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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]
	   -fdiagnostics-color=[auto|never|always]
	   -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 -fstack-protector-strong -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 -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 -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 -mpower8-fusion -mno-mpower8-fusion
	   -mpower8-vector -mno-power8-vector -mcrypto -mno-crypto
	   -mdirect-move -mno-direct-move -mquad-memory	-mno-quad-memory
	   -mquad-memory-atomic	-mno-quad-memory-atomic	-mcompat-align-parm
	   -mno-compat-align-parm

	   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 -muser-mode  -mno-user-mode -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	-fno-gnu-unique
	   -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:

	   o   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.

	   o   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:

	   o   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.

	   o   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.

	   o   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".

	   o   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.

	   o   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:

	   o   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:

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

	   o   Item 12:	 Prefer	initialization to assignment in	constructors.

	   o   Item 14:	 Make destructors virtual in base classes.

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

	   o   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:

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

	   o   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.

       -fdiagnostics-color[=WHEN]
       -fno-diagnostics-color
	   Use color in	diagnostics.  WHEN is never, always, or	auto.  The
	   default is auto.  auto means	to use color only when the standard
	   error is a terminal.	 The forms -fdiagnostics-color and
	   -fno-diagnostics-color are aliases for -fdiagnostics-color=always
	   and -fdiagnostics-color=never, respectively.

	   The colors are defined by the environment variable GCC_COLORS.  Its
	   value is a colon-separated list of capabilities and Select Graphic
	   Rendition (SGR) substrings. SGR commands are	interpreted by the
	   terminal or terminal	emulator.  (See	the section in the
	   documentation of your text terminal for permitted values and	their
	   meanings as character attributes.)  These substring values are
	   integers in decimal representation and can be concatenated with
	   semicolons.	Common values to concatenate include 1 for bold, 4 for
	   underline, 5	for blink, 7 for inverse, 39 for default foreground
	   color, 30 to	37 for foreground colors, 90 to	97 for 16-color	mode
	   foreground colors, 38;5;0 to	38;5;255 for 88-color and 256-color
	   modes foreground colors, 49 for default background color, 40	to 47
	   for background colors, 100 to 107 for 16-color mode background
	   colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes
	   background colors.

	   The default GCC_COLORS is
	   error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01
	   where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan,
	   01;32 is bold green and 01 is bold. Setting GCC_COLORS to the empty
	   string disables colors.  Supported capabilities are as follows.

	   "error="
	       SGR substring for error:	markers.

	   "warning="
	       SGR substring for warning: markers.

	   "note="
	       SGR substring for note: markers.

	   "caret="
	       SGR substring for caret line.

	   "locus="
	       SGR substring for location information, file:line or
	       file:line:column	etc.

	   "quote="
	       SGR substring for information printed within quotes.

       -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:

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

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

	   o   (C++ only) Ambiguous virtual bases.

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

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

	   o   (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.

	   o   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.

	   o   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.

	   o   A function-like macro that appears without arguments.

	   o   The unary plus operator.

	   o   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.

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

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

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

	   o   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.

	   o   Usage of	ISO string concatenation is detected.

	   o   Initialization of automatic aggregates.

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

	   o   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.

	   o   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.

	   o   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.

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

			 warning: stack	usage is 1120 bytes

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

			 warning: stack	usage might be 1648 bytes

	   o   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:

	   o   The name	of the function.

	   o   A number	of bytes.

	   o   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.

	   o   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.

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

	   o   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).

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

	   o   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.

       -fstack-protector-strong
	   Like	-fstack-protector but includes additional functions to be
	   protected --- those that have local array definitions, or have
	   references to local frame addresses.

       -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.

       -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".

       -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.

       -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.

       -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, armv7e-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 GNU/Linux, and not all architectures are recognized.  If the
	   auto-detect is unsuccessful the option has no effect.

       -mtune=name
	   This	option specifies the name of the target	ARM processor for
	   which GCC should tune the performance of the	code.  For some	ARM
	   implementations better performance can be obtained by using this
	   option.  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.

	   -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
	   GNU/Linux, and not all architectures	are recognized.	 If the	auto-
	   detect is unsuccessful the option has no effect.

       -mcpu=name
	   This	specifies the name of the target ARM processor.	 GCC uses this
	   name	to derive the name of the target ARM architecture (as if
	   specified by	-march)	and the	ARM processor type for which to	tune
	   for performance (as if specified by -mtune).	 Where this option is
	   used	in conjunction with -march or -mtune, those options take
	   precedence over the appropriate part	of this	option.

	   Permissible names for this option are the same as those for -mtune.

	   -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
	   GNU/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:

       o   The compiler	never sets "EIND".

       o   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.

       o   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.

       o   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.

       o   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.

       o   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.

       o   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/").

       o   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.

       o   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.

       o   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.>
       o   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.

       o   The startup code initializes	the "RAMP" special function registers
	   with	zero.

       o   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.

       o   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.

       o   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.

       o   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-use-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 function