re PR tree-optimization/81620 (ICE in is_inv_store_elimination_chain, at…

re PR tree-optimization/81620 (ICE in is_inv_store_elimination_chain, at tree-predcom.c:1651 with -O3)

	PR tree-optimization/81620
	* tree-predcom.c (add_ref_to_chain): Don't set has_max_use_after
	for store-store chain.

	gcc/testsuite
	* gcc.dg/tree-ssa/pr81620-1.c: New.
	* gcc.dg/tree-ssa/pr81620-2.c: New.

From-SVN: r250763

gcc/ChangeLog

+2017-08-01  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/81620
+	* tree-predcom.c (add_ref_to_chain): Don't set has_max_use_after
+	for store-store chain.
+
 2017-08-01  Jakub Jelinek  <jakub@redhat.com>
 
 	PR tree-optimization/81588

gcc/testsuite/ChangeLog

+2017-08-01  Bin Cheng  <bin.cheng@arm.com>
+
+	PR tree-optimization/81620
+	* gcc.dg/tree-ssa/pr81620-1.c: New.
+	* gcc.dg/tree-ssa/pr81620-2.c: New.
+
 2017-08-01  Dominique d'Humieres  <dominiq@lps.ens.fr>
 
 	PR testsuite/53542

gcc/testsuite/gcc.dg/tree-ssa/pr81620-1.c

+/* { dg-do run } */
+/* { dg-options "-O3 -fno-tree-loop-vectorize -fdump-tree-pcom-details" } */
+
+int a[7];
+char b;
+void abort (void);
+
+int main() {
+  b = 4;
+  for (; b; b--) {
+    a[b] = b;
+    a[b + 2] = 1;
+  }
+  if (a[0] != 0 || a[1] != 1 || a[2] != 2
+      || a[3] != 1 || a[4] != 1 || a[5] != 1 || a[6] != 1)
+    abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "Store-stores chain" 1 "pcom" } } */

gcc/testsuite/gcc.dg/tree-ssa/pr81620-2.c

+/* { dg-do run } */
+/* { dg-options "-O3 -fno-tree-loop-vectorize -fdump-tree-pcom-details" } */
+
+int a[200];
+char b;
+void abort (void);
+
+int main() {
+  int i;
+  b = 100;
+  for (; b; b--) {
+    a[b] = 2;
+    a[b + 2] = 1;
+  }
+
+  if (a[0] != 0 || a[1] != 2 || a[2] != 2)
+    abort ();
+  for (i = 3; i < 103; i++)
+    if (a[i] != 1)
+    abort ();
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "Store-stores chain" 1 "pcom" } } */

gcc/tree-predcom.c

@@ -1069,7 +1069,9 @@ add_ref_to_chain (chain_p chain, dref ref)
       chain->has_max_use_after = false;
     }
 
-  if (ref->distance == chain->length
+  /* Don't set the flag for store-store chain since there is no use.  */
+  if (chain->type != CT_STORE_STORE
+      && ref->distance == chain->length
       && ref->pos > root->pos)
     chain->has_max_use_after = true;