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

["tkoenig at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

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

--- Comment #27 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
(In reply to # David Edelsohn from comment #26)
> What is AVX-specific, as opposed to SIMD vector size-specific, about this
> feature? It seems that this should be enabled for all SIMD architectures of
> the appropriate width.

You're right, this might as well apply to other architectures where
SIMD instructions are available only on some architectures, but
cannot be turned on by default because they are not universally
implemented.

I would need three pieces of information:

- What to put into the libgfortran config file to check if
  the installed binutils support the SIMD extension in question

- How to check at runtime for the specific processor version

- Which options to pass to __attribute__((__target__ ..

Then it is relatively straightforward to put this in.