2013-05-10  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/57230
	* tree-ssa-strlen.c (handle_char_store): Add missing integer_zerop
	check.

	* gcc.dg/strlenopt-23.c: New test.

--- gcc/tree-ssa-strlen.c.jj	2013-04-26 08:49:53.000000000 +0200
+++ gcc/tree-ssa-strlen.c	2013-05-10 08:57:20.654523288 +0200
@@ -1703,7 +1703,7 @@ handle_char_store (gimple_stmt_iterator
 	       its length may be decreased.  */
 	    adjust_last_stmt (si, stmt, false);
 	}
-      else if (si != NULL)
+      else if (si != NULL && integer_zerop (gimple_assign_rhs1 (stmt)))
 	{
 	  si = unshare_strinfo (si);
 	  si->length = build_int_cst (size_type_node, 0);
--- gcc/testsuite/gcc.dg/strlenopt-23.c.jj	2013-05-10 09:01:27.808152595 +0200
+++ gcc/testsuite/gcc.dg/strlenopt-23.c	2013-05-10 09:02:08.042931124 +0200
@@ -0,0 +1,15 @@
+/* PR tree-optimization/57230 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+#include "strlenopt.h"
+
+int
+main ()
+{
+  char p[] = "hello world";
+  p[0] = (char) (strlen (p) - 1);
+  if (strlen (p) != 11)
+    abort ();
+  return 0;
+}