re PR tree-optimization/87132 (Gcc miscompiles at -O2 on valid code)

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.

From-SVN: r263959

gcc/ChangeLog

 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.
+
+2018-08-29  Richard Biener  <rguenther@suse.de>
+
 	* tree-core.h: Document use of deprecated_flag in SSA_NAME.
 	* tree.h (SSA_NAME_POINTS_TO_READONLY_MEMORY): Define.
 	* tree-into-ssa.c (pass_build_ssa::execute): Initialize

gcc/testsuite/ChangeLog

+2018-08-29  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/87132
+	* gcc.dg/torture/pr87132.c: New testcase.
+
 2018-08-29  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/85110

gcc/testsuite/gcc.dg/torture/pr87132.c

+/* { 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;
+}

gcc/tree-ssa-alias.c

@@ -2740,7 +2740,14 @@ 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;
     }