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tree-optimization/98291 - allow SLP more vectorization of reductions

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When the VF is one a SLP reduction is in-order and thus we can
vectorize even when the reduction op is not associative.

2021-01-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/98291
	* tree-vect-loop.c (vectorizable_reduction): Bypass
	associativity check for SLP reductions with VF 1.

	* gcc.dg/vect/slp-reduc-11.c: New testcase.
	* gcc.dg/vect/vect-reduc-in-order-4.c: Adjust.
This commit is contained in:
Richard Biener 2021-01-04 09:53:11 +01:00
parent ad64e807ff
commit 8837f82e4b
3 changed files with 28 additions and 4 deletions
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20
gcc/testsuite/gcc.dg/vect/slp-reduc-11.c Normal file
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@ -0,0 +1,20 @@
/* { dg-do compile } */
/* { dg-require-effective-target vect_double } */
double dotprod(const double *a, const double *b, unsigned long long n)
{
double d1 = 0.0;
double d2 = 0.0;
for (unsigned long long i = 0; i < n; i += 2) {
d1 += a[i] * b[i];
d2 += a[i + 1] * b[i + 1];
}
return (d1 + d2);
}
/* We should use a SLP reduction even without -ffast-math by using a
VF of one. */
/* { dg-final { scan-tree-dump "vectorizing stmts using SLP" "vect" } } */
/* { dg-final { scan-tree-dump "vectorized 1 loops" "vect" } } */

2
gcc/testsuite/gcc.dg/vect/vect-reduc-in-order-4.c
View file

@ -41,6 +41,4 @@ main ()
return 0;
}
/* { dg-final { scan-tree-dump {in-order unchained SLP reductions not supported} "vect" } } */
/* { dg-final { scan-tree-dump-not {vectorizing stmts using SLP} "vect" } } */
/* { dg-final { scan-tree-dump-times "VECT_PERM_EXPR" 0 "vect" } } */

10
gcc/tree-vect-loop.c
View file

@ -6868,8 +6868,14 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
cases, so we need to check that this is ok. One exception is when
vectorizing an outer-loop: the inner-loop is executed sequentially,
and therefore vectorizing reductions in the inner-loop during
outer-loop vectorization is safe. */
if (needs_fold_left_reduction_p (scalar_type, orig_code))
outer-loop vectorization is safe. Likewise when we are vectorizing
a series of reductions using SLP and the VF is one the reductions
are performed in scalar order. */
if (slp_node
&& !REDUC_GROUP_FIRST_ELEMENT (stmt_info)
&& known_eq (LOOP_VINFO_VECT_FACTOR (loop_vinfo), 1u))
;
else if (needs_fold_left_reduction_p (scalar_type, orig_code))
{
/* When vectorizing a reduction chain w/o SLP the reduction PHI
is not directy used in stmt. */