[PATCH] Fix PR87132

[Richard Biener]

Bootstrapped and tested on x86_64-unknown-linux-gnu, re-doing together
with the fix for the fallout.

Richard.

2018-08-29  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87132
	* tree-ssa-alias.c (get_continuation_for_phi): Do not translate
	when skipping defs reachable over backedges.

	* gcc.dg/torture/pr87132.c: New testcase.

Index: gcc/tree-ssa-alias.c
===================================================================
--- gcc/tree-ssa-alias.c	(revision 263944)
+++ gcc/tree-ssa-alias.c	(working copy)
@@ -2722,7 +2722,14 @@ next:;
       if (arg1 == arg0)
 	;
       else if (! maybe_skip_until (phi, arg0, ref, arg1, cnt, visited,
-				   abort_on_visited, translate, data))
+				   abort_on_visited,
+				   /* Do not translate when walking over
+				      backedges.  */
+				   dominated_by_p
+				     (CDI_DOMINATORS,
+				      gimple_bb (SSA_NAME_DEF_STMT (arg1)),
+				      phi_bb)
+				   ? NULL : translate, data))
 	return NULL_TREE;
     }
 
Index: gcc/testsuite/gcc.dg/torture/pr87132.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr87132.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr87132.c	(working copy)
@@ -0,0 +1,18 @@
+/* { dg-do run } */
+
+extern void abort (void);
+int c, d;
+int main()
+{
+  int e[] = {4, 4, 4, 4, 4, 4, 4, 4, 4};
+  d = 8;
+  for (; d; d--)
+    for (int a = 0; a <= 8; a++)
+      {
+	c = e[1];
+	e[d] = 0;
+      }
+  if (c != 0)
+    abort ();
+  return 0;
+}