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tree-optimization/103544 - SLP reduction chain as SLP reduction issue

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When SLP reduction chain vectorization support added handling of
an outer conversion in the chain picking a failed reduction up
as SLP reduction that broke the invariant that the whole reduction
was forward reachable.  The following plugs that hole noting
a future enhancement possibility.

2021-12-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/103544
	* tree-vect-slp.c (vect_analyze_slp): Only add a SLP reduction
	opportunity if the stmt in question is the reduction root.
	(dot_slp_tree): Add missing check for NULL child.

	* gcc.dg/vect/pr103544.c: New testcase.
This commit is contained in:
Richard Biener 2021-12-06 11:43:28 +01:00
parent 4dc6d19222
commit ee01694151
2 changed files with 33 additions and 3 deletions
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24
gcc/testsuite/gcc.dg/vect/pr103544.c Normal file
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@ -0,0 +1,24 @@
/* { dg-do compile } */
/* { dg-additional-options "-O3" } */
/* { dg-additional-options "-march=haswell" { target x86_64-*-* i?86-*-* } } */
int crash_me(char* ptr, unsigned long size)
{
short result[16] = {0};
unsigned long no_iters = 0;
for(unsigned long i = 0; i < size - 12; i+= 13){
for(unsigned long j = 0; j < 12; j++){
result[j] += ptr[i + j] - '0';
}
no_iters++;
}
int result_int = 0;
for(int j = 0; j < 12; j++){
int bit_value = result[j] > no_iters/2 ? 1 : 0;
result_int |= bit_value;
}
return result_int;
}

12
gcc/tree-vect-slp.c
View file

@ -2537,7 +2537,8 @@ dot_slp_tree (FILE *f, slp_tree node, hash_set<slp_tree> &visited)
fprintf (f, "\"%p\" -> \"%p\";", (void *)node, (void *)child);
for (slp_tree child : SLP_TREE_CHILDREN (node))
dot_slp_tree (f, child, visited);
if (child)
dot_slp_tree (f, child, visited);
}
DEBUG_FUNCTION void
@ -3418,8 +3419,13 @@ vect_analyze_slp (vec_info *vinfo, unsigned max_tree_size)
vinfo = next;
}
STMT_VINFO_DEF_TYPE (first_element) = vect_internal_def;
/* It can be still vectorized as part of an SLP reduction. */
loop_vinfo->reductions.safe_push (last);
/* It can be still vectorized as part of an SLP reduction.
??? But only if we didn't skip a conversion around the group.
In that case we'd have to reverse engineer that conversion
stmt following the chain using reduc_idx and from the PHI
using reduc_def. */
if (STMT_VINFO_DEF_TYPE (last) == vect_reduction_def)
loop_vinfo->reductions.safe_push (last);
}
/* Find SLP sequences starting from groups of reductions. */