Intel 386 Options
-----------------

   These `-m' options are defined for the i386 family of computers:

`-m486'
`-m386'
     Control whether or not code is optimized for a 486 instead of an
     386.  Code generated for an 486 will run on a 386 and vice versa.

`-mno-ieee-fp'
`-mieee-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 GNU CC.
     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.  As of
     revision 2.6.1, these instructions are not generated unless you
     also use the `-ffast-math' switch.

`-malign-double'
`-mno-align-double'
     Control whether GNU CC 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.

     *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.

`-msvr3-shlib'
`-mno-svr3-shlib'
     Control whether GNU CC places uninitialized locals into `bss' or
     `data'.  `-msvr3-shlib' places these locals into `bss'.  These
     options are meaningful only on System V Release 3.

`-mno-wide-multiply'
`-mwide-multiply'
     Control whether GNU CC uses the `mul' and `imul' that produce 64
     bit results in `eax:edx' from 32 bit operands to do `long long'
     multiplies and 32-bit division by constants.

`-mprofiler-epilogue'
`-mno-profiler-epilogue'
     Generate extra code to write profile information for function
     exits.  This option has no effect except in combination with `-g'
     or `-pg'.

`-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'. See Function Attributes

     *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.)

`-mreg-alloc=REGS'
     Control the default allocation order of integer registers.  The
     string REGS is a series of letters specifying a register.  The
     supported letters are: `a' allocate EAX; `b' allocate EBX; `c'
     allocate ECX; `d' allocate EDX; `S' allocate ESI; `D' allocate
     EDI; `B' allocate EBP.

`-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'.
     See Function Attributes

     *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.

`-malign-loops=NUM'
     Align loops to a 2 raised to a NUM byte boundary.  If
     `-malign-loops' is not specified, the default is 2.

`-malign-jumps=NUM'
     Align instructions that are only jumped to to a 2 raised to a NUM
     byte boundary.  If `-malign-jumps' is not specified, the default is
     2 if optimizing for a 386, and 4 if optimizing for a 486.

`-malign-functions=NUM'
     Align the start of functions to a 2 raised to NUM byte boundary.
     If `-malign-jumps' is not specified, the default is 2 if optimizing
     for a 386, and 4 if optimizing for a 486.