Re: [PATCH 6/8] vect: Add vector_mode paramater to simd_clone_usable

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Aug 30, 2023 at 5:02 PM Andre Vieira (lists)
<andre.simoesdiasvieira@arm.com> wrote:
>
>
>
> On 30/08/2023 14:01, Richard Biener wrote:
> > On Wed, Aug 30, 2023 at 11:15 AM Andre Vieira (lists) via Gcc-patches
> > <gcc-patches@gcc.gnu.org> wrote:
> >>
> >> This patch adds a machine_mode parameter to the TARGET_SIMD_CLONE_USABLE
> >> hook to enable rejecting SVE modes when the target architecture does not
> >> support SVE.
> >
> > How does the graph node of the SIMD clone lack this information?  That is, it
> > should have information on the types (and thus modes) for all formal arguments
> > and return values already, no?  At least the target would know how to
> > instantiate
> > it if it's not readily available at the point of use.
> >
>
> Yes it does, but that's the modes the simd clone itself uses, it does
> not know what vector_mode we are currently vectorizing for. Which is
> exactly why we need the vinfo's vector_mode to make sure the simd clone
> and its types are compatible with the vector mode.
>
> In practice, to make sure that a SVE simd clones are only used in loops
> being vectorized for SVE modes. Having said that... I just realized that
> the simdlen check already takes care of that currently...
>
> by simdlen check I mean the one that writes off simdclones that match:
>          if (!constant_multiple_p (vf, n->simdclone->simdlen, &num_calls)
>
> However, when using -msve-vector-bits this will become an issue, as the
> VF will be constant and we will match NEON simdclones.  This requires
> some further attention though given that we now also reject the use of
> SVE simdclones when using -msve-vector-bits, and I'm not entirely sure
> we should...

Hmm, but vectorizable_simdclone should check for compatible types here
and if they are compatible why should we reject them?  Are -msve-vector-bits
"SVE" modes different from "NEON" modes?  I suppose not, because otherwise
the type compatibility check would say incompatible.

> I'm going on holidays for 2 weeks now though, so I'll have a look at
> that scenario when I get back. Same with other feedback, didn't expect
> feedback this quickly ;) Thank you!!
>
> Kind regards,
> Andre
>