re PR tree-optimization/56250 (Wrong constant folding on unsigned int)

	PR tree-optimization/56250
	* fold-const.c (extract_muldiv_1) <case NEGATE_EXPR>: Don't optimize
	if type is unsigned and code isn't MULT_EXPR.

	* gcc.c-torture/execute/pr56250.c: New test.

From-SVN: r195888

gcc/ChangeLog

+2013-02-08  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/56250
+	* fold-const.c (extract_muldiv_1) <case NEGATE_EXPR>: Don't optimize
+	if type is unsigned and code isn't MULT_EXPR.
+
 2013-02-08  Georg-Johann Lay  <avr@gjlay.de>
 
 	PR tree-optimization/56064

gcc/fold-const.c

@@ -5695,6 +5695,11 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
         break;
       /* FALLTHROUGH */
     case NEGATE_EXPR:
+      /* For division and modulus, type can't be unsigned, as e.g.
+	 (-(x / 2U)) / 2U isn't equal to -((x / 2U) / 2U) for x >= 2.
+	 For signed types, even with wrapping overflow, this is fine.  */
+      if (code != MULT_EXPR && TYPE_UNSIGNED (type))
+	break;
       if ((t1 = extract_muldiv (op0, c, code, wide_type, strict_overflow_p))
 	  != 0)
 	return fold_build1 (tcode, ctype, fold_convert (ctype, t1));

gcc/testsuite/ChangeLog

+2013-02-08  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/56250
+	* gcc.c-torture/execute/pr56250.c: New test.
+
 2013-02-08  Georg-Johann Lay  <avr@gjlay.de>
 
 	PR tree-optimization/56064

gcc/testsuite/gcc.c-torture/execute/pr56250.c

+/* PR tree-optimization/56250 */
+
+extern void abort (void);
+
+int
+main ()
+{
+  unsigned int x = 2;
+  unsigned int y = (0U - x / 2) / 2;
+  if (-1U / x != y)
+    abort ();
+  return 0;
+}