On Tue, Aug 22, 2023 at 9:35 PM Hongtao Liu <crazy...@gmail.com> wrote:
>
> On Tue, Aug 22, 2023 at 9:24 PM Richard Biener
> <richard.guent...@gmail.com> wrote:
> >
> > On Tue, Aug 22, 2023 at 3:16 PM Jakub Jelinek <ja...@redhat.com> wrote:
> > >
> > > On Tue, Aug 22, 2023 at 09:02:29PM +0800, Hongtao Liu wrote:
> > > > > 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
> > > > But there's implicit negative (disallow 512-bit vector), I think
> > >
> > > That is wrong.
> > >
> > > > -mav512f -mavx10.1-256 or -mavx10.1-256 -mavx512f shouldn't enable
> > > > 512-bit vector.
> > >
> > > Because then the -mavx10.1-256 option behaves completely differently from
> > > all the other isa options.
> > >
> > > We have the -march= options which are processed separately, but the normal
> > > ISA options either only enable something (when -mwhatever), or only
> > > disable something
> > > (when -mno-whatever). -mavx512f -mavx10.1-256 should be a union of those
> > > ISAs, like say -mavx2 -mbmi is, not an intersection or something even
> > > harder to understand.
> > >
> > > > Further, we should disallow a mix of exex512 and non-evex512 (e.g.
> > > > -mavx10.1-512 -mavx10.2-256),they should be a unified separate switch
> > > > that either disallows both or allows both. Instead of some isa
> > > > allowing it and some isa disallowing it.
> > >
> > > No, it will be really terrible user experience if the new options behave
> > > completely differently from everything else. Because then we'll need to
> Ok, then we can't avoid TARGET_AVX10_1 in those existing 256/128-bit
> evex instruction patterns.
> > > document it in detail how it behaves and users will have hard time to
> > > figure
> > > it out, and specify what it does not just on the command line, but also
> > > when
> > > mixing with target attribute or pragmas. -mavx10.1-512 -mavx10.2-256
> > > should
> > > be a union of those two ISAs. Either internally there is an ISA flag
> > > whether
> > > the instructions in the avx10.2 ISA but not avx10.1 ISA can operate on
> > > 512-bit vectors or not, in that case -mavx10.1-512 -mavx10.2-256 should
> > > enable the AVX10.1 set including 512-bit vectors + just the < 512-bit
> > > instructions from the 10.1 to 10.2 delta, or if there is no such
> > > separation
> > > internally, it will just enable full AVX10.2-512. User has asked for it.
> >
> > I think having all three -mavx10.1, -mavx10.1-256 and -mavx10.1-512 is just
> > confusing. Please separate ISA (avx10.1) from size. If -m[no-]evex512
> > isn't
> > good propose something else. -mavx512f will enable 512bits, -mavx10.1
> > will not unless -mevex512. -mavx512f -mavx512vl -mno-evex512 will disable
> > 512bits.
> >
> > So scrap -mavx10.1-256 and -mavx10.1-512 please.
The related issue is what's the meaning of -mno-avx10.1-256/-mno-avx10.1-512
For -mno-avx10.1-256, maybe it just disable whole avx10.1
But for avx10.1-512 should it disable whole avx10.1 or just EVEX512,
or maybe we just doesn't provide -mno-avx10.1-512, just provide
-mno-avx10.1-256.
And use -mno-evex512 to disable 512-bit vectors.
>
> It sounds to me we would have something like
> avx512XXX
> ^
> |
> "independent": TARGET_AVX512VL || TARGET_AVX10_1 will enable
> 128/256-bit instruction.
> |
> avx10.1-256 <----implied---- avx10.1-512
> ^ ^
> | |
> | |
> implied implied
> | |
> | |
> avx10.2-256 <----implied -----avx10.2-512
> ^ ^
> | |
> | |
> implied Implied
> | |
> | |
> avx10.3-256 <---implied-------avx10.3-512
> .....
>
> And put every existing and new instruction under those flags
>
> >
> > Richard.
> >
> > > Jakub
> > >
>
>
>
> --
> BR,
> Hongtao
--
BR,
Hongtao
