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

[Richard Biener via Gcc-patches]

> Am 20.07.2023 um 16:09 schrieb Richard Sandiford <richard.sandif...@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.

Richard 


>  (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)