re PR tree-optimization/48022 (-Wstrict-overflow warning on code that doesn't have overflows)

	PR tree-optimization/48022
	* fold-const.c (fold_comparison): Don't call fold_overflow_warning
	for EQ/NE_EXPR.

	* gcc.dg/pr48022-1.c: New test.
	* gcc.dg/pr48022-2.c: New test.

From-SVN: r170772

gcc/ChangeLog

+2011-03-08  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/48022
+	* fold-const.c (fold_comparison): Don't call fold_overflow_warning
+	for EQ/NE_EXPR.
+
 2011-03-07  Jakub Jelinek  <jakub@redhat.com>
 
 	PR debug/47991

gcc/fold-const.c

 /* Fold a constant sub-tree into a single node for C-compiler
    Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
-   2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
+   2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
    Free Software Foundation, Inc.
 
 This file is part of GCC.
@@ -8572,6 +8572,7 @@ fold_comparison (location_t loc, enum tree_code code, tree type,
 	  && (TREE_CODE (lhs) != INTEGER_CST
 	      || !TREE_OVERFLOW (lhs)))
 	{
+	  if (code != EQ_EXPR && code != NE_EXPR)
 	    fold_overflow_warning ("assuming signed overflow does not occur "
 				   "when changing X +- C1 cmp C2 to "
 				   "X cmp C1 +- C2",

gcc/testsuite/ChangeLog

+2011-03-08  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/48022
+	* gcc.dg/pr48022-1.c: New test.
+	* gcc.dg/pr48022-2.c: New test.
+
 2011-03-07  Jason Merrill  <jason@redhat.com>
 
 	* g++.dg/template/nontype20.C: New.

gcc/testsuite/gcc.dg/pr48022-1.c

+/* PR tree-optimization/48022 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wstrict-overflow" } */
+
+int
+foo (const char *x)
+{
+  unsigned long l = 1;
+  const unsigned char *s = (const unsigned char *) (const char *) (x);
+  int r = s[0] - ((const unsigned char *) (const char *) ("/"))[0];
+  if (l > 0 && r == 0)
+    r = (s[1] - ((const unsigned char *) (const char *) ("/"))[1]);
+  return r;
+}

gcc/testsuite/gcc.dg/pr48022-2.c

+/* PR tree-optimization/48022 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wstrict-overflow" } */
+
+#include <string.h>
+
+int
+foo (const char *x)
+{
+  return strcmp (x, "/");
+}