-accumulate instructions are used,
           the intermediate product is calculated to infinite precision and is
           not subject to the FCSR Flush to Zero bit.  This may be undesirable
           in some circumstances.  On other processors the result is
           numerically identical to the equivalent computation using separate
           multiply, add, subtract and negate instructions.

       -nocpp
           Tell the MIPS assembler to not run its preprocessor over user
           assembler files (with a .s suffix) when assembling them.

       -mfix-24k
       -mno-fix-24k
           Work around the 24K E48 (lost data on stores during refill) errata.
           The workarounds are implemented by the assembler rather than by
           GCC.

       -mfix-r4000
       -mno-fix-r4000
           Work around certain R4000 CPU errata:

           -   A double-word or a variable shift may give an incorrect result
               if executed immediately after starting an integer division.

           -   A double-word or a variable shift may give an incorrect result
               if executed while an integer multiplication is in progress.

           -   An integer division may give an incorrect result if started in
               a delay slot of a taken branch or a jump.

       -mfix-r4400
       -mno-fix-r4400
           Work around certain R4400 CPU errata:

           -   A double-word or a variable shift may give an incorrect result
               if executed immediately after starting an integer division.

       -mfix-r10000
       -mno-fix-r10000
           Work around certain R10000 errata:

           -   "ll"/"sc" sequences may not behave atomically on revisions
               prior to 3.0.  They may deadlock on revisions 2.6 and earlier.

           This option can only be used if the target architecture supports
           branch-likely instructions.  -mfix-r10000 is the default when
           -march=r10000 is used; -mno-fix-r10000 is the default otherwise.

       -mfix-vr4120
       -mno-fix-vr4120
           Work around certain VR4120 errata:

           -   "dmultu" does not always produce the correct result.

           -   "div" and "ddiv" do not always produce the correct result if
               one of the operands is negative.

           The workarounds for the division errata rely on special functions
           in libgcc.a.  At present, these functions are only provided by the
           "mips64vr*-elf" configurations.

           Other VR4120 errata require a NOP to be inserted between certain
           pairs of instructions.  These errata are handled by the assembler,
           not by GCC itself.

       -mfix-vr4130
           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are
           implemented by the assembler rather than by GCC, although GCC
           avoids using "mflo" and "mfhi" if the VR4130 "macc", "macchi",
           "dmacc" and "dmacchi" instructions are available instead.

       -mfix-sb1
       -mno-fix-sb1
           Work around certain SB-1 CPU core errata.  (This flag currently
           works around the SB-1 revision 2 "F1" and "F2" floating-point
           errata.)

       -mr10k-cache-barrier=setting
           Specify whether GCC should insert cache barriers to avoid the side-
           effects of speculation on R10K processors.

           In common with many processors, the R10K tries to predict the
           outcome of a conditional branch and speculatively executes
           instructions from the "taken" branch.  It later aborts these
           instructions if the predicted outcome is wrong.  However, on the
           R10K, even aborted instructions can have side effects.

           This problem only affects kernel stores and, depending on the
           system, kernel loads.  As an example, a speculatively-executed
           store may load the target memory into cache and mark the cache line
           as dirty, even if the store itself is later aborted.  If a DMA
           operation writes to the same area of memory before the "dirty" line
           is flushed, the cached data overwrites the DMA-ed data.  See the
           R10K processor manual for a full description, including other
           potential problems.

           One workaround is to insert cache barrier instructions before every
           memory access that might be speculatively executed and that might
           have side effects even if aborted.  -mr10k-cache-barrier=setting
           controls GCC's implementation of this workaround.  It assumes that
           aborted accesses to any byte in the following regions does not have
           side effects:

           1.  the memory occupied by the current function's stack frame;

           2.  the memory occupied by an incoming stack argument;

           3.  the memory occupied by an object with a link-time-constant
               address.

           It is the kernel's responsibility to ensure that speculative
           accesses to these regions are indeed safe.

           If the input program contains a function declaration such as:

                   void foo (void);

           then the implementation of "foo" must allow "j foo" and "jal foo"
           to be executed speculatively.  GCC honors this restriction for
           functions it compiles itself.  It expects non-GCC functions (such
           as hand-written assembly code) to do the same.

           The option has three forms:

           -mr10k-cache-barrier=load-store
               Insert a cache barrier before a load or store that might be
               speculatively executed and that might have side effects even if
               aborted.

           -mr10k-cache-barrier=store
               Insert a cache barrier before a store that might be
               speculatively executed and that might have side effects even if
               aborted.

           -mr10k-cache-barrier=none
               Disable the insertion of cache barriers.  This is the default
               setting.

       -mflush-func=func
       -mno-flush-func
           Specifies the function to call to flush the I and D caches, or to
           not call any such function.  If called, the function must take the
           same arguments as the common "_flush_func()", that is, the address
           of the memory range for which the cache is being flushed, the size
           of the memory range, and the number 3 (to flush both caches).  The
           default depends on the target GCC was configured for, but commonly
           is either _flush_func or __cpu_flush.

       mbranch-cost=num
           Set the cost of branches to roughly num "simple" instructions.
           This cost is only a heuristic and is not guaranteed to produce
           consistent results across releases.  A zero cost redundantly
           selects the default, which is based on the -mtune setting.

       -mbranch-likely
       -mno-branch-likely
           Enable or disable use of Branch Likely instructions, regardless of
           the default for the selected architecture.  By default, Branch
           Likely instructions may be generated if they are supported by the
           selected architecture.  An exception is for the MIPS32 and MIPS64
           architectures and processors that implement those architectures;
           for those, Branch Likely instructions are not be generated by
           default because the MIPS32 and MIPS64 architectures specifically
           deprecate their use.

       -mfp-exceptions
       -mno-fp-exceptions
           Specifies whether FP exceptions are enabled.  This affects how FP
           instructions are scheduled for some processors.  The default is
           that FP exceptions are enabled.

           For instance, on the SB-1, if FP exceptions are disabled, and we
           are emitting 64-bit code, then we can use both FP pipes.
           Otherwise, we can only use one FP pipe.

       -mvr4130-align
       -mno-vr4130-align
           The VR4130 pipeline is two-way superscalar, but can only issue two
           instructions together if the first one is 8-byte aligned.  When
           this option is enabled, GCC aligns pairs of instructions that it
           thinks should execute in parallel.

           This option only has an effect when optimizing for the VR4130.  It
           normally makes code faster, but at the expense of making it bigger.
           It is enabled by default at optimization level -O3.

       -msynci
       -mno-synci
           Enable (disable) generation of "synci" instructions on
           architectures that support it.  The "synci" instructions (if
           enabled) are generated when "__builtin___clear_cache()" is
           compiled.

           This option defaults to "-mno-synci", but the default can be
           overridden by configuring with "--with-synci".

           When compiling code for single processor systems, it is generally
           safe to use "synci".  However, on many multi-core (SMP) systems, it
           does not invalidate the instruction caches on all cores and may
           lead to undefined behavior.

       -mrelax-pic-calls
       -mno-relax-pic-calls
           Try to turn PIC calls that are normally dispatched via register $25
           into direct calls.  This is only possible if the linker can resolve
           the destination at link-time and if the destination is within range
           for a direct call.

           -mrelax-pic-calls is the default if GCC was configured to use an
           assembler and a linker that support the ".reloc" assembly directive
           and "-mexplicit-relocs" is in effect.  With "-mno-explicit-relocs",
           this optimization can be performed by the assembler and the linker
           alone without help from the compiler.

       -mmcount-ra-address
       -mno-mcount-ra-address
           Emit (do not emit) code that allows "_mcount" to modify the calling
           function's return address.  When enabled, this option extends the
           usual "_mcount" interface with a new ra-address parameter, which
           has type "intptr_t *" and is passed in register $12.  "_mcount" can
           then modify the return address by doing both of the following:

              Returning the new address in register $31.

              Storing the new address in "*ra-address", if ra-address is
               nonnull.

           The default is -mno-mcount-ra-address.

       MMIX Options

       These options are defined for the MMIX:

       -mlibfuncs
       -mno-libfuncs
           Specify that intrinsic library functions are being compiled,
           passing all values in registers, no matter the size.

       -mepsilon
       -mno-epsilon
           Generate floating-point comparison instructions that compare with
           respect to the "rE" epsilon register.

       -mabi=mmixware
       -mabi=gnu
           Generate code that passes function parameters and return values
           that (in the called function) are seen as registers $0 and up, as
           opposed to the GNU ABI which uses global registers $231 and up.

       -mzero-extend
       -mno-zero-extend
           When reading data from memory in sizes shorter than 64 bits, use
           (do not use) zero-extending load instructions by default, rather
           than sign-extending ones.

       -mknuthdiv
       -mno-knuthdiv
           Make the result of a division yielding a remainder have the same
           sign as the divisor.  With the default, -mno-knuthdiv, the sign of
           the remainder follows the sign of the dividend.  Both methods are
           arithmetically valid, the latter being almost exclusively used.

       -mtoplevel-symbols
       -mno-toplevel-symbols
           Prepend (do not prepend) a : to all global symbols, so the assembly
           code can be used with the "PREFIX" assembly directive.

       -melf
           Generate an executable in the ELF format, rather than the default
           mmo format used by the mmix simulator.

       -mbranch-predict
       -mno-branch-predict
           Use (do not use) the probable-branch instructions, when static
           branch prediction indicates a probable branch.

       -mbase-addresses
       -mno-base-addresses
           Generate (do not generate) code that uses base addresses.  Using a
           base address automatically generates a request (handled by the
           assembler and the linker) for a constant to be set up in a global
           register.  The register is used for one or more base address
           requests within the range 0 to 255 from the value held in the
           register.  The generally leads to short and fast code, but the
           number of different data items that can be addressed is limited.
           This means that a program that uses lots of static data may require
           -mno-base-addresses.

       -msingle-exit
       -mno-single-exit
           Force (do not force) generated code to have a single exit point in
           each function.

       MN10300 Options

       These -m options are defined for Matsushita MN10300 architectures:

       -mmult-bug
           Generate code to avoid bugs in the multiply instructions for the
           MN10300 processors.  This is the default.

       -mno-mult-bug
           Do not generate code to avoid bugs in the multiply instructions for
           the MN10300 processors.

       -mam33
           Generate code using features specific to the AM33 processor.

       -mno-am33
           Do not generate code using features specific to the AM33 processor.
           This is the default.

       -mam33-2
           Generate code using features specific to the AM33/2.0 processor.

       -mam34
           Generate code using features specific to the AM34 processor.

       -mtune=cpu-type
           Use the timing characteristics of the indicated CPU type when
           scheduling instructions.  This does not change the targeted
           processor type.  The CPU type must be one of mn10300, am33, am33-2
           or am34.

       -mreturn-pointer-on-d0
           When generating a function that returns a pointer, return the
           pointer in both "a0" and "d0".  Otherwise, the pointer is returned
           only in "a0", and attempts to call such functions without a
           prototype result in errors.  Note that this option is on by
           default; use -mno-return-pointer-on-d0 to disable it.

       -mno-crt0
           Do not link in the C run-time initialization object file.

       -mrelax
           Indicate to the linker that it should perform a relaxation
           optimization pass to shorten branches, calls and absolute memory
           addresses.  This option only has an effect when used on the command
           line for the final link step.

           This option makes symbolic debugging impossible.

       -mliw
           Allow the compiler to generate Long Instruction Word instructions
           if the target is the AM33 or later.  This is the default.  This
           option defines the preprocessor macro __LIW__.

       -mnoliw
           Do not allow the compiler to generate Long Instruction Word
           instructions.  This option defines the preprocessor macro
           __NO_LIW__.

       -msetlb
           Allow the compiler to generate the SETLB and Lcc instructions if
           the target is the AM33 or later.  This is the default.  This option
           defines the preprocessor macro __SETLB__.

       -mnosetlb
           Do not allow the compiler to generate SETLB or Lcc instructions.
           This option defines the preprocessor macro __NO_SETLB__.

       Moxie Options

       -meb
           Generate big-endian code.  This is the default for moxie-*-*
           configurations.

       -mel
           Generate little-endian code.

       -mno-crt0
           Do not link in the C run-time initialization object file.

       PDP-11 Options

       These options are defined for the PDP-11:

       -mfpu
           Use hardware FPP floating point.  This is the default.  (FIS
           floating point on the PDP-11/40 is not supported.)

       -msoft-float
           Do not use hardware floating point.

       -mac0
           Return floating-point results in ac0 (fr0 in Unix assembler
           syntax).

       -mno-ac0
           Return floating-point results in memory.  This is the default.

       -m40
           Generate code for a PDP-11/40.

       -m45
           Generate code for a PDP-11/45.  This is the default.

       -m10
           Generate code for a PDP-11/10.

       -mbcopy-builtin
           Use inline "movmemhi" patterns for copying memory.  This is the
           default.

       -mbcopy
           Do not use inline "movmemhi" patterns for copying memory.

       -mint16
       -mno-int32
           Use 16-bit "int".  This is the default.

       -mint32
       -mno-int16
           Use 32-bit "int".

       -mfloat64
       -mno-float32
           Use 64-bit "float".  This is the default.

       -mfloat32
       -mno-float64
           Use 32-bit "float".

       -mabshi
           Use "abshi2" pattern.  This is the default.

       -mno-abshi
           Do not use "abshi2" pattern.

       -mbranch-expensive
           Pretend that branches are expensive.  This is for experimenting
           with code generation only.

       -mbranch-cheap
           Do not pretend that branches are expensive.  This is the default.

       -munix-asm
           Use Unix assembler syntax.  This is the default when configured for
           pdp11-*-bsd.

       -mdec-asm
           Use DEC assembler syntax.  This is the default when configured for
           any PDP-11 target other than pdp11-*-bsd.

       picoChip Options

       These -m options are defined for picoChip implementations:

       -mae=ae_type
           Set the instruction set, register set, and instruction scheduling
           parameters for array element type ae_type.  Supported values for
           ae_type are ANY, MUL, and MAC.

           -mae=ANY selects a completely generic AE type.  Code generated with
           this option runs on any of the other AE types.  The code is not as
           efficient as it would be if compiled for a specific AE type, and
           some types of operation (e.g., multiplication) do not work properly
           on all types of AE.

           -mae=MUL selects a MUL AE type.  This is the most useful AE type
           for compiled code, and is the default.

           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this
           option may suffer from poor performance of byte (char)
           manipulation, since the DSP AE does not provide hardware support
           for byte load/stores.

       -msymbol-as-address
           Enable the compiler to directly use a symbol name as an address in
           a load/store instruction, without first loading it into a register.
           Typically, the use of this option generates larger programs, which
           run faster than when the option isn't used.  However, the results
           vary from program to program, so it is left as a user option,
           rather than being permanently enabled.

       -mno-inefficient-warnings
           Disables warnings about the generation of inefficient code.  These
           warnings can be generated, for example, when compiling code that
           performs byte-level memory operations on the MAC AE type.  The MAC
           AE has no hardware support for byte-level memory operations, so all
           byte load/stores must be synthesized from word load/store
           operations.  This is inefficient and a warning is generated to
           indicate that you should rewrite the code to avoid byte operations,
           or to target an AE type that has the necessary hardware support.
           This option disables these warnings.

       PowerPC Options

       These are listed under

       RL78 Options

       -msim
           Links in additional target libraries to support operation within a
           simulator.

       -mmul=none
       -mmul=g13
       -mmul=rl78
           Specifies the type of hardware multiplication support to be used.
           The default is "none", which uses software multiplication
           functions.  The "g13" option is for the hardware multiply/divide
           peripheral only on the RL78/G13 targets.  The "rl78" option is for
           the standard hardware multiplication defined in the RL78 software
           manual.

       IBM RS/6000 and PowerPC Options

       These -m options are defined for the IBM RS/6000 and PowerPC:

       -mpowerpc-gpopt
       -mno-powerpc-gpopt
       -mpowerpc-gfxopt
       -mno-powerpc-gfxopt
       -mpowerpc64
       -mno-powerpc64
       -mmfcrf
       -mno-mfcrf
       -mpopcntb
       -mno-popcntb
       -mpopcntd
       -mno-popcntd
       -mfprnd
       -mno-fprnd
       -mcmpb
       -mno-cmpb
       -mmfpgpr
       -mno-mfpgpr
       -mhard-dfp
       -mno-hard-dfp
           You use these options to specify which instructions are available
           on the processor you are using.  The default value of these options
           is determined when configuring GCC.  Specifying the -mcpu=cpu_type
           overrides the specification of these options.  We recommend you use
           the -mcpu=cpu_type option rather than the options listed above.

           Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC
           architecture instructions in the General Purpose group, including
           floating-point square root.  Specifying -mpowerpc-gfxopt allows GCC
           to use the optional PowerPC architecture instructions in the
           Graphics group, including floating-point select.

           The -mmfcrf option allows GCC to generate the move from condition
           register field instruction implemented on the POWER4 processor and
           other processors that support the PowerPC V2.01 architecture.  The
           -mpopcntb option allows GCC to generate the popcount and double-
           precision FP reciprocal estimate instruction implemented on the
           POWER5 processor and other processors that support the PowerPC
           V2.02 architecture.  The -mpopcntd option allows GCC to generate
           the popcount instruction implemented on the POWER7 processor and
           other processors that support the PowerPC V2.06 architecture.  The
           -mfprnd option allows GCC to generate the FP round to integer
           instructions implemented on the POWER5+ processor and other
           processors that support the PowerPC V2.03 architecture.  The -mcmpb
           option allows GCC to generate the compare bytes instruction
           implemented on the POWER6 processor and other processors that
           support the PowerPC V2.05 architecture.  The -mmfpgpr option allows
           GCC to generate the FP move to/from general-purpose register
           instructions implemented on the POWER6X processor and other
           processors that support the extended PowerPC V2.05 architecture.
           The -mhard-dfp option allows GCC to generate the decimal floating-
           point instructions implemented on some POWER processors.

           The -mpowerpc64 option allows GCC to generate the additional 64-bit
           instructions that are found in the full PowerPC64 architecture and
           to treat GPRs as 64-bit, doubleword quantities.  GCC defaults to
           -mno-powerpc64.

       -mcpu=cpu_type
           Set architecture type, register usage, and instruction scheduling
           parameters for machine type cpu_type.  Supported values for
           cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476,
           476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400,
           7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3,
           e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3,
           power4, power5, power5+, power6, power6x, power7, power8, powerpc,
           powerpc64, and rs64.

           -mcpu=powerpc, and -mcpu=powerpc64 specify pure 32-bit PowerPC and
           64-bit PowerPC architecture machine types, with an appropriate,
           generic processor model assumed for scheduling purposes.

           The other options specify a specific processor.  Code generated
           under those options runs best on that processor, and may not run at
           all on others.

           The -mcpu options automatically enable or disable the following
           options:

           -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple -mpopcntb
           -mpopcntd  -mpowerpc64 -mpowerpc-gpopt  -mpowerpc-gfxopt
           -msingle-float -mdouble-float -msimple-fpu -mstring  -mmulhw
           -mdlmzb  -mmfpgpr -mvsx

           The particular options set for any particular CPU varies between
           compiler versions, depending on what setting seems to produce
           optimal code for that CPU; it doesn't necessarily reflect the
           actual hardware's capabilities.  If you wish to set an individual
           option to a particular value, you may specify it after the -mcpu
           option, like -mcpu=970 -mno-altivec.

           On AIX, the -maltivec and -mpowerpc64 options are not enabled or
           disabled by the -mcpu option at present because AIX does not have
           full support for these options.  You may still enable or disable
           them individually if you're sure it'll work in your environment.

       -mtune=cpu_type
           Set the instruction scheduling parameters for machine type
           cpu_type, but do not set the architecture type or register usage,
           as -mcpu=cpu_type does.  The same values for cpu_type are used for
           -mtune as for -mcpu.  If both are specified, the code generated
           uses the architecture and registers set by -mcpu, but the
           scheduling parameters set by -mtune.

       -mcmodel=small
           Generate PowerPC64 code for the small model: The TOC is limited to
           64k.

       -mcmodel=medium
           Generate PowerPC64 code for the medium model: The TOC and other
           static data may be up to a total of 4G in size.

       -mcmodel=large
           Generate PowerPC64 code for the large model: The TOC may be up to
           4G in size.  Other data and code is only limited by the 64-bit
           address space.

       -maltivec
       -mno-altivec
           Generate code that uses (does not use) AltiVec instructions, and
           also enable the use of built-in functions that allow more direct
           access to the AltiVec instruction set.  You may also need to set
           -mabi=altivec to adjust the current ABI with AltiVec ABI
           enhancements.

       -mvrsave
       -mno-vrsave
           Generate VRSAVE instructions when generating AltiVec code.

       -mgen-cell-microcode
           Generate Cell microcode instructions.

       -mwarn-cell-microcode
           Warn when a Cell microcode instruction is emitted.  An example of a
           Cell microcode instruction is a variable shift.

       -msecure-plt
           Generate code that allows ld and ld.so to build executables and
           shared libraries with non-executable ".plt" and ".got" sections.
           This is a PowerPC 32-bit SYSV ABI option.

       -mbss-plt
           Generate code that uses a BSS ".plt" section that ld.so fills in,
           and requires ".plt" and ".got" sections that are both writable and
           executable.  This is a PowerPC 32-bit SYSV ABI option.

       -misel
       -mno-isel
           This switch enables or disables the generation of ISEL
           instructions.

       -misel=yes/no
           This switch has been deprecated.  Use -misel and -mno-isel instead.

       -mspe
       -mno-spe
           This switch enables or disables the generation of SPE simd
           instructions.

       -mpaired
       -mno-paired
           This switch enables or disables the generation of PAIRED simd
           instructions.

       -mspe=yes/no
           This option has been deprecated.  Use -mspe and -mno-spe instead.

       -mvsx
       -mno-vsx
           Generate code that uses (does not use) vector/scalar (VSX)
           instructions, and also enable the use of built-in functions that
           allow more direct access to the VSX instruction set.

       -mfloat-gprs=yes/single/double/no
       -mfloat-gprs
           This switch enables or disables the generation of floating-point
           operations on the general-purpose registers for architectures that
           support it.

           The argument yes or single enables the use of single-precision
           floating-point operations.

           The argument double enables the use of single and double-precision
           floating-point operations.

           The argument no disables floating-point operations on the general-
           purpose registers.

           This option is currently only available on the MPC854x.

       -m32
       -m64
           Generate code for 32-bit or 64-bit environments of Darwin and SVR4
           targets (including GNU/Linux).  The 32-bit environment sets int,
           long and pointer to 32 bits and generates code that runs on any
           PowerPC variant.  The 64-bit environment sets int to 32 bits and
           long and pointer to 64 bits, and generates code for PowerPC64, as
           for -mpowerpc64.

       -mfull-toc
       -mno-fp-in-toc
       -mno-sum-in-toc
       -mminimal-toc
           Modify generation of the TOC (Table Of Contents), which is created
           for every executable file.  The -mfull-toc option is selected by
           default.  In that case, GCC allocates at least one TOC entry for
           each unique non-automatic variable reference in your program.  GCC
           also places floating-point constants in the TOC.  However, only
           16,384 entries are available in the TOC.

           If you receive a linker error message that saying you have
           overflowed the available TOC space, you can reduce the amount of
           TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
           -mno-fp-in-toc prevents GCC from putting floating-point constants
           in the TOC and -mno-sum-in-toc forces GCC to generate code to
           calculate the sum of an address and a constant at run time instead
           of putting that sum into the TOC.  You may specify one or both of
           these options.  Each causes GCC to produce very slightly slower and
           larger code at the expense of conserving TOC space.

           If you still run out of space in the TOC even when you specify both
           of these options, specify -mminimal-toc instead.  This option
           causes GCC to make only one TOC entry for every file.  When you
           specify this option, GCC produces code that is slower and larger
           but which uses extremely little TOC space.  You may wish to use
           this option only on files that contain less frequently-executed
           code.

       -maix64
       -maix32
           Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
           64-bit "long" type, and the infrastructure needed to support them.
           Specifying -maix64 implies -mpowerpc64, while -maix32 disables the
           64-bit ABI and implies -mno-powerpc64.  GCC defaults to -maix32.

       -mxl-compat
       -mno-xl-compat
           Produce code that conforms more closely to IBM XL compiler
           semantics when using AIX-compatible ABI.  Pass floating-point
           arguments to prototyped functions beyond the register save area
           (RSA) on the stack in addition to argument FPRs.  Do not assume
           that most significant double in 128-bit long double value is
           properly rounded when comparing values and converting to double.
           Use XL symbol names for long double support routines.

           The AIX calling convention was extended but not initially
           documented to handle an obscure K&R C case of calling a function
           that takes the address of its arguments with fewer arguments than
           declared.  IBM XL compilers access floating-point arguments that do
           not fit in the RSA from the stack when a subroutine is compiled
           without optimization.  Because always storing floating-point
           arguments on the stack is inefficient and rarely needed, this
           option is not enabled by default and only is necessary when calling
           subroutines compiled by IBM XL compilers without optimization.

       -mpe
           Support IBM RS/6000 SP Parallel Environment (PE).  Link an
           application written to use message passing with special startup
           code to enable the application to run.  The system must have PE
           installed in the standard location (/usr/lpp/ppe.poe/), or the
           specs file must be overridden with the -specs= option to specify
           the appropriate directory location.  The Parallel Environment does
           not support threads, so the -mpe option and the -pthread option are
           incompatible.

       -malign-natural
       -malign-power
           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
           -malign-natural overrides the ABI-defined alignment of larger
           types, such as floating-point doubles, on their natural size-based
           boundary.  The option -malign-power instructs GCC to follow the
           ABI-specified alignment rules.  GCC defaults to the standard
           alignment defined in the ABI.

           On 64-bit Darwin, natural alignment is the default, and
           -malign-power is not supported.

       -msoft-float
       -mhard-float
           Generate code that does not use (uses) the floating-point register
           set.  Software floating-point emulation is provided if you use the
           -msoft-float option, and pass the option to GCC when linking.

       -msingle-float
       -mdouble-float
           Generate code for single- or double-precision floating-point
           operations.  -mdouble-float implies -msingle-float.

       -msimple-fpu
           Do not generate "sqrt" and "div" instructions for hardware
           floating-point unit.

       -mfpu=name
           Specify type of floating-point unit.  Valid values for name are
           sp_lite (equivalent to -msingle-float -msimple-fpu), dp_lite
           (equivalent to -mdouble-float -msimple-fpu), sp_full (equivalent to
           -msingle-float), and dp_full (equivalent to -mdouble-float).

       -mxilinx-fpu
           Perform optimizations for the floating-point unit on Xilinx PPC
           405/440.

       -mmultiple
       -mno-multiple
           Generate code that uses (does not use) the load multiple word
           instructions and the store multiple word instructions.  These
           instructions are generated by default on POWER systems, and not
           generated on PowerPC systems.  Do not use -mmultiple on little-
           endian PowerPC systems, since those instructions do not work when
           the processor is in little-endian mode.  The exceptions are PPC740
           and PPC750 which permit these instructions in little-endian mode.

       -mstring
       -mno-string
           Generate code that uses (does not use) the load string instructions
           and the store string word instructions to save multiple registers
           and do small block moves.  These instructions are generated by
           default on POWER systems, and not generated on PowerPC systems.  Do
           not use -mstring on little-endian PowerPC systems, since those
           instructions do not work when the processor is in little-endian
           mode.  The exceptions are PPC740 and PPC750 which permit these
           instructions in little-endian mode.

       -mupdate
       -mno-update
           Generate code that uses (does not use) the load or store
           instructions that update the base register to the address of the
           calculated memory location.  These instructions are generated by
           default.  If you use -mno-update, there is a small window between
           the time that the stack pointer is updated and the address of the
           previous frame is stored, which means code that walks the stack
           frame across interrupts or signals may get corrupted data.

       -mavoid-indexed-addresses
       -mno-avoid-indexed-addresses
           Generate code that tries to avoid (not avoid) the use of indexed
           load or store instructions. These instructions can incur a
           performance penalty on Power6 processors in certain situations,
           such as when stepping through large arrays that cross a 16M
           boundary.  This option is enabled by default when targeting Power6
           and disabled otherwise.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use) the floating-point multiply
           and accumulate instructions.  These instructions are generated by
           default if hardware floating point is used.  The machine-dependent
           -mfused-madd option is now mapped to the machine-independent
           -ffp-contract=fast option, and -mno-fused-madd is mapped to
           -ffp-contract=off.

       -mmulhw
       -mno-mulhw
           Generate code that uses (does not use) the half-word multiply and
           multiply-accumulate instructions on the IBM 405, 440, 464 and 476
           processors.  These instructions are generated by default when
           targeting those processors.

       -mdlmzb
       -mno-dlmzb
           Generate code that uses (does not use) the string-search dlmzb
           instruction on the IBM 405, 440, 464 and 476 processors.  This
           instruction is generated by default when targeting those
           processors.

       -mno-bit-align
       -mbit-align
           On System V.4 and embedded PowerPC systems do not (do) force
           structures and unions that contain bit-fields to be aligned to the
           base type of the bit-field.

           For example, by default a structure containing nothing but 8
           "unsigned" bit-fields of length 1 is aligned to a 4-byte boundary
           and has a size of 4 bytes.  By using -mno-bit-align, the structure
           is aligned to a 1-byte boundary and is 1 byte in size.

       -mno-strict-align
       -mstrict-align
           On System V.4 and embedded PowerPC systems do not (do) assume that
           unaligned memory references are handled by the system.

       -mrelocatable
       -mno-relocatable
           Generate code that allows (does not allow) a static executable to
           be relocated to a different address at run time.  A simple embedded
           PowerPC system loader should relocate the entire contents of
           ".got2" and 4-byte locations listed in the ".fixup" section, a
           table of 32-bit addresses generated by this option.  For this to
           work, all objects linked together must be compiled with
           -mrelocatable or -mrelocatable-lib.  -mrelocatable code aligns the
           stack to an 8-byte boundary.

       -mrelocatable-lib
       -mno-relocatable-lib
           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section
           to allow static executables to be relocated at run time, but
           -mrelocatable-lib does not use the smaller stack alignment of
           -mrelocatable.  Objects compiled with -mrelocatable-lib may be
           linked with objects compiled with any combination of the
           -mrelocatable options.

       -mno-toc
       -mtoc
           On System V.4 and embedded PowerPC systems do not (do) assume that
           register 2 contains a pointer to a global area pointing to the
           addresses used in the program.

       -mlittle
       -mlittle-endian
           On System V.4 and embedded PowerPC systems compile code for the
           processor in little-endian mode.  The -mlittle-endian option is the
           same as -mlittle.

       -mbig
       -mbig-endian
           On System V.4 and embedded PowerPC systems compile code for the
           processor in big-endian mode.  The -mbig-endian option is the same
           as -mbig.

       -mdynamic-no-pic
           On Darwin and Mac OS X systems, compile code so that it is not
           relocatable, but that its external references are relocatable.  The
           resulting code is suitable for applications, but not shared
           libraries.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather
           than loading it in the prologue for each function.  The runtime
           system is responsible for initializing this register with an
           appropriate value before execution begins.

       -mprioritize-restricted-insns=priority
           This option controls the priority that is assigned to dispatch-slot
           restricted instructions during the second scheduling pass.  The
           argument priority takes the value 0, 1, or 2 to assign no, highest,
           or second-highest (respectively) priority to dispatch-slot
           restricted instructions.

       -msched-costly-dep=dependence_type
           This option controls which dependences are considered costly by the
           target during instruction scheduling.  The argument dependence_type
           takes one of the following values:

           no  No dependence is costly.

           all All dependences are costly.

           true_store_to_load
               A true dependence from store to load is costly.

           store_to_load
               Any dependence from store to load is costly.

           number
               Any dependence for which the latency is greater than or equal
               to number is costly.

       -minsert-sched-nops=scheme
           This option controls which NOP insertion scheme is used during the
           second scheduling pass.  The argument scheme takes one of the
           following values:

           no  Don't insert NOPs.

           pad Pad with NOPs any dispatch group that has vacant issue slots,
               according to the scheduler's grouping.

           regroup_exact
               Insert NOPs to force costly dependent insns into separate
               groups.  Insert exactly as many NOPs as needed to force an insn
               to a new group, according to the estimated processor grouping.

           number
               Insert NOPs to force costly dependent insns into separate
               groups.  Insert number NOPs to force an insn to a new group.

       -mcall-sysv
           On System V.4 and embedded PowerPC systems compile code using
           calling conventions that adhere to the March 1995 draft of the
           System V Application Binary Interface, PowerPC processor
           supplement.  This is the default unless you configured GCC using
           powerpc-*-eabiaix.

       -mcall-sysv-eabi
       -mcall-eabi
           Specify both -mcall-sysv and -meabi options.

       -mcall-sysv-noeabi
           Specify both -mcall-sysv and -mno-eabi options.

       -mcall-aixdesc
           On System V.4 and embedded PowerPC systems compile code for the AIX
           operating system.

       -mcall-linux
           On System V.4 and embedded PowerPC systems compile code for the
           Linux-based GNU system.

       -mcall-freebsd
           On System V.4 and embedded PowerPC systems compile code for the
           FreeBSD operating system.

       -mcall-netbsd
           On System V.4 and embedded PowerPC systems compile code for the
           NetBSD operating system.

       -mcall-openbsd
           On System V.4 and embedded PowerPC systems compile code for the
           OpenBSD operating system.

       -maix-struct-return
           Return all structures in memory (as specified by the AIX ABI).

       -msvr4-struct-return
           Return structures smaller than 8 bytes in registers (as specified
           by the SVR4 ABI).

       -mabi=abi-type
           Extend the current ABI with a particular extension, or remove such
           extension.  Valid values are altivec, no-altivec, spe, no-spe,
           ibmlongdouble, ieeelongdouble.

       -mabi=spe
           Extend the current ABI with SPE ABI extensions.  This does not
           change the default ABI, instead it adds the SPE ABI extensions to
           the current ABI.

       -mabi=no-spe
           Disable Book-E SPE ABI extensions for the current ABI.

       -mabi=ibmlongdouble
           Change the current ABI to use IBM extended-precision long double.
           This is a PowerPC 32-bit SYSV ABI option.

       -mabi=ieeelongdouble
           Change the current ABI to use IEEE extended-precision long double.
           This is a PowerPC 32-bit Linux ABI option.

       -mprototype
       -mno-prototype
           On System V.4 and embedded PowerPC systems assume that all calls to
           variable argument functions are properly prototyped.  Otherwise,
           the compiler must insert an instruction before every non-prototyped
           call to set or clear bit 6 of the condition code register (CR) to
           indicate whether floating-point values are passed in the floating-
           point registers in case the function takes variable arguments.
           With -mprototype, only calls to prototyped variable argument
           functions set or clear the bit.

       -msim
           On embedded PowerPC systems, assume that the startup module is
           called sim-crt0.o and that the standard C libraries are libsim.a
           and libc.a.  This is the default for powerpc-*-eabisim
           configurations.

       -mmvme
           On embedded PowerPC systems, assume that the startup module is
           called crt0.o and the standard C libraries are libmvme.a and
           libc.a.

       -mads
           On embedded PowerPC systems, assume that the startup module is
           called crt0.o and the standard C libraries are libads.a and libc.a.

       -myellowknife
           On embedded PowerPC systems, assume that the startup module is
           called crt0.o and the standard C libraries are libyk.a and libc.a.

       -mvxworks
           On System V.4 and embedded PowerPC systems, specify that you are
           compiling for a VxWorks system.

       -memb
           On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
           header to indicate that eabi extended relocations are used.

       -meabi
       -mno-eabi
           On System V.4 and embedded PowerPC systems do (do not) adhere to
           the Embedded Applications Binary Interface (EABI), which is a set
           of modifications to the System V.4 specifications.  Selecting
           -meabi means that the stack is aligned to an 8-byte boundary, a
           function "__eabi" is called from "main" to set up the EABI
           environment, and the -msdata option can use both "r2" and "r13" to
           point to two separate small data areas.  Selecting -mno-eabi means
           that the stack is aligned to a 16-byte boundary, no EABI
           initialization function is called from "main", and the -msdata
           option only uses "r13" to point to a single small data area.  The
           -meabi option is on by default if you configured GCC using one of
           the powerpc*-*-eabi* options.

       -msdata=eabi
           On System V.4 and embedded PowerPC systems, put small initialized
           "const" global and static data in the .sdata2 section, which is
           pointed to by register "r2".  Put small initialized non-"const"
           global and static data in the .sdata section, which is pointed to
           by register "r13".  Put small uninitialized global and static data
           in the .sbss section, which is adjacent to the .sdata section.  The
           -msdata=eabi option is incompatible with the -mrelocatable option.
           The -msdata=eabi option also sets the -memb option.

       -msdata=sysv
           On System V.4 and embedded PowerPC systems, put small global and
           static data in the .sdata section, which is pointed to by register
           "r13".  Put small uninitialized global and static data in the .sbss
           section, which is adjacent to the .sdata section.  The -msdata=sysv
           option is incompatible with the -mrelocatable option.

       -msdata=default
       -msdata
           On System V.4 and embedded PowerPC systems, if -meabi is used,
           compile code the same as -msdata=eabi, otherwise compile code the
           same as -msdata=sysv.

       -msdata=data
           On System V.4 and embedded PowerPC systems, put small global data
           in the .sdata section.  Put small uninitialized global data in the
           .sbss section.  Do not use register "r13" to address small data
           however.  This is the default behavior unless other -msdata options
           are used.

       -msdata=none
       -mno-sdata
           On embedded PowerPC systems, put all initialized global and static
           data in the .data section, and all uninitialized data in the .bss
           section.

       -mblock-move-inline-limit=num
           Inline all block moves (such as calls to "memcpy" or structure
           copies) less than or equal to num bytes.  The minimum value for num
           is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
           default value is target-specific.

       -G num
           On embedded PowerPC systems, put global and static items less than
           or equal to num bytes into the small data or BSS sections instead
           of the normal data or BSS section.  By default, num is 8.  The -G
           num switch is also passed to the linker.  All modules should be
           compiled with the same -G num value.

       -mregnames
       -mno-regnames
           On System V.4 and embedded PowerPC systems do (do not) emit
           register names in the assembly language output using symbolic
           forms.

       -mlongcall
       -mno-longcall
           By default assume that all calls are far away so that a longer and
           more expensive calling sequence is required.  This is required for
           calls farther than 32 megabytes (33,554,432 bytes) from the current
           location.  A short call is generated if the compiler knows the call
           cannot be that far away.  This setting can be overridden by the
           "shortcall" function attribute, or by "#pragma longcall(0)".

           Some linkers are capable of detecting out-of-range calls and
           generating glue code on the fly.  On these systems, long calls are
           unnecessary and generate slower code.  As of this writing, the AIX
           linker can do this, as can the GNU linker for PowerPC/64.  It is
           planned to add this feature to the GNU linker for 32-bit PowerPC
           systems as well.

           On Darwin/PPC systems, "#pragma longcall" generates "jbsr callee,
           L42", plus a branch island (glue code).  The two target addresses
           represent the callee and the branch island.  The Darwin/PPC linker
           prefers the first address and generates a "bl callee" if the PPC
           "bl" instruction reaches the callee directly; otherwise, the linker
           generates "bl L42" to call the branch island.  The branch island is
           appended to the body of the calling function; it computes the full
           32-bit address of the callee and jumps to it.

           On Mach-O (Darwin) systems, this option directs the compiler emit
           to the glue for every direct call, and the Darwin linker decides
           whether to use or discard it.

           In the future, GCC may ignore all longcall specifications when the
           linker is known to generate glue.

       -mtls-markers
       -mno-tls-markers
           Mark (do not mark) calls to "__tls_get_addr" with a relocation
           specifying the function argument.  The relocation allows the linker
           to reliably associate function call with argument setup
           instructions for TLS optimization, which in turn allows GCC to
           better schedule the sequence.

       -pthread
           Adds support for multithreading with the pthreads library.  This
           option sets flags for both the preprocessor and linker.

       -mrecip
       -mno-recip
           This option enables use of the reciprocal estimate and reciprocal
           square root estimate instructions with additional Newton-Raphson
           steps to increase precision instead of doing a divide or square
           root and divide for floating-point arguments.  You should use the
           -ffast-math option when using -mrecip (or at least
           -funsafe-math-optimizations, -finite-math-only, -freciprocal-math
           and -fno-trapping-math).  Note that while the throughput of the
           sequence is generally higher than the throughput of the non-
           reciprocal instruction, the precision of the sequence can be
           decreased by up to 2 ulp (i.e. the inverse of 1.0 equals
           0.99999994) for reciprocal square roots.

       -mrecip=opt
           This option controls which reciprocal estimate instructions may be
           used.  opt is a comma-separated list of options, which may be
           preceded by a "!" to invert the option: "all": enable all estimate
           instructions, "default": enable the default instructions,
           equivalent to -mrecip, "none": disable all estimate instructions,
           equivalent to -mno-recip; "div": enable the reciprocal
           approximation instructions for both single and double precision;
           "divf": enable the single-precision reciprocal approximation
           instructions; "divd": enable the double-precision reciprocal
           approximation instructions; "rsqrt": enable the reciprocal square
           root approximation instructions for both single and double
           precision; "rsqrtf": enable the single-precision reciprocal square
           root approximation instructions; "rsqrtd": enable the double-
           precision reciprocal square root approximation instructions;

           So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal
           estimate instructions, except for the "FRSQRTE", "XSRSQRTEDP", and
           "XVRSQRTEDP" instructions which handle the double-precision
           reciprocal square root calculations.

       -mrecip-precision
       -mno-recip-precision
           Assume (do not assume) that the reciprocal estimate instructions
           provide higher-precision estimates than is mandated by the PowerPC
           ABI.  Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8
           automatically selects -mrecip-precision.  The double-precision
           square root estimate instructions are not generated by default on
           low-precision machines, since they do not provide an estimate that
           converges after three steps.

       -mveclibabi=type
           Specifies the ABI type to use for vectorizing intrinsics using an
           external library.  The only type supported at present is "mass",
           which specifies to use IBM's Mathematical Acceleration Subsystem
           (MASS) libraries for vectorizing intrinsics using external
           libraries.  GCC currently emits calls to "acosd2", "acosf4",
           "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", "asinhf4",
           "atan2d2", "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4",
           "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2", "coshf4", "erfcd2",
           "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", "expd2", "expf4",
           "expm1d2", "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4",
           "log10d2", "log10f4", "log1pd2", "log1pf4", "log2d2", "log2f4",
           "logd2", "logf4", "powd2", "powf4", "sind2", "sinf4", "sinhd2",
           "sinhf4", "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and
           "tanhf4" when generating code for power7.  Both -ftree-vectorize
           and -funsafe-math-optimizations must also be enabled.  The MASS
           libraries must be specified at link time.

       -mfriz
       -mno-friz
           Generate (do not generate) the "friz" instruction when the
           -funsafe-math-optimizations option is used to optimize rounding of
           floating-point values to 64-bit integer and back to floating point.
           The "friz" instruction does not return the same value if the
           floating-point number is too large to fit in an integer.

       -mpointers-to-nested-functions
       -mno-pointers-to-nested-functions
           Generate (do not generate) code to load up the static chain
           register (r11) when calling through a pointer on AIX and 64-bit
           Linux systems where a function pointer points to a 3-word
           descriptor giving the function address, TOC value to be loaded in
           register r2, and static chain value to be loaded in register r11.
           The -mpointers-to-nested-functions is on by default.  You cannot
           call through pointers to nested functions or pointers to functions
           compiled in other languages that use the static chain if you use
           the -mno-pointers-to-nested-functions.

       -msave-toc-indirect
       -mno-save-toc-indirect
           Generate (do not generate) code to save the TOC value in the
           reserved stack location in the function prologue if the function
           calls through a pointer on AIX and 64-bit Linux systems.  If the
           TOC value is not saved in the prologue, it is saved just before the
           call through the pointer.  The -mno-save-toc-indirect option is the
           default.

       RX Options

       These command-line options are defined for RX targets:

       -m64bit-doubles
       -m32bit-doubles
           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits
           (-m32bit-doubles) in size.  The default is -m32bit-doubles.  Note
           RX floating-point hardware only works on 32-bit values, which is
           why the default is -m32bit-doubles.

       -fpu
       -nofpu
           Enables (-fpu) or disables (-nofpu) the use of RX floating-point
           hardware.  The default is enabled for the RX600 series and disabled
           for the RX200 series.

           Floating-point instructions are only generated for 32-bit floating-
           point values, however, so the FPU hardware is not used for doubles
           if the -m64bit-doubles option is used.

           Note If the -fpu option is enabled then -funsafe-math-optimizations
           is also enabled automatically.  This is because the RX FPU
           instructions are themselves unsafe.

       -mcpu=name
           Selects the type of RX CPU to be targeted.  Currently three types
           are supported, the generic RX600 and RX200 series hardware and the
           specific RX610 CPU.  The default is RX600.

           The only difference between RX600 and RX610 is that the RX610 does
           not support the "MVTIPL" instruction.

           The RX200 series does not have a hardware floating-point unit and
           so -nofpu is enabled by default when this type is selected.

       -mbig-endian-data
       -mlittle-endian-data
           Store data (but not code) in the big-endian format.  The default is
           -mlittle-endian-data, i.e. to store data in the little-endian
           format.

       -msmall-data-limit=N
           Specifies the maximum size in bytes of global and static variables
           which can be placed into the small data area.  Using the small data
           area can lead to smaller and faster code, but the size of area is
           limited and it is up to the programmer to ensure that the area does
           not overflow.  Also when the small data area is used one of the
           RX's registers (usually "r13") is reserved for use pointing to this
           area, so it is no longer available for use by the compiler.  This
           could result in slower and/or larger code if variables are pushed
           onto the stack instead of being held in this register.

           Note, common variables (variables that have not been initialized)
           and constants are not placed into the small data area as they are
           assigned to other sections in the output executable.

           The default value is zero, which disables this feature.  Note, this
           feature is not enabled by default with higher optimization levels
           (-O2 etc) because of the potentially detrimental effects of
           reserving a register.  It is up to the programmer to experiment and
           discover whether this feature is of benefit to their program.  See
           the description of the -mpid option for a description of how the
           actual register to hold the small data area pointer is chosen.

       -msim
       -mno-sim
           Use the simulator runtime.  The default is to use the libgloss
           board-specific runtime.

       -mas100-syntax
       -mno-as100-syntax
           When generating assembler output use a syntax that is compatible
           with Renesas's AS100 assembler.  This syntax can also be handled by
           the GAS assembler, but it has some restrictions so it is not
           generated by default.

       -mmax-constant-size=N
           Specifies the maximum size, in bytes, of a constant that can be
           used as an operand in a RX instruction.  Although the RX
           instruction set does allow constants of up to 4 bytes in length to
           be used in instructions, a longer value equates to a longer
           instruction.  Thus in some circumstances it can be beneficial to
           restrict the size of constants that are used in instructions.
           Constants that are too big are instead placed into a constant pool
           and referenced via register indirection.

           The value N can be between 0 and 4.  A value of 0 (the default) or
           4 means that constants of any size are allowed.

       -mrelax
           Enable linker relaxation.  Linker relaxation is a process whereby
           the linker attempts to reduce the size of a program by finding
           shorter versions of various instructions.  Disabled by default.

       -mint-register=N
           Specify the number of registers to reserve for fast interrupt
           handler functions.  The value N can be between 0 and 4.  A value of
           1 means that register "r13" is reserved for the exclusive use of
           fast interrupt handlers.  A value of 2 reserves "r13" and "r12".  A
           value of 3 reserves "r13", "r12" and "r11", and a value of 4
           reserves "r13" through "r10".  A value of 0, the default, does not
           reserve any registers.

       -msave-acc-in-interrupts
           Specifies that interrupt handler functions should preserve the
           accumulator register.  This is only necessary if normal code might
           use the accumulator register, for example because it performs
           64-bit multiplications.  The default is to ignore the accumulator
           as this makes the interrupt handlers faster.

       -mpid
       -mno-pid
           Enables the generation of position independent data.  When enabled
           any access to constant data is done via an offset from a base
           address held in a register.  This allows the location of constant
           data to be determined at run time without requiring the executable
           to be relocated, which is a benefit to embedded applications with
           tight memory constraints.  Data that can be modified is not
           affected by this option.

           Note, using this feature reserves a register, usually "r13", for
           the constant data base address.  This can result in slower and/or
           larger code, especially in complicated functions.

           The actual register chosen to hold the constant data base address
           depends upon whether the -msmall-data-limit and/or the
           -mint-register command-line options are enabled.  Starting with
           register "r13" and proceeding downwards, registers are allocated
           first to satisfy the requirements of -mint-register, then -mpid and
           finally -msmall-data-limit.  Thus it is possible for the small data
           area register to be "r8" if both -mint-register=4 and -mpid are
           specified on the command line.

           By default this feature is not enabled.  The default can be
           restored via the -mno-pid command-line option.

       -mno-warn-multiple-fast-interrupts
       -mwarn-multiple-fast-interrupts
           Prevents GCC from issuing a warning message if it finds more than
           one fast interrupt handler when it is compiling a file.  The
           default is to issue a warning for each extra fast interrupt handler
           found, as the RX only supports one such interrupt.

       Note: The generic GCC command-line option -ffixed-reg has special
       significance to the RX port when used with the "interrupt" function
       attribute.  This attribute indicates a function intended to process
       fast interrupts.  GCC ensures that it only uses the registers "r10",
       "r11", "r12" and/or "r13" and only provided that the normal use of the
       corresponding registers have been restricted via the -ffixed-reg or
       -mint-register command-line options.

       S/390 and zSeries Options

       These are the -m options defined for the S/390 and zSeries
       architecture.

       -mhard-float
       -msoft-float
           Use (do not use) the hardware floating-point instructions and
           registers for floating-point operations.  When -msoft-float is
           specified, functions in libgcc.a are used to perform floating-point
           operations.  When -mhard-float is specified, the compiler generates
           IEEE floating-point instructions.  This is the default.

       -mhard-dfp
       -mno-hard-dfp
           Use (do not use) the hardware decimal-floating-point instructions
           for decimal-floating-point operations.  When -mno-hard-dfp is
           specified, functions in libgcc.a are used to perform decimal-
           floating-point operations.  When -mhard-dfp is specified, the
           compiler generates decimal-floating-point hardware instructions.
           This is the default for -march=z9-ec or higher.

       -mlong-double-64
       -mlong-double-128
           These switches control the size of "long double" type. A size of 64
           bits makes the "long double" type equivalent to the "double" type.
           This is the default.

       -mbackchain
       -mno-backchain
           Store (do not store) the address of the caller's frame as backchain
           pointer into the callee's stack frame.  A backchain may be needed
           to allow debugging using tools that do not understand DWARF 2 call
           frame information.  When -mno-packed-stack is in effect, the
           backchain pointer is stored at the bottom of the stack frame; when
           -mpacked-stack is in effect, the backchain is placed into the
           topmost word of the 96/160 byte register save area.

           In general, code compiled with -mbackchain is call-compatible with
           code compiled with -mmo-backchain; however, use of the backchain
           for debugging purposes usually requires that the whole binary is
           built with -mbackchain.  Note that the combination of -mbackchain,
           -mpacked-stack and -mhard-float is not supported.  In order to
           build a linux kernel use -msoft-float.

           The default is to not maintain the backchain.

       -mpacked-stack
       -mno-packed-stack
           Use (do not use) the packed stack layout.  When -mno-packed-stack
           is specified, the compiler uses the all fields of the 96/160 byte
           register save area only for their default purpose; unused fields
           still take up stack space.  When -mpacked-stack is specified,
           register save slots are densely packed at the top of the register
           save area; unused space is reused for other purposes, allowing for
           more efficient use of the available stack space.  However, when
           -mbackchain is also in effect, the topmost word of the save area is
           always used to store the backchain, and the return address register
           is always saved two words below the backchain.

           As long as the stack frame backchain is not used, code generated
           with -mpacked-stack is call-compatible with code generated with
           -mno-packed-stack.  Note that some non-FSF releases of GCC 2.95 for
           S/390 or zSeries generated code that uses the stack frame backchain
           at run time, not just for debugging purposes.  Such code is not
           call-compatible with code compiled with -mpacked-stack.  Also, note
           that the combination of -mbackchain, -mpacked-stack and
           -mhard-float is not supported.  In order to build a linux kernel
           use -msoft-float.

           The default is to not use the packed stack layout.

       -msmall-exec
       -mno-small-exec
           Generate (or do not generate) code using the "bras" instruction to
           do subroutine calls.  This only works reliably if the total
           executable size does not exceed 64k.  The default is to use the
           "basr" instruction instead, which does not have this limitation.

       -m64
       -m31
           When -m31 is specified, generate code compliant to the GNU/Linux
           for S/390 ABI.  When -m64 is specified, generate code compliant to
           the GNU/Linux for zSeries ABI.  This allows GCC in particular to
           generate 64-bit instructions.  For the s390 targets, the default is
           -m31, while the s390x targets default to -m64.

       -mzarch
       -mesa
           When -mzarch is specified, generate code using the instructions
           available on z/Architecture.  When -mesa is specified, generate
           code using the instructions available on ESA/390.  Note that -mesa
           is not possible with -m64.  When generating code compliant to the
           GNU/Linux for S/390 ABI, the default is -mesa.  When generating
           code compliant to the GNU/Linux for zSeries ABI, the default is
           -mzarch.

       -mmvcle
       -mno-mvcle
           Generate (or do not generate) code using the "mvcle" instruction to
           perform block moves.  When -mno-mvcle is specified, use a "mvc"
           loop instead.  This is the default unless optimizing for size.

       -mdebug
       -mno-debug
           Print (or do not print) additional debug information when
           compiling.  The default is to not print debug information.

       -march=cpu-type
           Generate code that runs on cpu-type, which is the name of a system
           representing a certain processor type.  Possible values for cpu-
           type are g5, g6, z900, z990, z9-109, z9-ec and z10.  When
           generating code using the instructions available on z/Architecture,
           the default is -march=z900.  Otherwise, the default is -march=g5.

       -mtune=cpu-type
           Tune to cpu-type everything applicable about the generated code,
           except for the ABI and the set of available instructions.  The list
           of cpu-type values is the same as for -march.  The default is the
           value used for -march.

       -mtpf-trace
       -mno-tpf-trace
           Generate code that adds (does not add) in TPF OS specific branches
           to trace routines in the operating system.  This option is off by
           default, even when compiling for the TPF OS.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use) the floating-point multiply
           and accumulate instructions.  These instructions are generated by
           default if hardware floating point is used.

       -mwarn-framesize=framesize
           Emit a warning if the current function exceeds the given frame
           size.  Because this is a compile-time check it doesn't need to be a
           real problem when the program runs.  It is intended to identify
           functions that most probably cause a stack overflow.  It is useful
           to be used in an environment with limited stack size e.g. the linux
           kernel.

       -mwarn-dynamicstack
           Emit a warning if the function calls "alloca" or uses dynamically-
           sized arrays.  This is generally a bad idea with a limited stack
           size.

       -mstack-guard=stack-guard
       -mstack-size=stack-size
           If these options are provided the S/390 back end emits additional
           instructions in the function prologue that trigger a trap if the
           stack size is stack-guard bytes above the stack-size (remember that
           the stack on S/390 grows downward).  If the stack-guard option is
           omitted the smallest power of 2 larger than the frame size of the
           compiled function is chosen.  These options are intended to be used
           to help debugging stack overflow problems.  The additionally
           emitted code causes only little overhead and hence can also be used
           in production-like systems without greater performance degradation.
           The given values have to be exact powers of 2 and stack-size has to
           be greater than stack-guard without exceeding 64k.  In order to be
           efficient the extra code makes the assumption that the stack starts
           at an address aligned to the value given by stack-size.  The stack-
           guard option can only be used in conjunction with stack-size.

       -mhotpatch[=halfwords]
       -mno-hotpatch
           If the hotpatch option is enabled, a "hot-patching" function
           prologue is generated for all functions in the compilation unit.
           The funtion label is prepended with the given number of two-byte
           Nop instructions (halfwords, maximum 1000000) or 12 Nop
           instructions if no argument is present.  Functions with a hot-
           patching prologue are never inlined automatically, and a hot-
           patching prologue is never generated for functions functions that
           are explicitly inline.

           This option can be overridden for individual functions with the
           "hotpatch" attribute.

       Score Options

       These options are defined for Score implementations:

       -meb
           Compile code for big-endian mode.  This is the default.

       -mel
           Compile code for little-endian mode.

       -mnhwloop
           Disable generation of "bcnz" instructions.

       -muls
           Enable generation of unaligned load and store instructions.

       -mmac
           Enable the use of multiply-accumulate instructions. Disabled by
           default.

       -mscore5
           Specify the SCORE5 as the target architecture.

       -mscore5u
           Specify the SCORE5U of the target architecture.

       -mscore7
           Specify the SCORE7 as the target architecture. This is the default.

       -mscore7d
           Specify the SCORE7D as the target architecture.

       SH Options

       These -m options are defined for the SH implementations:

       -m1 Generate code for the SH1.

       -m2 Generate code for the SH2.

       -m2e
           Generate code for the SH2e.

       -m2a-nofpu
           Generate code for the SH2a without FPU, or for a SH2a-FPU in such a
           way that the floating-point unit is not used.

       -m2a-single-only
           Generate code for the SH2a-FPU, in such a way that no double-
           precision floating-point operations are used.

       -m2a-single
           Generate code for the SH2a-FPU assuming the floating-point unit is
           in single-precision mode by default.

       -m2a
           Generate code for the SH2a-FPU assuming the floating-point unit is
           in double-precision mode by default.

       -m3 Generate code for the SH3.

       -m3e
           Generate code for the SH3e.

       -m4-nofpu
           Generate code for the SH4 without a floating-point unit.

       -m4-single-only
           Generate code for the SH4 with a floating-point unit that only
           supports single-precision arithmetic.

       -m4-single
           Generate code for the SH4 assuming the floating-point unit is in
           single-precision mode by default.

       -m4 Generate code for the SH4.

       -m4a-nofpu
           Generate code for the SH4al-dsp, or for a SH4a in such a way that
           the floating-point unit is not used.

       -m4a-single-only
           Generate code for the SH4a, in such a way that no double-precision
           floating-point operations are used.

       -m4a-single
           Generate code for the SH4a assuming the floating-point unit is in
           single-precision mode by default.

       -m4a
           Generate code for the SH4a.

       -m4al
           Same as -m4a-nofpu, except that it implicitly passes -dsp to the
           assembler.  GCC doesn't generate any DSP instructions at the
           moment.

       -mb Compile code for the processor in big-endian mode.

       -ml Compile code for the processor in little-endian mode.

       -mdalign
           Align doubles at 64-bit boundaries.  Note that this changes the
           calling conventions, and thus some functions from the standard C
           library do not work unless you recompile it first with -mdalign.

       -mrelax
           Shorten some address references at link time, when possible; uses
           the linker option -relax.

       -mbigtable
           Use 32-bit offsets in "switch" tables.  The default is to use
           16-bit offsets.

       -mbitops
           Enable the use of bit manipulation instructions on SH2A.

       -mfmovd
           Enable the use of the instruction "fmovd".  Check -mdalign for
           alignment constraints.

       -mhitachi
           Comply with the calling conventions defined by Renesas.

       -mrenesas
           Comply with the calling conventions defined by Renesas.

       -mno-renesas
           Comply with the calling conventions defined for GCC before the
           Renesas conventions were available.  This option is the default for
           all targets of the SH toolchain.

       -mnomacsave
           Mark the "MAC" register as call-clobbered, even if -mhitachi is
           given.

       -mieee
       -mno-ieee
           Control the IEEE compliance of floating-point comparisons, which
           affects the handling of cases where the result of a comparison is
           unordered.  By default -mieee is implicitly enabled.  If
           -ffinite-math-only is enabled -mno-ieee is implicitly set, which
           results in faster floating-point greater-equal and less-equal
           comparisons.  The implcit settings can be overridden by specifying
           either -mieee or -mno-ieee.

       -minline-ic_invalidate
           Inline code to invalidate instruction cache entries after setting
           up nested function trampolines.  This option has no effect if
           -musermode is in effect and the selected code generation option
           (e.g. -m4) does not allow the use of the "icbi" instruction.  If
           the selected code generation option does not allow the use of the
           "icbi" instruction, and -musermode is not in effect, the inlined
           code manipulates the instruction cache address array directly with
           an associative write.  This not only requires privileged mode at
           run time, but it also fails if the cache line had been mapped via
           the TLB and has become unmapped.

       -misize
           Dump instruction size and location in the assembly code.

       -mpadstruct
           This option is deprecated.  It pads structures to multiple of 4
           bytes, which is incompatible with the SH ABI.

       -matomic-model=model
           Sets the model of atomic operations and additional parameters as a
           comma separated list.  For details on the atomic built-in functions
           see __atomic Builtins.  The following models and parameters are
           supported:

           none
               Disable compiler generated atomic sequences and emit library
               calls for atomic operations.  This is the default if the target
               is not "sh-*-linux*".

           soft-gusa
               Generate GNU/Linux compatible gUSA software atomic sequences
               for the atomic built-in functions.  The generated atomic
               sequences require additional support from the
               interrupt/exception handling code of the system and are only
               suitable for SH3* and SH4* single-core systems.  This option is
               enabled by default when the target is "sh-*-linux*" and SH3* or
               SH4*.  When the target is SH4A, this option will also partially
               utilize the hardware atomic instructions "movli.l" and
               "movco.l" to create more efficient code, unless strict is
               specified.

           soft-tcb
               Generate software atomic sequences that use a variable in the
               thread control block.  This is a variation of the gUSA
               sequences which can also be used on SH1* and SH2* targets.  The
               generated atomic sequences require additional support from the
               interrupt/exception handling code of the system and are only
               suitable for single-core systems.  When using this model, the
               gbr-offset= parameter has to be specified as well.

           soft-imask
               Generate software atomic sequences that temporarily disable
               interrupts by setting "SR.IMASK = 1111".  This model works only
               when the program runs in privileged mode and is only suitable
               for single-core systems.  Additional support from the
               interrupt/exception handling code of the system is not
               required.  This model is enabled by default when the target is
               "sh-*-linux*" and SH1* or SH2*.

           hard-llcs
               Generate hardware atomic sequences using the "movli.l" and
               "movco.l" instructions only.  This is only available on SH4A
               and is suitable for multi-core systems.  Since the hardware
               instructions support only 32 bit atomic variables access to 8
               or 16 bit variables is emulated with 32 bit accesses.  Code
               compiled with this option will also be compatible with other
               software atomic model interrupt/exception handling systems if
               executed on an SH4A system.  Additional support from the
               interrupt/exception handling code of the system is not required
               for this model.

           gbr-offset=
               This parameter specifies the offset in bytes of the variable in
               the thread control block structure that should be used by the
               generated atomic sequences when the soft-tcb model has been
               selected.  For other models this parameter is ignored.  The
               specified value must be an integer multiple of four and in the
               range 0-1020.

           strict
               This parameter prevents mixed usage of multiple atomic models,
               even though they would be compatible, and will make the
               compiler generate atomic sequences of the specified model only.

       -mtas
           Generate the "tas.b" opcode for "__atomic_test_and_set".  Notice
           that depending on the particular hardware and software
           configuration this can degrade overall performance due to the
           operand cache line flushes that are implied by the "tas.b"
           instruction.  On multi-core SH4A processors the "tas.b" instruction
           must be used with caution since it can result in data corruption
           for certain cache configurations.

       -mspace
           Optimize for space instead of speed.  Implied by -Os.

       -mprefergot
           When generating position-independent code, emit function calls
           using the Global Offset Table instead of the Procedure Linkage
           Table.

       -musermode
           Don't generate privileged mode only code.  This option implies
           -mno-inline-ic_invalidate if the inlined code would not work in
           user mode.  This is the default when the target is "sh-*-linux*".

       -multcost=number
           Set the cost to assume for a multiply insn.

       -mdiv=strategy
           Set the division strategy to be used for integer division
           operations.  For SHmedia strategy can be one of:

           fp  Performs the operation in floating point.  This has a very high
               latency, but needs only a few instructions, so it might be a
               good choice if your code has enough easily-exploitable ILP to
               allow the compiler to schedule the floating-point instructions
               together with other instructions.  Division by zero causes a
               floating-point exception.

           inv Uses integer operations to calculate the inverse of the
               divisor, and then multiplies the dividend with the inverse.
               This strategy allows CSE and hoisting of the inverse
               calculation.  Division by zero calculates an unspecified
               result, but does not trap.

           inv:minlat
               A variant of inv where, if no CSE or hoisting opportunities
               have been found, or if the entire operation has been hoisted to
               the same place, the last stages of the inverse calculation are
               intertwined with the final multiply to reduce the overall
               latency, at the expense of using a few more instructions, and
               thus offering fewer scheduling opportunities with other code.

           call
               Calls a library function that usually implements the inv:minlat
               strategy.  This gives high code density for "m5-*media-nofpu"
               compilations.

           call2
               Uses a different entry point of the same library function,
               where it assumes that a pointer to a lookup table has already
               been set up, which exposes the pointer load to CSE and code
               hoisting optimizations.

           inv:call
           inv:call2
           inv:fp
               Use the inv algorithm for initial code generation, but if the
               code stays unoptimized, revert to the call, call2, or fp
               strategies, respectively.  Note that the potentially-trapping
               side effect of division by zero is carried by a separate
               instruction, so it is possible that all the integer
               instructions are hoisted out, but the marker for the side
               effect stays where it is.  A recombination to floating-point
               operations or a call is not possible in that case.

           inv20u
           inv20l
               Variants of the inv:minlat strategy.  In the case that the
               inverse calculation is not separated from the multiply, they
               speed up division where the dividend fits into 20 bits (plus
               sign where applicable) by inserting a test to skip a number of
               operations in this case; this test slows down the case of
               larger dividends.  inv20u assumes the case of a such a small
               dividend to be unlikely, and inv20l assumes it to be likely.

           For targets other than SHmedia strategy can be one of:

           call-div1
               Calls a library function that uses the single-step division
               instruction "div1" to perform the operation.  Division by zero
               calculates an unspecified result and does not trap.  This is
               the default except for SH4, SH2A and SHcompact.

           call-fp
               Calls a library function that performs the operation in double
               precision floating point.  Division by zero causes a floating-
               point exception.  This is the default for SHcompact with FPU.
               Specifying this for targets that do not have a double precision
               FPU will default to "call-div1".

           call-table
               Calls a library function that uses a lookup table for small
               divisors and the "div1" instruction with case distinction for
               larger divisors.  Division by zero calculates an unspecified
               result and does not trap.  This is the default for SH4.
               Specifying this for targets that do not have dynamic shift
               instructions will default to "call-div1".

           When a division strategy has not been specified the default
           strategy will be selected based on the current target.  For SH2A
           the default strategy is to use the "divs" and "divu" instructions
           instead of library function calls.

       -maccumulate-outgoing-args
           Reserve space once for outgoing arguments in the function prologue
           rather than around each call.  Generally beneficial for performance
           and size.  Also needed for unwinding to avoid changing the stack
           frame around conditional code.

       -mdivsi3_libfunc=name
           Set the name of the library function used for 32-bit signed
           division to name.  This only affects the name used in the call and
           inv:call division strategies, and the compiler still expects the
           same sets of input/output/clobbered registers as if this option
           were not present.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.
           A fixed register is one that the register allocator can not use.
           This is useful when compiling kernel code.  A register range is
           specified as two registers separated by a dash.  Multiple register
           ranges can be specified separated by a comma.

       -mindexed-addressing
           Enable the use of the indexed addressing mode for
           SHmedia32/SHcompact.  This is only safe if the hardware and/or OS
           implement 32-bit wrap-around semantics for the indexed addressing
           mode.  The architecture allows the implementation of processors
           with 64-bit MMU, which the OS could use to get 32-bit addressing,
           but since no current hardware implementation supports this or any
           other way to make the indexed addressing mode safe to use in the
           32-bit ABI, the default is -mno-indexed-addressing.

       -mgettrcost=number
           Set the cost assumed for the "gettr" instruction to number.  The
           default is 2 if -mpt-fixed is in effect, 100 otherwise.

       -mpt-fixed
           Assume "pt*" instructions won't trap.  This generally generates
           better-scheduled code, but is unsafe on current hardware.  The
           current architecture definition says that "ptabs" and "ptrel" trap
           when the target anded with 3 is 3.  This has the unintentional
           effect of making it unsafe to schedule these instructions before a
           branch, or hoist them out of a loop.  For example,
           "__do_global_ctors", a part of libgcc that runs constructors at
           program startup, calls functions in a list which is delimited by
           -1.  With the -mpt-fixed option, the "ptabs" is done before testing
           against -1.  That means that all the constructors run a bit more
           quickly, but when the loop comes to the end of the list, the
           program crashes because "ptabs" loads -1 into a target register.

           Since this option is unsafe for any hardware implementing the
           current architecture specification, the default is -mno-pt-fixed.
           Unless specified explicitly with -mgettrcost, -mno-pt-fixed also
           implies -mgettrcost=100; this deters register allocation from using
           target registers for storing ordinary integers.

       -minvalid-symbols
           Assume symbols might be invalid.  Ordinary function symbols
           generated by the compiler are always valid to load with
           "movi"/"shori"/"ptabs" or "movi"/"shori"/"ptrel", but with
           assembler and/or linker tricks it is possible to generate symbols
           that cause "ptabs" or "ptrel" to trap.  This option is only
           meaningful when -mno-pt-fixed is in effect.  It prevents cross-
           basic-block CSE, hoisting and most scheduling of symbol loads.  The
           default is -mno-invalid-symbols.

       -mbranch-cost=num
           Assume num to be the cost for a branch instruction.  Higher numbers
           make the compiler try to generate more branch-free code if
           possible.  If not specified the value is selected depending on the
           processor type that is being compiled for.

       -mzdcbranch
       -mno-zdcbranch
           Assume (do not assume) that zero displacement conditional branch
           instructions "bt" and "bf" are fast.  If -mzdcbranch is specified,
           the compiler will try to prefer zero displacement branch code
           sequences.  This is enabled by default when generating code for SH4
           and SH4A.  It can be explicitly disabled by specifying
           -mno-zdcbranch.

       -mcbranchdi
           Enable the "cbranchdi4" instruction pattern.

       -mcmpeqdi
           Emit the "cmpeqdi_t" instruction pattern even when -mcbranchdi is
           in effect.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use) the floating-point multiply
           and accumulate instructions.  These instructions are generated by
           default if hardware floating point is used.  The machine-dependent
           -mfused-madd option is now mapped to the machine-independent
           -ffp-contract=fast option, and -mno-fused-madd is mapped to
           -ffp-contract=off.

       -mfsca
       -mno-fsca
           Allow or disallow the compiler to emit the "fsca" instruction for
           sine and cosine approximations.  The option "-mfsca" must be used
           in combination with "-funsafe-math-optimizations".  It is enabled
           by default when generating code for SH4A.  Using "-mno-fsca"
           disables sine and cosine approximations even if
           "-funsafe-math-optimizations" is in effect.

       -mfsrra
       -mno-fsrra
           Allow or disallow the compiler to emit the "fsrra" instruction for
           reciprocal square root approximations.  The option "-mfsrra" must
           be used in combination with "-funsafe-math-optimizations" and
           "-ffinite-math-only".  It is enabled by default when generating
           code for SH4A.  Using "-mno-fsrra" disables reciprocal square root
           approximations even if "-funsafe-math-optimizations" and
           "-ffinite-math-only" are in effect.

       -mpretend-cmove
           Prefer zero-displacement conditional branches for conditional move
           instruction patterns.  This can result in faster code on the SH4
           processor.

       Solaris 2 Options

       These -m options are supported on Solaris 2:

       -mimpure-text
           -mimpure-text, used in addition to -shared, tells the compiler to
           not pass -z text to the linker when linking a shared object.  Using
           this option, you can link position-dependent code into a shared
           object.

           -mimpure-text suppresses the "relocations remain against
           allocatable but non-writable sections" linker error message.
           However, the necessary relocations trigger copy-on-write, and the
           shared object is not actually shared across processes.  Instead of
           using -mimpure-text, you should compile all source code with -fpic
           or -fPIC.

       These switches are supported in addition to the above on Solaris 2:

       -pthreads
           Add support for multithreading using the POSIX threads library.
           This option sets flags for both the preprocessor and linker.  This
           option does not affect the thread safety of object code produced
           by the compiler or that of libraries supplied with it.

       -pthread
           This is a synonym for -pthreads.

       SPARC Options

       These -m options are supported on the SPARC:

       -mno-app-regs
       -mapp-regs
           Specify -mapp-regs to generate output using the global registers 2
           through 4, which the SPARC SVR4 ABI reserves for applications.
           This is the default.

           To be fully SVR4 ABI-compliant at the cost of some performance
           loss, specify -mno-app-regs.  You should compile libraries and
           system software with this option.

       -mflat
       -mno-flat
           With -mflat, the compiler does not generate save/restore
           instructions and uses a "flat" or single register window model.
           This model is compatible with the regular register window model.
           The local registers and the input registers (0--5) are still
           treated as "call-saved" registers and are saved on the stack as
           needed.

           With -mno-flat (the default), the compiler generates save/restore
           instructions (except for leaf functions).  This is the normal
           operating mode.

       -mfpu
       -mhard-float
           Generate output containing floating-point instructions.  This is
           the default.

       -mno-fpu
       -msoft-float
           Generate output containing library calls for floating point.
           Warning: the requisite libraries are not available for all SPARC
           targets.  Normally the facilities of the machine's usual C compiler
           are used, but this cannot be done directly in cross-compilation.
           You must make your own arrangements to provide suitable library
           functions for cross-compilation.  The embedded targets sparc-*-aout
           and sparclite-*-* do provide software floating-point support.

           -msoft-float changes the calling convention in the output file;
           therefore, it is only useful if you compile all of a program with
           this option.  In particular, you need to compile libgcc.a, the
           library that comes with GCC, with -msoft-float in order for this to
           work.

       -mhard-quad-float
           Generate output containing quad-word (long double) floating-point
           instructions.

       -msoft-quad-float
           Generate output containing library calls for quad-word (long
           double) floating-point instructions.  The functions called are
           those specified in the SPARC ABI.  This is the default.

           As of this writing, there are no SPARC implementations that have
           hardware support for the quad-word floating-point instructions.
           They all invoke a trap handler for one of these instructions, and
           then the trap handler emulates the effect of the instruction.
           Because of the trap handler overhead, this is much slower than
           calling the ABI library routines.  Thus the -msoft-quad-float
           option is the default.

       -mno-unaligned-doubles
       -munaligned-doubles
           Assume that doubles have 8-byte alignment.  This is the default.

           With -munaligned-doubles, GCC assumes that doubles have 8-byte
           alignment only if they are contained in another type, or if they
           have an absolute address.  Otherwise, it assumes they have 4-byte
           alignment.  Specifying this option avoids some rare compatibility
           problems with code generated by other compilers.  It is not the
           default because it results in a performance loss, especially for
           floating-point code.

       -mno-faster-structs
       -mfaster-structs
           With -mfaster-structs, the compiler assumes that structures should
           have 8-byte alignment.  This enables the use of pairs of "ldd" and
           "std" instructions for copies in structure assignment, in place of
           twice as many "ld" and "st" pairs.  However, the use of this
           changed alignment directly violates the SPARC ABI.  Thus, it's
           intended only for use on targets where the developer acknowledges
           that their resulting code is not directly in line with the rules of
           the ABI.

       -mcpu=cpu_type
           Set the instruction set, register set, and instruction scheduling
           parameters for machine type cpu_type.  Supported values for
           cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, leon3,
           sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9,
           ultrasparc, ultrasparc3, niagara, niagara2, niagara3 and niagara4.

           Native Solaris and GNU/Linux toolchains also support the value
           native, which selects the best architecture option for the host
           processor.  -mcpu=native has no effect if GCC does not recognize
           the processor.

           Default instruction scheduling parameters are used for values that
           select an architecture and not an implementation.  These are v7,
           v8, sparclite, sparclet, v9.

           Here is a list of each supported architecture and their supported
           implementations.

           v7  cypress

           v8  supersparc, hypersparc, leon, leon3

           sparclite
               f930, f934, sparclite86x

           sparclet
               tsc701

           v9  ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4

           By default (unless configured otherwise), GCC generates code for
           the V7 variant of the SPARC architecture.  With -mcpu=cypress, the
           compiler additionally optimizes it for the Cypress CY7C602 chip, as
           used in the SPARCStation/SPARCServer 3xx series.  This is also
           appropriate for the older SPARCStation 1, 2, IPX etc.

           With -mcpu=v8, GCC generates code for the V8 variant of the SPARC
           architecture.  The only difference from V7 code is that the
           compiler emits the integer multiply and integer divide instructions
           which exist in SPARC-V8 but not in SPARC-V7.  With
           -mcpu=supersparc, the compiler additionally optimizes it for the
           SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
           series.

           With -mcpu=sparclite, GCC generates code for the SPARClite variant
           of the SPARC architecture.  This adds the integer multiply, integer
           divide step and scan ("ffs") instructions which exist in SPARClite
           but not in SPARC-V7.  With -mcpu=f930, the compiler additionally
           optimizes it for the Fujitsu MB86930 chip, which is the original
           SPARClite, with no FPU.  With -mcpu=f934, the compiler additionally
           optimizes it for the Fujitsu MB86934 chip, which is the more recent
           SPARClite with FPU.

           With -mcpu=sparclet, GCC generates code for the SPARClet variant of
           the SPARC architecture.  This adds the integer multiply,
           multiply/accumulate, integer divide step and scan ("ffs")
           instructions which exist in SPARClet but not in SPARC-V7.  With
           -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC
           SPARClet chip.

           With -mcpu=v9, GCC generates code for the V9 variant of the SPARC
           architecture.  This adds 64-bit integer and floating-point move
           instructions, 3 additional floating-point condition code registers
           and conditional move instructions.  With -mcpu=ultrasparc, the
           compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
           chips.  With -mcpu=ultrasparc3, the compiler additionally optimizes
           it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips.  With
           -mcpu=niagara, the compiler additionally optimizes it for Sun
           UltraSPARC T1 chips.  With -mcpu=niagara2, the compiler
           additionally optimizes it for Sun UltraSPARC T2 chips. With
           -mcpu=niagara3, the compiler additionally optimizes it for Sun
           UltraSPARC T3 chips.  With -mcpu=niagara4, the compiler
           additionally optimizes it for Sun UltraSPARC T4 chips.

       -mtune=cpu_type
           Set the instruction scheduling parameters for machine type
           cpu_type, but do not set the instruction set or register set that
           the option -mcpu=cpu_type does.

           The same values for -mcpu=cpu_type can be used for -mtune=cpu_type,
           but the only useful values are those that select a particular CPU
           implementation.  Those are cypress, supersparc, hypersparc, leon,
           leon3, f930, f934, sparclite86x, tsc701, ultrasparc, ultrasparc3,
           niagara, niagara2, niagara3 and niagara4.  With native Solaris and
           GNU/Linux toolchains, native can also be used.

       -mv8plus
       -mno-v8plus
           With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The
           difference from the V8 ABI is that the global and out registers are
           considered 64 bits wide.  This is enabled by default on Solaris in
           32-bit mode for all SPARC-V9 processors.

       -mvis
       -mno-vis
           With -mvis, GCC generates code that takes advantage of the
           UltraSPARC Visual Instruction Set extensions.  The default is
           -mno-vis.

       -mvis2
       -mno-vis2
           With -mvis2, GCC generates code that takes advantage of version 2.0
           of the UltraSPARC Visual Instruction Set extensions.  The default
           is -mvis2 when targeting a cpu that supports such instructions,
           such as UltraSPARC-III and later.  Setting -mvis2 also sets -mvis.

       -mvis3
       -mno-vis3
           With -mvis3, GCC generates code that takes advantage of version 3.0
           of the UltraSPARC Visual Instruction Set extensions.  The default
           is -mvis3 when targeting a cpu that supports such instructions,
           such as niagara-3 and later.  Setting -mvis3 also sets -mvis2 and
           -mvis.

       -mcbcond
       -mno-cbcond
           With -mcbcond, GCC generates code that takes advantage of compare-
           and-branch instructions, as defined in the Sparc Architecture 2011.
           The default is -mcbcond when targeting a cpu that supports such
           instructions, such as niagara-4 and later.

       -mpopc
       -mno-popc
           With -mpopc, GCC generates code that takes advantage of the
           UltraSPARC population count instruction.  The default is -mpopc
           when targeting a cpu that supports such instructions, such as
           Niagara-2 and later.

       -mfmaf
       -mno-fmaf
           With -mfmaf, GCC generates code that takes advantage of the
           UltraSPARC Fused Multiply-Add Floating-point extensions.  The
           default is -mfmaf when targeting a cpu that supports such
           instructions, such as Niagara-3 and later.

       -mfix-at697f
           Enable the documented workaround for the single erratum of the
           Atmel AT697F processor (which corresponds to erratum #13 of the
           AT697E processor).

       -mfix-ut699
           Enable the documented workarounds for the floating-point errata and
           the data cache nullify errata of the UT699 processor.

       These -m options are supported in addition to the above on SPARC-V9
       processors in 64-bit environments:

       -m32
       -m64
           Generate code for a 32-bit or 64-bit environment.  The 32-bit
           environment sets int, long and pointer to 32 bits.  The 64-bit
           environment sets int to 32 bits and long and pointer to 64 bits.

       -mcmodel=which
           Set the code model to one of

           medlow
               The Medium/Low code model: 64-bit addresses, programs must be
               linked in the low 32 bits of memory.  Programs can be
               statically or dynamically linked.

           medmid
               The Medium/Middle code model: 64-bit addresses, programs must
               be linked in the low 44 bits of memory, the text and data
               segments must be less than 2GB in size and the data segment
               must be located within 2GB of the text segment.

           medany
               The Medium/Anywhere code model: 64-bit addresses, programs may
               be linked anywhere in memory, the text and data segments must
               be less than 2GB in size and the data segment must be located
               within 2GB of the text segment.

           embmedany
               The Medium/Anywhere code model for embedded systems: 64-bit
               addresses, the text and data segments must be less than 2GB in
               size, both starting anywhere in memory (determined at link
               time).  The global register %g4 points to the base of the data
               segment.  Programs are statically linked and PIC is not
               supported.

       -mmemory-model=mem-model
           Set the memory model in force on the processor to one of

           default
               The default memory model for the processor and operating
               system.

           rmo Relaxed Memory Order

           pso Partial Store Order

           tso Total Store Order

           sc  Sequential Consistency

           These memory models are formally defined in Appendix D of the Sparc
           V9 architecture manual, as set in the processor's "PSTATE.MM"
           field.

       -mstack-bias
       -mno-stack-bias
           With -mstack-bias, GCC assumes that the stack pointer, and frame
           pointer if present, are offset by -2047 which must be added back
           when making stack frame references.  This is the default in 64-bit
           mode.  Otherwise, assume no such offset is present.

       SPU Options

       These -m options are supported on the SPU:

       -mwarn-reloc
       -merror-reloc
           The loader for SPU does not handle dynamic relocations.  By
           default, GCC gives an error when it generates code that requires a
           dynamic relocation.  -mno-error-reloc disables the error,
           -mwarn-reloc generates a warning instead.

       -msafe-dma
       -munsafe-dma
           Instructions that initiate or test completion of DMA must not be
           reordered with respect to loads and stores of the memory that is
           being accessed.  With -munsafe-dma you must use the "volatile"
           keyword to protect memory accesses, but that can lead to
           inefficient code in places where the memory is known to not change.
           Rather than mark the memory as volatile, you can use -msafe-dma to
           tell the compiler to treat the DMA instructions as potentially
           affecting all memory.

       -mbranch-hints
           By default, GCC generates a branch hint instruction to avoid
           pipeline stalls for always-taken or probably-taken branches.  A
           hint is not generated closer than 8 instructions away from its
           branch.  There is little reason to disable them, except for
           debugging purposes, or to make an object a little bit smaller.

       -msmall-mem
       -mlarge-mem
           By default, GCC generates code assuming that addresses are never
           larger than 18 bits.  With -mlarge-mem code is generated that
           assumes a full 32-bit address.

       -mstdmain
           By default, GCC links against startup code that assumes the SPU-
           style main function interface (which has an unconventional
           parameter list).  With -mstdmain, GCC links your program against
           startup code that assumes a C99-style interface to "main",
           including a local copy of "argv" strings.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.
           A fixed register is one that the register allocator cannot use.
           This is useful when compiling kernel code.  A register range is
           specified as two registers separated by a dash.  Multiple register
           ranges can be specified separated by a comma.

       -mea32
       -mea64
           Compile code assuming that pointers to the PPU address space
           accessed via the "__ea" named address space qualifier are either 32
           or 64 bits wide.  The default is 32 bits.  As this is an ABI-
           changing option, all object code in an executable must be compiled
           with the same setting.

       -maddress-space-conversion
       -mno-address-space-conversion
           Allow/disallow treating the "__ea" address space as superset of the
           generic address space.  This enables explicit type casts between
           "__ea" and generic pointer as well as implicit conversions of
           generic pointers to "__ea" pointers.  The default is to allow
           address space pointer conversions.

       -mcache-size=cache-size
           This option controls the version of libgcc that the compiler links
           to an executable and selects a software-managed cache for accessing
           variables in the "__ea" address space with a particular cache size.
           Possible options for cache-size are 8, 16, 32, 64 and 128.  The
           default cache size is 64KB.

       -matomic-updates
       -mno-atomic-updates
           This option controls the version of libgcc that the compiler links
           to an executable and selects whether atomic updates to the
           software-managed cache of PPU-side variables are used.  If you use
           atomic updates, changes to a PPU variable from SPU code using the
           "__ea" named address space qualifier do not interfere with changes
           to other PPU variables residing in the same cache line from PPU
           code.  If you do not use atomic updates, such interference may
           occur; however, writing back cache lines is more efficient.  The
           default behavior is to use atomic updates.

       -mdual-nops
       -mdual-nops=n
           By default, GCC inserts nops to increase dual issue when it expects
           it to increase performance.  n can be a value from 0 to 10.  A
           smaller n inserts fewer nops.  10 is the default, 0 is the same as
           -mno-dual-nops.  Disabled with -Os.

       -mhint-max-nops=n
           Maximum number of nops to insert for a branch hint.  A branch hint
           must be at least 8 instructions away from the branch it is
           affecting.  GCC inserts up to n nops to enforce this, otherwise it
           does not generate the branch hint.

       -mhint-max-distance=n
           The encoding of the branch hint instruction limits the hint to be
           within 256 instructions of the branch it is affecting.  By default,
           GCC makes sure it is within 125.

       -msafe-hints
           Work around a hardware bug that causes the SPU to stall
           indefinitely.  By default, GCC inserts the "hbrp" instruction to
           make sure this stall won't happen.

       Options for System V

       These additional options are available on System V Release 4 for
       compatibility with other compilers on those systems:

       -G  Create a shared object.  It is recommended that -symbolic or
           -shared be used instead.

       -Qy Identify the versions of each tool used by the compiler, in a
           ".ident" assembler directive in the output.

       -Qn Refrain from adding ".ident" directives to the output file (this is
           the default).

       -YP,dirs
           Search the directories dirs, and no others, for libraries specified
           with -l.

       -Ym,dir
           Look in the directory dir to find the M4 preprocessor.  The
           assembler uses this option.

       TILE-Gx Options

       These -m options are supported on the TILE-Gx:

       -mcmodel=small
           Generate code for the small model.  The distance for direct calls
           is limited to 500M in either direction.  PC-relative addresses are
           32 bits.  Absolute addresses support the full address range.

       -mcmodel=large
           Generate code for the large model.  There is no limitation on call
           distance, pc-relative addresses, or absolute addresses.

       -mcpu=name
           Selects the type of CPU to be targeted.  Currently the only
           supported type is tilegx.

       -m32
       -m64
           Generate code for a 32-bit or 64-bit environment.  The 32-bit
           environment sets int, long, and pointer to 32 bits.  The 64-bit
           environment sets int to 32 bits and long and pointer to 64 bits.

       TILEPro Options

       These -m options are supported on the TILEPro:

       -mcpu=name
           Selects the type of CPU to be targeted.  Currently the only
           supported type is tilepro.

       -m32
           Generate code for a 32-bit environment, which sets int, long, and
           pointer to 32 bits.  This is the only supported behavior so the
           flag is essentially ignored.

       V850 Options

       These -m options are defined for V850 implementations:

       -mlong-calls
       -mno-long-calls
           Treat all calls as being far away (near).  If calls are assumed to
           be far away, the compiler always loads the function's address into
           a register, and calls indirect through the pointer.

       -mno-ep
       -mep
           Do not optimize (do optimize) basic blocks that use the same index
           pointer 4 or more times to copy pointer into the "ep" register, and
           use the shorter "sld" and "sst" instructions.  The -mep option is
           on by default if you optimize.

       -mno-prolog-function
       -mprolog-function
           Do not use (do use) external functions to save and restore
           registers at the prologue and epilogue of a function.  The external
           functions are slower, but use less code space if more than one
           function saves the same number of registers.  The -mprolog-function
           option is on by default if you optimize.

       -mspace
           Try to make the code as small as possible.  At present, this just
           turns on the -mep and -mprolog-function options.

       -mtda=n
           Put static or global variables whose size is n bytes or less into
           the tiny data area that register "ep" points to.  The tiny data
           area can hold up to 256 bytes in total (128 bytes for byte
           references).

       -msda=n
           Put static or global variables whose size is n bytes or less into
           the small data area that register "gp" points to.  The small data
           area can hold up to 64 kilobytes.

       -mzda=n
           Put static or global variables whose size is n bytes or less into
           the first 32 kilobytes of memory.

       -mv850
           Specify that the target processor is the V850.

       -mv850e3v5
           Specify that the target processor is the V850E3V5.  The
           preprocessor constant __v850e3v5__ is defined if this option is
           used.

       -mv850e2v4
           Specify that the target processor is the V850E3V5.  This is an
           alias for the -mv850e3v5 option.

       -mv850e2v3
           Specify that the target processor is the V850E2V3.  The
           preprocessor constant __v850e2v3__ is defined if this option is
           used.

       -mv850e2
           Specify that the target processor is the V850E2.  The preprocessor
           constant __v850e2__ is defined if this option is used.

       -mv850e1
           Specify that the target processor is the V850E1.  The preprocessor
           constants __v850e1__ and __v850e__ are defined if this option is
           used.

       -mv850es
           Specify that the target processor is the V850ES.  This is an alias
           for the -mv850e1 option.

       -mv850e
           Specify that the target processor is the V850E.  The preprocessor
           constant __v850e__ is defined if this option is used.

           If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor
           -mv850e2v3 nor -mv850e3v5 are defined then a default target
           processor is chosen and the relevant __v850*__ preprocessor
           constant is defined.

           The preprocessor constants __v850 and __v851__ are always defined,
           regardless of which processor variant is the target.

       -mdisable-callt
       -mno-disable-callt
           This option suppresses generation of the "CALLT" instruction for
           the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the
           v850 architecture.

           This option is enabled by default when the RH850 ABI is in use (see
           -mrh850-abi), and disabled by default when the GCC ABI is in use.
           If "CALLT" instructions are being generated then the C preprocessor
           symbol "__V850_CALLT__" will be defined.

       -mrelax
       -mno-relax
           Pass on (or do not pass on) the -mrelax command line option to the
           assembler.

       -mlong-jumps
       -mno-long-jumps
           Disable (or re-enable) the generation of PC-relative jump
           instructions.

       -msoft-float
       -mhard-float
           Disable (or re-enable) the generation of hardware floating point
           instructions.  This option is only significant when the target
           architecture is V850E2V3 or higher.  If hardware floating point
           instructions are being generated then the C preprocessor symbol
           "__FPU_OK__" will be defined, otherwise the symbol "__NO_FPU__"
           will be defined.

       -mloop
           Enables the use of the e3v5 LOOP instruction.  The use of this
           instruction is not enabled by default when the e3v5 architecture is
           selected because its use is still experimental.

       -mrh850-abi
       -mghs
           Enables support for the RH850 version of the V850 ABI.  This is the
           default.  With this version of the ABI the following rules apply:

              Integer sized structures and unions are returned via a memory
               pointer rather than a register.

              Large structures and unions (more than 8 bytes in size) are
               passed by value.

              Functions are aligned to 16-bit boundaries.

              The -m8byte-align command line option is supported.

              The -mdisable-callt command line option is enabled by default.
               The -mno-disable-callt command line option is not supported.

           When this version of the ABI is enabled the C preprocessor symbol
           "__V850_RH850_ABI__" is defined.

       -mgcc-abi
           Enables support for the old GCC version of the V850 ABI.  With this
           version of the ABI the following rules apply:

              Integer sized structures and unions are returned in register
               "r10".

              Large structures and unions (more than 8 bytes in size) are
               passed by reference.

              Functions are aligned to 32-bit boundaries, unless optimizing
               for size.

              The -m8byte-align command line option is not supported.

              The -mdisable-callt command line option is supported but not
               enabled by default.

           When this version of the ABI is enabled the C preprocessor symbol
           "__V850_GCC_ABI__" is defined.

       -m8byte-align
       -mno-8byte-align
           Enables support for "doubles" and "long long" types to be aligned
           on 8-byte boundaries.  The default is to restrict the alignment of
           all objects to at most 4-bytes.  When -m8byte-align is in effect
           the C preprocessor symbol "__V850_8BYTE_ALIGN__" will be defined.

       -mbig-switch
           Generate code suitable for big switch tables.  Use this option only
           if the assembler/linker complain about out of range branches within
           a switch table.

       -mapp-regs
           This option causes r2 and r5 to be used in the code generated by
           the compiler.  This setting is the default.

       -mno-app-regs
           This option causes r2 and r5 to be treated as fixed registers.

       VAX Options

       These -m options are defined for the VAX:

       -munix
           Do not output certain jump instructions ("aobleq" and so on) that
           the Unix assembler for the VAX cannot handle across long ranges.

       -mgnu
           Do output those jump instructions, on the assumption that the GNU
           assembler is being used.

       -mg Output code for G-format floating-point numbers instead of
           D-format.

       VMS Options

       These -m options are defined for the VMS implementations:

       -mvms-return-codes
           Return VMS condition codes from "main". The default is to return
           POSIX-style condition (e.g. error) codes.

       -mdebug-main=prefix
           Flag the first routine whose name starts with prefix as the main
           routine for the debugger.

       -mmalloc64
           Default to 64-bit memory allocation routines.

       -mpointer-size=size
           Set the default size of pointers. Possible options for size are 32
           or short for 32 bit pointers, 64 or long for 64 bit pointers, and
           no for supporting only 32 bit pointers.  The later option disables
           "pragma pointer_size".

       VxWorks Options

       The options in this section are defined for all VxWorks targets.
       Options specific to the target hardware are listed with the other
       options for that target.

       -mrtp
           GCC can generate code for both VxWorks kernels and real time
           processes (RTPs).  This option switches from the former to the
           latter.  It also defines the preprocessor macro "__RTP__".

       -non-static
           Link an RTP executable against shared libraries rather than static
           libraries.  The options -static and -shared can also be used for
           RTPs; -static is the default.

       -Bstatic
       -Bdynamic
           These options are passed down to the linker.  They are defined for
           compatibility with Diab.

       -Xbind-lazy
           Enable lazy binding of function calls.  This option is equivalent
           to -Wl,-z,now and is defined for compatibility with Diab.

       -Xbind-now
           Disable lazy binding of function calls.  This option is the default
           and is defined for compatibility with Diab.

       x86-64 Options

       These are listed under

       Xstormy16 Options

       These options are defined for Xstormy16:

       -msim
           Choose startup files and linker script suitable for the simulator.

       Xtensa Options

       These options are supported for Xtensa targets:

       -mconst16
       -mno-const16
           Enable or disable use of "CONST16" instructions for loading
           constant values.  The "CONST16" instruction is currently not a
           standard option from Tensilica.  When enabled, "CONST16"
           instructions are always used in place of the standard "L32R"
           instructions.  The use of "CONST16" is enabled by default only if
           the "L32R" instruction is not available.

       -mfused-madd
       -mno-fused-madd
           Enable or disable use of fused multiply/add and multiply/subtract
           instructions in the floating-point option.  This has no effect if
           the floating-point option is not also enabled.  Disabling fused
           multiply/add and multiply/subtract instructions forces the compiler
           to use separate instructions for the multiply and add/subtract
           operations.  This may be desirable in some cases where strict IEEE
           754-compliant results are required: the fused multiply add/subtract
           instructions do not round the intermediate result, thereby
           producing results with more bits of precision than specified by the
           IEEE standard.  Disabling fused multiply add/subtract instructions
           also ensures that the program output is not sensitive to the
           compiler's ability to combine multiply and add/subtract operations.

       -mserialize-volatile
       -mno-serialize-volatile
           When this option is enabled, GCC inserts "MEMW" instructions before
           "volatile" memory references to guarantee sequential consistency.
           The default is -mserialize-volatile.  Use -mno-serialize-volatile
           to omit the "MEMW" instructions.

       -mforce-no-pic
           For targets, like GNU/Linux, where all user-mode Xtensa code must
           be position-independent code (PIC), this option disables PIC for
           compiling kernel code.

       -mtext-section-literals
       -mno-text-section-literals
           Control the treatment of literal pools.  The default is
           -mno-text-section-literals, which places literals in a separate
           section in the output file.  This allows the literal pool to be
           placed in a data RAM/ROM, and it also allows the linker to combine
           literal pools from separate object files to remove redundant
           literals and improve code size.  With -mtext-section-literals, the
           literals are interspersed in the text section in order to keep them
           as close as possible to their references.  This may be necessary
           for large assembly files.

       -mtarget-align
       -mno-target-align
           When this option is enabled, GCC instructs the assembler to
           automatically align instructions to reduce branch penalties at the
           expense of some code density.  The assembler attempts to widen
           density instructions to align branch targets and the instructions
           following call instructions.  If there are not enough preceding
           safe density instructions to align a target, no widening is
           performed.  The default is -mtarget-align.  These options do not
           affect the treatment of auto-aligned instructions like "LOOP",
           which the assembler always aligns, either by widening density
           instructions or by inserting NOP instructions.

       -mlongcalls
       -mno-longcalls
           When this option is enabled, GCC instructs the assembler to
           translate direct calls to indirect calls unless it can determine
           that the target of a direct call is in the range allowed by the
           call instruction.  This translation typically occurs for calls to
           functions in other source files.  Specifically, the assembler
           translates a direct "CALL" instruction into an "L32R" followed by a
           "CALLX" instruction.  The default is -mno-longcalls.  This option
           should be used in programs where the call target can potentially be
           out of range.  This option is implemented in the assembler, not the
           compiler, so the assembly code generated by GCC still shows direct
           call instructions---look at the disassembled object code to see the
           actual instructions.  Note that the assembler uses an indirect call
           for every cross-file call, not just those that really are out of
           range.

       zSeries Options

       These are listed under

   Options for Code Generation Conventions
       These machine-independent options control the interface conventions
       used in code generation.

       Most of them have both positive and negative forms; the negative form
       of -ffoo is -fno-foo.  In the table below, only one of the forms is
       listed---the one that is not the default.  You can figure out the other
       form by either removing no- or adding it.

       -fbounds-check
           For front ends that support it, generate additional code to check
           that indices used to access arrays are within the declared range.
           This is currently only supported by the Java and Fortran front
           ends, where this option defaults to true and false respectively.

       -fstack-reuse=reuse-level
           This option controls stack space reuse for user declared local/auto
           variables and compiler generated temporaries.  reuse_level can be
           all, named_vars, or none. all enables stack reuse for all local
           variables and temporaries, named_vars enables the reuse only for
           user defined local variables with names, and none disables stack
           reuse completely. The default value is all. The option is needed
           when the program extends the lifetime of a scoped local variable or
           a compiler generated temporary beyond the end point defined by the
           language.  When a lifetime of a variable ends, and if the variable
           lives in memory, the optimizing compiler has the freedom to reuse
           its stack space with other temporaries or scoped local variables
           whose live range does not overlap with it. Legacy code extending
           local lifetime will likely to break with the stack reuse
           optimization.

           For example,

                      int *p;
                      {
                        int local1;

                        p = &local1;
                        local1 = 10;
                        ....
                      }
                      {
                         int local2;
                         local2 = 20;
                         ...
                      }

                      if (*p == 10)  // out of scope use of local1
                        {

                        }

           Another example:

                      struct A
                      {
                          A(int k) : i(k), j(k) { }
                          int i;
                          int j;
                      };

                      A *ap;

                      void foo(const A& ar)
                      {
                         ap = &ar;
                      }

                      void bar()
                      {
                         foo(A(10)); // temp object's lifetime ends when foo returns

                         {
                           A a(20);
                           ....
                         }
                         ap->i+= 10;  // ap references out of scope temp whose space
                                      // is reused with a. What is the value of ap->i?
                      }

           The lifetime of a compiler generated temporary is well defined by
           the C++ standard. When a lifetime of a temporary ends, and if the
           temporary lives in memory, the optimizing compiler has the freedom
           to reuse its stack space with other temporaries or scoped local
           variables whose live range does not overlap with it. However some
           of the legacy code relies on the behavior of older compilers in
           which temporaries' stack space is not reused, the aggressive stack
           reuse can lead to runtime errors. This option is used to control
           the temporary stack reuse optimization.

       -ftrapv
           This option generates traps for signed overflow on addition,
           subtraction, multiplication operations.

       -fwrapv
           This option instructs the compiler to assume that signed arithmetic
           overflow of addition, subtraction and multiplication wraps around
           using twos-complement representation.  This flag enables some
           optimizations and disables others.  This option is enabled by
           default for the Java front end, as required by the Java language
           specification.

       -fexceptions
           Enable exception handling.  Generates extra code needed to
           propagate exceptions.  For some targets, this implies GCC generates
           frame unwind information for all functions, which can produce
           significant data size overhead, although it does not affect
           execution.  If you do not specify this option, GCC enables it by
           default for languages like C++ that normally require exception
           handling, and disables it for languages like C that do not normally
           require it.  However, you may need to enable this option when
           compiling C code that needs to interoperate properly with exception
           handlers written in C++.  You may also wish to disable this option
           if you are compiling older C++ programs that don't use exception
           handling.

       -fnon-call-exceptions
           Generate code that allows trapping instructions to throw
           exceptions.  Note that this requires platform-specific runtime
           support that does not exist everywhere.  Moreover, it only allows
           trapping instructions to throw exceptions, i.e. memory references
           or floating-point instructions.  It does not allow exceptions to be
           thrown from arbitrary signal handlers such as "SIGALRM".

       -fdelete-dead-exceptions
           Consider that instructions that may throw exceptions but don't
           otherwise contribute to the execution of the program can be
           optimized away.  This option is enabled by default for the Ada
           front end, as permitted by the Ada language specification.
           Optimization passes that cause dead exceptions to be removed are
           enabled independently at different optimization levels.

       -funwind-tables
           Similar to -fexceptions, except that it just generates any needed
           static data, but does not affect the generated code in any other
           way.  You normally do not need to enable this option; instead, a
           language processor that needs this handling enables it on your
           behalf.

       -fasynchronous-unwind-tables
           Generate unwind table in DWARF 2 format, if supported by target
           machine.  The table is exact at each instruction boundary, so it
           can be used for stack unwinding from asynchronous events (such as
           debugger or garbage collector).

       -fpcc-struct-return
           Return "short" "struct" and "union" values in memory like longer
           ones, rather than in registers.  This convention is less efficient,
           but it has the advantage of allowing intercallability between GCC-
           compiled files and files compiled with other compilers,
           particularly the Portable C Compiler (pcc).

           The precise convention for returning structures in memory depends
           on the target configuration macros.

           Short structures and unions are those whose size and alignment
           match that of some integer type.

           Warning: code compiled with the -fpcc-struct-return switch is not
           binary compatible with code compiled with the -freg-struct-return
           switch.  Use it to conform to a non-default application binary
           interface.

       -freg-struct-return
           Return "struct" and "union" values in registers when possible.
           This is more efficient for small structures than
           -fpcc-struct-return.

           If you specify neither -fpcc-struct-return nor -freg-struct-return,
           GCC defaults to whichever convention is standard for the target.
           If there is no standard convention, GCC defaults to
           -fpcc-struct-return, except on targets where GCC is the principal
           compiler.  In those cases, we can choose the standard, and we chose
           the more efficient register return alternative.

           Warning: code compiled with the -freg-struct-return switch is not
           binary compatible with code compiled with the -fpcc-struct-return
           switch.  Use it to conform to a non-default application binary
           interface.

       -fshort-enums
           Allocate to an "enum" type only as many bytes as it needs for the
           declared range of possible values.  Specifically, the "enum" type
           is equivalent to the smallest integer type that has enough room.

           Warning: the -fshort-enums switch causes GCC to generate code that
           is not binary compatible with code generated without that switch.
           Use it to conform to a non-default application binary interface.

       -fshort-double
           Use the same size for "double" as for "float".

           Warning: the -fshort-double switch causes GCC to generate code that
           is not binary compatible with code generated without that switch.
           Use it to conform to a non-default application binary interface.

       -fshort-wchar
           Override the underlying type for wchar_t to be short unsigned int
           instead of the default for the target.  This option is useful for
           building programs to run under WINE.

           Warning: the -fshort-wchar switch causes GCC to generate code that
           is not binary compatible with code generated without that switch.
           Use it to conform to a non-default application binary interface.

       -fno-common
           In C code, controls the placement of uninitialized global
           variables.  Unix C compilers have traditionally permitted multiple
           definitions of such variables in different compilation units by
           placing the variables in a common block.  This is the behavior
           specified by -fcommon, and is the default for GCC on most targets.
           On the other hand, this behavior is not required by ISO C, and on
           some targets may carry a speed or code size penalty on variable
           references.  The -fno-common option specifies that the compiler
           should place uninitialized global variables in the data section of
           the object file, rather than generating them as common blocks.
           This has the effect that if the same variable is declared (without
           "extern") in two different compilations, you get a multiple-
           definition error when you link them.  In this case, you must
           compile with -fcommon instead.  Compiling with -fno-common is
           useful on targets for which it provides better performance, or if
           you wish to verify that the program will work on other systems that
           always treat uninitialized variable declarations this way.

       -fno-ident
           Ignore the #ident directive.

       -finhibit-size-directive
           Don't output a ".size" assembler directive, or anything else that
           would cause trouble if the function is split in the middle, and the
           two halves are placed at locations far apart in memory.  This
           option is used when compiling crtstuff.c; you should not need to
           use it for anything else.

       -fverbose-asm
           Put extra commentary information in the generated assembly code to
           make it more readable.  This option is generally only of use to
           those who actually need to read the generated assembly code
           (perhaps while debugging the compiler itself).

           -fno-verbose-asm, the default, causes the extra information to be
           omitted and is useful when comparing two assembler files.

       -frecord-gcc-switches
           This switch causes the command line used to invoke the compiler to
           be recorded into the object file that is being created.  This
           switch is only implemented on some targets and the exact format of
           the recording is target and binary file format dependent, but it
           usually takes the form of a section containing ASCII text.  This
           switch is related to the -fverbose-asm switch, but that switch only
           records information in the assembler output file as comments, so it
           never reaches the object file.  See also -grecord-gcc-switches for
           another way of storing compiler options into the object file.

       -fpic
           Generate position-independent code (PIC) suitable for use in a
           shared library, if supported for the target machine.  Such code
           accesses all constant addresses through a global offset table
           (GOT).  The dynamic loader resolves the GOT entries when the
           program starts (the dynamic loader is not part of GCC; it is part
           of the operating system).  If the GOT size for the linked
           executable exceeds a machine-specific maximum size, you get an
           error message from the linker indicating that -fpic does not work;
           in that case, recompile with -fPIC instead.  (These maximums are 8k
           on the SPARC and 32k on the m68k and RS/6000.  The 386 has no such
           limit.)

           Position-independent code requires special support, and therefore
           works only on certain machines.  For the 386, GCC supports PIC for
           System V but not for the Sun 386i.  Code generated for the IBM
           RS/6000 is always position-independent.

           When this flag is set, the macros "__pic__" and "__PIC__" are
           defined to 1.

       -fPIC
           If supported for the target machine, emit position-independent
           code, suitable for dynamic linking and avoiding any limit on the
           size of the global offset table.  This option makes a difference on
           the m68k, PowerPC and SPARC.

           Position-independent code requires special support, and therefore
           works only on certain machines.

           When this flag is set, the macros "__pic__" and "__PIC__" are
           defined to 2.

       -fpie
       -fPIE
           These options are similar to -fpic and -fPIC, but generated
           position independent code can be only linked into executables.
           Usually these options are used when -pie GCC option is used during
           linking.

           -fpie and -fPIE both define the macros "__pie__" and "__PIE__".
           The macros have the value 1 for -fpie and 2 for -fPIE.

       -fno-jump-tables
           Do not use jump tables for switch statements even where it would be
           more efficient than other code generation strategies.  This option
           is of use in conjunction with -fpic or -fPIC for building code that
           forms part of a dynamic linker and cannot reference the address of
           a jump table.  On some targets, jump tables do not require a GOT
           and this option is not needed.

       -ffixed-reg
           Treat the register named reg as a fixed register; generated code
           should never refer to it (except perhaps as a stack pointer, frame
           pointer or in some other fixed role).

           reg must be the name of a register.  The register names accepted
           are machine-specific and are defined in the "REGISTER_NAMES" macro
           in the machine description macro file.

           This flag does not have a negative form, because it specifies a
           three-way choice.

       -fcall-used-reg
           Treat the register named reg as an allocable register that is
           clobbered by function calls.  It may be allocated for temporaries
           or variables that do not live across a call.  Functions compiled
           this way do not save and restore the register reg.

           It is an error to use this flag with the frame pointer or stack
           pointer.  Use of this flag for other registers that have fixed
           pervasive roles in the machine's execution model produces
           disastrous results.

           This flag does not have a negative form, because it specifies a
           three-way choice.

       -fcall-saved-reg
           Treat the register named reg as an allocable register saved by
           functions.  It may be allocated even for temporaries or variables
           that live across a call.  Functions compiled this way save and
           restore the register reg if they use it.

           It is an error to use this flag with the frame pointer or stack
           pointer.  Use of this flag for other registers that have fixed
           pervasive roles in the machine's execution model produces
           disastrous results.

           A different sort of disaster results from the use of this flag for
           a register in which function values may be returned.

           This flag does not have a negative form, because it specifies a
           three-way choice.

       -fpack-struct[=n]
           Without a value specified, pack all structure members together
           without holes.  When a value is specified (which must be a small
           power of two), pack structure members according to this value,
           representing the maximum alignment (that is, objects with default
           alignment requirements larger than this are output potentially
           unaligned at the next fitting location.

           Warning: the -fpack-struct switch causes GCC to generate code that
           is not binary compatible with code generated without that switch.
           Additionally, it makes the code suboptimal.  Use it to conform to a
           non-default application binary interface.

       -finstrument-functions
           Generate instrumentation calls for entry and exit to functions.
           Just after function entry and just before function exit, the
           following profiling functions are called with the address of the
           current function and its call site.  (On some platforms,
           "__builtin_return_address" does not work beyond the current
           function, so the call site information may not be available to the
           profiling functions otherwise.)

                   void __cyg_profile_func_enter (void *this_fn,
                                                  void *call_site);
                   void __cyg_profile_func_exit  (void *this_fn,
                                                  void *call_site);

           The first argument is the address of the start of the current
           function, which may be looked up exactly in the symbol table.

           This instrumentation is also done for functions expanded inline in
           other functions.  The profiling calls indicate where, conceptually,
           the inline function is entered and exited.  This means that
           addressable versions of such functions must be available.  If all
           your uses of a function are expanded inline, this may mean an
           additional expansion of code size.  If you use extern inline in
           your C code, an addressable version of such functions must be
           provided.  (This is normally the case anyway, but if you get lucky
           and the optimizer always expands the functions inline, you might
           have gotten away without providing static copies.)

           A function may be given the attribute "no_instrument_function", in
           which case this instrumentation is not done.  This can be used, for
           example, for the profiling functions listed above, high-priority
           interrupt routines, and any functions from which the profiling
           functions cannot safely be called (perhaps signal handlers, if the
           profiling routines generate output or allocate memory).

       -finstrument-functions-exclude-file-list=file,file,...
           Set the list of functions that are excluded from instrumentation
           (see the description of "-finstrument-functions").  If the file
           that contains a function definition matches with one of file, then
           that function is not instrumented.  The match is done on
           substrings: if the file parameter is a substring of the file name,
           it is considered to be a match.

           For example:

                   -finstrument-functions-exclude-file-list=/bits/stl,include/sys

           excludes any inline function defined in files whose pathnames
           contain "/bits/stl" or "include/sys".

           If, for some reason, you want to include letter ',' in one of sym,
           write ','. For example,
           "-finstrument-functions-exclude-file-list=',,tmp'" (note the single
           quote surrounding the option).

       -finstrument-functions-exclude-function-list=sym,sym,...
           This is similar to "-finstrument-functions-exclude-file-list", but
           this option sets the list of function names to be excluded from
           instrumentation.  The function name to be matched is its user-
           visible name, such as "vector<int> blah(const vector<int> &)", not
           the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE").  The
           match is done on substrings: if the sym parameter is a substring of
           the function name, it is considered to be a match.  For C99 and C++
           extended identifiers, the function name must be given in UTF-8, not
           using universal character names.

       -fstack-check
           Generate code to verify that you do not go beyond the boundary of
           the stack.  You should specify this flag if you are running in an
           environment with multiple threads, but you only rarely need to
           specify it in a single-threaded environment since stack overflow is
           automatically detected on nearly all systems if there is only one
           stack.

           Note that this switch does not actually cause checking to be done;
           the operating system or the language runtime must do that.  The
           switch causes generation of code to ensure that they see the stack
           being extended.

           You can additionally specify a string parameter: "no" means no
           checking, "generic" means force the use of old-style checking,
           "specific" means use the best checking method and is equivalent to
           bare -fstack-check.

           Old-style checking is a generic mechanism that requires no specific
           target support in the compiler but comes with the following
           drawbacks:

           1.  Modified allocation strategy for large objects: they are always
               allocated dynamically if their size exceeds a fixed threshold.

           2.  Fixed limit on the size of the static frame of functions: when
               it is topped by a particular function, stack checking is not
               reliable and a warning is issued by the compiler.

           3.  Inefficiency: because of both the modified allocation strategy
               and the generic implementation, code performance is hampered.

           Note that old-style stack checking is also the fallback method for
           "specific" if no target support has been added in the compiler.

       -fstack-limit-register=reg
       -fstack-limit-symbol=sym
       -fno-stack-limit
           Generate code to ensure that the stack does not grow beyond a
           certain value, either the value of a register or the address of a
           symbol.  If a larger stack is required, a signal is raised at run
           time.  For most targets, the signal is raised before the stack
           overruns the boundary, so it is possible to catch the signal
           without taking special precautions.

           For instance, if the stack starts at absolute address 0x80000000
           and grows downwards, you can use the flags
           -fstack-limit-symbol=__stack_limit and
           -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of
           128KB.  Note that this may only work with the GNU linker.

       -fsplit-stack
           Generate code to automatically split the stack before it overflows.
           The resulting program has a discontiguous stack which can only
           overflow if the program is unable to allocate any more memory.
           This is most useful when running threaded programs, as it is no
           longer necessary to calculate a good stack size to use for each
           thread.  This is currently only implemented for the i386 and x86_64
           back ends running GNU/Linux.

           When code compiled with -fsplit-stack calls code compiled without
           -fsplit-stack, there may not be much stack space available for the
           latter code to run.  If compiling all code, including library code,
           with -fsplit-stack is not an option, then the linker can fix up
           these calls so that the code compiled without -fsplit-stack always
           has a large stack.  Support for this is implemented in the gold
           linker in GNU binutils release 2.21 and later.

       -fleading-underscore
           This option and its counterpart, -fno-leading-underscore, forcibly
           change the way C symbols are represented in the object file.  One
           use is to help link with legacy assembly code.

           Warning: the -fleading-underscore switch causes GCC to generate
           code that is not binary compatible with code generated without that
           switch.  Use it to conform to a non-default application binary
           interface.  Not all targets provide complete support for this
           switch.

       -ftls-model=model
           Alter the thread-local storage model to be used.  The model
           argument should be one of "global-dynamic", "local-dynamic",
           "initial-exec" or "local-exec".

           The default without -fpic is "initial-exec"; with -fpic the default
           is "global-dynamic".

       -fvisibility=default|internal|hidden|protected
           Set the default ELF image symbol visibility to the specified
           option---all symbols are marked with this unless overridden within
           the code.  Using this feature can very substantially improve
           linking and load times of shared object libraries, produce more
           optimized code, provide near-perfect API export and prevent symbol
           clashes.  It is strongly recommended that you use this in any
           shared objects you distribute.

           Despite the nomenclature, "default" always means public; i.e.,
           available to be linked against from outside the shared object.
           "protected" and "internal" are pretty useless in real-world usage
           so the only other commonly used option is "hidden".  The default if
           -fvisibility isn't specified is "default", i.e., make every symbol
           public---this causes the same behavior as previous versions of GCC.

           A good explanation of the benefits offered by ensuring ELF symbols
           have the correct visibility is given by "How To Write Shared
           Libraries" by Ulrich Drepper (which can be found at
           <http://people.redhat.com/~drepper/>)---however a superior solution
           made possible by this option to marking things hidden when the
           default is public is to make the default hidden and mark things
           public.  This is the norm with DLLs on Windows and with
           -fvisibility=hidden and "__attribute__ ((visibility("default")))"
           instead of "__declspec(dllexport)" you get almost identical
           semantics with identical syntax.  This is a great boon to those
           working with cross-platform projects.

           For those adding visibility support to existing code, you may find
           #pragma GCC visibility of use.  This works by you enclosing the
           declarations you wish to set visibility for with (for example)
           #pragma GCC visibility push(hidden) and #pragma GCC visibility pop.
           Bear in mind that symbol visibility should be viewed as part of the
           API interface contract and thus all new code should always specify
           visibility when it is not the default; i.e., declarations only for
           use within the local DSO should always be marked explicitly as
           hidden as so to avoid PLT indirection overheads---making this
           abundantly clear also aids readability and self-documentation of
           the code.  Note that due to ISO C++ specification requirements,
           "operator new" and "operator delete" must always be of default
           visibility.

           Be aware that headers from outside your project, in particular
           system headers and headers from any other library you use, may not
           be expecting to be compiled with visibility other than the default.
           You may need to explicitly say #pragma GCC visibility push(default)
           before including any such headers.

           extern declarations are not affected by -fvisibility, so a lot of
           code can be recompiled with -fvisibility=hidden with no
           modifications.  However, this means that calls to "extern"
           functions with no explicit visibility use the PLT, so it is more
           effective to use "__attribute ((visibility))" and/or "#pragma GCC
           visibility" to tell the compiler which "extern" declarations should
           be treated as hidden.

           Note that -fvisibility does affect C++ vague linkage entities. This
           means that, for instance, an exception class that is be thrown
           between DSOs must be explicitly marked with default visibility so
           that the type_info nodes are unified between the DSOs.

           An overview of these techniques, their benefits and how to use them
           is at <http://gcc.gnu.org/wiki/Visibility>.

       -fstrict-volatile-bitfields
           This option should be used if accesses to volatile bit-fields (or
           other structure fields, although the compiler usually honors those
           types anyway) should use a single access of the width of the
           field's type, aligned to a natural alignment if possible.  For
           example, targets with memory-mapped peripheral registers might
           require all such accesses to be 16 bits wide; with this flag you
           can declare all peripheral bit-fields as "unsigned short" (assuming
           short is 16 bits on these targets) to force GCC to use 16-bit
           accesses instead of, perhaps, a more efficient 32-bit access.

           If this option is disabled, the compiler uses the most efficient
           instruction.  In the previous example, that might be a 32-bit load
           instruction, even though that accesses bytes that do not contain
           any portion of the bit-field, or memory-mapped registers unrelated
           to the one being updated.

           If the target requires strict alignment, and honoring the field
           type would require violating this alignment, a warning is issued.
           If the field has "packed" attribute, the access is done without
           honoring the field type.  If the field doesn't have "packed"
           attribute, the access is done honoring the field type.  In both
           cases, GCC assumes that the user knows something about the target
           hardware that it is unaware of.

           The default value of this option is determined by the application
           binary interface for the target processor.

       -fsync-libcalls
           This option controls whether any out-of-line instance of the
           "__sync" family of functions may be used to implement the C++11
           "__atomic" family of functions.

           The default value of this option is enabled, thus the only useful
           form of the option is -fno-sync-libcalls.  This option is used in
           the implementation of the libatomic runtime library.

ENVIRONMENT
       This section describes several environment variables that affect how
       GCC operates.  Some of them work by specifying directories or prefixes
       to use when searching for various kinds of files.  Some are used to
       specify other aspects of the compilation environment.

       Note that you can also specify places to search using options such as
       -B, -I and -L.  These take precedence over places specified using
       environment variables, which in turn take precedence over those
       specified by the configuration of GCC.

       LANG
       LC_CTYPE
       LC_MESSAGES
       LC_ALL
           These environment variables control the way that GCC uses
           localization information which allows GCC to work with different
           national conventions.  GCC inspects the locale categories LC_CTYPE
           and LC_MESSAGES if it has been configured to do so.  These locale
           categories can be set to any value supported by your installation.
           A typical value is en_GB.UTF-8 for English in the United Kingdom
           encoded in UTF-8.

           The LC_CTYPE environment variable specifies character
           classification.  GCC uses it to determine the character boundaries
           in a string; this is needed for some multibyte encodings that
           contain quote and escape characters that are otherwise interpreted
           as a string end or escape.

           The LC_MESSAGES environment variable specifies the language to use
           in diagnostic messages.

           If the LC_ALL environment variable is set, it overrides the value
           of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES
           default to the value of the LANG environment variable.  If none of
           these variables are set, GCC defaults to traditional C English
           behavior.

       TMPDIR
           If TMPDIR is set, it specifies the directory to use for temporary
           files.  GCC uses temporary files to hold the output of one stage of
           compilation which is to be used as input to the next stage: for
           example, the output of the preprocessor, which is the input to the
           compiler proper.

       GCC_COMPARE_DEBUG
           Setting GCC_COMPARE_DEBUG is nearly equivalent to passing
           -fcompare-debug to the compiler driver.  See the documentation of
           this option for more details.

       GCC_EXEC_PREFIX
           If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the
           names of the subprograms executed by the compiler.  No slash is
           added when this prefix is combined with the name of a subprogram,
           but you can specify a prefix that ends with a slash if you wish.

           If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an
           appropriate prefix to use based on the pathname it is invoked with.

           If GCC cannot find the subprogram using the specified prefix, it
           tries looking in the usual places for the subprogram.

           The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where
           prefix is the prefix to the installed compiler. In many cases
           prefix is the value of "prefix" when you ran the configure script.

           Other prefixes specified with -B take precedence over this prefix.

           This prefix is also used for finding files such as crt0.o that are
           used for linking.

           In addition, the prefix is used in an unusual way in finding the
           directories to search for header files.  For each of the standard
           directories whose name normally begins with /usr/local/lib/gcc
           (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries
           replacing that beginning with the specified prefix to produce an
           alternate directory name.  Thus, with -Bfoo/, GCC searches foo/bar
           just before it searches the standard directory /usr/local/lib/bar.
           If a standard directory begins with the configured prefix then the
           value of prefix is replaced by GCC_EXEC_PREFIX when looking for
           header files.

       COMPILER_PATH
           The value of COMPILER_PATH is a colon-separated list of
           directories, much like PATH.  GCC tries the directories thus
           specified when searching for subprograms, if it can't find the
           subprograms using GCC_EXEC_PREFIX.

       LIBRARY_PATH
           The value of LIBRARY_PATH is a colon-separated list of directories,
           much like PATH.  When configured as a native compiler, GCC tries
           the directories thus specified when searching for special linker
           files, if it can't find them using GCC_EXEC_PREFIX.  Linking using
           GCC also uses these directories when searching for ordinary
           libraries for the -l option (but directories specified with -L come
           first).

       LANG
           This variable is used to pass locale information to the compiler.
           One way in which this information is used is to determine the
           character set to be used when character literals, string literals
           and comments are parsed in C and C++.  When the compiler is
           configured to allow multibyte characters, the following values for
           LANG are recognized:

           C-JIS
               Recognize JIS characters.

           C-SJIS
               Recognize SJIS characters.

           C-EUCJP
               Recognize EUCJP characters.

           If LANG is not defined, or if it has some other value, then the
           compiler uses "mblen" and "mbtowc" as defined by the default locale
           to recognize and translate multibyte characters.

       Some additional environment variables affect the behavior of the
       preprocessor.

       CPATH
       C_INCLUDE_PATH
       CPLUS_INCLUDE_PATH
       OBJC_INCLUDE_PATH
           Each variable's value is a list of directories separated by a
           special character, much like PATH, in which to look for header
           files.  The special character, "PATH_SEPARATOR", is target-
           dependent and determined at GCC build time.  For Microsoft Windows-
           based targets it is a semicolon, and for almost all other targets
           it is a colon.

           CPATH specifies a list of directories to be searched as if
           specified with -I, but after any paths given with -I options on the
           command line.  This environment variable is used regardless of
           which language is being preprocessed.

           The remaining environment variables apply only when preprocessing
           the particular language indicated.  Each specifies a list of
           directories to be searched as if specified with -isystem, but after
           any paths given with -isystem options on the command line.

           In all these variables, an empty element instructs the compiler to
           search its current working directory.  Empty elements can appear at
           the beginning or end of a path.  For instance, if the value of
           CPATH is ":/special/include", that has the same effect as
           -I. -I/special/include.

       DEPENDENCIES_OUTPUT
           If this variable is set, its value specifies how to output
           dependencies for Make based on the non-system header files
           processed by the compiler.  System header files are ignored in the
           dependency output.

           The value of DEPENDENCIES_OUTPUT can be just a file name, in which
           case the Make rules are written to that file, guessing the target
           name from the source file name.  Or the value can have the form
           file target, in which case the rules are written to file file using
           target as the target name.

           In other words, this environment variable is equivalent to
           combining the options -MM and -MF, with an optional -MT switch too.

       SUNPRO_DEPENDENCIES
           This variable is the same as DEPENDENCIES_OUTPUT (see above),
           except that system header files are not ignored, so it implies -M
           rather than -MM.  However, the dependence on the main input file is
           omitted.

       CPP_RESTRICTED
           If this variable is defined, cpp will skip any include file which
           is not a regular file, and will continue searching for the
           requested name (this is always done if the found file is a
           directory).

BUGS
       For instructions on reporting bugs, see
       <http://www.NetBSD.org/Misc/send-pr.html>.

FOOTNOTES
       1.  On some systems, gcc -shared needs to build supplementary stub code
           for constructors to work.  On multi-libbed systems, gcc -shared
           must select the correct support libraries to link against.  Failing
           to supply the correct flags may lead to subtle defects.  Supplying
           them in cases where they are not necessary is innocuous.

SEE ALSO
       gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1),
       adb(1), dbx(1), sdb(1) and the Info entries for gcc, cpp, as, ld,
       binutils and gdb.

AUTHOR
       See the Info entry for gcc, or
       <http://gcc.gnu.org/onlinedocs/gcc/Contributors.html>, for contributors
       to GCC.

COPYRIGHT
       Copyright (c) 1988-2013 Free Software Foundation, Inc.

       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3 or
       any later version published by the Free Software Foundation; with the
       Invariant Sections being "GNU General Public License" and "Funding Free
       Software", the Front-Cover texts being (a) (see below), and with the
       Back-Cover Texts being (b) (see below).  A copy of the license is
       included in the gfdl(7) man page.

       (a) The FSF's Front-Cover Text is:

            A GNU Manual

       (b) The FSF's Back-Cover Text is:

            You have freedom to copy and modify this GNU Manual, like GNU
            software.  Copies published by the Free Software Foundation raise
            funds for GNU development.



gcc-4.8.3                         2014-01-16                            GCC(1)

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