Re: [PATCH] Optimize nested permutation to single VEC_PERM_EXPR [PR54346]

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

On Mon, Sep 26, 2022 at 8:58 AM Liwei Xu <liwei.xu@intel.com> wrote:
>
>         This patch implemented the optimization in PR 54346, which Merges
>
>         c = VEC_PERM_EXPR <a, b, VCST0>;
>         d = VEC_PERM_EXPR <c, c, VCST1>;
>                 to
>         d = VEC_PERM_EXPR <a, b, NEW_VCST>;
>
>         Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}
>         tree-ssa/forwprop-19.c fail to pass but I'm not sure whether it
>         is ok to removed it.

Looks good, but leave Richard a chance to ask for VLA vector support which
might be trivial to do.

Btw, doesn't this handle the VEC_PERM + VEC_PERM case in
tree-ssa-forwprop.cc:simplify_permutation as well?  Note _that_ does
seem to handle VLA vectors.

Thanks,
Richard.

> gcc/ChangeLog:
>
>         PR target/54346
>         * match.pd: Merge the index of VCST then generates the new vec_perm.
>
> gcc/testsuite/ChangeLog:
>
>         PR target/54346
>         * gcc.dg/pr54346.c: New test.
>
> Co-authored-by: liuhongt <hongtao.liu@intel.com>
> ---
>  gcc/match.pd                   | 41 ++++++++++++++++++++++++++++++++++
>  gcc/testsuite/gcc.dg/pr54346.c | 13 +++++++++++
>  2 files changed, 54 insertions(+)
>  create mode 100755 gcc/testsuite/gcc.dg/pr54346.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 345bcb701a5..9219b0a10e1 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -8086,6 +8086,47 @@ and,
>    (minus (mult (vec_perm @1 @1 @3) @2) @4)))
>
>
> +/* (PR54346) Merge
> +   c = VEC_PERM_EXPR <a, b, VCST0>;
> +   d = VEC_PERM_EXPR <c, c, VCST1>;
> +   to
> +   d = VEC_PERM_EXPR <a, b, NEW_VCST>; */
> +
> +(simplify
> + (vec_perm (vec_perm@0 @1 @2 VECTOR_CST@3) @0 VECTOR_CST@4)
> + (with
> +  {
> +    if(!TYPE_VECTOR_SUBPARTS (type).is_constant())
> +      return NULL_TREE;
> +
> +    tree op0;
> +    machine_mode result_mode = TYPE_MODE (type);
> +    machine_mode op_mode = TYPE_MODE (TREE_TYPE (@1));
> +    int nelts = TYPE_VECTOR_SUBPARTS (type).to_constant();
> +    vec_perm_builder builder0;
> +    vec_perm_builder builder1;
> +    vec_perm_builder builder2 (nelts, nelts, 1);
> +
> +    if (!tree_to_vec_perm_builder (&builder0, @3)
> +    || !tree_to_vec_perm_builder (&builder1, @4))
> +      return NULL_TREE;
> +
> +    vec_perm_indices sel0 (builder0, 2, nelts);
> +    vec_perm_indices sel1 (builder1, 1, nelts);
> +
> +    for (int i = 0; i < nelts; i++)
> +      builder2.quick_push (sel0[sel1[i].to_constant()]);
> +
> +    vec_perm_indices sel2 (builder2, 2, nelts);
> +
> +    if (!can_vec_perm_const_p (result_mode, op_mode, sel2, false))
> +      return NULL_TREE;
> +
> +    op0 = vec_perm_indices_to_tree (TREE_TYPE (@4), sel2);
> +  }
> +  (vec_perm @1 @2 { op0; })))
> +
> +
>  /* Match count trailing zeroes for simplify_count_trailing_zeroes in fwprop.
>     The canonical form is array[((x & -x) * C) >> SHIFT] where C is a magic
>     constant which when multiplied by a power of 2 contains a unique value
> diff --git a/gcc/testsuite/gcc.dg/pr54346.c b/gcc/testsuite/gcc.dg/pr54346.c
> new file mode 100755
> index 00000000000..d87dc3a79a5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr54346.c
> @@ -0,0 +1,13 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-dse1" } */
> +
> +typedef int veci __attribute__ ((vector_size (4 * sizeof (int))));
> +
> +void fun (veci a, veci b, veci *i)
> +{
> +  veci c = __builtin_shuffle (a, b, __extension__ (veci) {1, 4, 2, 7});
> +  *i = __builtin_shuffle (c, __extension__ (veci) { 7, 2, 1, 5 });
> +}
> +
> +/* { dg-final { scan-tree-dump "VEC_PERM_EXPR.*{ 3, 6, 0, 0 }" "dse1" } } */
> +/* { dg-final { scan-tree-dump-times "VEC_PERM_EXPR" 1 "dse1" } } */
> \ No newline at end of file
> --
> 2.18.2
>