[gcc r12-1765] tree-optimization/101105 - fix runtime alias test optimization

[gcc r12-1765] tree-optimization/101105 - fix runtime alias test optimization

[Richard Biener]

https://gcc.gnu.org/g:50374fdacbd121bc4a61b073e559208ff61bee06

commit r12-1765-g50374fdacbd121bc4a61b073e559208ff61bee06
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Jun 23 12:43:03 2021 +0200

    tree-optimization/101105 - fix runtime alias test optimization
    
    We were ignoring DR_STEP for VF == 1 which is OK only in case
    the scalar order is preserved or both DR steps are the same.
    
    2021-06-23  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/101105
            * tree-vect-data-refs.c (vect_prune_runtime_alias_test_list):
            Only ignore steps when they are equal or scalar order is preserved.
    
            * gcc.dg/torture/pr101105.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr101105.c | 19 +++++++++++++++++++
 gcc/tree-vect-data-refs.c               |  9 +++++++--
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/torture/pr101105.c b/gcc/testsuite/gcc.dg/torture/pr101105.c
new file mode 100644
index 00000000000..9222351683d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr101105.c
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+
+short a;
+int b[5][4] = {2, 2};
+int d;
+short e(int f) { return f == 0 || a && f == 1 ? 0 : a; }
+int main() {
+  int g, h;
+  g = 3;
+  for (; g >= 0; g--) {
+    h = 3;
+    for (; h >= 0; h--)
+      b[g][h] = b[0][1] && e(1);
+  }
+  d = b[0][1];
+  if (d != 0)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index be067c8923b..579149dfd61 100644
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -3479,9 +3479,9 @@ vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
   /* Step values are irrelevant for aliasing if the number of vector
      iterations is equal to the number of scalar iterations (which can
      happen for fully-SLP loops).  */
-  bool ignore_step_p = known_eq (LOOP_VINFO_VECT_FACTOR (loop_vinfo), 1U);
+  bool vf_one_p = known_eq (LOOP_VINFO_VECT_FACTOR (loop_vinfo), 1U);
 
-  if (!ignore_step_p)
+  if (!vf_one_p)
     {
       /* Convert the checks for nonzero steps into bound tests.  */
       tree value;
@@ -3534,6 +3534,11 @@ vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
 
       bool preserves_scalar_order_p
 	= vect_preserves_scalar_order_p (dr_info_a, dr_info_b);
+      bool ignore_step_p
+	  = (vf_one_p
+	     && (preserves_scalar_order_p
+		 || operand_equal_p (DR_STEP (dr_info_a->dr),
+				     DR_STEP (dr_info_b->dr))));
 
       /* Skip the pair if inter-iteration dependencies are irrelevant
 	 and intra-iteration dependencies are guaranteed to be honored.  */