tree-optimization/113431 - wrong dependence with invariant load

The vectorizer dependence analysis is confused with invariant loads
when figuring whether the circumstances are so that we preserve
scalar stmt execution order.  The following rectifies this.

	PR tree-optimization/113431
	* tree-vect-data-refs.cc (vect_preserves_scalar_order_p):
	When there is an invariant load we might not preserve
	scalar order.

	* gcc.dg/vect/pr113431.c: New testcase.

diff --git a/gcc/testsuite/gcc.dg/vect/pr113431.c b/gcc/testsuite/gcc.dg/vect/pr113431.c
new file mode 100644 (file)
index 0000000..04448d9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr113431.c
@@ -0,0 +1,18 @@
+/* { dg-additional-options "-O3 -fdump-tree-slp1-details" } */
+
+#include "tree-vect.h"
+
+int a[2][9];
+int b;
+int main()
+{
+  check_vect ();
+  for (b = 0; b < 2; b++)
+    for (long e = 8; e > 0; e--)
+      a[b][e] = a[0][1] == 0;
+  if (a[1][1] != 0)
+    __builtin_abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "optimized: basic block part vectorized" 2 "slp1" { target vect_int } } } */

diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
index 0495842b35050d024018c08a150d04a6dce0a86d..f592aeb8028afd4fd70e2175104efab2a2c0d82e 100644 (file)
--- a/gcc/tree-vect-data-refs.cc
+++ b/gcc/tree-vect-data-refs.cc
@@ -282,6 +282,12 @@ vect_preserves_scalar_order_p (dr_vec_info *dr_info_a, dr_vec_info *dr_info_b)
       && !STMT_VINFO_GROUPED_ACCESS (stmtinfo_b))
     return true;
 
+  /* If there is a loop invariant read involved we might vectorize it in
+     the prologue, breaking scalar oder with respect to the in-loop store.  */
+  if ((DR_IS_READ (dr_info_a->dr) && integer_zerop (DR_STEP (dr_info_a->dr)))
+      || (DR_IS_READ (dr_info_b->dr) && integer_zerop (DR_STEP (dr_info_b->dr))))
+    return false;
+
   /* STMT_A and STMT_B belong to overlapping groups.  All loads are
      emitted at the position of the first scalar load.
      Stores in a group are emitted at the position of the last scalar store.