[backport gcc-4.8.1 r197693 <mikpe@it.uu.se>]

gcc/

2013-04-11  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/56899
	* fold-const.c (extract_muldiv_1): Apply distributive law
	only if TYPE_OVERFLOW_WRAPS (ctype).

gcc/testsuite/

2013-04-11  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/56899
	* gcc.c-torture/execute/pr56899.c: New test.

--- gcc-4.7.3/gcc/fold-const.c.~1~	2013-02-19 18:26:04.000000000 +0100
+++ gcc-4.7.3/gcc/fold-const.c	2013-05-12 13:20:01.225667903 +0200
@@ -5859,8 +5859,10 @@ extract_muldiv_1 (tree t, tree c, enum t
 
       /* The last case is if we are a multiply.  In that case, we can
 	 apply the distributive law to commute the multiply and addition
-	 if the multiplication of the constants doesn't overflow.  */
-      if (code == MULT_EXPR)
+	 if the multiplication of the constants doesn't overflow
+	 and overflow is defined.  With undefined overflow
+	 op0 * c might overflow, while (op0 + orig_op1) * c doesn't.  */
+      if (code == MULT_EXPR && TYPE_OVERFLOW_WRAPS (ctype))
 	return fold_build2 (tcode, ctype,
 			    fold_build2 (code, ctype,
 					 fold_convert (ctype, op0),
--- gcc-4.7.3/gcc/testsuite/gcc.c-torture/execute/pr56899.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.3/gcc/testsuite/gcc.c-torture/execute/pr56899.c	2013-05-12 13:20:01.225667903 +0200
@@ -0,0 +1,47 @@
+/* PR tree-optimization/56899 */
+
+#if __SIZEOF_INT__ == 4 && __CHAR_BIT__ == 8
+__attribute__((noinline, noclone)) void
+f1 (int v)
+{
+  int x = -214748365 * (v - 1);
+  if (x != -1932735285)
+    __builtin_abort ();
+}
+
+__attribute__((noinline, noclone)) void
+f2 (int v)
+{
+  int x = 214748365 * (v + 1);
+  if (x != -1932735285)
+    __builtin_abort ();
+}
+
+__attribute__((noinline, noclone)) void
+f3 (unsigned int v)
+{
+  unsigned int x = -214748365U * (v - 1);
+  if (x != -1932735285U)
+    __builtin_abort ();
+}
+
+__attribute__((noinline, noclone)) void
+f4 (unsigned int v)
+{
+  unsigned int x = 214748365U * (v + 1);
+  if (x != -1932735285U)
+    __builtin_abort ();
+}
+#endif
+
+int
+main ()
+{
+#if __SIZEOF_INT__ == 4 && __CHAR_BIT__ == 8
+  f1 (10);
+  f2 (-10);
+  f3 (10);
+  f4 (-10U);
+#endif
+  return 0;
+}