These `-m' options are defined for the i386 family of computers:
-m486
-m386
-mieee-fp
-mno-ieee-fp
-msoft-float
-mno-fp-ret-in-387
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
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
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
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
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.
-mrtd
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 section Declaring Attributes of Functions
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
a
allocate EAX; b
allocate EBX;
c
allocate ECX; d
allocate EDX; S
allocate ESI;
D
allocate EDI; B
allocate EBP.
-mregparm=num
-malign-loops=num
-malign-jumps=num
-malign-functions=num