[backport gcc-4.8.1 r198814 <mikpe@it.uu.se>]

gcc/

2013-05-13  Jakub Jelinek  <jakub@redhat.com>

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

gcc/testsuite/

2013-05-13  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/57230
	* gcc.dg/strlenopt-23.c: New test.

--- gcc-4.7.3/gcc/testsuite/gcc.dg/strlenopt-23.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.3/gcc/testsuite/gcc.dg/strlenopt-23.c	2013-05-18 11:21:57.039861156 +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;
+}
--- gcc-4.7.3/gcc/tree-ssa-strlen.c.~1~	2013-02-04 13:04:35.000000000 +0100
+++ gcc-4.7.3/gcc/tree-ssa-strlen.c	2013-05-18 11:21:57.039861156 +0200
@@ -1693,7 +1693,7 @@ 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);