On Wed, Aug 23, 2023 at 4:31 PM Jakub Jelinek <ja...@redhat.com> wrote:
>
> On Wed, Aug 23, 2023 at 08:03:58AM +0000, Jiang, Haochen wrote:
> > We could first work on -mevex512 then further discuss -mavx10.1-256/512
> > since
> > these -mavx10.1-256/512 is quite controversial.
> >
> > Just to clarify, -mno-evex512 -mavx512f should not enable 512 bit vector
> > right?
>
> I think it should enable them because -mavx512f is after it. But it seems the
> option handling is more complex than I thought, e.g. -mavx512bw -mno-avx512bw
> just cancels each other, rather than
> enabling AVX512BW, AVX512F, AVX2 and all its dependencies (like -mavx512bw
> alone does) and then just disabling AVX512BW (like -mno-avx512bw does).
> But, if one uses separate target pragmas, it behaves like that:
> #pragma GCC target ("avx512bw")
> #ifdef __AVX512F__
> int a;
> #endif
> #ifdef __AVX512BW__
> int b;
> #endif
> #pragma GCC target ("no-avx512bw")
> #ifdef __AVX512F__
> int c;
> #endif
> #ifdef __AVX512BW__
> int d;
> #endif
> The above defines a, b and c vars even without any special -march= or other
> command line option.
>
> So, first important decision would be whether to make EVEX512
> OPTION_MASK_ISA_EVEX512 or OPTION_MASK_ISA2_EVEX512, the former would need
> to move some other ISA flag from the first to second set.
> That OPTION_MASK_ISA*_EVEX512 then should be added to
> OPTION_MASK_ISA_AVX512F_SET or OPTION_MASK_ISA2_AVX512F_SET (but, if it is
> the latter, we also need to do that for tons of other AVX512*_SET),
> and then just arrange for -mavx10.1-256 to enable
> OPTION_MASK_ISA*_AVX512*_SET of everything it needs except the EVEX512 set
> (but, only disable it from the newly added set, not actually act as
> -mavx512{f,bw,...} -mno-evex512).
> OPTION_MASK_ISA*_EVEX512_SET dunno, should it enable OPTION_MASK_ISA_AVX512F
> or just EVEX512?
> And then the UNSET cases...
We can make OPTION_MASK_ISA2_EVEX512, but not set/unset that in
ix86_handle_option, but in ix86_option_override_internal, after all
set/unset for the existing AVX512***, if there's still
OPTION_MASK_ISA_AVX512F and no explicit set/unset for
OPTION_MASK_ISA2_EVEX512, then we set OPTION_MASK_ISA2_EVEX512.
That would make -mavx512*** implicitly set -mevex-512, but when
there's explicit -mno-evex512, -mavx512f won't set -mevex512 no matter
where -mno-evex512 is put.(-mno-evex512 -mavx512f still disable
512-bit).
>
> Jakub
>
--
BR,
Hongtao
