[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 #14 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
(In reply to Thomas Koenig from comment #12)
> 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?
> 

I have three different machines here. I am sure they are all similar as they
are A series. The first is for testing results posted here:

$ cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 21
model           : 16
model name      : AMD A10-5800K APU with Radeon(tm) HD Graphics
stepping        : 1

2nd:

$ cat /proc/cpuinfo
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 18
model           : 1
model name      : AMD A6-3620 APU with Radeon(tm) HD Graphics
stepping        : 0

3rd:

$ cat /proc/cpuinfo 
processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 22
model           : 48
model name      : AMD A8-6410 APU with AMD Radeon R5 Graphics
stepping        : 1


(In reply to Thomas Koenig from comment #13)
> $(M4) -Dfile=$@ -Darch=avx512f ...
> 
> In the generated C files, we enclose the whole content inside HAVE_AVX512F,
> so nothing happens if the architecture is not supported by the compiler.
> The target attribute is also set there.
> 
> On the first call to matmul, we check for the availability of AVX
> etc, we also check for prefrences such as AVX128 from the CPU model,
> and then set a static function pointer to the function we want to call.
> On each subsequent invocation, all we do is that (tail) call.
> 
> How does this sound?

This seems a bit complicated. The machines I have do OK without the aux-matmul
and no machine specific compilation other than the current defaults that gcc
uses with the flags I have inside the Makefile on current trunk. Can this be
done without the first call to matmul?