[gcc r13-1203] data-ref: Improve non-loop disambiguation [PR106019]

[gcc r13-1203] data-ref: Improve non-loop disambiguation [PR106019]

[Richard Sandiford]

https://gcc.gnu.org/g:038b077689bb5310386b04d40a2cea234f01e6aa

commit r13-1203-g038b077689bb5310386b04d40a2cea234f01e6aa
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Wed Jun 22 11:27:15 2022 +0100

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

Diff:
---
 gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c | 15 +++++++++++++++
 gcc/tree-data-ref.cc                        | 19 +++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c
new file mode 100644
index 00000000000..218d7cca33d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c
@@ -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 } } */
diff --git a/gcc/tree-data-ref.cc b/gcc/tree-data-ref.cc
index ae05fe74b95..ff9327f6deb 100644
--- a/gcc/tree-data-ref.cc
+++ b/gcc/tree-data-ref.cc
@@ -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);