On Wed, 19 Apr 2023 at 16:17, Richard Biener <richard.guenther@gmail.com> wrote:
>
> On Wed, Apr 19, 2023 at 11:21 AM Prathamesh Kulkarni
> <prathamesh.kulkarni@linaro.org> wrote:
> >
> > On Tue, 11 Apr 2023 at 19:36, Prathamesh Kulkarni
> > <prathamesh.kulkarni@linaro.org> wrote:
> > >
> > > On Tue, 11 Apr 2023 at 14:17, Richard Biener <richard.guenther@gmail.com> wrote:
> > > >
> > > > 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
> > > Hi Richard,
> > > Thanks for the suggestions. The attached patch modifies
> > > is_combined_permutation_identity
> > > to recognize the above pattern.
> > > Does it look OK ?
> > > Bootstrap+test in progress on aarch64-linux-gnu and x86_64-linux-gnu.
> > Hi,
> > ping https://gcc.gnu.org/pipermail/gcc-patches/2023-April/615502.html
>
> Can you instead of def_stmt pass in a bool whether rhs1 is equal to rhs2
> and amend the function comment accordingly, say,
>
>   tem = VEC_PERM <op0, op1, MASK1>;
>   res = VEC_PERM <tem, tem, MASK2>;
>
> SAME_P specifies whether op0 and op1 compare equal.  */
>
> +  if (def_stmt)
> +    gcc_checking_assert (is_gimple_assign (def_stmt)
> +                        && gimple_assign_rhs_code (def_stmt) == VEC_PERM_EXPR);
> this is then unnecessary
>
>    mask = fold_ternary (VEC_PERM_EXPR, TREE_TYPE (mask1), mask1, mask1, mask2);
> +
> +  /* For VLA masks, check for the following pattern:
> +     v1 = VEC_PERM_EXPR (v0, v0, mask)
> +     v2 = VEC_PERM_EXPR (v1, v1, mask)
> +     -->
> +     v2 = v0
>
> you are not using 'mask' so please defer fold_ternary until after your
> special-case.
>
> +  if (operand_equal_p (mask1, mask2, 0)
> +      && !VECTOR_CST_NELTS (mask1).is_constant ()
> +      && def_stmt
> +      && operand_equal_p (gimple_assign_rhs1 (def_stmt),
> +                         gimple_assign_rhs2 (def_stmt), 0))
> +    {
> +      vec_perm_builder builder;
> +      if (tree_to_vec_perm_builder (&builder, mask1))
> +       {
> +         poly_uint64 nelts = TYPE_VECTOR_SUBPARTS (TREE_TYPE (mask1));
> +         vec_perm_indices sel (builder, 1, nelts);
> +         if (sel.series_p (0, 1, nelts - 1, -1))
> +           return 1;
> +       }
> +      return 0;
>
> I'm defering to Richard whether this is the correct way to check for a vector
> reversing mask (I wonder how constructing such mask is even possible)
Hi Richard,
Thanks for the suggestions, I have updated the patch accordingly.

The following hunk from svrev_impl::fold() constructs mask in reverse:
    /* Permute as { nelts - 1, nelts - 2, nelts - 3, ... }.  */
    poly_int64 nelts = TYPE_VECTOR_SUBPARTS (TREE_TYPE (f.lhs));
    vec_perm_builder builder (nelts, 1, 3);
    for (int i = 0; i < 3; ++i)
      builder.quick_push (nelts - i - 1);
    return fold_permute (f, builder);

To see if mask chooses elements in reverse, I borrowed it from function comment
for series_p in vec-perm-indices.cc:
/* Return true if index OUT_BASE + I * OUT_STEP selects input
   element IN_BASE + I * IN_STEP.  For example, the call to test
   whether a permute reverses a vector of N elements would be:

     series_p (0, 1, N - 1, -1)

   which would return true for { N - 1, N - 2, N - 3, ... }.  */

Thanks,
Prathamesh
>
> Richard.
>
> > Thanks,
> > Prathamesh
> > >
> > > Thanks,
> > > Prathamesh
> > > >
> > > > Richard.
> > > >
> > > > >
> > > > > Thanks,
> > > > > Prathamesh