On Tue, Aug 22, 2023 at 09:36:15AM +0200, Richard Biener via Gcc-patches wrote:
> I think internally we should have conditional 512bit support work across
> AVX512 and AVX10.
>
> I also think it makes sense to _internally_ have AVX10.1 (10.1!) just
> enable the respective AVX512 features. AVX10.2 would then internally
> cover the ISA extensions added in 10.2 only. Both would reduce the
> redundancy and possibly make providing inter-operation between
> AVX10.1 (10.1!) and AVX512 to the user easier. I see AVX 10.1 (10.1!)
> just as "re-branding" latest AVX512, so we should treat it that way
> (making it an alias to the AVX512 features).
>
> Whether we want allow -mavx10.1 -mno-avx512cd or whether
> we only allow the "positive" -mavx512f -mavx512... (omitting avx512cd)
> is an entirely separate
> question. But I think to not wreck the core idea (more interoperability,
> here between small/big cores) we absolutely have to
> provide a subset of avx10.1 but with disabled 512bit vectors which
> effectively means AVX512 with disabled 512bit support.
Agreed. And I still think -mevex512 vs. -mno-evex512 is the best option
name to represent whether the effective ISA set allows 512-bit vectors or
not. I think -mavx10.1 -mno-avx512cd should be fine. And, -mavx10.1-256
option IMHO should be in the same spirit to all the others a positive
enablement,
not both positive (enable avx512{f,cd,bw,dq,...} and negative (disallow
512-bit vectors). So, if one uses -mavx512f -mavx10.1-256, because the
former would allow 512-bit vectors, the latter shouldn't disable those again
because it isn't a -mno-* option. Sure, instructions which are specific to
AVX10.1 (aren't present in any currently existing AVX512* ISA set) might be
enabled only in 128/256 bit variants if we differentiate that level.
But, if one uses -mavx2 -mavx10.1-256, because no AVX512* has been enabled
it can enable all the AVX10.1 implied AVX512* parts without EVEX.512.
Jakub
