MMX instruction and gcc

Ian Lance Taylor
Thu Mar 15 15:13:00 GMT 2007

Galloth <> writes:

> I want ask, if there is posibilities that gcc will be automaticaly
> generates MMX instruction? I tried -mtune, -march  -mmmx. But gcc stil
> generates code without MMX instruction. On net I found only
> information about inline assembler function or citation from man page.
> I tried to compile program for adding two arrays of 24 chars.

This question is appropriate for the mailing list, not for  Please take any
follow-ups to gcc-help.  Thanks.

In some cases gcc may be able to automatically generate MMX
instructions if you use the -ftree-vectorize option.

Otherwise, you need to write your code using the macros defined in the
header file mmintrin.h.  This can be found in the gcc source code in
gcc/config/i386/mmintrin.h.  It will also be installed with gcc
somewhere on your system.  It implements an interface documented by
Intel; the documentation is available somewhere on the Intel web


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