Re: [PATCH] tree-optimization/110742 - fix latent issue with permuting existing vectors

[Richard Sandiford <richard.sandiford@arm.com>]

Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> When we materialize a layout we push edge permutes to constant/external
> defs without checking we can actually do so.  For externals defined
> by vector stmts rather than scalar components we can't.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> OK?
>
> Thanks,
> Richard.
>
> 	PR tree-optimization/110742
> 	* tree-vect-slp.cc (vect_optimize_slp_pass::get_result_with_layout):
> 	Do not materialize an edge permutation in an external node with
> 	vector defs.
> 	(vect_slp_analyze_node_operations_1): Guard purely internal
> 	nodes better.
>
> 	* g++.dg/torture/pr110742.C: New testcase.
> ---
>  gcc/testsuite/g++.dg/torture/pr110742.C | 47 +++++++++++++++++++++++++
>  gcc/tree-vect-slp.cc                    |  8 +++--
>  2 files changed, 53 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/torture/pr110742.C
>
> diff --git a/gcc/testsuite/g++.dg/torture/pr110742.C b/gcc/testsuite/g++.dg/torture/pr110742.C
> new file mode 100644
> index 00000000000..d41ac0479d2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/torture/pr110742.C
> @@ -0,0 +1,47 @@
> +// { dg-do compile }
> +
> +struct HARD_REG_SET {
> +  HARD_REG_SET operator~() const {
> +    HARD_REG_SET res;
> +    for (unsigned int i = 0; i < (sizeof(elts) / sizeof((elts)[0])); ++i)
> +      res.elts[i] = ~elts[i];
> +    return res;
> +  }
> +  HARD_REG_SET operator&(const HARD_REG_SET &other) const {
> +    HARD_REG_SET res;
> +    for (unsigned int i = 0; i < (sizeof(elts) / sizeof((elts)[0])); ++i)
> +      res.elts[i] = elts[i] & other.elts[i];
> +    return res;
> +  }
> +  unsigned long elts[4];
> +};
> +typedef const HARD_REG_SET &const_hard_reg_set;
> +inline bool hard_reg_set_subset_p(const_hard_reg_set x, const_hard_reg_set y) {
> +  unsigned long bad = 0;
> +  for (unsigned int i = 0; i < (sizeof(x.elts) / sizeof((x.elts)[0])); ++i)
> +    bad |= (x.elts[i] & ~y.elts[i]);
> +  return bad == 0;
> +}
> +inline bool hard_reg_set_empty_p(const_hard_reg_set x) {
> +  unsigned long bad = 0;
> +  for (unsigned int i = 0; i < (sizeof(x.elts) / sizeof((x.elts)[0])); ++i)
> +    bad |= x.elts[i];
> +  return bad == 0;
> +}
> +extern HARD_REG_SET rr[2];
> +extern int t[2];
> +extern HARD_REG_SET nn;
> +static HARD_REG_SET mm;
> +void setup_reg_class_relations(void) {
> +  HARD_REG_SET intersection_set, union_set, temp_set2;
> +  for (int cl2 = 0; cl2 < 2; cl2++) {
> +    temp_set2 = rr[cl2] & ~nn;
> +    if (hard_reg_set_empty_p(mm) && hard_reg_set_empty_p(temp_set2)) {
> +      mm = rr[0] & nn;
> +      if (hard_reg_set_subset_p(mm, intersection_set))
> +        if (!hard_reg_set_subset_p(mm, temp_set2) ||
> +            hard_reg_set_subset_p(rr[0], rr[t[cl2]]))
> +          t[cl2] = 0;
> +    }
> +  }
> +}
> diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
> index 693621ca990..1d79c77e8ce 100644
> --- a/gcc/tree-vect-slp.cc
> +++ b/gcc/tree-vect-slp.cc
> @@ -5198,7 +5198,10 @@ vect_optimize_slp_pass::get_result_with_layout (slp_tree node,
>      return result;
>  
>    if (SLP_TREE_DEF_TYPE (node) == vect_constant_def
> -      || SLP_TREE_DEF_TYPE (node) == vect_external_def)
> +      || (SLP_TREE_DEF_TYPE (node) == vect_external_def
> +	  && (to_layout_i == 0
> +	      /* We can't permute vector defs.  */
> +	      || SLP_TREE_VEC_DEFS (node).is_empty ())))

Guess it's personal preference, but IMO it's easier to follow without the
to_layout_i condition, so that it ties directly to the create_partitions
test.  (Would be nice to have a name for whatever a node matching the new
condition is, but I don't have any good ideas.)

LGTM otherwise FWIW.

Thanks,
Richard

>      {
>        /* If the vector is uniform or unchanged, there's nothing to do.  */
>        if (to_layout_i == 0 || vect_slp_tree_uniform_p (node))
> @@ -5944,7 +5947,8 @@ vect_slp_analyze_node_operations_1 (vec_info *vinfo, slp_tree node,
>       calculated by the recursive call).  Otherwise it is the number of
>       scalar elements in one scalar iteration (DR_GROUP_SIZE) multiplied by
>       VF divided by the number of elements in a vector.  */
> -  if (!STMT_VINFO_DATA_REF (stmt_info)
> +  if (SLP_TREE_CODE (node) != VEC_PERM_EXPR
> +      && !STMT_VINFO_DATA_REF (stmt_info)
>        && REDUC_GROUP_FIRST_ELEMENT (stmt_info))
>      {
>        for (unsigned i = 0; i < SLP_TREE_CHILDREN (node).length (); ++i)