@cindex order of options
@cindex options, order
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 @option{-L} more than once,
-the directories are searched in the order specified.
+you use doesn't matter. Order does matter when you use several
+options of the same kind; for example, if you specify @option{-L} more
+than once, the directories are searched in the order specified. Also,
+the placement of the @option{-l} option is significant.
Many options have long names starting with @samp{-f} or with
@samp{-W}---for example,
@item Warning Options
@xref{Warning Options,,Options to Request or Suppress Warnings}.
@gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
--w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
+-w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
-Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
-Wchar-subscripts -Wclobbered -Wcomment @gol
--Wconversion -Wcoverage-mismatch -Wno-deprecated-declarations @gol
+-Wconversion -Wcoverage-mismatch -Wno-deprecated-declarations @gol
-Wdisabled-optimization -Wno-div-by-zero @gol
-Wempty-body -Wno-endif-labels @gol
-Werror -Werror=* @gol
-Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
-Wredundant-decls @gol
-Wreturn-type -Wsequence-point -Wshadow @gol
--Wsign-compare -Wstack-protector @gol
--Wstrict-aliasing -Wstrict-aliasing=2 @gol
+-Wsign-compare -Wsign-conversion -Wstack-protector @gol
+-Wstrict-aliasing -Wstrict-aliasing=n @gol
-Wstrict-overflow -Wstrict-overflow=@var{n} @gol
-Wswitch -Wswitch-default -Wswitch-enum @gol
--Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
+-Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
-Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
-Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
-Wunused-value -Wunused-variable @gol
@item Debugging Options
@xref{Debugging Options,,Options for Debugging Your Program or GCC}.
@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
+-fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
-fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
-fdump-ipa-all -fdump-ipa-cgraph @gol
-ffinite-math-only -fno-signed-zeros @gol
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
-fomit-frame-pointer -foptimize-register-move @gol
--foptimize-sibling-calls -fprefetch-loop-arrays @gol
+-foptimize-sibling-calls -fpredictive-commoning -fprefetch-loop-arrays @gol
-fprofile-generate -fprofile-use @gol
-fregmove -frename-registers @gol
-freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
-fcheck-data-deps @gol
-ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
-ftree-ch -ftree-sra -ftree-ter -ftree-fre -ftree-vectorize @gol
--ftree-vect-loop-version -ftree-salias -fipa-pta -fweb @gol
+-ftree-vect-loop-version -fvect-cost-model -ftree-salias -fipa-pta -fweb @gol
-ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
--param @var{name}=@var{value}
-O -O0 -O1 -O2 -O3 -Os}
-mcall-prologues -mno-tablejump -mtiny-stack -mint8}
@emph{Blackfin Options}
-@gccoptlist{-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
--mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
--mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
--mno-id-shared-library -mshared-library-id=@var{n} @gol
--mleaf-id-shared-library -mno-leaf-id-shared-library @gol
--msep-data -mno-sep-data -mlong-calls -mno-long-calls}
+@gccoptlist{-mcpu=@var{cpu} -msim -momit-leaf-frame-pointer @gol
+-mno-omit-leaf-frame-pointer -mspecld-anomaly -mno-specld-anomaly @gol
+-mcsync-anomaly -mno-csync-anomaly -mlow-64k -mno-low64k @gol
+-mstack-check-l1 -mid-shared-library -mno-id-shared-library @gol
+-mshared-library-id=@var{n} -mleaf-id-shared-library @gol
+-mno-leaf-id-shared-library -msep-data -mno-sep-data -mlong-calls @gol
+-mno-long-calls}
@emph{CRIS Options}
@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
-masm=@var{dialect} -mno-fancy-math-387 @gol
-mno-fp-ret-in-387 -msoft-float @gol
-mno-wide-multiply -mrtd -malign-double @gol
--mpreferred-stack-boundary=@var{num} -mcx16 -msahf @gol
--mmmx -msse -msse2 -msse3 -mssse3 -msse4a -m3dnow -mpopcnt -mabm @gol
+-mpreferred-stack-boundary=@var{num} -mcx16 -msahf -mrecip @gol
+-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 @gol
+-msse4a -m3dnow -mpopcnt -mabm @gol
-mthreads -mno-align-stringops -minline-all-stringops @gol
-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
-m96bit-long-double -mregparm=@var{num} -msseregparm @gol
@item -Wreturn-type
@opindex Wreturn-type
-Warn whenever a function is defined with a return-type that defaults to
-@code{int}. Also warn about any @code{return} statement with no
-return-value in a function whose return-type is not @code{void}.
+@opindex Wno-return-type
+Warn whenever a function is defined with a return-type that defaults
+to @code{int}. Also warn about any @code{return} statement with no
+return-value in a function whose return-type is not @code{void}
+(falling off the end of the function body is considered returning
+without a value), and about a @code{return} statement with a
+expression in a function whose return-type is @code{void}.
Also warn if the return type of a function has a type qualifier
such as @code{const}. For ISO C such a type qualifier has no effect,
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 @option{-Wall}.
+It is equivalent to -Wstrict-aliasing=3
-@item -Wstrict-aliasing=2
-@opindex Wstrict-aliasing=2
+@item -Wstrict-aliasing=n
+@opindex Wstrict-aliasing=n
This option is only active when @option{-fstrict-aliasing} is active.
It warns about code which might break the strict aliasing rules that the
-compiler is using for optimization. This warning catches more cases than
-@option{-Wstrict-aliasing}, but it will also give a warning for some ambiguous
-cases that are safe.
+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.
+@option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
+with n=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 frontend 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 frontend only.
+
+Level 3 (default for @option{-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 punn+dereference pattern in the frontend:
+@code{*(int*)&some_float}.
+If optimization is enabled, it also runs in the backend, 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.
@item -Wstrict-overflow
@item -Wstrict-overflow=@var{n}
@itemize @bullet
@item
-A function can return either with or without a value. (Falling
-off the end of the function body is considered returning without
-a value.) For example, this function would evoke such a
-warning:
-
-@smallexample
-@group
-foo (a)
-@{
- if (a > 0)
- return a;
-@}
-@end group
-@end smallexample
-
-@item
-An unsigned value is compared against zero with @samp{<} or @samp{>=}.
+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
+@samp{<} or @samp{>=}. This warning can be independently controlled
+by @option{-Wtype-limits}.
@item @r{(C only)}
Storage-class specifiers like @code{static} are not the first things
@samp{do while} statement. This warning can be independently
controlled by @option{-Wempty-body}.
+@item @r{(C++ only)}
+An empty body occurs in a @samp{while} or @samp{for} statement with no
+whitespacing before the semicolon. This warning can be independently
+controlled by @option{-Wempty-body}.
+
@item
A pointer is compared against integer zero with @samp{<}, @samp{<=},
@samp{>}, or @samp{>=}.
to functions. In C++, warn also when an arithmetic operation involves
@code{NULL}. This warning is also enabled by @option{-pedantic}.
+@item -Wtype-limits
+@opindex Wtype-limits
+@opindex Wno-type-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
+@samp{<} or @samp{>=}. This warning is also enabled by
+@option{-Wextra}.
+
@item -Wbad-function-cast @r{(C only)}
@opindex Wbad-function-cast
Warn whenever a function call is cast to a non-matching type.
@item -Wconversion
@opindex Wconversion
+@opindex Wno-conversion
Warn for implicit conversions that may alter a value. This includes
conversions between real and integer, like @code{abs (x)} when
@code{x} is @code{double}; conversions between signed and unsigned,
like @code{unsigned ui = -1}; and conversions to smaller types, like
@code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
-changed by the conversion like in @code{abs (2.0)}.
+changed by the conversion like in @code{abs (2.0)}. Warnings about
+conversions between signed and unsigned integers can be disabled by
+using @option{-Wno-sign-conversion}.
For C++, also warn for conversions between @code{NULL} and non-pointer
types; confusing overload resolution for user-defined conversions; and
conversions that will never use a type conversion operator:
conversions to @code{void}, the same type, a base class or a reference
-to them.
+to them. Warnings about conversions between signed and unsigned
+integers are disabled by default in C++ unless
+@option{-Wsign-conversion} is explicitly enabled.
@item -Wempty-body
@opindex Wempty-body
-An empty body occurs in an @samp{if}, @samp{else} or @samp{do while}
-statement. This warning is also enabled by @option{-Wextra}.
+Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
+while} statement. Additionally, in C++, warn when an empty body occurs
+in a @samp{while} or @samp{for} statement with no whitespacing before
+the semicolon. This warning is also enabled by @option{-Wextra}.
@item -Wsign-compare
@opindex Wsign-compare
This warning is also enabled by @option{-Wextra}; to get the other warnings
of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
+@item -Wsign-conversion
+@opindex Wsign-conversion
+@opindex Wno-sign-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 @option{-Wconversion}.
+
@item -Waddress
@opindex Waddress
@opindex Wno-address
generate test coverage data. Coverage data will match the source files
more closely, if you do not optimize.
+@item -fdbg-cnt-list
+@opindex fdbg-cnt-list
+Print the name and the counter upperbound for all debug counters.
+
+@item -fdbg-cnt=@var{counter-value-list}
+@opindex fdbg-cnt
+Set the internal debug counter upperbound. @var{counter-value-list}
+is a comma-separated list of @var{name}:@var{value} pairs
+which sets the upperbound of each debug counter @var{name} to @var{value}.
+All debug counters have the initial upperbound of @var{UINT_MAX},
+thus dbg_cnt() returns true always unless the upperbound is set by this option.
+e.g. With -fdbg-cnt=dce:10,tail_call:0
+dbg_cnt(dce) will return true only for first 10 invocations
+and dbg_cnt(tail_call) will return false always.
+
@item -d@var{letters}
@item -fdump-rtl-@var{pass}
@opindex d
@item -fdump-unnumbered
@opindex fdump-unnumbered
When doing debugging dumps (see @option{-d} option above), suppress instruction
-numbers, line number note and address output. This makes it more feasible to
+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 @option{-g}.
@opindex O3
Optimize yet more. @option{-O3} turns on all optimizations specified by
@option{-O2} and also turns on the @option{-finline-functions},
-@option{-funswitch-loops} and @option{-fgcse-after-reload} options.
+@option{-funswitch-loops}, @option{-fpredictive-commoning} and
+@option{-fgcse-after-reload} options.
@item -O0
@opindex O0
to control which version is executed. This option is enabled by default
except at level @option{-Os} where it is disabled.
+@item -fvect-cost-model
+Enable cost model for vectorization.
+
@item -ftree-vrp
Perform Value Range Propagation on trees. This is similar to the
constant propagation pass, but instead of values, ranges of values are
With this option, the compiler will create multiple copies of some
local variables when unrolling a loop which can result in superior code.
+@item -fpredictive-commoning
+@opindex 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 @option{-O3}.
+
@item -fprefetch-loop-arrays
@opindex fprefetch-loop-arrays
If supported by the target machine, generate instructions to prefetch
prints a banner like:
@smallexample
-Assember options
-================
+Assembler options
+=================
Use "-Wa,OPTION" to pass "OPTION" to the assembler.
@end smallexample
@cindex Blackfin Options
@table @gcctabopt
+@item -mcpu=@var{cpu}
+@opindex mcpu=
+Specifies the name of the target Blackfin processor. Currently, @var{cpu}
+can be one of @samp{bf531}, @samp{bf532}, @samp{bf533},
+@samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf561}.
+Without this option, @samp{bf532} is used as the processor by default.
+The corresponding predefined processor macros for @var{cpu} is to
+be defined. For the @samp{bfin-elf} toolchain, this causes the hardware
+BSP provided by libgloss to be linked in if @samp{-msim} is not given.
+Support for @samp{bf561} is incomplete; only the processor macro is defined.
+
+@item -msim
+@opindex 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 @samp{bfin-elf} toolchain.
+
@item -momit-leaf-frame-pointer
@opindex momit-leaf-frame-pointer
Don't keep the frame pointer in a register for leaf functions. This
is @var{version}. Typical values of @var{version} include @code{10.1},
@code{10.2}, and @code{10.3.9}.
-The default for this option is to make choices that seem to be most
-useful.
+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 which
+are compatible with as many systems and code bases as possible.
@item -mkernel
@opindex mkernel
@opindex mcpu
A deprecated synonym for @option{-mtune}.
-@item -m386
-@itemx -m486
-@itemx -mpentium
-@itemx -mpentiumpro
-@opindex m386
-@opindex m486
-@opindex mpentium
-@opindex mpentiumpro
-These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
-@option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
-These synonyms are deprecated.
-
@item -mfpmath=@var{unit}
@opindex march
Generate floating point arithmetics for selected unit @var{unit}. The choices
@opindex mpc80
Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
-is specified, the significand of floating-point operations is rounded to 24
-bits (single precision), @option{-mpc64} rounds the significand of
-floating-point operations to 53 bits (double precision) and @option{-mpc80}
-rounds the significand of floating-point operations to 64 bits (extended
-double precision). Note that a change of default precision control may
-affect the results returned by some of the mathematical functions.
+is specified, the significands of results of floating-point operations are
+rounded to 24 bits (single precision); @option{-mpc64} rounds the the
+significands of results of floating-point operations to 53 bits (double
+precision) and @option{-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.
@item -mstackrealign
@opindex mstackrealign
@itemx -mno-sse3
@item -mssse3
@itemx -mno-ssse3
+@item -msse4.1
+@itemx -mno-sse4.1
+@item -msse4.2
+@itemx -mno-sse4.2
+@item -msse4
+@itemx -mno-sse4
@item -msse4a
@item -mno-sse4a
@item -m3dnow
@opindex m3dnow
@opindex mno-3dnow
These switches enable or disable the use of instructions in the MMX,
-SSE, SSE2, SSE3, SSSE3, SSE4A, ABM or 3DNow! extended instruction sets.
+SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4A, ABM or 3DNow! extended
+instruction sets.
These extensions are also available as built-in functions: see
@ref{X86 Built-in Functions}, for details of the functions enabled and
disabled by these switches.
In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
+@item -mrecip
+@opindex mrecip
+This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
+vectorized variants RCPPS and RSQRTPS) instead of DIVSS and SQRTSS (and their
+vectorized variants). These instructions will be generated only when
+@option{-funsafe-math-optimizatons} is enabled.
+
@item -mpush-args
@itemx -mno-push-args
@opindex mpush-args
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