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

[jvdelisle at gcc dot gnu.org]

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

--- Comment #11 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
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?