g++-4.6(1) - GNU project C and C++ compiler
-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 will exit 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 will instead return with
    numerically highest error produced by any phase that returned an error indication.  The C, C++, and
    Fortran frontends 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 which don't require preprocessing are ignored.
-o file
    Place output in file file.  This applies regardless 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.
-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 will also be 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 which have no documentation
    associated with them will also be 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=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), which have a description the following can be used:
--help=warnings,^joined,^undocumented
        --help=target,optimizers

The --help= option can be repeated on the command line.  Each successive use will display 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:
        -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 will invoke all subprograms of gcc under gdb --args, thus the invocation of cc1 will be gdb
    --args cc1 ....
-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.
-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.
-ansi
    In C mode, this is equivalent to -std=c90. In C++ mode, it is equivalent to -std=c++98.
-std=
    Determine the language standard.   This option is currently only supported when compiling C or C++.
-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.
-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 that 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 takes place in 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 takes place in 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.
-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 which 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.
-no-integrated-cpp
    Performs a compilation in two passes: preprocessing and compiling.  This option allows a user
    supplied "cc1", "cc1plus", or "cc1obj" via the -B option.  The user supplied compilation step can
    then add in an additional preprocessing step after normal preprocessing but before compiling.  The
    default is to use the integrated cpp (internal cpp)

    The semantics of this option will change if "cc1", "cc1plus", and "cc1obj" are merged.
-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; but 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.  Version 2 is the version of the C++ ABI that first appeared in G++
    3.4.  Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.  Version 0 will always
    be the version that conforms most closely to the C++ ABI specification.  Therefore, the ABI obtained
    using version 0 will change as ABI bugs are fixed.
-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"
    will only return 0 if it is declared throw(), in which case the compiler will always check 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).
-fconserve-space
    Put uninitialized or runtime-initialized global variables into the common segment, as C does.  This
    saves space in the executable at the cost of not diagnosing duplicate definitions.  If you compile
    with this flag and your program mysteriously crashes after "main()" has completed, you may have an
    object that is being destroyed twice because two definitions were merged.

    This option is no longer useful on most targets, now that support has been added for putting
    variables into BSS without making them common.
-fconstexpr-depth=n
    Set the maximum nested evaluation depth for C++0x constexpr functions to n.  A limit is needed to
    detect endless recursion during constant expression evaluation.  The minimum specified by the
    standard is 512.
-fno-deduce-init-list
    Disable 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 option is present because this deduction is an extension to the current specification in the
    C++0x working draft, and there was some concern about potential overload resolution problems.
-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 which 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 which 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 runtime.  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 will still optimize based on the specifications, so throwing
    an unexpected exception will result in undefined behavior.
-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++.

    The default if neither flag is given 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 which 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 will 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 will cause linker errors if these functions are not inlined everywhere they are
    called.
-fms-extensions
    Disable pedantic 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 though 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 will
    actually make 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 will result 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 will allow some nonconforming code to compile.
-fno-pretty-templates
    When an error message refers to a specialization of a function template, the compiler will normally
    print 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 will omit any template arguments which match the default template arguments for that
    template.  If either of these behaviors make it harder to understand the error message rather than
    easier, using -fno-pretty-templates will 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++ runtime
    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 it will generate it as needed. The dynamic_cast operator can still be used for casts
    that do not require runtime 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 enumeration type can only be one
    of the values of the enumeration (as defined in the C++ standard; basically, a value which 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 enumeration
    type.
-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++0x).
-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 will only work if your C library supports "__cxa_atexit".
-fno-use-cxa-get-exception-ptr
    Don't use the "__cxa_get_exception_ptr" runtime routine.  This will cause "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 methods where the
    addresses of the two functions were 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 will have
    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:
-fno-weak
    Do not use weak symbol support, even if it is provided by the linker.  By default, G++ will use weak
    symbols if they are available.  This option exists only for testing, and should not be used by end-
    users; it will result in inferior code and has no benefits.  This option may be removed in a future
    release of G++.
-fno-default-inline
    Do not assume inline for functions defined inside a class scope.
      Note that these functions will have linkage like inline functions; they just won't be inlined by
    default.
-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 will rearrange 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.

The following -W... options are not affected by -Wall.
-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.
-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++ would try to
    preserve unsignedness, but the standard mandates the current behavior.
-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, will override 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 that will
    run 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 that will run all such default
    destructors, in reverse order.

    The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods thusly generated will 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 will be invoked by the runtime
    immediately after a new object instance is allocated; the "- (void) .cxx_destruct" methods will be
    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.
-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.
    -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, ...).  The options described below can be used to control the diagnostic messages formatting
    algorithm, e.g. how many characters per line, how often source location information should be reported.
    Right now, only the C++ front end can honor these options.  However it is expected, in the near future,
    that the remaining front ends would be able to digest them correctly.
-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 will be done; each error message will appear on a single line.
-fdiagnostics-show-location=once
    Only meaningful in line-wrapping mode.  Instructs the diagnostic messages reporter to emit once
    source location information; that is, in case the message is too long to fit on a single physical
    line and has to be wrapped, the source location won't be emitted (as prefix) again, over and over, in
    subsequent continuation lines.  This is the default behavior.
-fdiagnostics-show-location=every-line
    Only meaningful in line-wrapping mode.  Instructs the diagnostic messages reporter to emit the same
    source location information (as prefix) for physical lines that result from the process of breaking a
    message which is too long to fit on a single line.
-fno-diagnostics-show-option
    By default, each diagnostic emitted includes text which indicates 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.
    -Wcoverage-mismatch
        Warn if feedback profiles do not match when using the -fprofile-use option.  If a source file was
        changed between -fprofile-gen and -fprofile-use, the files with the profile feedback can fail to
        match the source file and GCC can not 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.  Disable the error for this warning
        can result in poorly optimized code, so disabling the error 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.

Options to Request or Suppress Warnings
    Warnings are diagnostic messages that report constructions which are not inherently erroneous but which
    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 which 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 -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 will emit a diagnostic
stating that the option is not recognized.  However, if the -Wno- form is used, the behavior is slightly
different: No diagnostic will be 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 will warn that an unrecognized option was used.
-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.
-pedantic-errors
    Like -pedantic, 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++0x-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)
    -Wmissing-braces -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.)
-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-cpp
    (C, Objective-C, C++, Objective-C++ and Fortran only)
-Wformat
    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
    -pedantic is used with -Wformat, warnings will be 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).

    Since -Wformat also checks for null format arguments for several functions, -Wformat also implies
    -Wnonnull.
-Wformat is included in -Wall.  For more control over some aspects of format checking, the options
-Wformat-y2k, -Wno-format-extra-args, -Wno-format-zero-length, -Wformat-nonliteral,
-Wformat-security, and -Wformat=2 are available, but are not included in -Wall.

NOTE: In Ubuntu 8.10 and later versions this option is enabled by default for C, C++, ObjC, ObjC++.
To disable, use -Wformat=0.
-Wformat-y2k
    If -Wformat is specified, also warn about "strftime" formats which may yield only a two-digit year.
-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 will suppress 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 (C and Objective-C only)
    If -Wformat is specified, do not warn about zero-length formats.  The C standard specifies that zero-
    length formats are allowed.
-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.)

    NOTE: In Ubuntu 8.10 and later versions this option is enabled by default for C, C++, ObjC, ObjC++.
    To disable, use -Wno-format-security, or disable all format warnings with -Wformat=0.  To make format
    security warnings fatal, specify -Werror=format-security.
-Wnonnull (C and Objective-C only)
    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.
-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 -pedantic.
-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.

            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.
-Wsequence-point
    Warn about code that may have undefined semantics because of violations of sequence point rules in
    the C and C++ standards.
-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-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] will cause
    a warning, while x[(void)i,j] will 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.
-Wunknown-pragmas
    Warn when a #pragma directive is encountered which is not understood by GCC.  If this command line
    option is used, warnings will even be issued for unknown pragmas in system header files.  This is not
    the case if the warnings were 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 which 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 which 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=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 -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 frontend: "*(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.
-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 which 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 which 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 will require, in particular when
    determining whether a loop will be executed at all.
-Wsuggest-attribute=[pure|const|noreturn]
    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 which 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 nor returns 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.
-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 will 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.
-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
    will not warn if a local variable shadows a struct/class/enum, but will warn if it shadows an
    explicit typedef.
-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.
-Wunsafe-loop-optimizations
    Warn if the loop cannot be optimized because the compiler could not assume anything on the bounds of
    the loop indices.  With -funsafe-loop-optimizations warn if the compiler made such assumptions.
-Wno-pedantic-ms-format (MinGW targets only)
    Disables the warnings about non-ISO "printf" / "scanf" format width specifiers "I32", "I64", and "I"
    used on Windows targets depending on the MS runtime, when you are using the options -Wformat and
    -pedantic without gnu-extensions.
-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
    -pedantic.
-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++0x-compat (C++ and Objective-C++ only)
    Warn about C++ constructs whose meaning differs between ISO C++ 1998 and ISO C++ 200x, e.g.,
    identifiers in ISO C++ 1998 that will become keywords in ISO C++ 200x.  This warning 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 which 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 will get a warning.  These warnings will 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 will just be 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 will 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.
-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 enum types. In C++ this 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 which 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.
-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-attributes
    Do not warn if an unexpected "__attribute__" is used, such as unrecognized attributes, function
    attributes applied to variables, etc.  This will 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__".
-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 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 would
    cause 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 would 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.
-Wmissing-format-attribute
    Warn about function pointers which might be candidates for "format" attributes.  Note these are only
    possible candidates, not absolute ones.  GCC will guess 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 will also warn about function definitions which might be candidates for "format" attributes.
    Again, these are only possible candidates.  GCC will guess 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.
-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 which have not been
    normalized; this option controls that warning.

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

    Unfortunately, there are some characters which ISO C and ISO C++ allow in identifiers that when
    turned into NFC aren't allowable as 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 would only want
    to do this if you were 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", will display just like a regular "n" which 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 will warn 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 is unable to 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" will be 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.
-Winline
    Warn if a function can not be inlined and it was declared as inline.  Even with this option, the
    compiler will 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 -pedantic 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.
-Wvla
    Warn if variable length array is used in the code.  -Wno-vla will prevent the -pedantic 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 were unable to
    handle the code effectively.  Often, the problem is that your code is too big or too complex; GCC
    will refuse 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 -pedantic, 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 will not
    be protected against stack smashing.
-Wno-mudflap
    Suppress warnings about constructs that cannot be instrumented by -fmudflap.
    -Woverlength-strings
        Warn about string constants which are longer than the "minimum maximum" length specified in the C
        standard.  Modern compilers generally allow string constants which 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 -pedantic, and can be disabled with -Wno-overlength-strings.

    -Wunsuffixed-float-constants (C and Objective-C only)
        GCC will issue a warning for any floating constant that does not have a suffix.  When used together
        with -Wsystem-headers it will warn 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 will probably make 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 were already at hand; some statements may execute in different places because
    they were 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.
-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.
-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 which 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 will
    increase the size of debugging information by as much as a factor of two.
-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.
-gdwarf-version
    Produce debugging information in DWARF format (if that is supported).  This is the format used by DBX
    on IRIX 6.  The value of version may be either 2, 3 or 4; the default version is 2.

    Note that with DWARF version 2 some ports require, and will 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.
-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 VMS debug format (if that is supported).  This is the format used by
    DEBUG on 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 would have generated 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.
-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 will be 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-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 DWARF2 debugging information by eliminating duplicated information about each symbol.  This
    option only makes sense when generating DWARF2 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 was 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 was 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 will generate debug information.  The intent is
    to reduce duplicate struct debug information between different object files within the same program.
-fenable-icf-debug
    Generate additional debug information to support identical code folding (ICF).  This option only
    works with DWARF version 2 or higher.
-fno-merge-debug-strings
    Direct the linker to not merge together strings in the debugging information which 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.
-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.
-fpre-ipa-mem-report
-fpost-ipa-mem-report
    Makes the compiler print some statistics about permanent memory allocation before or after
    interprocedural optimization.
-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:
-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.
-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 will
    match 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.  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.
-dletters
-fdump-rtl-pass
    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.  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 sub-expression
    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 pro 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.
-fdump-rtl-all
    Produce all the dumps listed above.
-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-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 will cause counters to be summed
    over the whole compilation unit while -details will dump 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
    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.  If the -options form is used, options is a list of
    - separated options that control the details of the dump.  Not all options are applicable to all
    dumps, those which are not meaningful will be ignored.  The following options are available
-ftree-vectorizer-verbose=n
    This option controls the amount of debugging output the vectorizer prints.  This information is
    written to standard error, unless -fdump-tree-all or -fdump-tree-vect is specified, in which case it
    is output to the usual dump listing file, .vect.  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 also reports non-vectorized loops that passed the first analysis
    phase (vect_analyze_loop_form) - i.e. countable, inner-most, single-bb, single-entry/exit loops.
    This is the same verbosity level that -fdump-tree-vect-stats uses.  Higher verbosity levels mean
    either more information dumped for each reported loop, or same amount of information reported for
    more loops: if n=3, vectorizer cost model information is reported.  If n=4, alignment related
    information is added to the reports.  If n=5, data-references related information (e.g. memory
    dependences, memory access-patterns) is added to the reports.  If n=6, the vectorizer reports also
    non-vectorized inner-most loops that did not pass the first analysis phase (i.e., may not be
    countable, or may have complicated control-flow).  If n=7, the vectorizer reports also non-vectorized
    nested loops.  If n=8, SLP related information is added to the reports.  For n=9, all the information
    the vectorizer generates during its analysis and transformation is reported.  This is the same
    verbosity level that -fdump-tree-vect-details uses.
-frandom-seed=string
    This option provides a seed that GCC uses when it would otherwise use random numbers.  It is used to
    generate 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 would produce 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:
-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).
-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 will be 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 will search---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 will be 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.)
-feliminate-unused-debug-types
    Normally, when producing DWARF2 output, GCC will emit debugging information for all types declared in
    a compilation unit, regardless of whether or not they are actually used in that compilation unit.
    Sometimes this is useful, such as 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.  With this option, GCC will avoid producing debug symbol output for types
    that are nowhere used in the source file being compiled.
-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-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 -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-pre -ftree-vrp

Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos.

NOTE: In Ubuntu 8.10 and later versions, -D_FORTIFY_SOURCE=2 is set by default, and is activated when
-O is set to 2 or higher.  This enables additional compile-time and run-time checks for several libc
functions.  To disable, specify either -U_FORTIFY_SOURCE or -D_FORTIFY_SOURCE=0.
-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
    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.

    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 would be -fno-foo.  In the table below, only one of the forms is
listed---the one you typically will 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 which
    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.
-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 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
    Don't pay attention to the "inline" keyword.  Normally this option is used to keep the compiler from
    expanding any functions inline.  Note that if you are not optimizing, no functions can be expanded
    inline.
-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.

    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
    Integrate all simple functions into their callers.  The compiler heuristically decides which
    functions are simple enough to be 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.
-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 the variable was
    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 will result 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 will be deleted which will trigger 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 will be 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 where we 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 will follow 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 which 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 has been 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 runtime
    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 will attempt to move loads which
    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 gcse is enabled.
-fgcse-sm
    When -fgcse-sm is enabled, a store motion pass is run after global common subexpression elimination.
    This pass will attempt 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 cleanup redundant spilling.
-funsafe-loop-optimizations
    If given, the loop optimizer will assume that loop indices do not overflow, and that the 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.  Using
    -Wunsafe-loop-optimizations, the compiler will warn you if it finds this kind of loop.
-fcrossjumping
    Perform cross-jumping transformation.  This transformation unifies equivalent code and save 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 include 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 which 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.
-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 specified coloring algorithm for the integrated register allocator.  The algorithm argument
    should be "priority" or "CB".  The first algorithm specifies Chow's priority coloring, the second one
    specifies Chaitin-Briggs coloring.  The second algorithm can be unimplemented for some architectures.
    If it is implemented, it is the default because Chaitin-Briggs coloring as a rule generates a better
    code.
-fira-region=region
    Use specified regions for the integrated register allocator.  The region argument should be one of
    "all", "mixed", or "one".  The first value means using all loops as register allocation regions, the
    second value which is the default means using all loops except for loops with small register pressure
    as the regions, and third one means using all function as a single region.  The first value can give
    best result for machines with small size and irregular register set, the third one results in faster
    and generates decent code and the smallest size code, and the default value usually give the best
    results in most cases and for most architectures.
-fira-loop-pressure
    Use IRA to evaluate register pressure in loops for decision to move loop invariants.  Usage of this
    option usually results in generation of faster and smaller code on machines with big register files
    (>= 32 registers) but it can slow compiler down.

    This option is enabled at level -O3 for some targets.
-fno-ira-share-save-slots
    Switch off sharing stack slots used for saving call used hard registers living through a call.  Each
    hard register will get a separate stack slot and as a result function stack frame will be bigger.
-fno-ira-share-spill-slots
    Switch off sharing stack slots allocated for pseudo-registers.  Each pseudo-register which did not
    get a hard register will get a separate stack slot and as a result function stack frame will be
    bigger.
-fira-verbose=n
    Set up how verbose dump file for the integrated register allocator will be.  Default value is 5.  If
    the value is greater or equal to 10, the dump file will be stderr as if the value were 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 the 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 as a consequence register
    spills in the 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 will be
    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) will be examined for a dependency on a stalled insn that is
    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, do use superblock scheduling algorithm.  Superblock
    scheduling allows motion across basic block boundaries resulting on 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
    The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled we may
    want to prevent the later scheduling passes from changing its schedule, we use this option to control
    that.
-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
    until 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 until -fsel-sched-pipelining is turned on.
-fcaller-saves
    Enable values to be allocated in registers that will be 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 than would otherwise be produced.

    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 will attempt 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-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.
-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 cannot escape the compilation unit.  Enabled by default
    at -O and higher.
-fipa-struct-reorg
    Perform structure reorganization optimization, that change C-like structures layout in order to
    better utilize spatial locality.  This transformation is affective for programs containing arrays of
    structures.  Available in two compilation modes: profile-based (enabled with -fprofile-generate) or
    static (which uses built-in heuristics).  It works only in whole program mode, so it requires
    -fwhole-program to be enabled.  Structures considered cold by this transformation are not affected
    (see --param struct-reorg-cold-struct-ratio=value).

    With this flag, the program debug info reflects a new structure layout.
-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 will perform 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.
-fipa-matrix-reorg
    Perform matrix flattening and transposing.  Matrix flattening tries to replace an m-dimensional
    matrix with its equivalent n-dimensional matrix, where n < m.  This reduces the level of indirection
    needed for accessing the elements of the matrix. The second optimization is matrix transposing that
    attempts to change the order of the matrix's dimensions in order to improve cache locality.  Both
    optimizations need the -fwhole-program flag.  Transposing is enabled only if profiling information is
    available.
-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-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 builtin 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 which
    will later be 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:
-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:
-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:
-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-flatten
    Removes the loop nesting structure: transforms the loop nest into a single loop.  This transformation
    can be useful to vectorize all the levels of the loop nest.
-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;

    would be transformed to
-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
-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
-ftree-loop-im
    Perform loop invariant motion on trees.  This pass moves only invariants that would be 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 the loop for that 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-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-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 runtime 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.
-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 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 expressing 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.

    Combination of -fweb and CSE is often sufficient to obtain the same effect.  However in cases the
    loop body is more complicated than a single basic block, this is not reliable.  It also does not work
    at all on some of the architectures due to restrictions in the CSE pass.

    This optimization is enabled by default.
-fvariable-expansion-in-unroller
    With this option, the compiler will create 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 will use 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 will be 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 in 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.
-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 will not happen.  This permits various
    optimizations.  For example, the compiler will assume that an expression like "i + 10 > i" will
    always be 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 will overflow 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 would align 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 will not be
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 will not be 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.  The hope is
    that the loop will be executed many times, which will make up for any execution of the dummy
    operations.
-fno-align-loops and -falign-loops=1 are equivalent and mean that loops will not be 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 will not be 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 will not
    be removed.  This option is intended to support existing code which relies on a particular ordering.
    For new code, it is better to use attributes.

    Enabled at level -O0.  When disabled explicitly, it also imply -fno-section-anchors that 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 will 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. If gold is used as the linker plugin, "externally_visible" attributes are
    automatically added to functions (not variable yet due to a current gold issue) that are accessed
    outside of LTO objects according to resolution file produced by gold.  For other linkers that cannot
    generate resolution file, explicit "externally_visible" attributes are still necessary.  While this
    option is equivalent to proper use of the "static" keyword for programs consisting of a single file,
    in combination with option -flto this flag can be used to compile many smaller scale programs since
    the functions and variables become local for the whole combined compilation unit, not for the single
    source file itself.

    This option implies -fwhole-file for Fortran programs.
-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.
-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).  Specifying "none" as an algorithm disables partitioning
    and streaming completely. The default value is "balanced".
-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 the linker
    plugin support in linker that 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).
-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.
-fcprop-registers
    After register allocation and post-register allocation instruction splitting, we 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 will use heuristics to correct or
    smooth out such inconsistencies. By default, GCC will emit 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.  By default, GCC will use the
    current directory as path, thus the profile data file will appear 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 will look 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"

    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 will look 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 will follow 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 which 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
    which 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
    which 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 a code which 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
    which 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 which 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 constant as single precision constant instead of implicitly converting it to
    double precision constant.
-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 the 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, it instructs the compiler to add a 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 operation 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 will most benefit processors with lots of registers.
    Depending on the debug information format adopted by the target, however, it can make debugging
    impossible, since variables will 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 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 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 the loops for that 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 will create larger object and executable files and will also be
    slower.  You will not be able to 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 in
    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.

    NOTE: In Ubuntu 6.10 and later versions this option is enabled by default for C, C++, ObjC, ObjC++,
    if none of -fno-stack-protector, -nostdlib, nor -ffreestanding are found.
-fstack-protector-all
    Like -fstack-protector except that all functions are protected.
-fsection-anchors
    Try to reduce the number of symbolic address calculations by using shared "anchor" symbols to address
    nearby objects.  This transformation can help to reduce the number of GOT entries and GOT accesses on
    some targets.
--param name=value
    In some places, GCC uses various constants to control the amount of optimization that is done.  For
    example, GCC will not inline functions that contain more that a certain number of instructions.  You
    can control some of these constants on the command-line using the --param option.
-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 which GCC does not know how to 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.
-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.
-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.
-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
-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.
-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.
-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++.
-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.
-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.
-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 which GCC does not know how to 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 will be passed
    to the linker, options specifying linkage of the system libraries, such as "-static-libgcc" or
    "-shared-libgcc", will be 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 will be passed to the linker, options specifying linkage of the system
    libraries, such as "-static-libgcc" or "-shared-libgcc", will be 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 that 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.  (For example,
    __main, used to ensure C++ constructors will be called.)
-pie
    Produce a position independent executable on targets which support it.  For predictable results, you
    must also specify the same set of options that were used to generate code (-fpie, -fPIE, or model
    suboptions) when you specify this 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
    that were used to generate code (-fpic, -fPIC, or model suboptions) when you specify this 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 will not
    always be 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 will link the shared
    version of libgcc into shared libraries by default.  Otherwise, it will take advantage of the linker
    and optimize 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.
-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
    which GCC does not know how to 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.

    NOTE: In Ubuntu 8.10 and later versions, for LDFLAGS, the option -Wl,-z,relro is used.  To disable,
    use -Wl,-z,norelro.
    -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 will be ignored.  The directory will still be 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 which 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.
-specs=file
    Process file after the compiler reads in the standard specs file, in order to override the defaults
    that 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 would
    normally search for headers in /usr/include and libraries in /usr/lib, it will instead search
    dir/usr/include and dir/usr/lib.
-EL Compile code for little endian mode.  This is the default.

-EB Compile code for big endian mode.
-mmangle-cpu
    Prepend the name of the CPU to all public symbol names.  In multiple-processor systems, there are
    many ARC variants with different instruction and register set characteristics.  This flag prevents
    code compiled for one CPU to be linked with code compiled for another.  No facility exists for
    handling variants that are "almost identical".  This is an all or nothing option.
-mcpu=cpu
    Compile code for ARC variant cpu.  Which variants are supported depend on the configuration.  All
    variants support -mcpu=base, this is the default.
-mtext=text-section
-mdata=data-section
-mrodata=readonly-data-section
    Put functions, data, and readonly data in text-section, data-section, and readonly-data-section
    respectively by default.  This can be overridden with the "section" attribute.

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 will cause 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 which supports calling between the ARM and Thumb instruction sets.  Without this option
    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.
-mno-sched-prolog
    Prevent the reordering of instructions in the function prolog, or the merging of those instruction
    with the instructions in the function's body.  This means that all functions will 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 if 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.
-mhard-float
    Equivalent to -mfloat-abi=hard.
-msoft-float
    Equivalent to -mfloat-abi=soft.
-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.
-mcpu=name
    This specifies the name of the target ARM processor.  GCC uses this name to determine what kind of
    instructions it can emit when generating assembly code.  Permissible names are: arm2, arm250, arm3,
    arm6, arm60, arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi, arm70, arm700,
    arm700i, arm710, arm710c, arm7100, arm720, arm7500, arm7500fe, arm7tdmi, arm7tdmi-s, arm710t,
    arm720t, arm740t, strongarm, strongarm110, strongarm1100, strongarm1110, arm8, arm810, arm9, arm9e,
    arm920, arm920t, arm922t, arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi, arm10tdmi,
    arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp,
    arm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s, cortex-a5, cortex-a7, cortex-a8, cortex-a9,
    cortex-a15, cortex-r4, cortex-r4f, cortex-r5, cortex-m4, cortex-m3, cortex-m1, cortex-m0, xscale,
    iwmmxt, iwmmxt2, ep9312.

    -mcpu=generic-arch is also permissible, and is equivalent to -march=arch -mtune=generic-arch.  See
    -mtune for more information.

    -mcpu=native causes the compiler to auto-detect the CPU of the build computer.  At present, this
    feature is only supported on Linux, and not all architectures are recognised.  If the auto-detect is
    unsuccessful the option has no effect.
-mtune=name
    This option is very similar to the -mcpu= option, except that instead of specifying the actual target
    processor type, and hence restricting which instructions can be used, it specifies that GCC should
    tune the performance of the code as if the target were of the type specified in this option, but
    still choosing the instructions that it will generate based on the CPU specified by a -mcpu= option.
    For some ARM implementations better performance can be obtained by using this option.
-mtune=generic-arch specifies that GCC should tune the performance for a blend of processors within
architecture arch.  The aim is to generate code that run well on the current most popular processors,
balancing between optimizations that benefit some CPUs in the range, and avoiding performance
pitfalls of other CPUs.  The effects of this option may change in future GCC versions as CPU models
come and go.

-mtune=native causes the compiler to auto-detect the CPU of the build computer.  At present, this
feature is only supported on Linux, and not all architectures are recognised.  If the auto-detect is
unsuccessful the option has no effect.
-march=name
    This specifies the name of the target ARM architecture.  GCC uses this name to determine what kind of
    instructions it can emit when generating assembly code.  This option can be used in conjunction with
    or instead of the -mcpu= option.  Permissible names are: armv2, armv2a, armv3, armv3m, armv4, armv4t,
    armv5, armv5t, armv5e, armv5te, armv6, armv6j, armv6t2, armv6z, armv6zk, armv6-m, armv7, armv7-a,
    armv7-r, armv7-m, iwmmxt, iwmmxt2, ep9312.

    -march=native causes the compiler to auto-detect the architecture of the build computer.  At present,
    this feature is only supported on Linux, and not all architectures are recognised.  If the auto-
    detect is unsuccessful the option has no effect.
-mfpu=name
-mfpe=number
-mfp=number
    This specifies what floating point hardware (or hardware emulation) is available on the target.
    Permissible names are: fpa, fpe2, fpe3, maverick, vfp, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16,
    vfpv3xd, vfpv3xd-fp16, neon, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16 and neon-vfpv4.  -mfp and -mfpe
    are synonyms for -mfpu=fpenumber, for compatibility with older versions of GCC.

    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 will not be used 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 size of all structures and unions will be 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 the 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 will be 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 will lie 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 will be turned into long calls.  The heuristic
    is that static functions, functions which 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, will not be turned into long calls.  The exception to
    this rule is 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, will always be
    turned into long calls.

    This feature is not enabled by default.  Specifying -mno-long-calls will restore the default
    behavior, as will 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 run-time 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.  The default is R10 unless stack-checking is
    enabled, when R9 is used.
-mcirrus-fix-invalid-insns
    Insert NOPs into the instruction stream to in order to work around problems with invalid Maverick
    instruction combinations.  This option is only valid if the -mcpu=ep9312 option has been used to
    enable generation of instructions for the Cirrus Maverick floating point co-processor.  This option
    is not enabled by default, since the problem is only present in older Maverick implementations.  The
    default can be re-enabled by use of the -mno-cirrus-fix-invalid-insns switch.
-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
    Generate code for the Thumb instruction set.  The default is to use the 32-bit ARM instruction set.
    This option automatically enables either 16-bit Thumb-1 or mixed 16/32-bit Thumb-2 instructions based
    on the -mcpu=name and -march=name options.  This option is not passed to the assembler. If you want
    to force assembler files to be interpreted as Thumb code, either add a .thumb directive to the source
    or pass the -mthumb option directly to the assembler by prefixing it with -Wa.
-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.
-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.

AVR Options

These options are defined for AVR implementations:
-mmcu=mcu
    Specify ATMEL AVR instruction set or MCU type.
-mno-interrupts
    Generated code is not compatible with hardware interrupts.  Code size will be smaller.
-mcall-prologues
    Functions prologues/epilogues expanded as call to appropriate subroutines.  Code size will be
    smaller.
-mtiny-stack
    Change only the low 8 bits of the stack pointer.
-mint8
    Assume int to be 8 bit integer.  This affects the sizes of all types: A char will be 1 byte, an int
    will be 1 byte, a long will be 2 bytes and long long will be 4 bytes.  Please note that this option
    does not comply to the C standards, but it will provide you with smaller code size.
-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 will ensure 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 will ensure 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
    will be generated for jump and call insns.
-mshared-library-id=n
    Specified the identification number of the ID based shared library being compiled.  Specifying a
    value of 0 will generate more compact code, specifying other values will force 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 will lie 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 will restore 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 standalone application for multicore Blackfin processor. Proper start files and link scripts
    will be used to support multicore.  This option defines "__BFIN_MULTICORE". It can only be used with
    -mcpu=bf561[-sirevision]. It can be used with -mcorea or -mcoreb. If it's used without -mcorea or
    -mcoreb, single application/dual core programming model is used. In this model, the main function of
    Core B should be named as coreb_main. If it's used with -mcorea or -mcoreb, one application per core
    programming model is used.  If this option is not used, single core application programming model is
    used.
-mcorea
    Build standalone application for Core A of BF561 when using one application per core programming
    model. Proper start files and link scripts will be used to support Core A. This option defines
    "__BFIN_COREA". It must be used with -mmulticore.
-mcoreb
    Build standalone application for Core B of BF561 when using one application per core programming
    model. Proper start files and link scripts will be used to support Core B. This option defines
    "__BFIN_COREB". When this option is used, coreb_main should be used instead of main. It must be used
    with -mmulticore.
-msdram
    Build standalone application for SDRAM. Proper start files and link scripts will be used to put the
    application into SDRAM.  Loader should initialize SDRAM before loading the application into SDRAM.
    This option defines "__BFIN_SDRAM".
-micplb
    Assume that ICPLBs are enabled at runtime.  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.

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 to turn 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) arranges (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 that sets 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 variable 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.

CRX Options

These options are defined specifically for the CRX ports.
-mmac
    Enable the use of multiply-accumulate instructions. Disabled by default.
-mpush-args
    Push instructions will be used to pass outgoing arguments when functions are called. Enabled by
    default.
-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 will be 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 which
    are compatible with as many systems and code bases as possible.
-mkernel
    Enable kernel development mode.  The -mkernel option sets -static, -fno-common, -fno-cxa-atexit,
    -fno-exceptions, -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti where applicable.
    This mode also sets -mno-altivec, -msoft-float, -fno-builtin and -mlong-branch for PowerPC targets.
-mone-byte-bool
    Override the defaults for bool so that sizeof(bool)==1.  By default sizeof(bool) is 4 when compiling
    for Darwin/PowerPC and 1 when compiling for Darwin/x86, so this option has no effect on x86.

    Warning: The -mone-byte-bool switch causes GCC to generate code that is not binary compatible with
    code generated without that switch.  Using this switch may require recompiling all other modules in a
    program, including system libraries.  Use this switch to conform to a non-default data model.
-mfix-and-continue
-ffix-and-continue
-findirect-data
    Generate code suitable for fast turn around development.  Needed to enable 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 be loading the build output file being linked.  See
    man ld(1) for more information.
-dynamiclib
    When passed this option, GCC will produce 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 will be 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 will 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.  Under DEC
    Unix, this has the effect that IEEE-conformant math library routines will be linked in.
-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 will output the constant as a literal and
    generate code to load it from the data segment at runtime.

    Use this option to require GCC to construct all integer constants using code, even if it takes more
    instructions (the maximum is six).

    You would 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.
-malpha-as
-mgas
    Select whether to generate code to be assembled by the vendor-supplied assembler (-malpha-as) or by
    the GNU assembler -mgas.
-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 was 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.
-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.
-mvms-return-codes
    Return VMS condition codes from main.  The default is to return POSIX style condition (e.g. error)
    codes.
-mdebug-main=prefix
    Flag the first routine whose name starts with prefix as the main routine for the debugger.
-mmalloc64
    Default to 64bit memory allocation routines.

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 will fit into a 20-bit range.
-mno-lsim
    Assume that run-time 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, that 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.
-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 will run 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 which perform lazy context switching of floating point registers.  If you use this option and
    attempt to perform floating point operations, the compiler will abort.
-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 which
    performs faster indirect calls.

    This option will 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 can not use.  This is useful when compiling kernel code.  A register range is
    specified as two registers separated by a dash.  Multiple register ranges can be specified separated
    by a comma.
-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 GNU ld specific options.  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
    have any affect on 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 HP ld specific options.  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 have any affect on 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 will degrade 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.
-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:
-mtune=cpu-type
    Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of
    available instructions.  The choices for cpu-type are:
-march=cpu-type
    Generate instructions for the machine type cpu-type.  The choices for cpu-type are the same as for
    -mtune.  Moreover, specifying -march=cpu-type implies -mtune=cpu-type.
-mcpu=cpu-type
    A deprecated synonym for -mtune.
-mfpmath=unit
    Generate floating point arithmetics for selected unit unit.  The choices for unit are:
-masm=dialect
    Output asm instructions using selected dialect.  Supported choices are intel or att (the default
    one).  Darwin does not support intel.
-mieee-fp
-mno-ieee-fp
    Control whether or not the compiler uses IEEE floating point comparisons.  These handle correctly 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 will always have an FPU
    and so the instruction will not need emulation.  As of revision 2.6.1, 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 will produce 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 will be aligned
    differently than the published application binary interface specifications for the 386 and will not
    be 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) would prefer "long double" to be aligned to an 8 or 16 byte
    boundary.  In arrays or structures conforming to the ABI, this would not be possible.  So specifying
    a -m128bit-long-double will align "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 to be 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, the structures and arrays containing
    "long double" variables will change their size as well as function calling convention for function
    taking "long double" will be modified.  Hence they will not be binary compatible with arrays or
    structures in code compiled without that switch.
-mlarge-data-threshold=number
    When -mcmodel=medium is specified, the data greater than threshold are placed in large data section.
    This value must be the same across all object 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 will be generated for calls to those functions.

    In addition, seriously incorrect code will result 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 will generate an alternate
    prologue and epilogue that realigns the runtime stack if necessary.  This supports mixing legacy
    codes that keep a 4-byte aligned stack with modern codes that keep a 16-byte stack 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).
-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 will be
    used.

    On Pentium and PentiumPro, "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 will most likely misalign 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
-maes
-mno-aes
-mpclmul
-mno-pclmul
-mfsgsbase
-mno-fsgsbase
-mrdrnd
-mno-rdrnd
-mf16c
-mno-f16c
-msse4a
-mno-sse4a
-mfma4
-mno-fma4
-mxop
-mno-xop
-mlwp
-mno-lwp
-m3dnow
-mno-3dnow
-mpopcnt
-mno-popcnt
-mabm
-mno-abm
-mbmi
-mno-bmi
-mtbm
-mno-tbm
    These switches enable or disable the use of instructions in the MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1,
    AVX, AES, PCLMUL, FSGSBASE, RDRND, F16C, SSE4A, FMA4, XOP, LWP, ABM, BMI, 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 have SSE/SSE2 instructions generated 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 will enable GCC to use these extended instructions in generated code, even without
    -mfpmath=sse.  Applications which perform runtime 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.
-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.
-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 AVX to SSE transition penalty as well as remove unnecessary zeroupper
    intrinsics.
-mcx16
    This option will enable GCC to use CMPXCHG16B instruction in generated code.  CMPXCHG16B allows for
    atomic operations on 128-bit double quadword (or oword) data types.  This is useful for high
    resolution counters that could be updated by multiple processors (or cores).  This instruction is
    generated as part of atomic built-in functions: see Atomic Builtins for details.
-msahf
    This option will enable GCC to use SAHF instruction in generated 64-bit code.  Early Intel CPUs with
    Intel 64 lacked LAHF and SAHF instructions supported by AMD64 until introduction of Pentium 4 G1 step
    in December 2005.  LAHF and SAHF are load and store instructions, respectively, for certain status
    flags.  In 64-bit mode, SAHF instruction is used to optimize "fmod", "drem" or "remainder" built-in
    functions: see Other Builtins for details.
-mmovbe
    This option will enable GCC to use movbe instruction to implement "__builtin_bswap32" and
    "__builtin_bswap64".
-mcrc32
    This option will enable 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 will enable GCC to use 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.
-mveclibabi=type
    Specifies the ABI type to use for vectorizing intrinsics using an external library.  Supported types
    are "svml" for the Intel short vector math library and "acml" for the AMD math core library style of
    interfacing.  GCC will currently emit 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
    corresponding function type when -mveclibabi=acml is used. Both -ftree-vectorize and
    -funsafe-math-optimizations have to be enabled. A SVML or ACML ABI compatible library will have to be
    specified at link time.
-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 Windows.  On all other systems, the default is the SYSV ABI.  You can control this
    behavior for a specific function by using the function attribute ms_abi/sysv_abi.
-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 will be computed in the
    function prologue.  This is faster on most modern CPUs because of reduced dependencies, improved
    scheduling and reduced stack usage when 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 Mingw32.  Code that relies 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 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 destination is known to be aligned at least to 4
    byte boundary.  This enables more inlining, increase code size, but may improve performance of code
    that depends on fast memcpy, strlen and memset for short lengths.
-minline-stringops-dynamically
    For string operation of unknown size, inline runtime checks so for small blocks inline code is used,
    while for large blocks library call is used.
-mstringop-strategy=alg
    Overwrite internal decision heuristic about particular algorithm to inline string operation with.
    The allowed values are "rep_byte", "rep_4byte", "rep_8byte" for expanding using i386 "rep" prefix of
    specified size, "byte_loop", "loop", "unrolled_loop" for expanding inline loop, "libcall" for always
    expanding 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-frame-pointer removes the frame pointer for all 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
    legal depends on the operating system, and whether it maps the segment to cover the entire TLS area.

    For systems that use GNU libc, 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 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, 8bit unsigned integer divide is much faster than 32bit/64bit
    integer divide.  This option will generate a runt-time check.  If both dividend and divisor are
    within range of 0 to 255, 8bit unsigned integer divide will be used instead of 32bit/64bit 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 AMD x86-64 processors in 64-bit environments.
-m32
-m64
    Generate code for a 32-bit or 64-bit environment.  The 32-bit environment sets int, long and pointer
    to 32 bits and generates code that runs on any i386 system.  The 64-bit environment sets int to 32
    bits and long and pointer to 64 bits and generates code for AMD's x86-64 architecture. For darwin
    only the -m64 option turns off the -fno-pic and -mdynamic-no-pic options.
-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 will not be 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.

i386 and x86-64 Windows Options

These additional options are available for Windows targets:
-mconsole
    This option is available for Cygwin and MinGW targets.  It 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 is the default behavior for Cygwin and MinGW 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 specifies that the UNICODE macro is getting pre-
    defined and that the unicode capable runtime startup code is chosen.
-mwin32
    This option is available for Cygwin and MinGW targets.  It specifies that the typical Windows pre-
    defined 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 stack used by
    nested functions isn't set. This is necessary for binaries running in kernel mode of Windows, as
    there the user32 API, which is used to set executable privileges, isn't available.
-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 will be 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 DWARF2 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 can not use.  This is useful when compiling kernel code.  A register range is
    specified as two registers separated by a dash.  Multiple register ranges can be specified separated
    by a comma.
-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 will result in generation of the 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 will result in generation of the 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 will result 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 will be chosen for schedule only if there are no other
    choices at the moment.  This will make 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 will be chosen for schedule only if there are no other
    choices at the moment.  This will make 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 will be considered during computation of the instructions
    priorities.  This will make 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
    Disallow more than `msched-max-memory-insns' in instruction group.  Otherwise, limit is `soft'
    meaning that we would prefer non-memory operations when limit is reached but may still schedule
    memory operations.

IA-64/VMS Options

These -m options are defined for the IA-64/VMS implementations:
-mvms-return-codes
    Return VMS condition codes from main. The default is to return POSIX style condition (e.g. error)
    codes.
-mdebug-main=prefix
    Flag the first routine whose name starts with prefix as the main routine for the debugger.
-mmalloc64
    Default to 64bit memory allocation routines.

LM32 Options

These -m options are defined for the Lattice Mico32 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 will use during code generation.  These
    pseudo-registers will be 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 the default runtime libraries gcc builds.

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 will generate "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 will generate "seth/add3"
    instructions to load their addresses), and assume subroutines may not be reachable with the "bl"
    instruction (the compiler will generate the much slower "seth/add3/jl" instruction sequence).
-msdata=none
    Disable use of the small data area.  Variables will be 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 will give an error message---incorrect code will not be
    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 will be preferred over conditional code, if it
    is 2, then the opposite will apply.
-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 will only be 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 51cn 51em 51qe
    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 which
    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 which
    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 will be generated for calls to those functions.

    In addition, seriously incorrect code will result if you call a function with too many arguments.
    (Normally, extra arguments are harmlessly ignored.)

    The "rtd" instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32 processors, but
    not by the 68000 or 5200.
-mno-rtd
    Do not use the calling conventions selected by -mrtd.  This is the default.
-malign-int
-mno-align-int
    Control whether GCC aligns "int", "long", "long long", "float", "double", and "long double" variables
    on a 32-bit boundary (-malign-int) or a 16-bit boundary (-mno-align-int).  Aligning variables on
    32-bit boundaries produces code that runs somewhat faster on processors with 32-bit busses at the
    expense of more memory.

    Warning: if you use the -malign-int switch, GCC will align structures containing the above types
    differently than most published application binary interface specifications for the m68k.
-mpcrel
    Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table.
    At present, this option implies -fpic, allowing at most a 16-bit offset for pc-relative addressing.
    -fPIC is not presently supported with -mpcrel, though this could be supported for 68020 and higher
    processors.
-mno-strict-align
-mstrict-align
    Do not (do) assume that unaligned memory references will be handled by the system.
-msep-data
    Generate code that allows the data segment to be located in a different area of memory from the text
    segment.  This allows for execute in place in an environment without virtual memory management.  This
    option implies -fPIC.
-mno-sep-data
    Generate code that assumes that the data segment follows the text segment.  This is the default.
-mid-shared-library
    Generate code that supports shared libraries via the library ID method.  This allows for execute in
    place and shared libraries in an environment without virtual memory management.  This option implies
    -fPIC.
-mno-id-shared-library
    Generate code that doesn't assume ID based shared libraries are being used.  This is the default.
-mshared-library-id=n
    Specified the identification number of the ID based shared library being compiled.  Specifying a
    value of 0 will generate more compact code, specifying other values will force the allocation of that
    number to the current library but is no more space or time efficient than omitting this option.
-mxgot
-mno-xgot
    When generating position-independent code for ColdFire, generate code that works if the GOT has more
    than 8192 entries.  This code is larger and slower than code generated without this option.  On
    M680x0 processors, this option is not needed; -fPIC suffices.
-m6811
-m68hc11
    Generate output for a 68HC11.  This is the default when the compiler is configured for 68HC11-based
    systems.
-m6812
-m68hc12
    Generate output for a 68HC12.  This is the default when the compiler is configured for 68HC12-based
    systems.
-m68S12
-m68hcs12
    Generate output for a 68HCS12.
-mauto-incdec
    Enable the use of 68HC12 pre and post auto-increment and auto-decrement addressing modes.
-minmax
-mnominmax
    Enable the use of 68HC12 min and max instructions.
-mlong-calls
-mno-long-calls
    Treat all calls as being far away (near).  If calls are assumed to be far away, the compiler will use
    the "call" instruction to call a function and the "rtc" instruction for returning.
-mshort
    Consider type "int" to be 16 bits wide, like "short int".
-msoft-reg-count=count
    Specify the number of pseudo-soft registers which are used for the code generation.  The maximum
    number is 32.  Using more pseudo-soft register may or may not result in better code depending on the
    program.  The default is 4 for 68HC11 and 2 for 68HC12.

MCore Options

These are the -m options defined for the Motorola M*Core processors.
-mhardlit
-mno-hardlit
    Inline constants into the code stream if it can be done in two instructions or less.
-mdiv
-mno-div
    Use the divide instruction.  (Enabled by default).
-mrelax-immediate
-mno-relax-immediate
    Allow arbitrary sized immediates in bit operations.
-mwide-bitfields
-mno-wide-bitfields
    Always treat bit-fields as int-sized.
-m4byte-functions
-mno-4byte-functions
    Force all functions to be aligned to a four byte boundary.
-mcallgraph-data
-mno-callgraph-data
    Emit callgraph information.
-mslow-bytes
-mno-slow-bytes
    Prefer word access when reading byte quantities.
-mlittle-endian
-mbig-endian
    Generate code for a little endian target.
-m210
-m340
    Generate code for the 210 processor.
-mno-lsim
    Assume that run-time support has been provided and so omit the simulator library (libsim.a) from the
    linker command line.
-mstack-increment=size
    Set the maximum amount for a single stack increment operation.  Large values can increase the speed
    of programs which contain functions that need a large amount of stack space, but they can also
    trigger a segmentation fault if the stack is extended too much.  The default value is 0x1000.

MeP Options
-mabsdiff
    Enables the "abs" instruction, which is the absolute difference between two registers.
-mall-opts
    Enables all the optional instructions - average, multiply, divide, bit operations, leading zero,
    absolute difference, min/max, clip, and saturation.
-maverage
    Enables the "ave" instruction, which computes the average of two registers.
-mbased=n
    Variables of size n bytes or smaller will be placed in the ".based" section by default.  Based
    variables use the $tp register as a base register, and there is a 128 byte limit to the ".based"
    section.
-mbitops
    Enables the bit operation instructions - bit test ("btstm"), set ("bsetm"), clear ("bclrm"), invert
    ("bnotm"), and test-and-set ("tas").
-mc=name
    Selects which section constant data will be placed in.  name may be "tiny", "near", or "far".
-mclip
    Enables the "clip" instruction.  Note that "-mclip" is not useful unless you also provide "-mminmax".
-mconfig=name
    Selects one of the build-in core configurations.  Each MeP chip has one or more modules in it; each
    module has a core CPU and a variety of coprocessors, optional instructions, and peripherals.  The
    "MeP-Integrator" tool, not part of GCC, provides these configurations through this option; using this
    option is the same as using all the corresponding command line options.  The default configuration is
    "default".
-mcop
    Enables the coprocessor instructions.  By default, this is a 32-bit coprocessor.  Note that the
    coprocessor is normally enabled via the "-mconfig=" option.
-mcop32
    Enables the 32-bit coprocessor's instructions.
-mcop64
    Enables the 64-bit coprocessor's instructions.
-mivc2
    Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.
-mdc
    Causes constant variables to be placed in the ".near" section.
-mdiv
    Enables the "div" and "divu" instructions.
-meb
    Generate big-endian code.
-mel
    Generate little-endian code.
-mio-volatile
    Tells the compiler that any variable marked with the "io" attribute is to be considered volatile.

-ml Causes variables to be assigned to the ".far" section by default.
-mleadz
    Enables the "leadz" (leading zero) instruction.

-mm Causes variables to be assigned to the ".near" section by default.
-mminmax
    Enables the "min" and "max" instructions.
-mmult
    Enables the multiplication and multiply-accumulate instructions.
-mno-opts
    Disables all the optional instructions enabled by "-mall-opts".
-mrepeat
    Enables the "repeat" and "erepeat" instructions, used for low-overhead looping.

-ms Causes all variables to default to the ".tiny" section.  Note that there is a 65536 byte limit to
    this section.  Accesses to these variables use the %gp base register.
-msatur
    Enables the saturation instructions.  Note that the compiler does not currently generate these
    itself, but this option is included for compatibility with other tools, like "as".
-msdram
    Link the SDRAM-based runtime instead of the default ROM-based runtime.
-msim
    Link the simulator runtime libraries.
-msimnovec
    Link the simulator runtime libraries, excluding built-in support for reset and exception vectors and
    tables.
-mtf
    Causes all functions to default to the ".far" section.  Without this option, functions default to the
    ".near" section.
-mtiny=n
    Variables that are n bytes or smaller will be allocated to the ".tiny" section.  These variables use
    the $gp base register.  The default for this option is 4, but note that there's a 65536 byte limit to
    the ".tiny" section.

MicroBlaze Options
-msoft-float
    Use software emulation for floating point (default).
-mhard-float
    Use hardware floating point instructions.
-mmemcpy
    Do not optimize block moves, use "memcpy".
-mno-clearbss
    This option is deprecated.  Use -fno-zero-initialized-in-bss instead.
-mcpu=cpu-type
    Use features of and schedule code for given CPU.  Supported values are in the format vX.YY.Z, where X
    is a major version, YY is the minor version, and Z is compatibility code.  Example values are
    v3.00.a, v4.00.b, v5.00.a, v5.00.b, v5.00.b, v6.00.a.
-mxl-soft-mul
    Use software multiply emulation (default).
-mxl-soft-div
    Use software emulation for divides (default).
-mxl-barrel-shift
    Use the hardware barrel shifter.
-mxl-pattern-compare
    Use pattern compare instructions.
-msmall-divides
    Use table lookup optimization for small signed integer divisions.
-mxl-stack-check
    This option is deprecated.  Use -fstack-check instead.
-mxl-gp-opt
    Use GP relative sdata/sbss sections.
-mxl-multiply-high
    Use multiply high instructions for high part of 32x32 multiply.
-mxl-float-convert
    Use hardware floating point conversion instructions.
-mxl-float-sqrt
    Use hardware floating point square root instruction.
-mxl-mode-app-model
    Select application model app-model.  Valid models are
-EB Generate big-endian code.
-EL Generate little-endian code.  This is the default for mips*el-*-* configurations.
-march=arch
    Generate code that will run on arch, which can be the name of a generic MIPS ISA, or the name of a
    particular processor.  The ISA names are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips64 and
    mips64r2.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd, 5kc, 5kf, 20kc,
    24kc, 24kf2_1, 24kf1_1, 24kec, 24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 74kc, 74kf2_1, 74kf1_1,
    74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, loongson2e, loongson2f, loongson3a, m4k, octeon, orion, r2000,
    r3000, r3900, r4000, r4400, r4600, r4650, r6000, r8000, rm7000, rm9000, r10000, r12000, r14000,
    r16000, sb1, sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500 and xlr.  The
    special value from-abi selects the most compatible architecture for the selected ABI (that is, mips1
    for 32-bit ABIs and mips3 for 64-bit ABIs).
-mtune=arch
    Optimize for arch.  Among other things, this option controls the way instructions are scheduled, and
    the perceived cost of arithmetic operations.  The list of arch values is the same as for -march.

    When this option is not used, GCC will optimize for the processor specified by -march.  By using
    -march and -mtune together, it is possible to generate code that will run on a family of processors,
    but optimize the code for one particular member of that family.

    -mtune defines the macros _MIPS_TUNE and _MIPS_TUNE_foo, which work in the same way as the -march
    ones described above.
-mips1
    Equivalent to -march=mips1.
-mips2
    Equivalent to -march=mips2.
-mips3
    Equivalent to -march=mips3.
-mips4
    Equivalent to -march=mips4.
-mips32
    Equivalent to -march=mips32.
-mips32r2
    Equivalent to -march=mips32r2.
-mips64
    Equivalent to -march=mips64.
-mips64r2
    Equivalent to -march=mips64r2.
-mips16
-mno-mips16
    Generate (do not generate) MIPS16 code.  If GCC is targetting a MIPS32 or MIPS64 architecture, it
    will make use of the MIPS16e ASE.

    MIPS16 code generation can also be controlled on a per-function basis by means of "mips16" and
    "nomips16" attributes.
-mflip-mips16
    Generate MIPS16 code on alternating functions.  This option is provided for regression testing of
    mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary use in compiling user code.
-minterlink-mips16
-mno-interlink-mips16
    Require (do not require) that non-MIPS16 code be link-compatible with MIPS16 code.

    For example, non-MIPS16 code cannot jump directly to MIPS16 code; it must either use a call or an
    indirect jump.  -minterlink-mips16 therefore disables direct jumps unless GCC knows that the target
    of the jump is not MIPS16.
-mabicalls
-mno-abicalls
    Generate (do not generate) code that is suitable for SVR4-style dynamic objects.  -mabicalls is the
    default for SVR4-based systems.
-mshared
-mno-shared
    Generate (do not generate) code that is fully position-independent, and that can therefore be linked
    into shared libraries.  This option only affects -mabicalls.

    All -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and
    -fpic.  However, as an extension, the GNU toolchain allows executables to use absolute accesses for
    locally-binding symbols.  It can also use shorter GP initialization sequences and generate direct
    calls to locally-defined functions.  This mode is selected by -mno-shared.

    -mno-shared depends on binutils 2.16 or higher and generates objects that can only be linked by the
    GNU linker.  However, the option does not affect the ABI of the final executable; it only affects the
    ABI of relocatable objects.  Using -mno-shared will generally make executables both smaller and
    quicker.
-mshared is the default.
-mplt
-mno-plt
    Assume (do not assume) that the static and dynamic linkers support PLTs and copy relocations.  This
    option only affects -mno-shared -mabicalls.  For the n64 ABI, this option has no effect without
    -msym32.

    You can make -mplt the default by configuring GCC with --with-mips-plt.  The default is -mno-plt
    otherwise.
-mxgot
-mno-xgot
    Lift (do not lift) the usual restrictions on the size of the global offset table.
-mgp32
    Assume that general-purpose registers are 32 bits wide.
-mgp64
    Assume that general-purpose registers are 64 bits wide.
-mfp32
    Assume that floating-point registers are 32 bits wide.
-mfp64
    Assume that floating-point registers are 64 bits wide.
-mhard-float
    Use floating-point coprocessor instructions.
-msoft-float
    Do not use floating-point coprocessor instructions.  Implement floating-point calculations using
    library calls instead.
-msingle-float
    Assume that the floating-point coprocessor only supports single-precision operations.
-mdouble-float
    Assume that the floating-point coprocessor supports double-precision operations.  This is the
    default.
-mllsc
-mno-llsc
    Use (do not use) ll, sc, and sync instructions to implement atomic memory built-in functions.  When
    neither option is specified, GCC will use the instructions if the target architecture supports them.

    -mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc can be useful
    when compiling for nonstandard ISAs.  You can make either option the default by configuring GCC with
    --with-llsc and --without-llsc respectively.  --with-llsc is the default for some configurations; see
    the installation documentation for details.
-mdsp
-mno-dsp
    Use (do not use) revision 1 of the MIPS DSP ASE.
      This option defines the preprocessor macro __mips_dsp.  It also defines __mips_dsp_rev to 1.
-mdspr2
-mno-dspr2
    Use (do not use) revision 2 of the MIPS DSP ASE.
      This option defines the preprocessor macros __mips_dsp and __mips_dspr2.  It also defines
    __mips_dsp_rev to 2.
-msmartmips
-mno-smartmips
    Use (do not use) the MIPS SmartMIPS ASE.
-mpaired-single
-mno-paired-single
    Use (do not use) paired-single floating-point instructions.
      This option requires hardware floating-point support to be enabled.
-mdmx
-mno-mdmx
    Use (do not use) MIPS Digital Media Extension instructions.  This option can only be used when
    generating 64-bit code and requires hardware floating-point support to be enabled.
-mips3d
-mno-mips3d
    Use (do not use) the MIPS-3D ASE.  The option -mips3d implies -mpaired-single.
-mmt
-mno-mt
    Use (do not use) MT Multithreading instructions.
-mlong64
    Force "long" types to be 64 bits wide.  See -mlong32 for an explanation of the default and the way
    that the pointer size is determined.
-mlong32
    Force "long", "int", and pointer types to be 32 bits wide.

    The default size of "int"s, "long"s and pointers depends on the ABI.  All the supported ABIs use
    32-bit "int"s.  The n64 ABI uses 64-bit "long"s, as does the 64-bit EABI; the others use 32-bit
    "long"s.  Pointers are the same size as "long"s, or the same size as integer registers, whichever is
    smaller.
-msym32
-mno-sym32
    Assume (do not assume) that all symbols have 32-bit values, regardless of the selected ABI.  This
    option is useful in combination with -mabi=64 and -mno-abicalls because it allows GCC to generate
    shorter and faster references to symbolic addresses.
-G num
    Put definitions of externally-visible data in a small data section if that data is no bigger than num
    bytes.  GCC can then access the data more efficiently; see -mgpopt for details.

    The default -G option depends on the configuration.
-mlocal-sdata
-mno-local-sdata
    Extend (do not extend) the -G behavior to local data too, such as to static variables in C.
    -mlocal-sdata is the default for all configurations.

    If the linker complains that an application is using too much small data, you might want to try
    rebuilding the less performance-critical parts with -mno-local-sdata.  You might also want to build
    large libraries with -mno-local-sdata, so that the libraries leave more room for the main program.
-mextern-sdata
-mno-extern-sdata
    Assume (do not assume) that externally-defined data will be in a small data section if that data is
    within the -G limit.  -mextern-sdata is the default for all configurations.

    If you compile a module Mod with -mextern-sdata -G num -mgpopt, and Mod references a variable Var
    that is no bigger than num bytes, you must make sure that Var is placed in a small data section.  If
    Var is defined by another module, you must either compile that module with a high-enough -G setting
    or attach a "section" attribute to Var's definition.  If Var is common, you must link the application
    with a high-enough -G setting.

    The easiest way of satisfying these restrictions is to compile and link every module with the same -G
    option.  However, you may wish to build a library that supports several different small data limits.
    You can do this by compiling the library with the highest supported -G setting and additionally using
    -mno-extern-sdata to stop the library from making assumptions about externally-defined data.
-mgpopt
-mno-gpopt
    Use (do not use) GP-relative accesses for symbols that are known to be in a small data section; see
    -G, -mlocal-sdata and -mextern-sdata.  -mgpopt is the default for all configurations.

    -mno-gpopt is useful for cases where the $gp register might not hold the value of "_gp".  For
    example, if the code is part of a library that might be used in a boot monitor, programs that call
    boot monitor routines will pass an unknown value in $gp.  (In such situations, the boot monitor
    itself would usually be compiled with -G0.)

    -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
-membedded-data
-mno-embedded-data
    Allocate variables to the read-only data section first if possible, then next in the small data
    section if possible, otherwise in data.  This gives slightly slower code than the default, but
    reduces the amount of RAM required when executing, and thus may be preferred for some embedded
    systems.
-muninit-const-in-rodata
-mno-uninit-const-in-rodata
    Put uninitialized "const" variables in the read-only data section.  This option is only meaningful in
    conjunction with -membedded-data.
-mcode-readable=setting
    Specify whether GCC may generate code that reads from executable sections.  There are three possible
    settings:
-mcode-readable=yes
    Instructions may freely access executable sections.  This is the default setting.
-mcode-readable=pcrel
    MIPS16 PC-relative load instructions can access executable sections, but other instructions must
    not do so.  This option is useful on 4KSc and 4KSd processors when the code TLBs have the Read
    Inhibit bit set.  It is also useful on processors that can be configured to have a dual
    instruction/data SRAM interface and that, like the M4K, automatically redirect PC-relative loads
    to the instruction RAM.
-mcode-readable=no
    Instructions must not access executable sections.  This option can be useful on targets that are
    configured to have a dual instruction/data SRAM interface but that (unlike the M4K) do not
    automatically redirect PC-relative loads to the instruction RAM.
-msplit-addresses
-mno-split-addresses
    Enable (disable) use of the "%hi()" and "%lo()" assembler relocation operators.  This option has been
    superseded by -mexplicit-relocs but is retained for backwards compatibility.
-mexplicit-relocs
-mno-explicit-relocs
    Use (do not use) assembler relocation operators when dealing with symbolic addresses.  The
    alternative, selected by -mno-explicit-relocs, is to use assembler macros instead.

    -mexplicit-relocs is the default if GCC was configured to use an assembler that supports relocation
    operators.
-mcheck-zero-division
-mno-check-zero-division
    Trap (do not trap) on integer division by zero.

    The default is -mcheck-zero-division.
-mdivide-traps
-mdivide-breaks
    MIPS systems check for division by zero by generating either a conditional trap or a break
    instruction.  Using traps results in smaller code, but is only supported on MIPS II and later.  Also,
    some versions of the Linux kernel have a bug that prevents trap from generating the proper signal
    ("SIGFPE").  Use -mdivide-traps to allow conditional traps on architectures that support them and
    -mdivide-breaks to force the use of breaks.

    The default is usually -mdivide-traps, but this can be overridden at configure time using
    --with-divide=breaks.  Divide-by-zero checks can be completely disabled using
    -mno-check-zero-division.
-mmemcpy
-mno-memcpy
    Force (do not force) the use of "memcpy()" for non-trivial block moves.  The default is -mno-memcpy,
    which allows GCC to inline most constant-sized copies.
-mlong-calls
-mno-long-calls
    Disable (do not disable) use of the "jal" instruction.  Calling functions using "jal" is more
    efficient but requires the caller and callee to be in the same 256 megabyte segment.

    This option has no effect on abicalls code.  The default is -mno-long-calls.
-mmad
-mno-mad
    Enable (disable) use of the "mad", "madu" and "mul" instructions, as provided by the R4650 ISA.
-mfused-madd
-mno-fused-madd
    Enable (disable) use of the floating point multiply-accumulate instructions, when they are available.
    The default is -mfused-madd.

    When multiply-accumulate instructions are used, the intermediate product is calculated to infinite
    precision and is not subject to the FCSR Flush to Zero bit.  This may be undesirable in some
    circumstances.
-nocpp
    Tell the MIPS assembler to not run its preprocessor over user assembler files (with a .s suffix) when
    assembling them.
-mfix-r4000
-mno-fix-r4000
    Work around certain R4000 CPU errata:

    -   A double-word or a variable shift may give an incorrect result if executed immediately after
        starting an integer division.

    -   A double-word or a variable shift may give an incorrect result if executed while an integer
        multiplication is in progress.

    -   An integer division may give an incorrect result if started in a delay slot of a taken branch or
        a jump.
-mfix-r4400
-mno-fix-r4400
    Work around certain R4400 CPU errata:

    -   A double-word or a variable shift may give an incorrect result if executed immediately after
        starting an integer division.
-mfix-r10000
-mno-fix-r10000
    Work around certain R10000 errata:

    -   "ll"/"sc" sequences may not behave atomically on revisions prior to 3.0.  They may deadlock on
        revisions 2.6 and earlier.

    This option can only be used if the target architecture supports branch-likely instructions.
    -mfix-r10000 is the default when -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
-mfix-vr4120
-mno-fix-vr4120
    Work around certain VR4120 errata:

    -   "dmultu" does not always produce the correct result.

    -   "div" and "ddiv" do not always produce the correct result if one of the operands is negative.

    The workarounds for the division errata rely on special functions in libgcc.a.  At present, these
    functions are only provided by the "mips64vr*-elf" configurations.

    Other VR4120 errata require a nop to be inserted between certain pairs of instructions.  These errata
    are handled by the assembler, not by GCC itself.
-mfix-vr4130
    Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are implemented by the assembler rather
    than by GCC, although GCC will avoid using "mflo" and "mfhi" if the VR4130 "macc", "macchi", "dmacc"
    and "dmacchi" instructions are available instead.
-mfix-sb1
-mno-fix-sb1
    Work around certain SB-1 CPU core errata.  (This flag currently works around the SB-1 revision 2 "F1"
    and "F2" floating point errata.)
-mr10k-cache-barrier=setting
    Specify whether GCC should insert cache barriers to avoid the side-effects of speculation on R10K
    processors.
-mr10k-cache-barrier=load-store
    Insert a cache barrier before a load or store that might be speculatively executed and that might
    have side effects even if aborted.
-mr10k-cache-barrier=store
    Insert a cache barrier before a store that might be speculatively executed and that might have
    side effects even if aborted.
-mr10k-cache-barrier=none
    Disable the insertion of cache barriers.  This is the default setting.
-mflush-func=func
-mno-flush-func
    Specifies the function to call to flush the I and D caches, or to not call any such function.  If
    called, the function must take the same arguments as the common "_flush_func()", that is, the address
    of the memory range for which the cache is being flushed, the size of the memory range, and the
    number 3 (to flush both caches).  The default depends on the target GCC was configured for, but
    commonly is either _flush_func or __cpu_flush.

mbranch-cost=num
    Set the cost of branches to roughly num "simple" instructions.  This cost is only a heuristic and is
    not guaranteed to produce consistent results across releases.  A zero cost redundantly selects the
    default, which is based on the -mtune setting.
-mbranch-likely
-mno-branch-likely
    Enable or disable use of Branch Likely instructions, regardless of the default for the selected
    architecture.  By default, Branch Likely instructions may be generated if they are supported by the
    selected architecture.  An exception is for the MIPS32 and MIPS64 architectures and processors which
    implement those architectures; for those, Branch Likely instructions will not be generated by default
    because the MIPS32 and MIPS64 architectures specifically deprecate their use.
-mfp-exceptions
-mno-fp-exceptions
    Specifies whether FP exceptions are enabled.  This affects how we schedule FP instructions for some
    processors.  The default is that FP exceptions are enabled.

    For instance, on the SB-1, if FP exceptions are disabled, and we are emitting 64-bit code, then we
    can use both FP pipes.  Otherwise, we can only use one FP pipe.
-mvr4130-align
-mno-vr4130-align
    The VR4130 pipeline is two-way superscalar, but can only issue two instructions together if the first
    one is 8-byte aligned.  When this option is enabled, GCC will align pairs of instructions that it
    thinks should execute in parallel.

    This option only has an effect when optimizing for the VR4130.  It normally makes code faster, but at
    the expense of making it bigger.  It is enabled by default at optimization level -O3.
-msynci
-mno-synci
    Enable (disable) generation of "synci" instructions on architectures that support it.  The "synci"
    instructions (if enabled) will be generated when "__builtin___clear_cache()" is compiled.

    This option defaults to "-mno-synci", but the default can be overridden by configuring with
    "--with-synci".

    When compiling code for single processor systems, it is generally safe to use "synci".  However, on
    many multi-core (SMP) systems, it will not invalidate the instruction caches on all cores and may
    lead to undefined behavior.
-mrelax-pic-calls
-mno-relax-pic-calls
    Try to turn PIC calls that are normally dispatched via register $25 into direct calls.  This is only
    possible if the linker can resolve the destination at link-time and if the destination is within
    range for a direct call.

    -mrelax-pic-calls is the default if GCC was configured to use an assembler and a linker that supports
    the ".reloc" assembly directive and "-mexplicit-relocs" is in effect.  With "-mno-explicit-relocs",
    this optimization can be performed by the assembler and the linker alone without help from the
    compiler.
-mmcount-ra-address
-mno-mcount-ra-address
    Emit (do not emit) code that allows "_mcount" to modify the calling function's return address.  When
    enabled, this option extends the usual "_mcount" interface with a new ra-address parameter, which has
    type "intptr_t *" and is passed in register $12.  "_mcount" can then modify the return address by
    doing both of the following:
-mlibfuncs
-mno-libfuncs
    Specify that intrinsic library functions are being compiled, passing all values in registers, no
    matter the size.
-mepsilon
-mno-epsilon
    Generate floating-point comparison instructions that compare with respect to the "rE" epsilon
    register.
-mabi=mmixware
-mabi=gnu
    Generate code that passes function parameters and return values that (in the called function) are
    seen as registers $0 and up, as opposed to the GNU ABI which uses global registers $231 and up.
-mzero-extend
-mno-zero-extend
    When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load
    instructions by default, rather than sign-extending ones.
-mknuthdiv
-mno-knuthdiv
    Make the result of a division yielding a remainder have the same sign as the divisor.  With the
    default, -mno-knuthdiv, the sign of the remainder follows the sign of the dividend.  Both methods are
    arithmetically valid, the latter being almost exclusively used.
-mtoplevel-symbols
-mno-toplevel-symbols
    Prepend (do not prepend) a : to all global symbols, so the assembly code can be used with the
    "PREFIX" assembly directive.
-melf
    Generate an executable in the ELF format, rather than the default mmo format used by the mmix
    simulator.
-mbranch-predict
-mno-branch-predict
    Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable
    branch.
-mbase-addresses
-mno-base-addresses
    Generate (do not generate) code that uses base addresses.  Using a base address automatically
    generates a request (handled by the assembler and the linker) for a constant to be set up in a global
    register.  The register is used for one or more base address requests within the range 0 to 255 from
    the value held in the register.  The generally leads to short and fast code, but the number of
    different data items that can be addressed is limited.  This means that a program that uses lots of
    static data may require -mno-base-addresses.
-msingle-exit
-mno-single-exit
    Force (do not force) generated code to have a single exit point in each function.

MN10300 Options

These -m options are defined for Matsushita MN10300 architectures:
-mmult-bug
    Generate code to avoid bugs in the multiply instructions for the MN10300 processors.  This is the
    default.
-mno-mult-bug
    Do not generate code to avoid bugs in the multiply instructions for the MN10300 processors.
-mam33
    Generate code which uses features specific to the AM33 processor.
-mno-am33
    Do not generate code which uses features specific to the AM33 processor.  This is the default.
-mam33-2
    Generate code which uses features specific to the AM33/2.0 processor.
-mam34
    Generate code which uses features specific to the AM34 processor.
-mtune=cpu-type
    Use the timing characteristics of the indicated CPU type when scheduling instructions.  This does not
    change the targeted processor type.  The CPU type must be one of mn10300, am33, am33-2 or am34.
-mreturn-pointer-on-d0
    When generating a function which returns a pointer, return the pointer in both "a0" and "d0".
    Otherwise, the pointer is returned only in a0, and attempts to call such functions without a
    prototype would result in errors.  Note that this option is on by default; use
    -mno-return-pointer-on-d0 to disable it.
-mno-crt0
    Do not link in the C run-time initialization object file.
-mrelax
    Indicate to the linker that it should perform a relaxation optimization pass to shorten branches,
    calls and absolute memory addresses.  This option only has an effect when used on the command line
    for the final link step.

    This option makes symbolic debugging impossible.
-mliw
    Allow the compiler to generate Long Instruction Word instructions if the target is the AM33 or later.
    This is the default.  This option defines the preprocessor macro __LIW__.
-mnoliw
    Do not allow the compiler to generate Long Instruction Word instructions.  This option defines the
    preprocessor macro __NO_LIW__.

PDP-11 Options

These options are defined for the PDP-11:
-mfpu
    Use hardware FPP floating point.  This is the default.  (FIS floating point on the PDP-11/40 is not
    supported.)
-msoft-float
    Do not use hardware floating point.
-mac0
    Return floating-point results in ac0 (fr0 in Unix assembler syntax).
-mno-ac0
    Return floating-point results in memory.  This is the default.
-m40
    Generate code for a PDP-11/40.
-m45
    Generate code for a PDP-11/45.  This is the default.
-m10
    Generate code for a PDP-11/10.
-mbcopy-builtin
    Use inline "movmemhi" patterns for copying memory.  This is the default.
-mbcopy
    Do not use inline "movmemhi" patterns for copying memory.
-mint16
-mno-int32
    Use 16-bit "int".  This is the default.
-mint32
-mno-int16
    Use 32-bit "int".
-mfloat64
-mno-float32
    Use 64-bit "float".  This is the default.
-mfloat32
-mno-float64
    Use 32-bit "float".
-mabshi
    Use "abshi2" pattern.  This is the default.
-mno-abshi
    Do not use "abshi2" pattern.
-mbranch-expensive
    Pretend that branches are expensive.  This is for experimenting with code generation only.
-mbranch-cheap
    Do not pretend that branches are expensive.  This is the default.
-munix-asm
    Use Unix assembler syntax.  This is the default when configured for pdp11-*-bsd.
-mdec-asm
    Use DEC assembler syntax.  This is the default when configured for any PDP-11 target other than
    pdp11-*-bsd.

picoChip Options

These -m options are defined for picoChip implementations:
-mae=ANY selects a completely generic AE type.  Code generated with this option will run on any of
the other AE types.  The code will not be as efficient as it would be if compiled for a specific AE
type, and some types of operation (e.g., multiplication) will not work properly on all types of AE.
-mae=MUL selects a MUL AE type.  This is the most useful AE type for compiled code, and is the
default.
-mae=MAC selects a DSP-style MAC AE.  Code compiled with this option may suffer from poor performance
of byte (char) manipulation, since the DSP AE does not provide hardware support for byte load/stores.
-msymbol-as-address
    Enable the compiler to directly use a symbol name as an address in a load/store instruction, without
    first loading it into a register.  Typically, the use of this option will generate larger programs,
    which run faster than when the option isn't used.  However, the results vary from program to program,
    so it is left as a user option, rather than being permanently enabled.
-mno-inefficient-warnings
    Disables warnings about the generation of inefficient code.  These warnings can be generated, for
    example, when compiling code which performs byte-level memory operations on the MAC AE type.  The MAC
    AE has no hardware support for byte-level memory operations, so all byte load/stores must be
    synthesized from word load/store operations.  This is inefficient and a warning will be generated
    indicating to the programmer that they should rewrite the code to avoid byte operations, or to target
    an AE type which has the necessary hardware support.  This option enables the warning to be turned
    off.

PowerPC Options

These are listed under

IBM RS/6000 and PowerPC Options

These -m options are defined for the IBM RS/6000 and PowerPC:
-mpower
-mno-power
-mpower2
-mno-power2
-mpowerpc
-mno-powerpc
-mpowerpc-gpopt
-mno-powerpc-gpopt
-mpowerpc-gfxopt
-mno-powerpc-gfxopt
-mpowerpc64
-mno-powerpc64
-mmfcrf
-mno-mfcrf
-mpopcntb
-mno-popcntb
-mpopcntd
-mno-popcntd
-mfprnd
-mno-fprnd
-mcmpb
-mno-cmpb
-mmfpgpr
-mno-mfpgpr
-mhard-dfp
-mno-hard-dfp
    GCC supports two related instruction set architectures for the RS/6000 and PowerPC.  The POWER
    instruction set are those instructions supported by the rios chip set used in the original RS/6000
    systems and the PowerPC instruction set is the architecture of the Freescale MPC5xx, MPC6xx, MPC8xx
    microprocessors, and the IBM 4xx, 6xx, and follow-on microprocessors.
-mnew-mnemonics
-mold-mnemonics
    Select which mnemonics to use in the generated assembler code.  With -mnew-mnemonics, GCC uses the
    assembler mnemonics defined for the PowerPC architecture.  With -mold-mnemonics it uses the assembler
    mnemonics defined for the POWER architecture.  Instructions defined in only one architecture have
    only one mnemonic; GCC uses that mnemonic irrespective of which of these options is specified.

    GCC defaults to the mnemonics appropriate for the architecture in use.  Specifying -mcpu=cpu_type
    sometimes overrides the value of these option.  Unless you are building a cross-compiler, you should
    normally not specify either -mnew-mnemonics or -mold-mnemonics, but should instead accept the
    default.
-mcpu=common selects a completely generic processor.  Code generated under this option will run on
any POWER or PowerPC processor.  GCC will use only the instructions in the common subset of both
architectures, and will not use the MQ register.  GCC assumes a generic processor model for
scheduling purposes.
-mcpu=power, -mcpu=power2, -mcpu=powerpc, and -mcpu=powerpc64 specify generic POWER, POWER2, pure
32-bit PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine types, with an
appropriate, generic processor model assumed for scheduling purposes.

The other options specify a specific processor.  Code generated under those options will run best on
that processor, and may not run at all on others.

The -mcpu options automatically enable or disable the following options:
-maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple -mnew-mnemonics  -mpopcntb -mpopcntd  -mpower
-mpower2  -mpowerpc64 -mpowerpc-gpopt  -mpowerpc-gfxopt  -msingle-float -mdouble-float -msimple-fpu
-mstring  -mmulhw  -mdlmzb  -mmfpgpr -mvsx

The particular options set for any particular CPU will vary between compiler versions, depending on
what setting seems to produce optimal code for that CPU; it doesn't necessarily reflect the actual
hardware's capabilities.  If you wish to set an individual option to a particular value, you may
specify it after the -mcpu option, like -mcpu=970 -mno-altivec.

On AIX, the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu option at
present because AIX does not have full support for these options.  You may still enable or disable
them individually if you're sure it'll work in your environment.
-mcmodel=small
    Generate PowerPC64 code for the small model: The TOC is limited to 64k.
-mcmodel=medium
    Generate PowerPC64 code for the medium model: The TOC and other static data may be up to a total of
    4G in size.
-mcmodel=large
    Generate PowerPC64 code for the large model: The TOC may be up to 4G in size.  Other data and code is
    only limited by the 64-bit address space.
-maltivec
-mno-altivec
    Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in
    functions that allow more direct access to the AltiVec instruction set.  You may also need to set
    -mabi=altivec to adjust the current ABI with AltiVec ABI enhancements.
-mvrsave
-mno-vrsave
    Generate VRSAVE instructions when generating AltiVec code.
-mgen-cell-microcode
    Generate Cell microcode instructions
-mwarn-cell-microcode
    Warning when a Cell microcode instruction is going to emitted.  An example of a Cell microcode
    instruction is a variable shift.
-msecure-plt
    Generate code that allows ld and ld.so to build executables and shared libraries with non-exec .plt
    and .got sections.  This is a PowerPC 32-bit SYSV ABI option.
-mbss-plt
    Generate code that uses a BSS .plt section that ld.so fills in, and requires .plt and .got sections
    that are both writable and executable.  This is a PowerPC 32-bit SYSV ABI option.
-misel
-mno-isel
    This switch enables or disables the generation of ISEL instructions.
-misel=yes/no
    This switch has been deprecated.  Use -misel and -mno-isel instead.
-mspe
-mno-spe
    This switch enables or disables the generation of SPE simd instructions.
-mpaired
-mno-paired
    This switch enables or disables the generation of PAIRED simd instructions.
-mspe=yes/no
    This option has been deprecated.  Use -mspe and -mno-spe instead.
-mvsx
-mno-vsx
    Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of
    built-in functions that allow more direct access to the VSX instruction set.
-mfloat-gprs=yes/single/double/no
-mfloat-gprs
    This switch enables or disables the generation of floating point operations on the general purpose
    registers for architectures that support it.

    The argument yes or single enables the use of single-precision floating point operations.

    The argument double enables the use of single and double-precision floating point operations.

    The argument no disables floating point operations on the general purpose registers.

    This option is currently only available on the MPC854x.
-m32
-m64
    Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including GNU/Linux).
    The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any
    PowerPC variant.  The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and
    generates code for PowerPC64, as for -mpowerpc64.
-mfull-toc
-mno-fp-in-toc
-mno-sum-in-toc
-mminimal-toc
    Modify generation of the TOC (Table Of Contents), which is created for every executable file.  The
    -mfull-toc option is selected by default.  In that case, GCC will allocate at least one TOC entry for
    each unique non-automatic variable reference in your program.  GCC will also place floating-point
    constants in the TOC.  However, only 16,384 entries are available in the TOC.

    If you receive a linker error message that saying you have overflowed the available TOC space, you
    can reduce the amount of TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options.
    -mno-fp-in-toc prevents GCC from putting floating-point constants in the TOC and -mno-sum-in-toc
    forces GCC to generate code to calculate the sum of an address and a constant at run-time instead of
    putting that sum into the TOC.  You may specify one or both of these options.  Each causes GCC to
    produce very slightly slower and larger code at the expense of conserving TOC space.

    If you still run out of space in the TOC even when you specify both of these options, specify
    -mminimal-toc instead.  This option causes GCC to make only one TOC entry for every file.  When you
    specify this option, GCC will produce code that is slower and larger but which uses extremely little
    TOC space.  You may wish to use this option only on files that contain less frequently executed code.
-maix64
-maix32
    Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit "long" type, and the
    infrastructure needed to support them.  Specifying -maix64 implies -mpowerpc64 and -mpowerpc, while
    -maix32 disables the 64-bit ABI and implies -mno-powerpc64.  GCC defaults to -maix32.
-mxl-compat
-mno-xl-compat
    Produce code that conforms more closely to IBM XL compiler semantics when using AIX-compatible ABI.
    Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the
    stack in addition to argument FPRs.  Do not assume that most significant double in 128-bit long
    double value is properly rounded when comparing values and converting to double.  Use XL symbol names
    for long double support routines.

    The AIX calling convention was extended but not initially documented to handle an obscure K&R C case
    of calling a function that takes the address of its arguments with fewer arguments than declared.
    IBM XL compilers access floating point arguments which do not fit in the RSA from the stack when a
    subroutine is compiled without optimization.  Because always storing floating-point arguments on the
    stack is inefficient and rarely needed, this option is not enabled by default and only is necessary
    when calling subroutines compiled by IBM XL compilers without optimization.
-mpe
    Support IBM RS/6000 SP Parallel Environment (PE).  Link an application written to use message passing
    with special startup code to enable the application to run.  The system must have PE installed in the
    standard location (/usr/lpp/ppe.poe/), or the specs file must be overridden with the -specs= option
    to specify the appropriate directory location.  The Parallel Environment does not support threads, so
    the -mpe option and the -pthread option are incompatible.
-malign-natural
-malign-power
    On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural overrides the ABI-
    defined alignment of larger types, such as floating-point doubles, on their natural size-based
    boundary.  The option -malign-power instructs GCC to follow the ABI-specified alignment rules.  GCC
    defaults to the standard alignment defined in the ABI.

    On 64-bit Darwin, natural alignment is the default, and -malign-power is not supported.
-msoft-float
-mhard-float
    Generate code that does not use (uses) the floating-point register set.  Software floating point
    emulation is provided if you use the -msoft-float option, and pass the option to GCC when linking.
-msingle-float
-mdouble-float
    Generate code for single or double-precision floating point operations.  -mdouble-float implies
    -msingle-float.
-msimple-fpu
    Do not generate sqrt and div instructions for hardware floating point unit.
-mfpu
    Specify type of floating point unit.  Valid values are sp_lite (equivalent to -msingle-float
    -msimple-fpu), dp_lite (equivalent to -mdouble-float -msimple-fpu), sp_full (equivalent to
    -msingle-float), and dp_full (equivalent to -mdouble-float).
-mxilinx-fpu
    Perform optimizations for floating point unit on Xilinx PPC 405/440.
-mmultiple
-mno-multiple
    Generate code that uses (does not use) the load multiple word instructions and the store multiple
    word instructions.  These instructions are generated by default on POWER systems, and not generated
    on PowerPC systems.  Do not use -mmultiple on little endian PowerPC systems, since those instructions
    do not work when the processor is in little endian mode.  The exceptions are PPC740 and PPC750 which
    permit the instructions usage in little endian mode.
-mstring
-mno-string
    Generate code that uses (does not use) the load string instructions and the store string word
    instructions to save multiple registers and do small block moves.  These instructions are generated
    by default on POWER systems, and not generated on PowerPC systems.  Do not use -mstring on little
    endian PowerPC systems, since those instructions do not work when the processor is in little endian
    mode.  The exceptions are PPC740 and PPC750 which permit the instructions usage in little endian
    mode.
-mupdate
-mno-update
    Generate code that uses (does not use) the load or store instructions that update the base register
    to the address of the calculated memory location.  These instructions are generated by default.  If
    you use -mno-update, there is a small window between the time that the stack pointer is updated and
    the address of the previous frame is stored, which means code that walks the stack frame across
    interrupts or signals may get corrupted data.
-mavoid-indexed-addresses
-mno-avoid-indexed-addresses
    Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These
    instructions can incur a performance penalty on Power6 processors in certain situations, such as when
    stepping through large arrays that cross a 16M boundary.  This option is enabled by default when
    targetting Power6 and disabled otherwise.
-mfused-madd
-mno-fused-madd
    Generate code that uses (does not use) the floating point multiply and accumulate instructions.
    These instructions are generated by default if hardware floating point is used.  The machine
    dependent -mfused-madd option is now mapped to the machine independent -ffp-contract=fast option, and
    -mno-fused-madd is mapped to -ffp-contract=off.
-mmulhw
-mno-mulhw
    Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on
    the IBM 405, 440, 464 and 476 processors.  These instructions are generated by default when
    targetting those processors.
-mdlmzb
-mno-dlmzb
    Generate code that uses (does not use) the string-search dlmzb instruction on the IBM 405, 440, 464
    and 476 processors.  This instruction is generated by default when targetting those processors.
-mno-bit-align
-mbit-align
    On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-
    fields to be aligned to the base type of the bit-field.

    For example, by default a structure containing nothing but 8 "unsigned" bit-fields of length 1 would
    be aligned to a 4 byte boundary and have a size of 4 bytes.  By using -mno-bit-align, the structure
    would be aligned to a 1 byte boundary and be one byte in size.
-mno-strict-align
-mstrict-align
    On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references will
    be handled by the system.
-mrelocatable
-mno-relocatable
    Generate code that allows (does not allow) a static executable to be relocated to a different address
    at runtime.  A simple embedded PowerPC system loader should relocate the entire contents of ".got2"
    and 4-byte locations listed in the ".fixup" section, a table of 32-bit addresses generated by this
    option.  For this to work, all objects linked together must be compiled with -mrelocatable or
    -mrelocatable-lib.  -mrelocatable code aligns the stack to an 8 byte boundary.
-mrelocatable-lib
-mno-relocatable-lib
    Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section to allow static executables to be
    relocated at runtime, but -mrelocatable-lib does not use the smaller stack alignment of
    -mrelocatable.  Objects compiled with -mrelocatable-lib may be linked with objects compiled with any
    combination of the -mrelocatable options.
-mno-toc
-mtoc
    On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a
    global area pointing to the addresses used in the program.
-mlittle
-mlittle-endian
    On System V.4 and embedded PowerPC systems compile code for the processor in little endian mode.  The
    -mlittle-endian option is the same as -mlittle.
-mbig
-mbig-endian
    On System V.4 and embedded PowerPC systems compile code for the processor in big endian mode.  The
    -mbig-endian option is the same as -mbig.
-mdynamic-no-pic
    On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that its external
    references are relocatable.  The resulting code is suitable for applications, but not shared
    libraries.
-msingle-pic-base
    Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for
    each function.  The run-time system is responsible for initializing this register with an appropriate
    value before execution begins.
-mprioritize-restricted-insns=priority
    This option controls the priority that is assigned to dispatch-slot restricted instructions during
    the second scheduling pass.  The argument priority takes the value 0/1/2 to assign
    no/highest/second-highest priority to dispatch slot restricted instructions.
-minsert-sched-nops=scheme
    This option controls which nop insertion scheme will be used during the second scheduling pass.  The
    argument scheme takes one of the following values: no: Don't insert nops.  pad: Pad with nops any
    dispatch group which has vacant issue slots, according to the scheduler's grouping.  regroup_exact:
    Insert nops to force costly dependent insns into separate groups.  Insert exactly as many nops as
    needed to force an insn to a new group, according to the estimated processor grouping.  number:
    Insert nops to force costly dependent insns into separate groups.  Insert number nops to force an
    insn to a new group.
-mcall-sysv
    On System V.4 and embedded PowerPC systems compile code using calling conventions that adheres to the
    March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement.  This is
    the default unless you configured GCC using powerpc-*-eabiaix.
-mcall-sysv-eabi
-mcall-eabi
    Specify both -mcall-sysv and -meabi options.
-mcall-sysv-noeabi
    Specify both -mcall-sysv and -mno-eabi options.
-mcall-aixdesc
    On System V.4 and embedded PowerPC systems compile code for the AIX operating system.
-mcall-linux
    On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system.
-mcall-gnu
    On System V.4 and embedded PowerPC systems compile code for the Hurd-based GNU system.
-mcall-freebsd
    On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system.
-mcall-netbsd
    On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system.
-mcall-openbsd
    On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system.
-maix-struct-return
    Return all structures in memory (as specified by the AIX ABI).
-msvr4-struct-return
    Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI).
-mabi=abi-type
    Extend the current ABI with a particular extension, or remove such extension.  Valid values are
    altivec, no-altivec, spe, no-spe, ibmlongdouble, ieeelongdouble.
-mabi=spe
    Extend the current ABI with SPE ABI extensions.  This does not change the default ABI, instead it
    adds the SPE ABI extensions to the current ABI.
-mabi=no-spe
    Disable Booke SPE ABI extensions for the current ABI.
-mabi=ibmlongdouble
    Change the current ABI to use IBM extended precision long double.  This is a PowerPC 32-bit SYSV ABI
    option.
-mabi=ieeelongdouble
    Change the current ABI to use IEEE extended precision long double.  This is a PowerPC 32-bit Linux
    ABI option.
-mprototype
-mno-prototype
    On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are
    properly prototyped.  Otherwise, the compiler must insert an instruction before every non prototyped
    call to set or clear bit 6 of the condition code register (CR) to indicate whether floating point
    values were passed in the floating point registers in case the function takes a variable arguments.
    With -mprototype, only calls to prototyped variable argument functions will set or clear the bit.
-msim
    On embedded PowerPC systems, assume that the startup module is called sim-crt0.o and that the
    standard C libraries are libsim.a and libc.a.  This is the default for powerpc-*-eabisim
    configurations.
-mmvme
    On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C
    libraries are libmvme.a and libc.a.
-mads
    On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C
    libraries are libads.a and libc.a.
-myellowknife
    On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C
    libraries are libyk.a and libc.a.
-mvxworks
    On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system.
-memb
    On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags header to indicate that eabi
    extended relocations are used.
-meabi
-mno-eabi
    On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary
    Interface (eabi) which is a set of modifications to the System V.4 specifications.  Selecting -meabi
    means that the stack is aligned to an 8 byte boundary, a function "__eabi" is called to from "main"
    to set up the eabi environment, and the -msdata option can use both "r2" and "r13" to point to two
    separate small data areas.  Selecting -mno-eabi means that the stack is aligned to a 16 byte
    boundary, do not call an initialization function from "main", and the -msdata option will only use
    "r13" to point to a single small data area.  The -meabi option is on by default if you configured GCC
    using one of the powerpc*-*-eabi* options.
-msdata=eabi
    On System V.4 and embedded PowerPC systems, put small initialized "const" global and static data in
    the .sdata2 section, which is pointed to by register "r2".  Put small initialized non-"const" global
    and static data in the .sdata section, which is pointed to by register "r13".  Put small
    uninitialized global and static data in the .sbss section, which is adjacent to the .sdata section.
    The -msdata=eabi option is incompatible with the -mrelocatable option.  The -msdata=eabi option also
    sets the -memb option.
-msdata=sysv
    On System V.4 and embedded PowerPC systems, put small global and static data in the .sdata section,
    which is pointed to by register "r13".  Put small uninitialized global and static data in the .sbss
    section, which is adjacent to the .sdata section.  The -msdata=sysv option is incompatible with the
    -mrelocatable option.
-msdata=default
-msdata
    On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same as -msdata=eabi,
    otherwise compile code the same as -msdata=sysv.
-msdata=data
    On System V.4 and embedded PowerPC systems, put small global data in the .sdata section.  Put small
    uninitialized global data in the .sbss section.  Do not use register "r13" to address small data
    however.  This is the default behavior unless other -msdata options are used.
-msdata=none
-mno-sdata
    On embedded PowerPC systems, put all initialized global and static data in the .data section, and all
    uninitialized data in the .bss section.
-mblock-move-inline-limit=num
    Inline all block moves (such as calls to "memcpy" or structure copies) less than or equal to num
    bytes.  The minimum value for num is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets.  The
    default value is target-specific.
-G num
    On embedded PowerPC systems, put global and static items less than or equal to num bytes into the
    small data or bss sections instead of the normal data or bss section.  By default, num is 8.  The -G
    num switch is also passed to the linker.  All modules should be compiled with the same -G num value.
-mregnames
-mno-regnames
    On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language
    output using symbolic forms.
-mlongcall
-mno-longcall
    By default assume that all calls are far away so that a longer more expensive calling sequence is
    required.  This is required for calls further than 32 megabytes (33,554,432 bytes) from the current
    location.  A short call will be generated if the compiler knows the call cannot be that far away.
    This setting can be overridden by the "shortcall" function attribute, or by "#pragma longcall(0)".

    Some linkers are capable of detecting out-of-range calls and generating glue code on the fly.  On
    these systems, long calls are unnecessary and generate slower code.  As of this writing, the AIX
    linker can do this, as can the GNU linker for PowerPC/64.  It is planned to add this feature to the
    GNU linker for 32-bit PowerPC systems as well.

    On Darwin/PPC systems, "#pragma longcall" will generate "jbsr callee, L42", plus a "branch island"
    (glue code).  The two target addresses represent the callee and the "branch island".  The Darwin/PPC
    linker will prefer the first address and generate a "bl callee" if the PPC "bl" instruction will
    reach the callee directly; otherwise, the linker will generate "bl L42" to call the "branch island".
    The "branch island" is appended to the body of the calling function; it computes the full 32-bit
    address of the callee and jumps to it.

    On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call,
    and the Darwin linker decides whether to use or discard it.

    In the future, we may cause GCC to ignore all longcall specifications when the linker is known to
    generate glue.
-mtls-markers
-mno-tls-markers
    Mark (do not mark) calls to "__tls_get_addr" with a relocation specifying the function argument.  The
    relocation allows ld to reliably associate function call with argument setup instructions for TLS
    optimization, which in turn allows gcc to better schedule the sequence.
-pthread
    Adds support for multithreading with the pthreads library.  This option sets flags for both the
    preprocessor and linker.
-mrecip
-mno-recip
    This option will enable GCC to use the reciprocal estimate and reciprocal square root estimate
    instructions with additional Newton-Raphson steps to increase precision instead of doing a divide or
    square root and divide for floating point arguments.  You should use the -ffast-math option when
    using -mrecip (or at least -funsafe-math-optimizations, -finite-math-only, -freciprocal-math and
    -fno-trapping-math).  Note that while the throughput of the sequence is generally higher than the
    throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to
    2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots.
-mrecip=opt
    This option allows to control which reciprocal estimate instructions may be used.  opt is a comma
    separated list of options, that may be preceded by a "!" to invert the option: "all": enable all
    estimate instructions, "default": enable the default instructions, equivalent to -mrecip, "none":
    disable all estimate instructions, equivalent to -mno-recip; "div": enable the reciprocal
    approximation instructions for both single and double precision; "divf": enable the single precision
    reciprocal approximation instructions; "divd": enable the double precision reciprocal approximation
    instructions; "rsqrt": enable the reciprocal square root approximation instructions for both single
    and double precision; "rsqrtf": enable the single precision reciprocal square root approximation
    instructions; "rsqrtd": enable the double precision reciprocal square root approximation
    instructions;

    So for example, -mrecip=all,!rsqrtd would enable the all of the reciprocal estimate instructions,
    except for the "FRSQRTE", "XSRSQRTEDP", and "XVRSQRTEDP" instructions which handle the double
    precision reciprocal square root calculations.
-mrecip-precision
-mno-recip-precision
    Assume (do not assume) that the reciprocal estimate instructions provide higher precision estimates
    than is mandated by the powerpc ABI.  Selecting -mcpu=power6 or -mcpu=power7 automatically selects
    -mrecip-precision.  The double precision square root estimate instructions are not generated by
    default on low precision machines, since they do not provide an estimate that converges after three
    steps.
-mveclibabi=type
    Specifies the ABI type to use for vectorizing intrinsics using an external library.  The only type
    supported at present is "mass", which specifies to use IBM's Mathematical Acceleration Subsystem
    (MASS) libraries for vectorizing intrinsics using external libraries.  GCC will currently emit calls
    to "acosd2", "acosf4", "acoshd2", "acoshf4", "asind2", "asinf4", "asinhd2", "asinhf4", "atan2d2",
    "atan2f4", "atand2", "atanf4", "atanhd2", "atanhf4", "cbrtd2", "cbrtf4", "cosd2", "cosf4", "coshd2",
    "coshf4", "erfcd2", "erfcf4", "erfd2", "erff4", "exp2d2", "exp2f4", "expd2", "expf4", "expm1d2",
    "expm1f4", "hypotd2", "hypotf4", "lgammad2", "lgammaf4", "log10d2", "log10f4", "log1pd2", "log1pf4",
    "log2d2", "log2f4", "logd2", "logf4", "powd2", "powf4", "sind2", "sinf4", "sinhd2", "sinhf4",
    "sqrtd2", "sqrtf4", "tand2", "tanf4", "tanhd2", and "tanhf4" when generating code for power7.  Both
    -ftree-vectorize and -funsafe-math-optimizations have to be enabled.  The MASS libraries will have to
    be specified at link time.
-mfriz
-mno-friz
    Generate (do not generate) the "friz" instruction when the -funsafe-math-optimizations option is used
    to optimize rounding a floating point value to 64-bit integer and back to floating point.  The "friz"
    instruction does not return the same value if the floating point number is too large to fit in an
    integer.

RX Options

These command line options are defined for RX targets:
-m64bit-doubles
-m32bit-doubles
    Make the "double" data type be 64-bits (-m64bit-doubles) or 32-bits (-m32bit-doubles) in size.  The
    default is -m32bit-doubles.  Note RX floating point hardware only works on 32-bit values, which is
    why the default is -m32bit-doubles.
-fpu
-nofpu
    Enables (-fpu) or disables (-nofpu) the use of RX floating point hardware.  The default is enabled
    for the RX600 series and disabled for the RX200 series.

    Floating point instructions will only be generated for 32-bit floating point values however, so if
    the -m64bit-doubles option is in use then the FPU hardware will not be used for doubles.

    Note If the -fpu option is enabled then -funsafe-math-optimizations is also enabled automatically.
    This is because the RX FPU instructions are themselves unsafe.
-mcpu=name
    Selects the type of RX CPU to be targeted.  Currently three types are supported, the generic RX600
    and RX200 series hardware and the specific RX610 CPU.  The default is RX600.

    The only difference between RX600 and RX610 is that the RX610 does not support the "MVTIPL"
    instruction.

    The RX200 series does not have a hardware floating point unit and so -nofpu is enabled by default
    when this type is selected.
-mbig-endian-data
-mlittle-endian-data
    Store data (but not code) in the big-endian format.  The default is -mlittle-endian-data, i.e. to
    store data in the little endian format.
-msmall-data-limit=N
    Specifies the maximum size in bytes of global and static variables which can be placed into the small
    data area.  Using the small data area can lead to smaller and faster code, but the size of area is
    limited and it is up to the programmer to ensure that the area does not overflow.  Also when the
    small data area is used one of the RX's registers ("r13") is reserved for use pointing to this area,
    so it is no longer available for use by the compiler.  This could result in slower and/or larger code
    if variables which once could have been held in "r13" are now pushed onto the stack.

    Note, common variables (variables which have not been initialised) and constants are not placed into
    the small data area as they are assigned to other sections in the output executable.

    The default value is zero, which disables this feature.  Note, this feature is not enabled by default
    with higher optimization levels (-O2 etc) because of the potentially detrimental effects of reserving
    register "r13".  It is up to the programmer to experiment and discover whether this feature is of
    benefit to their program.
-msim
-mno-sim
    Use the simulator runtime.  The default is to use the libgloss board specific runtime.
-mas100-syntax
-mno-as100-syntax
    When generating assembler output use a syntax that is compatible with Renesas's AS100 assembler.
    This syntax can also be handled by the GAS assembler but it has some restrictions so generating it is
    not the default option.
-mmax-constant-size=N
    Specifies the maximum size, in bytes, of a constant that can be used as an operand in a RX
    instruction.  Although the RX instruction set does allow constants of up to 4 bytes in length to be
    used in instructions, a longer value equates to a longer instruction.  Thus in some circumstances it
    can be beneficial to restrict the size of constants that are used in instructions.  Constants that
    are too big are instead placed into a constant pool and referenced via register indirection.

    The value N can be between 0 and 4.  A value of 0 (the default) or 4 means that constants of any size
    are allowed.
-mrelax
    Enable linker relaxation.  Linker relaxation is a process whereby the linker will attempt to reduce
    the size of a program by finding shorter versions of various instructions.  Disabled by default.
-mint-register=N
    Specify the number of registers to reserve for fast interrupt handler functions.  The value N can be
    between 0 and 4.  A value of 1 means that register "r13" will be reserved for the exclusive use of
    fast interrupt handlers.  A value of 2 reserves "r13" and "r12".  A value of 3 reserves "r13", "r12"
    and "r11", and a value of 4 reserves "r13" through "r10".  A value of 0, the default, does not
    reserve any registers.
-msave-acc-in-interrupts
    Specifies that interrupt handler functions should preserve the accumulator register.  This is only
    necessary if normal code might use the accumulator register, for example because it performs 64-bit
    multiplications.  The default is to ignore the accumulator as this makes the interrupt handlers
    faster.

Note: The generic GCC command line -ffixed-reg has special significance to the RX port when used with the
"interrupt" function attribute.  This attribute indicates a function intended to process fast interrupts.
GCC will will ensure that it only uses the registers "r10", "r11", "r12" and/or "r13" and only provided
that the normal use of the corresponding registers have been restricted via the -ffixed-reg or
-mint-register command line options.

S/390 and zSeries Options

These are the -m options defined for the S/390 and zSeries architecture.
-mhard-float
-msoft-float
    Use (do not use) the hardware floating-point instructions and registers for floating-point
    operations.  When -msoft-float is specified, functions in libgcc.a will be used to perform floating-
    point operations.  When -mhard-float is specified, the compiler generates IEEE floating-point
    instructions.  This is the default.
-mhard-dfp
-mno-hard-dfp
    Use (do not use) the hardware decimal-floating-point instructions for decimal-floating-point
    operations.  When -mno-hard-dfp is specified, functions in libgcc.a will be used to perform decimal-
    floating-point operations.  When -mhard-dfp is specified, the compiler generates decimal-floating-
    point hardware instructions.  This is the default for -march=z9-ec or higher.
-mlong-double-64
-mlong-double-128
    These switches control the size of "long double" type. A size of 64bit makes the "long double" type
    equivalent to the "double" type. This is the default.
-mbackchain
-mno-backchain
    Store (do not store) the address of the caller's frame as backchain pointer into the callee's stack
    frame.  A backchain may be needed to allow debugging using tools that do not understand DWARF-2 call
    frame information.  When -mno-packed-stack is in effect, the backchain pointer is stored at the
    bottom of the stack frame; when -mpacked-stack is in effect, the backchain is placed into the topmost
    word of the 96/160 byte register save area.

    In general, code compiled with -mbackchain is call-compatible with code compiled with -mmo-backchain;
    however, use of the backchain for debugging purposes usually requires that the whole binary is built
    with -mbackchain.  Note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not
    supported.  In order to build a linux kernel use -msoft-float.

    The default is to not maintain the backchain.
-mpacked-stack
-mno-packed-stack
    Use (do not use) the packed stack layout.  When -mno-packed-stack is specified, the compiler uses the
    all fields of the 96/160 byte register save area only for their default purpose; unused fields still
    take up stack space.  When -mpacked-stack is specified, register save slots are densely packed at the
    top of the register save area; unused space is reused for other purposes, allowing for more efficient
    use of the available stack space.  However, when -mbackchain is also in effect, the topmost word of
    the save area is always used to store the backchain, and the return address register is always saved
    two words below the backchain.

    As long as the stack frame backchain is not used, code generated with -mpacked-stack is call-
    compatible with code generated with -mno-packed-stack.  Note that some non-FSF releases of GCC 2.95
    for S/390 or zSeries generated code that uses the stack frame backchain at run time, not just for
    debugging purposes.  Such code is not call-compatible with code compiled with -mpacked-stack.  Also,
    note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported.  In order
    to build a linux kernel use -msoft-float.

    The default is to not use the packed stack layout.
-msmall-exec
-mno-small-exec
    Generate (or do not generate) code using the "bras" instruction to do subroutine calls.  This only
    works reliably if the total executable size does not exceed 64k.  The default is to use the "basr"
    instruction instead, which does not have this limitation.
-m64
-m31
    When -m31 is specified, generate code compliant to the GNU/Linux for S/390 ABI.  When -m64 is
    specified, generate code compliant to the GNU/Linux for zSeries ABI.  This allows GCC in particular
    to generate 64-bit instructions.  For the s390 targets, the default is -m31, while the s390x targets
    default to -m64.
-mzarch
-mesa
    When -mzarch is specified, generate code using the instructions available on z/Architecture.  When
    -mesa is specified, generate code using the instructions available on ESA/390.  Note that -mesa is
    not possible with -m64.  When generating code compliant to the GNU/Linux for S/390 ABI, the default
    is -mesa.  When generating code compliant to the GNU/Linux for zSeries ABI, the default is -mzarch.
-mmvcle
-mno-mvcle
    Generate (or do not generate) code using the "mvcle" instruction to perform block moves.  When
    -mno-mvcle is specified, use a "mvc" loop instead.  This is the default unless optimizing for size.
-mdebug
-mno-debug
    Print (or do not print) additional debug information when compiling.  The default is to not print
    debug information.
-march=cpu-type
    Generate code that will run on cpu-type, which is the name of a system representing a certain
    processor type.  Possible values for cpu-type are g5, g6, z900, z990, z9-109, z9-ec and z10.  When
    generating code using the instructions available on z/Architecture, the default is -march=z900.
    Otherwise, the default is -march=g5.
-mtune=cpu-type
    Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of
    available instructions.  The list of cpu-type values is the same as for -march.  The default is the
    value used for -march.
-mtpf-trace
-mno-tpf-trace
    Generate code that adds (does not add) in TPF OS specific branches to trace routines in the operating
    system.  This option is off by default, even when compiling for the TPF OS.
-mfused-madd
-mno-fused-madd
    Generate code that uses (does not use) the floating point multiply and accumulate instructions.
    These instructions are generated by default if hardware floating point is used.
-mwarn-framesize=framesize
    Emit a warning if the current function exceeds the given frame size.  Because this is a compile time
    check it doesn't need to be a real problem when the program runs.  It is intended to identify
    functions which most probably cause a stack overflow.  It is useful to be used in an environment with
    limited stack size e.g. the linux kernel.
-mwarn-dynamicstack
    Emit a warning if the function calls alloca or uses dynamically sized arrays.  This is generally a
    bad idea with a limited stack size.
-mstack-guard=stack-guard
-mstack-size=stack-size
    If these options are provided the s390 back end emits additional instructions in the function
    prologue which trigger a trap if the stack size is stack-guard bytes above the stack-size (remember
    that the stack on s390 grows downward).  If the stack-guard option is omitted the smallest power of 2
    larger than the frame size of the compiled function is chosen.  These options are intended to be used
    to help debugging stack overflow problems.  The additionally emitted code causes only little overhead
    and hence can also be used in production like systems without greater performance degradation.  The
    given values have to be exact powers of 2 and stack-size has to be greater than stack-guard without
    exceeding 64k.  In order to be efficient the extra code makes the assumption that the stack starts at
    an address aligned to the value given by stack-size.  The stack-guard option can only be used in
    conjunction with stack-size.

Score Options

These options are defined for Score implementations:
-meb
    Compile code for big endian mode.  This is the default.
-mel
    Compile code for little endian mode.
-mnhwloop
    Disable generate bcnz instruction.
-muls
    Enable generate unaligned load and store instruction.
-mmac
    Enable the use of multiply-accumulate instructions. Disabled by default.
-mscore5
    Specify the SCORE5 as the target architecture.
-mscore5u
    Specify the SCORE5U of the target architecture.
-mscore7
    Specify the SCORE7 as the target architecture. This is the default.
-mscore7d
    Specify the SCORE7D as the target architecture.

SH Options

These -m options are defined for the SH implementations:
-m1 Generate code for the SH1.
-m2 Generate code for the SH2.
-m2e
    Generate code for the SH2e.
-m2a-nofpu
    Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way that the floating-point unit
    is not used.
-m2a-single-only
    Generate code for the SH2a-FPU, in such a way that no double-precision floating point operations are
    used.
-m2a-single
    Generate code for the SH2a-FPU assuming the floating-point unit is in single-precision mode by
    default.
-m2a
    Generate code for the SH2a-FPU assuming the floating-point unit is in double-precision mode by
    default.
-m3 Generate code for the SH3.
-m3e
    Generate code for the SH3e.
-m4-nofpu
    Generate code for the SH4 without a floating-point unit.
-m4-single-only
    Generate code for the SH4 with a floating-point unit that only supports single-precision arithmetic.
-m4-single
    Generate code for the SH4 assuming the floating-point unit is in single-precision mode by default.
-m4 Generate code for the SH4.
-m4a-nofpu
    Generate code for the SH4al-dsp, or for a SH4a in such a way that the floating-point unit is not
    used.
-m4a-single-only
    Generate code for the SH4a, in such a way that no double-precision floating point operations are
    used.
-m4a-single
    Generate code for the SH4a assuming the floating-point unit is in single-precision mode by default.
-m4a
    Generate code for the SH4a.
-m4al
    Same as -m4a-nofpu, except that it implicitly passes -dsp to the assembler.  GCC doesn't generate any
    DSP instructions at the moment.

-mb Compile code for the processor in big endian mode.

-ml Compile code for the processor in little endian mode.
-mdalign
    Align doubles at 64-bit boundaries.  Note that this changes the calling conventions, and thus some
    functions from the standard C library will not work unless you recompile it first with -mdalign.
-mrelax
    Shorten some address references at link time, when possible; uses the linker option -relax.
-mbigtable
    Use 32-bit offsets in "switch" tables.  The default is to use 16-bit offsets.
-mbitops
    Enable the use of bit manipulation instructions on SH2A.
-mfmovd
    Enable the use of the instruction "fmovd".  Check -mdalign for alignment constraints.
-mhitachi
    Comply with the calling conventions defined by Renesas.
-mrenesas
    Comply with the calling conventions defined by Renesas.
-mno-renesas
    Comply with the calling conventions defined for GCC before the Renesas conventions were available.
    This option is the default for all targets of the SH toolchain except for sh-symbianelf.
-mnomacsave
    Mark the "MAC" register as call-clobbered, even if -mhitachi is given.
-mieee
    Increase IEEE-compliance of floating-point code.  At the moment, this is equivalent to
    -fno-finite-math-only.  When generating 16 bit SH opcodes, getting IEEE-conforming results for
    comparisons of NANs / infinities incurs extra overhead in every floating point comparison, therefore
    the default is set to -ffinite-math-only.
-minline-ic_invalidate
    Inline code to invalidate instruction cache entries after setting up nested function trampolines.
    This option has no effect if -musermode is in effect and the selected code generation option (e.g.
    -m4) does not allow the use of the icbi instruction.  If the selected code generation option does not
    allow the use of the icbi instruction, and -musermode is not in effect, the inlined code will
    manipulate the instruction cache address array directly with an associative write.  This not only
    requires privileged mode, but it will also fail if the cache line had been mapped via the TLB and has
    become unmapped.
-misize
    Dump instruction size and location in the assembly code.
-mpadstruct
    This option is deprecated.  It pads structures to multiple of 4 bytes, which is incompatible with the
    SH ABI.
-mspace
    Optimize for space instead of speed.  Implied by -Os.
-mprefergot
    When generating position-independent code, emit function calls using the Global Offset Table instead
    of the Procedure Linkage Table.
-musermode
    Don't generate privileged mode only code; implies -mno-inline-ic_invalidate if the inlined code would
    not work in user mode.  This is the default when the target is "sh-*-linux*".
-multcost=number
    Set the cost to assume for a multiply insn.
-mdiv=strategy
    Set the division strategy to use for SHmedia code.  strategy must be one of: call, call2, fp, inv,
    inv:minlat, inv20u, inv20l, inv:call, inv:call2, inv:fp .  "fp" performs the operation in floating
    point.  This has a very high latency, but needs only a few instructions, so it might be a good choice
    if your code has enough easily exploitable ILP to allow the compiler to schedule the floating point
    instructions together with other instructions.  Division by zero causes a floating point exception.
    "inv" uses integer operations to calculate the inverse of the divisor, and then multiplies the
    dividend with the inverse.  This strategy allows cse and hoisting of the inverse calculation.
    Division by zero calculates an unspecified result, but does not trap.  "inv:minlat" is a variant of
    "inv" where if no cse / hoisting opportunities have been found, or if the entire operation has been
    hoisted to the same place, the last stages of the inverse calculation are intertwined with the final
    multiply to reduce the overall latency, at the expense of using a few more instructions, and thus
    offering fewer scheduling opportunities with other code.  "call" calls a library function that
    usually implements the inv:minlat strategy.  This gives high code density for m5-*media-nofpu
    compilations.  "call2" uses a different entry point of the same library function, where it assumes
    that a pointer to a lookup table has already been set up, which exposes the pointer load to cse /
    code hoisting optimizations.  "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for
    initial code generation, but if the code stays unoptimized, revert to the "call", "call2", or "fp"
    strategies, respectively.  Note that the potentially-trapping side effect of division by zero is
    carried by a separate instruction, so it is possible that all the integer instructions are hoisted
    out, but the marker for the side effect stays where it is.  A recombination to fp operations or a
    call is not possible in that case.  "inv20u" and "inv20l" are variants of the "inv:minlat" strategy.
    In the case that the inverse calculation was nor separated from the multiply, they speed up division
    where the dividend fits into 20 bits (plus sign where applicable), by inserting a test to skip a
    number of operations in this case; this test slows down the case of larger dividends.  inv20u assumes
    the case of a such a small dividend to be unlikely, and inv20l assumes it to be likely.
-maccumulate-outgoing-args
    Reserve space once for outgoing arguments in the function prologue rather than around each call.
    Generally beneficial for performance and size.  Also needed for unwinding to avoid changing the stack
    frame around conditional code.
-mdivsi3_libfunc=name
    Set the name of the library function used for 32 bit signed division to name.  This only affect the
    name used in the call and inv:call division strategies, and the compiler will still expect the same
    sets of input/output/clobbered registers as if this option was not present.
-mfixed-range=register-range
    Generate code treating the given register range as fixed registers.  A fixed register is one that the
    register allocator can not use.  This is useful when compiling kernel code.  A register range is
    specified as two registers separated by a dash.  Multiple register ranges can be specified separated
    by a comma.
-madjust-unroll
    Throttle unrolling to avoid thrashing target registers.  This option only has an effect if the gcc
    code base supports the TARGET_ADJUST_UNROLL_MAX target hook.
-mindexed-addressing
    Enable the use of the indexed addressing mode for SHmedia32/SHcompact.  This is only safe if the
    hardware and/or OS implement 32 bit wrap-around semantics for the indexed addressing mode.  The
    architecture allows the implementation of processors with 64 bit MMU, which the OS could use to get
    32 bit addressing, but since no current hardware implementation supports this or any other way to
    make the indexed addressing mode safe to use in the 32 bit ABI, the default is
    -mno-indexed-addressing.
-mgettrcost=number
    Set the cost assumed for the gettr instruction to number.  The default is 2 if -mpt-fixed is in
    effect, 100 otherwise.
-mpt-fixed
    Assume pt* instructions won't trap.  This will generally generate better scheduled code, but is
    unsafe on current hardware.  The current architecture definition says that ptabs and ptrel trap when
    the target anded with 3 is 3.  This has the unintentional effect of making it unsafe to schedule
    ptabs / ptrel before a branch, or hoist it out of a loop.  For example, __do_global_ctors, a part of
    libgcc that runs constructors at program startup, calls functions in a list which is delimited by -1.
    With the -mpt-fixed option, the ptabs will be done before testing against -1.  That means that all
    the constructors will be run a bit quicker, but when the loop comes to the end of the list, the
    program crashes because ptabs loads -1 into a target register.  Since this option is unsafe for any
    hardware implementing the current architecture specification, the default is -mno-pt-fixed.  Unless
    the user specifies a specific cost with -mgettrcost, -mno-pt-fixed also implies -mgettrcost=100; this
    deters register allocation using target registers for storing ordinary integers.
-minvalid-symbols
    Assume symbols might be invalid.  Ordinary function symbols generated by the compiler will always be
    valid to load with movi/shori/ptabs or movi/shori/ptrel, but with assembler and/or linker tricks it
    is possible to generate symbols that will cause ptabs / ptrel to trap.  This option is only
    meaningful when -mno-pt-fixed is in effect.  It will then prevent cross-basic-block cse, hoisting and
    most scheduling of symbol loads.  The default is -mno-invalid-symbols.

Solaris 2 Options

These -m options are supported on Solaris 2:
-mimpure-text
    -mimpure-text, used in addition to -shared, tells the compiler to not pass -z text to the linker when
    linking a shared object.  Using this option, you can link position-dependent code into a shared
    object.

    -mimpure-text suppresses the "relocations remain against allocatable but non-writable sections"
    linker error message.  However, the necessary relocations will trigger copy-on-write, and the shared
    object is not actually shared across processes.  Instead of using -mimpure-text, you should compile
    all source code with -fpic or -fPIC.

These switches are supported in addition to the above on Solaris 2:
-threads
    Add support for multithreading using the Solaris threads library.  This option sets flags for both
    the preprocessor and linker.  This option does not affect the thread safety of object code produced
    by the compiler or that of libraries supplied with it.
-pthreads
    Add support for multithreading using the POSIX threads library.  This option sets flags for both the
    preprocessor and linker.  This option does not affect the thread safety of object code produced  by
    the compiler or that of libraries supplied with it.
-pthread
    This is a synonym for -pthreads.

SPARC Options

These -m options are supported on the SPARC:
-mno-app-regs
-mapp-regs
    Specify -mapp-regs to generate output using the global registers 2 through 4, which the SPARC SVR4
    ABI reserves for applications.  This is the default.

    To be fully SVR4 ABI compliant at the cost of some performance loss, specify -mno-app-regs.  You
    should compile libraries and system software with this option.
-mfpu
-mhard-float
    Generate output containing floating point instructions.  This is the default.
-mno-fpu
-msoft-float
    Generate output containing library calls for floating point.  Warning: the requisite libraries are
    not available for all SPARC targets.  Normally the facilities of the machine's usual C compiler are
    used, but this cannot be done directly in cross-compilation.  You must make your own arrangements to
    provide suitable library functions for cross-compilation.  The embedded targets sparc-*-aout and
    sparclite-*-* do provide software floating point support.

    -msoft-float changes the calling convention in the output file; therefore, it is only useful if you
    compile all of a program with this option.  In particular, you need to compile libgcc.a, the library
    that comes with GCC, with -msoft-float in order for this to work.
-mhard-quad-float
    Generate output containing quad-word (long double) floating point instructions.
-msoft-quad-float
    Generate output containing library calls for quad-word (long double) floating point instructions.
    The functions called are those specified in the SPARC ABI.  This is the default.

    As of this writing, there are no SPARC implementations that have hardware support for the quad-word
    floating point instructions.  They all invoke a trap handler for one of these instructions, and then
    the trap handler emulates the effect of the instruction.  Because of the trap handler overhead, this
    is much slower than calling the ABI library routines.  Thus the -msoft-quad-float option is the
    default.
-mno-unaligned-doubles
-munaligned-doubles
    Assume that doubles have 8 byte alignment.  This is the default.

    With -munaligned-doubles, GCC assumes that doubles have 8 byte alignment only if they are contained
    in another type, or if they have an absolute address.  Otherwise, it assumes they have 4 byte
    alignment.  Specifying this option avoids some rare compatibility problems with code generated by
    other compilers.  It is not the default because it results in a performance loss, especially for
    floating point code.
-mno-faster-structs
-mfaster-structs
    With -mfaster-structs, the compiler assumes that structures should have 8 byte alignment.  This
    enables the use of pairs of "ldd" and "std" instructions for copies in structure assignment, in place
    of twice as many "ld" and "st" pairs.  However, the use of this changed alignment directly violates
    the SPARC ABI.  Thus, it's intended only for use on targets where the developer acknowledges that
    their resulting code will not be directly in line with the rules of the ABI.
-mv8plus
-mno-v8plus
    With -mv8plus, GCC generates code for the SPARC-V8+ ABI.  The difference from the V8 ABI is that the
    global and out registers are considered 64-bit wide.  This is enabled by default on Solaris in 32-bit
    mode for all SPARC-V9 processors.
-mvis
-mno-vis
    With -mvis, GCC generates code that takes advantage of the UltraSPARC Visual Instruction Set
    extensions.  The default is -mno-vis.
-mfix-at697f
    Enable the documented workaround for the single erratum of the Atmel AT697F processor (which
    corresponds to erratum #13 of the AT697E processor).

These -m options are supported in addition to the above on SPARC-V9 processors in 64-bit environments:
-mlittle-endian
    Generate code for a processor running in little-endian mode.  It is only available for a few
    configurations and most notably not on Solaris and Linux.
-m32
-m64
    Generate code for a 32-bit or 64-bit environment.  The 32-bit environment sets int, long and pointer
    to 32 bits.  The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.
-mcmodel=medlow
    Generate code for the Medium/Low code model: 64-bit addresses, programs must be linked in the low 32
    bits of memory.  Programs can be statically or dynamically linked.
-mcmodel=medmid
    Generate code for the Medium/Middle code model: 64-bit addresses, programs must be linked in the low
    44 bits of memory, the text and data segments must be less than 2GB in size and the data segment must
    be located within 2GB of the text segment.
-mcmodel=medany
    Generate code for the Medium/Anywhere code model: 64-bit addresses, programs may be linked anywhere
    in memory, the text and data segments must be less than 2GB in size and the data segment must be
    located within 2GB of the text segment.
-mcmodel=embmedany
    Generate code for the Medium/Anywhere code model for embedded systems: 64-bit addresses, the text and
    data segments must be less than 2GB in size, both starting anywhere in memory (determined at link
    time).  The global register %g4 points to the base of the data segment.  Programs are statically
    linked and PIC is not supported.
-mstack-bias
-mno-stack-bias
    With -mstack-bias, GCC assumes that the stack pointer, and frame pointer if present, are offset by
    -2047 which must be added back when making stack frame references.  This is the default in 64-bit
    mode.  Otherwise, assume no such offset is present.

SPU Options

These -m options are supported on the SPU:
-mwarn-reloc
-merror-reloc
    The loader for SPU does not handle dynamic relocations.  By default, GCC will give an error when it
    generates code that requires a dynamic relocation.  -mno-error-reloc disables the error, -mwarn-reloc
    will generate a warning instead.
-msafe-dma
-munsafe-dma
    Instructions which initiate or test completion of DMA must not be reordered with respect to loads and
    stores of the memory which is being accessed.  Users typically address this problem using the
    volatile keyword, but that can lead to inefficient code in places where the memory is known to not
    change.  Rather than mark the memory as volatile we treat the DMA instructions as potentially
    effecting all memory.  With -munsafe-dma users must use the volatile keyword to protect memory
    accesses.
-mbranch-hints
    By default, GCC will generate a branch hint instruction to avoid pipeline stalls for always taken or
    probably taken branches.  A hint will not be generated closer than 8 instructions away from its
    branch.  There is little reason to disable them, except for debugging purposes, or to make an object
    a little bit smaller.
-msmall-mem
-mlarge-mem
    By default, GCC generates code assuming that addresses are never larger than 18 bits.  With
    -mlarge-mem code is generated that assumes a full 32 bit address.
-mstdmain
    By default, GCC links against startup code that assumes the SPU-style main function interface (which
    has an unconventional parameter list).  With -mstdmain, GCC will link your program against startup
    code that assumes a C99-style interface to "main", including a local copy of "argv" strings.
-mfixed-range=register-range
    Generate code treating the given register range as fixed registers.  A fixed register is one that the
    register allocator can not use.  This is useful when compiling kernel code.  A register range is
    specified as two registers separated by a dash.  Multiple register ranges can be specified separated
    by a comma.
-mea32
-mea64
    Compile code assuming that pointers to the PPU address space accessed via the "__ea" named address
    space qualifier are either 32 or 64 bits wide.  The default is 32 bits.  As this is an ABI changing
    option, all object code in an executable must be compiled with the same setting.
-maddress-space-conversion
-mno-address-space-conversion
    Allow/disallow treating the "__ea" address space as superset of the generic address space.  This
    enables explicit type casts between "__ea" and generic pointer as well as implicit conversions of
    generic pointers to "__ea" pointers.  The default is to allow address space pointer conversions.
-mcache-size=cache-size
    This option controls the version of libgcc that the compiler links to an executable and selects a
    software-managed cache for accessing variables in the "__ea" address space with a particular cache
    size.  Possible options for cache-size are 8, 16, 32, 64 and 128.  The default cache size is 64KB.
-matomic-updates
-mno-atomic-updates
    This option controls the version of libgcc that the compiler links to an executable and selects
    whether atomic updates to the software-managed cache of PPU-side variables are used.  If you use
    atomic updates, changes to a PPU variable from SPU code using the "__ea" named address space
    qualifier will not interfere with changes to other PPU variables residing in the same cache line from
    PPU code.  If you do not use atomic updates, such interference may occur; however, writing back cache
    lines will be more efficient.  The default behavior is to use atomic updates.
-mdual-nops
-mdual-nops=n
    By default, GCC will insert nops to increase dual issue when it expects it to increase performance.
    n can be a value from 0 to 10.  A smaller n will insert fewer nops.  10 is the default, 0 is the same
    as -mno-dual-nops.  Disabled with -Os.
-mhint-max-nops=n
    Maximum number of nops to insert for a branch hint.  A branch hint must be at least 8 instructions
    away from the branch it is effecting.  GCC will insert up to n nops to enforce this, otherwise it
    will not generate the branch hint.
-mhint-max-distance=n
    The encoding of the branch hint instruction limits the hint to be within 256 instructions of the
    branch it is effecting.  By default, GCC makes sure it is within 125.
-msafe-hints
    Work around a hardware bug which causes the SPU to stall indefinitely.  By default, GCC will insert
    the "hbrp" instruction to make sure this stall won't happen.

Options for System V

These additional options are available on System V Release 4 for compatibility with other compilers on
those systems:
-G  Create a shared object.  It is recommended that -symbolic or -shared be used instead.

-Qy Identify the versions of each tool used by the compiler, in a ".ident" assembler directive in the
    output.

-Qn Refrain from adding ".ident" directives to the output file (this is the default).
-YP,dirs
    Search the directories dirs, and no others, for libraries specified with -l.
-Ym,dir
    Look in the directory dir to find the M4 preprocessor.  The assembler uses this option.

V850 Options

These -m options are defined for V850 implementations:
-mlong-calls
-mno-long-calls
    Treat all calls as being far away (near).  If calls are assumed to be far away, the compiler will
    always load the functions address up into a register, and call indirect through the pointer.
-mno-ep
-mep
    Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more times to copy
    pointer into the "ep" register, and use the shorter "sld" and "sst" instructions.  The -mep option is
    on by default if you optimize.
-mno-prolog-function
-mprolog-function
    Do not use (do use) external functions to save and restore registers at the prologue and epilogue of
    a function.  The external functions are slower, but use less code space if more than one function
    saves the same number of registers.  The -mprolog-function option is on by default if you optimize.
-mspace
    Try to make the code as small as possible.  At present, this just turns on the -mep and
    -mprolog-function options.
-mtda=n
    Put static or global variables whose size is n bytes or less into the tiny data area that register
    "ep" points to.  The tiny data area can hold up to 256 bytes in total (128 bytes for byte
    references).
-msda=n
    Put static or global variables whose size is n bytes or less into the small data area that register
    "gp" points to.  The small data area can hold up to 64 kilobytes.
-mzda=n
    Put static or global variables whose size is n bytes or less into the first 32 kilobytes of memory.
-mv850
    Specify that the target processor is the V850.
-mbig-switch
    Generate code suitable for big switch tables.  Use this option only if the assembler/linker complain
    about out of range branches within a switch table.
-mapp-regs
    This option will cause r2 and r5 to be used in the code generated by the compiler.  This setting is
    the default.
-mno-app-regs
    This option will cause r2 and r5 to be treated as fixed registers.
-mv850e2v3
    Specify that the target processor is the V850E2V3.  The preprocessor constants __v850e2v3__ will be
    defined if this option is used.
-mv850e2
    Specify that the target processor is the V850E2.  The preprocessor constants __v850e2__ will be
    defined if
-mv850e1
    Specify that the target processor is the V850E1.  The preprocessor constants __v850e1__ and __v850e__
    will be defined if
-mv850es
    Specify that the target processor is the V850ES.  This is an alias for the -mv850e1 option.
-mv850e
    Specify that the target processor is the V850E.  The preprocessor constant __v850e__ will be defined
    if this option is used.

    If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor -mv850e2v3 are defined then a default
    target processor will be chosen and the relevant __v850*__ preprocessor constant will be defined.

    The preprocessor constants __v850 and __v851__ are always defined, regardless of which processor
    variant is the target.
-mdisable-callt
    This option will suppress generation of the CALLT instruction for the v850e, v850e1, v850e2 and
    v850e2v3 flavors of the v850 architecture.  The default is -mno-disable-callt which allows the CALLT
    instruction to be used.

VAX Options

These -m options are defined for the VAX:
-munix
    Do not output certain jump instructions ("aobleq" and so on) that the Unix assembler for the VAX
    cannot handle across long ranges.
-mgnu
    Do output those jump instructions, on the assumption that you will assemble with the GNU assembler.

-mg Output code for g-format floating point numbers instead of d-format.

VxWorks Options

The options in this section are defined for all VxWorks targets.  Options specific to the target hardware
are listed with the other options for that target.
-mrtp
    GCC can generate code for both VxWorks kernels and real time processes (RTPs).  This option switches
    from the former to the latter.  It also defines the preprocessor macro "__RTP__".
-non-static
    Link an RTP executable against shared libraries rather than static libraries.  The options -static
    and -shared can also be used for RTPs; -static is the default.
-Bstatic
-Bdynamic
    These options are passed down to the linker.  They are defined for compatibility with Diab.
-Xbind-lazy
    Enable lazy binding of function calls.  This option is equivalent to -Wl,-z,now and is defined for
    compatibility with Diab.
-Xbind-now
    Disable lazy binding of function calls.  This option is the default and is defined for compatibility
    with Diab.

x86-64 Options

These are listed under

Xstormy16 Options

These options are defined for Xstormy16:
-msim
    Choose startup files and linker script suitable for the simulator.

Xtensa Options

These options are supported for Xtensa targets:
-mconst16
-mno-const16
    Enable or disable use of "CONST16" instructions for loading constant values.  The "CONST16"
    instruction is currently not a standard option from Tensilica.  When enabled, "CONST16" instructions
    are always used in place of the standard "L32R" instructions.  The use of "CONST16" is enabled by
    default only if the "L32R" instruction is not available.
-mfused-madd
-mno-fused-madd
    Enable or disable use of fused multiply/add and multiply/subtract instructions in the floating-point
    option.  This has no effect if the floating-point option is not also enabled.  Disabling fused
    multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for
    the multiply and add/subtract operations.  This may be desirable in some cases where strict IEEE
    754-compliant results are required: the fused multiply add/subtract instructions do not round the
    intermediate result, thereby producing results with more bits of precision than specified by the IEEE
    standard.  Disabling fused multiply add/subtract instructions also ensures that the program output is
    not sensitive to the compiler's ability to combine multiply and add/subtract operations.
-mserialize-volatile
-mno-serialize-volatile
    When this option is enabled, GCC inserts "MEMW" instructions before "volatile" memory references to
    guarantee sequential consistency.  The default is -mserialize-volatile.  Use -mno-serialize-volatile
    to omit the "MEMW" instructions.
-mforce-no-pic
    For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC),
    this option disables PIC for compiling kernel code.
-mtext-section-literals
-mno-text-section-literals
    Control the treatment of literal pools.  The default is -mno-text-section-literals, which places
    literals in a separate section in the output file.  This allows the literal pool to be placed in a
    data RAM/ROM, and it also allows the linker to combine literal pools from separate object files to
    remove redundant literals and improve code size.  With -mtext-section-literals, the literals are
    interspersed in the text section in order to keep them as close as possible to their references.
    This may be necessary for large assembly files.
-mtarget-align
-mno-target-align
    When this option is enabled, GCC instructs the assembler to automatically align instructions to
    reduce branch penalties at the expense of some code density.  The assembler attempts to widen density
    instructions to align branch targets and the instructions following call instructions.  If there are
    not enough preceding safe density instructions to align a target, no widening will be performed.  The
    default is -mtarget-align.  These options do not affect the treatment of auto-aligned instructions
    like "LOOP", which the assembler will always align, either by widening density instructions or by
    inserting no-op instructions.
    -mlongcalls
    -mno-longcalls
        When this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls
        unless it can determine that the target of a direct call is in the range allowed by the call
        instruction.  This translation typically occurs for calls to functions in other source files.
        Specifically, the assembler translates a direct "CALL" instruction into an "L32R" followed by a
        "CALLX" instruction.  The default is -mno-longcalls.  This option should be used in programs where
        the call target can potentially be out of range.  This option is implemented in the assembler, not
        the compiler, so the assembly code generated by GCC will still show direct call instructions---look
        at the disassembled object code to see the actual instructions.  Note that the assembler will use an
        indirect call for every cross-file call, not just those that really will be out of range.

    zSeries Options

    These are listed under

Options for Code Generation Conventions
    These machine-independent options control the interface conventions used in code generation.

    Most of them have both positive and negative forms; the negative form of -ffoo would be -fno-foo.  In the
    table below, only one of the forms is listed---the one which is not the default.  You can figure out the
    other form by either removing no- or adding it.
-fbounds-check
    For front-ends that support it, generate additional code to check that indices used to access arrays
    are within the declared range.  This is currently only supported by the Java and Fortran front-ends,
    where this option defaults to true and false respectively.
-ftrapv
    This option generates traps for signed overflow on addition, subtraction, multiplication operations.
-fwrapv
    This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction
    and multiplication wraps around using twos-complement representation.  This flag enables some
    optimizations and disables others.  This option is enabled by default for the Java front-end, as
    required by the Java language specification.
-fexceptions
    Enable exception handling.  Generates extra code needed to propagate exceptions.  For some targets,
    this implies GCC will generate frame unwind information for all functions, which can produce
    significant data size overhead, although it does not affect execution.  If you do not specify this
    option, GCC will enable it by default for languages like C++ which normally require exception
    handling, and disable it for languages like C that do not normally require it.  However, you may need
    to enable this option when compiling C code that needs to interoperate properly with exception
    handlers written in C++.  You may also wish to disable this option if you are compiling older C++
    programs that don't use exception handling.
-fnon-call-exceptions
    Generate code that allows trapping instructions to throw exceptions.  Note that this requires
    platform-specific runtime support that does not exist everywhere.  Moreover, it only allows trapping
    instructions to throw exceptions, i.e. memory references or floating point instructions.  It does not
    allow exceptions to be thrown from arbitrary signal handlers such as "SIGALRM".
-funwind-tables
    Similar to -fexceptions, except that it will just generate any needed static data, but will not
    affect the generated code in any other way.  You will normally not enable this option; instead, a
    language processor that needs this handling would enable it on your behalf.
-fasynchronous-unwind-tables
    Generate unwind table in dwarf2 format, if supported by target machine.  The table is exact at each
    instruction boundary, so it can be used for stack unwinding from asynchronous events (such as
    debugger or garbage collector).
-fpcc-struct-return
    Return "short" "struct" and "union" values in memory like longer ones, rather than in registers.
    This convention is less efficient, but it has the advantage of allowing intercallability between GCC-
    compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc).

    The precise convention for returning structures in memory depends on the target configuration macros.

    Short structures and unions are those whose size and alignment match that of some integer type.

    Warning: code compiled with the -fpcc-struct-return switch is not binary compatible with code
    compiled with the -freg-struct-return switch.  Use it to conform to a non-default application binary
    interface.
-freg-struct-return
    Return "struct" and "union" values in registers when possible.  This is more efficient for small
    structures than -fpcc-struct-return.

    If you specify neither -fpcc-struct-return nor -freg-struct-return, GCC defaults to whichever
    convention is standard for the target.  If there is no standard convention, GCC defaults to
    -fpcc-struct-return, except on targets where GCC is the principal compiler.  In those cases, we can
    choose the standard, and we chose the more efficient register return alternative.

    Warning: code compiled with the -freg-struct-return switch is not binary compatible with code
    compiled with the -fpcc-struct-return switch.  Use it to conform to a non-default application binary
    interface.
-fshort-enums
    Allocate to an "enum" type only as many bytes as it needs for the declared range of possible values.
    Specifically, the "enum" type will be equivalent to the smallest integer type which has enough room.

    Warning: the -fshort-enums switch causes GCC to generate code that is not binary compatible with code
    generated without that switch.  Use it to conform to a non-default application binary interface.
-fshort-double
    Use the same size for "double" as for "float".

    Warning: the -fshort-double switch causes GCC to generate code that is not binary compatible with
    code generated without that switch.  Use it to conform to a non-default application binary interface.
-fshort-wchar
    Override the underlying type for wchar_t to be short unsigned int instead of the default for the
    target.  This option is useful for building programs to run under WINE.

    Warning: the -fshort-wchar switch causes GCC to generate code that is not binary compatible with code
    generated without that switch.  Use it to conform to a non-default application binary interface.
-fno-common
    In C code, controls the placement of uninitialized global variables.  Unix C compilers have
    traditionally permitted multiple definitions of such variables in different compilation units by
    placing the variables in a common block.  This is the behavior specified by -fcommon, and is the
    default for GCC on most targets.  On the other hand, this behavior is not required by ISO C, and on
    some targets may carry a speed or code size penalty on variable references.  The -fno-common option
    specifies that the compiler should place uninitialized global variables in the data section of the
    object file, rather than generating them as common blocks.  This has the effect that if the same
    variable is declared (without "extern") in two different compilations, you will get a multiple-
    definition error when you link them.  In this case, you must compile with -fcommon instead.
    Compiling with -fno-common is useful on targets for which it provides better performance, or if you
    wish to verify that the program will work on other systems which always treat uninitialized variable
    declarations this way.
-fno-ident
    Ignore the #ident directive.
-finhibit-size-directive
    Don't output a ".size" assembler directive, or anything else that would cause trouble if the function
    is split in the middle, and the two halves are placed at locations far apart in memory.  This option
    is used when compiling crtstuff.c; you should not need to use it for anything else.
-fverbose-asm
    Put extra commentary information in the generated assembly code to make it more readable.  This
    option is generally only of use to those who actually need to read the generated assembly code
    (perhaps while debugging the compiler itself).

    -fno-verbose-asm, the default, causes the extra information to be omitted and is useful when
    comparing two assembler files.
-frecord-gcc-switches
    This switch causes the command line that was used to invoke the compiler to be recorded into the
    object file that is being created.  This switch is only implemented on some targets and the exact
    format of the recording is target and binary file format dependent, but it usually takes the form of
    a section containing ASCII text.  This switch is related to the -fverbose-asm switch, but that switch
    only records information in the assembler output file as comments, so it never reaches the object
    file.
-fpic
    Generate position-independent code (PIC) suitable for use in a shared library, if supported for the
    target machine.  Such code accesses all constant addresses through a global offset table (GOT).  The
    dynamic loader resolves the GOT entries when the program starts (the dynamic loader is not part of
    GCC; it is part of the operating system).  If the GOT size for the linked executable exceeds a
    machine-specific maximum size, you get an error message from the linker indicating that -fpic does
    not work; in that case, recompile with -fPIC instead.  (These maximums are 8k on the SPARC and 32k on
    the m68k and RS/6000.  The 386 has no such limit.)

    Position-independent code requires special support, and therefore works only on certain machines.
    For the 386, GCC supports PIC for System V but not for the Sun 386i.  Code generated for the IBM
    RS/6000 is always position-independent.

    When this flag is set, the macros "__pic__" and "__PIC__" are defined to 1.
-fPIC
    If supported for the target machine, emit position-independent code, suitable for dynamic linking and
    avoiding any limit on the size of the global offset table.  This option makes a difference on the
    m68k, PowerPC and SPARC.

    Position-independent code requires special support, and therefore works only on certain machines.

    When this flag is set, the macros "__pic__" and "__PIC__" are defined to 2.
-fpie
-fPIE
    These options are similar to -fpic and -fPIC, but generated position independent code can be only
    linked into executables.  Usually these options are used when -pie GCC option will be used during
    linking.

    -fpie and -fPIE both define the macros "__pie__" and "__PIE__".  The macros have the value 1 for
    -fpie and 2 for -fPIE.
-fno-jump-tables
    Do not use jump tables for switch statements even where it would be more efficient than other code
    generation strategies.  This option is of use in conjunction with -fpic or -fPIC for building code
    which forms part of a dynamic linker and cannot reference the address of a jump table.  On some
    targets, jump tables do not require a GOT and this option is not needed.
-ffixed-reg
    Treat the register named reg as a fixed register; generated code should never refer to it (except
    perhaps as a stack pointer, frame pointer or in some other fixed role).

    reg must be the name of a register.  The register names accepted are machine-specific and are defined
    in the "REGISTER_NAMES" macro in the machine description macro file.

    This flag does not have a negative form, because it specifies a three-way choice.
-fcall-used-reg
    Treat the register named reg as an allocable register that is clobbered by function calls.  It may be
    allocated for temporaries or variables that do not live across a call.  Functions compiled this way
    will not save and restore the register reg.

    It is an error to used this flag with the frame pointer or stack pointer.  Use of this flag for other
    registers that have fixed pervasive roles in the machine's execution model will produce disastrous
    results.

    This flag does not have a negative form, because it specifies a three-way choice.
-fcall-saved-reg
    Treat the register named reg as an allocable register saved by functions.  It may be allocated even
    for temporaries or variables that live across a call.  Functions compiled this way will save and
    restore the register reg if they use it.

    It is an error to used this flag with the frame pointer or stack pointer.  Use of this flag for other
    registers that have fixed pervasive roles in the machine's execution model will produce disastrous
    results.

    A different sort of disaster will result from the use of this flag for a register in which function
    values may be returned.

    This flag does not have a negative form, because it specifies a three-way choice.
-fpack-struct[=n]
    Without a value specified, pack all structure members together without holes.  When a value is
    specified (which must be a small power of two), pack structure members according to this value,
    representing the maximum alignment (that is, objects with default alignment requirements larger than
    this will be output potentially unaligned at the next fitting location.

    Warning: the -fpack-struct switch causes GCC to generate code that is not binary compatible with code
    generated without that switch.  Additionally, it makes the code suboptimal.  Use it to conform to a
    non-default application binary interface.
-finstrument-functions
    Generate instrumentation calls for entry and exit to functions.  Just after function entry and just
    before function exit, the following profiling functions will be called with the address of the
    current function and its call site.  (On some platforms, "__builtin_return_address" does not work
    beyond the current function, so the call site information may not be available to the profiling
    functions otherwise.)

            void __cyg_profile_func_enter (void *this_fn,
                                           void *call_site);
            void __cyg_profile_func_exit  (void *this_fn,
                                           void *call_site);

    The first argument is the address of the start of the current function, which may be looked up
    exactly in the symbol table.

    This instrumentation is also done for functions expanded inline in other functions.  The profiling
    calls will indicate where, conceptually, the inline function is entered and exited.  This means that
    addressable versions of such functions must be available.  If all your uses of a function are
    expanded inline, this may mean an additional expansion of code size.  If you use extern inline in
    your C code, an addressable version of such functions must be provided.  (This is normally the case
    anyways, but if you get lucky and the optimizer always expands the functions inline, you might have
    gotten away without providing static copies.)

    A function may be given the attribute "no_instrument_function", in which case this instrumentation
    will not be done.  This can be used, for example, for the profiling functions listed above, high-
    priority interrupt routines, and any functions from which the profiling functions cannot safely be
    called (perhaps signal handlers, if the profiling routines generate output or allocate memory).
-finstrument-functions-exclude-file-list=file,file,...
    Set the list of functions that are excluded from instrumentation (see the description of
    "-finstrument-functions").  If the file that contains a function definition matches with one of file,
    then that function is not instrumented.  The match is done on substrings: if the file parameter is a
    substring of the file name, it is considered to be a match.

    For example:
-finstrument-functions-exclude-function-list=sym,sym,...
    This is similar to "-finstrument-functions-exclude-file-list", but this option sets the list of
    function names to be excluded from instrumentation.  The function name to be matched is its user-
    visible name, such as "vector<int> blah(const vector<int> &)", not the internal mangled name (e.g.,
    "_Z4blahRSt6vectorIiSaIiEE").  The match is done on substrings: if the sym parameter is a substring
    of the function name, it is considered to be a match.  For C99 and C++ extended identifiers, the
    function name must be given in UTF-8, not using universal character names.
-fstack-check
    Generate code to verify that you do not go beyond the boundary of the stack.  You should specify this
    flag if you are running in an environment with multiple threads, but only rarely need to specify it
    in a single-threaded environment since stack overflow is automatically detected on nearly all systems
    if there is only one stack.
-fstack-limit-register=reg
-fstack-limit-symbol=sym
-fno-stack-limit
    Generate code to ensure that the stack does not grow beyond a certain value, either the value of a
    register or the address of a symbol.  If the stack would grow beyond the value, a signal is raised.
    For most targets, the signal is raised before the stack overruns the boundary, so it is possible to
    catch the signal without taking special precautions.

    For instance, if the stack starts at absolute address 0x80000000 and grows downwards, you can use the
    flags -fstack-limit-symbol=__stack_limit and -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack
    limit of 128KB.  Note that this may only work with the GNU linker.
-fsplit-stack
    Generate code to automatically split the stack before it overflows.  The resulting program has a
    discontiguous stack which can only overflow if the program is unable to allocate any more memory.
    This is most useful when running threaded programs, as it is no longer necessary to calculate a good
    stack size to use for each thread.  This is currently only implemented for the i386 and x86_64
    backends running GNU/Linux.

    When code compiled with -fsplit-stack calls code compiled without -fsplit-stack, there may not be
    much stack space available for the latter code to run.  If compiling all code, including library
    code, with -fsplit-stack is not an option, then the linker can fix up these calls so that the code
    compiled without -fsplit-stack always has a large stack.  Support for this is implemented in the gold
    linker in GNU binutils release 2.21 and later.
-fleading-underscore
    This option and its counterpart, -fno-leading-underscore, forcibly change the way C symbols are
    represented in the object file.  One use is to help link with legacy assembly code.

    Warning: the -fleading-underscore switch causes GCC to generate code that is not binary compatible
    with code generated without that switch.  Use it to conform to a non-default application binary
    interface.  Not all targets provide complete support for this switch.
-ftls-model=model
    Alter the thread-local storage model to be used.  The model argument should be one of
    "global-dynamic", "local-dynamic", "initial-exec" or "local-exec".

    The default without -fpic is "initial-exec"; with -fpic the default is "global-dynamic".
-fvisibility=default|internal|hidden|protected
    Set the default ELF image symbol visibility to the specified option---all symbols will be marked with
    this unless overridden within the code.  Using this feature can very substantially improve linking
    and load times of shared object libraries, produce more optimized code, provide near-perfect API
    export and prevent symbol clashes.  It is strongly recommended that you use this in any shared
    objects you distribute.
-fstrict-volatile-bitfields
    This option should be used if accesses to volatile bitfields (or other structure fields, although the
    compiler usually honors those types anyway) should use a single access of the width of the field's
    type, aligned to a natural alignment if possible.  For example, targets with memory-mapped peripheral
    registers might require all such accesses to be 16 bits wide; with this flag the user could declare
    all peripheral bitfields as "unsigned short" (assuming short is 16 bits on these targets) to force
    GCC to use 16 bit accesses instead of, perhaps, a more efficient 32 bit access.