re PR tree-optimization/78542 (wrong code at -Og results in endless loop)

2016-11-28  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/78542
	* tree-ssa-ccp.c (evaluate_stmt): Only valueize simplification
	if allowed.

	* gcc.dg/torture/pr78542.c: New testcase.

From-SVN: r242920

gcc/ChangeLog

+2016-11-28  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/78542
+	* tree-ssa-ccp.c (evaluate_stmt): Only valueize simplification
+	if allowed.
+
 2016-11-28  Paolo Bonzini  <bonzini@gnu.org>
 
 	* combine.c (simplify_if_then_else): Simplify IF_THEN_ELSE

gcc/testsuite/ChangeLog

 2016-11-28  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/78542
+	* gcc.dg/torture/pr78542.c: New testcase.
+
+2016-11-28  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/78343
 	* gcc.dg/tree-ssa/20030808-1.c: Fix dump to generate.
 	* gcc.dg/tree-ssa/20040305-1.c: Likewise.

gcc/testsuite/gcc.dg/torture/pr78542.c

+/* { dg-do run } */
+/* { dg-additional-options "-w -Wno-psabi" } */
+
+typedef unsigned V __attribute__ ((vector_size (16)));
+
+V
+foo (unsigned x, V v)
+{
+  do {
+      v %= x;
+      x = 1;
+  } while (v[1]);
+  return v;
+}
+
+int
+main ()
+{
+  V x = foo (5, (V) { 0, 1 });
+  if (x[0] || x[1] || x[2] || x[3])
+    __builtin_abort();
+  return 0;
+}

gcc/tree-ssa-ccp.c

@@ -1744,7 +1744,12 @@ evaluate_stmt (gimple *stmt)
     {
       fold_defer_overflow_warnings ();
       simplified = ccp_fold (stmt);
-      if (simplified && TREE_CODE (simplified) == SSA_NAME)
+      if (simplified
+	  && TREE_CODE (simplified) == SSA_NAME
+	  /* We may not use values of something that may be simulated again,
+	     see valueize_op_1.  */
+	  && (SSA_NAME_IS_DEFAULT_DEF (simplified)
+	      || ! prop_simulate_again_p (SSA_NAME_DEF_STMT (simplified))))
 	{
 	  ccp_prop_value_t *val = get_value (simplified);
 	  if (val && val->lattice_val != VARYING)