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data-ref: Improve non-loop disambiguation [PR106019]

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When dr_may_alias_p is called without a loop context, it tries
to use the tree-affine interface to calculate the difference
between the two addresses and use that difference to check whether
the gap between the accesses is known at compile time.  However, as the
example in the PR shows, this doesn't expand SSA_NAMEs and so can easily
be defeated by things like reassociation.

One fix would have been to use aff_combination_expand to expand the
SSA_NAMEs, but we'd then need some way of maintaining the associated
cache.  This patch instead reuses the innermost_loop_behavior fields
(which exist even when no loop context is provided).

It might still be useful to do the aff_combination_expand thing too,
if an example turns out to need it.

gcc/
	PR tree-optimization/106019
	* tree-data-ref.cc (dr_may_alias_p): Try using the
	innermost_loop_behavior to disambiguate non-loop queries.

gcc/testsuite/
	PR tree-optimization/106019
	* gcc.dg/vect/bb-slp-pr106019.c: New test.
This commit is contained in:
Richard Sandiford 2022-06-22 11:27:15 +01:00
parent 98b6e62cf5
commit 038b077689
2 changed files with 34 additions and 0 deletions
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15
gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c Normal file
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@ -0,0 +1,15 @@
/* { dg-do compile } */
void f(double *p, long i)
{
p[i+0] += 1;
p[i+1] += 1;
}
void g(double *p, long i)
{
double *q = p + i;
q[0] += 1;
q[1] += 1;
}
/* { dg-final { scan-tree-dump-not "can't determine dependence" slp2 } } */

19
gcc/tree-data-ref.cc
View File

@ -2968,6 +2968,25 @@ dr_may_alias_p (const struct data_reference *a, const struct data_reference *b,
disambiguation. */
if (!loop_nest)
{
tree tree_size_a = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (a)));
tree tree_size_b = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (b)));
if (DR_BASE_ADDRESS (a)
&& DR_BASE_ADDRESS (b)
&& operand_equal_p (DR_BASE_ADDRESS (a), DR_BASE_ADDRESS (b))
&& operand_equal_p (DR_OFFSET (a), DR_OFFSET (b))
&& poly_int_tree_p (tree_size_a)
&& poly_int_tree_p (tree_size_b)
&& !ranges_maybe_overlap_p (wi::to_widest (DR_INIT (a)),
wi::to_widest (tree_size_a),
wi::to_widest (DR_INIT (b)),
wi::to_widest (tree_size_b)))
{
gcc_assert (integer_zerop (DR_STEP (a))
&& integer_zerop (DR_STEP (b)));
return false;
}
aff_tree off1, off2;
poly_widest_int size1, size2;
get_inner_reference_aff (DR_REF (a), &off1, &size1);