Re: [match.pd] [SVE] Add pattern to transform svrev(svrev(v)) --> v

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

On Wed, Apr 5, 2023 at 10:39 AM Prathamesh Kulkarni via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
> For the following test:
>
> svint32_t f(svint32_t v)
> {
>   return svrev_s32 (svrev_s32 (v));
> }
>
> We generate 2 rev instructions instead of nop:
> f:
>         rev     z0.s, z0.s
>         rev     z0.s, z0.s
>         ret
>
> The attached patch tries to fix that by trying to recognize the following
> pattern in match.pd:
> v1 = VEC_PERM_EXPR (v0, v0, mask)
> v2 = VEC_PERM_EXPR (v1, v1, mask)
> -->
> v2 = v0
> if mask is { nelts - 1, nelts - 2, nelts - 3, ... }
>
> Code-gen with patch:
> f:
>         ret
>
> Bootstrap+test passes on aarch64-linux-gnu, and SVE bootstrap in progress.
> Does it look OK for stage-1 ?

I didn't look at the patch but tree-ssa-forwprop.cc:simplify_permutation should
handle two consecutive permutes with the is_combined_permutation_identity
which might need tweaking for VLA vectors

Richard.

>
> Thanks,
> Prathamesh