What's the proper way to use different versions of SSE intrinsics in GCC?

Question

I will ask my question by giving an example. Now I have a function called do_something().

It has three versions: do_something(), do_something_sse3(), and do_something_sse4(). When my program runs, it will detect the CPU feature (see if it supports SSE3 or SSE4) and call one of the three versions accordingly.

The problem is: When I build my program with GCC, I have to set -msse4 for do_something_sse4() to compile (e.g. for the header file <smmintrin.h> to be included).

However, if I set -msse4, then gcc is allowed to use SSE4 instructions, and some intrinsics in do_something_sse3() is also translated to some SSE4 instructions. So if my program runs on CPU that has only SSE3 (but no SSE4) support, it causes "illegal instruction" when calls do_something_sse3().

Maybe I have some bad practice. Could you give some suggestions? Thanks.

Answer 1

I think that the Mystical's tip is fine, but if you really want to do it in the one file, you can use proper pragmas, for instance:

#pragma GCC target("sse4.1")

GCC 4.4 is needed, AFAIR.