[PATCH] Avoid using POINTER_DIFF_EXPR for overlap checks [PR119399]

[Richard Sandiford]

In r10-4803-g8489e1f45b50600c I'd used POINTER_DIFF_EXPR to subtract
the two pointers involved in an overlap test.  I'm not sure whether
I'd specifically chosen that over MINUS_EXPR or not; if so, the only
reason I can think of is that it is probably faster on targets with
PSImode pointers.  Regardless, as the PR points out, subtracting
unrelated pointers using POINTER_DIFF_EXPR is undefined behaviour.

Tested on aarch64-linux-gnu & x86_64-linux-gnu.  OK for trunk, and
for backports after a grace period?

Richard


gcc/
        PR tree-optimization/119399
        * tree-data-ref.cc (create_waw_or_war_checks): Use a MINUS_EXPR
        on two converted pointers, rather than converting a POINTER_DIFF_EXPR
        on the pointers.

gcc/testsuite/
        PR tree-optimization/119399
        * gcc.dg/vect/pr119399.c: New test.
---
 gcc/testsuite/gcc.dg/vect/pr119399.c | 10 ++++++++++
 gcc/tree-data-ref.cc                 |  7 ++++---
 2 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr119399.c

diff --git a/gcc/testsuite/gcc.dg/vect/pr119399.c 
b/gcc/testsuite/gcc.dg/vect/pr119399.c
new file mode 100644
index 00000000000..8d868f44b67
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr119399.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdump-tree-vect-raw" } */
+
+void foo(int *p, int *q, int n)
+{
+  for (int i = 0; i < n; i++)
+    p[i] = q[i] + 1;
+}
+
+/* { dg-final { scan-tree-dump-not {<pointer_diff_expr,} "vect" } } */
diff --git a/gcc/tree-data-ref.cc b/gcc/tree-data-ref.cc
index 18d9f0fa766..8a46e6daabb 100644
--- a/gcc/tree-data-ref.cc
+++ b/gcc/tree-data-ref.cc
@@ -2498,9 +2498,10 @@ create_waw_or_war_checks (tree *cond_expr,
   limit = fold_build2 (PLUS_EXPR, sizetype, limit,
                       size_int (last_chunk_a + last_chunk_b));
 
-  tree subject = fold_build2 (POINTER_DIFF_EXPR, ssizetype, addr_b, addr_a);
-  subject = fold_build2 (PLUS_EXPR, sizetype,
-                        fold_convert (sizetype, subject), bias);
+  tree subject = fold_build2 (MINUS_EXPR, sizetype,
+                             fold_convert (sizetype, addr_b),
+                             fold_convert (sizetype, addr_a));
+  subject = fold_build2 (PLUS_EXPR, sizetype, subject, bias);
 
   *cond_expr = fold_build2 (GT_EXPR, boolean_type_node, subject, limit);
   if (dump_enabled_p ())
-- 
2.43.0