[Bug libfortran/78379] Processor-specific versions for matmul

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78379

--- Comment #12 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
(In reply to Jerry DeLisle from comment #11)
> One could consider running a reference matrix multiply of size 32 in a loop
> and do timing tests to determine whether to use -mprefer-avx128. 0n this
> machine from comment 8
> 
> mavx = 1.276     mavx mprefer-avx128 = 3.460
> 
> There is some margin there for a fairly good test. Or is there another way
> to tell?

I read some advice on the net that certain types of AMD processors
have AVX, but AVX128 is better for them.

What exactly is your CPU model?  What does /proc/cpuinfo say?

gcc determines the cpu model (see runk/libgcc/config/i386/cpuinfo.c).
We should be able to query the CPU model and dispatch for AVX128
or AVX (or the other variants) based on that.