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

[Richard Biener <rguenther@suse.de>]

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On Thu, 20 Jul 2023, Richard Sandiford wrote:

> Richard Biener <rguenther@suse.de> writes:
> >> Am 20.07.2023 um 18:59 schrieb Richard Sandiford <richard.sandiford@arm.com>:
> >> 
> >> Richard Biener <rguenther@suse.de> writes:
> >>>>> Am 20.07.2023 um 16:09 schrieb 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.
> >>> 
> >>> I don?t understand- in the code guarding this we seem to expect to_layout_i == 0 and that?s the case we can handle as noop.  I didn?t understand why the function doesn?t always just do nothing in this case though, so I must have missed something.
> >> 
> >> OK, so I guess that disproves that my way is easier to understand :)
> >> 
> >> I think logically, the code is doing the equivalent of:
> >> 
> >>  int partition_i = m_vertices[node->vertex].partition;
> >>  if (partition < 0)
> >>    {
> >>      /* If the vector is uniform or unchanged, there's nothing to do.  */
> >>      ...      
> >>    }
> >>  else
> >>    {
> >>      ... Return node if to_layout_i matches this partition's chosen layout...
> >>    }
> >> 
> >> And I guess I should have written it that way.
> >> 
> >> So when there is no partition, we have a constant or external def
> >> built from individual scalars.  We can use the node as-is if the
> >> caller wants an unpermuted node or if all elements are equal
> >> (so that the permutation doesn't matter).  Otherwise we need
> >> to permute the scalars.
> >> 
> >> When there is a partition, we can use the node as-is if the caller
> >> wants the layout that was chosen for that partition.  Otherwise we
> >> need a new VEC_PERM_EXPR node.
> >> 
> >> In the particular case of external defs built from vectors, we're
> >> guaranteed that the node's chosen layout is 0 (i.e. the original layout),
> >> and so both ways work.
> >
> > Hmm, but I arrived here with that not being the case ? (the chosen Lay-out not zero)
> 
> By chosen layout for the partition, I meant:
> 
>       unsigned int from_layout_i = m_partitions[partition_i].layout;
> 
> That should be 0 for these external vector nodes due to the
> start_choosing_layout code that you mentioned in the PR.  to_layout_i
> (the layout that the caller wants for a use of the node) can be anything,
> so yeah, to_layout_i != 0 has to go through the "else" arm and generate
> a VEC_PERM_EXPR.  But because from_layout_i == 0 for these nodes,
> the "else" arm should handle all cases correctly, not just the
> to_layout_i != 0 case.

Ah, yes - of course.  I'll remove the extra test, re-test and push.

Thanks,
Richard.