[backport from gcc-4.7.1 r188010, sans the restrict-2.c changes <mikpe@it.uu.se>]

gcc/

2012-05-30  Richard Guenther  <rguenther@suse.de>

	PR middle-end/53501
	* fold-const.c (fold_binary_loc): Make sure to call
	fold_plusminus_mult_expr with the original sign of operands.

gcc/testsuite/

2012-05-30  Richard Guenther  <rguenther@suse.de>

	PR middle-end/53501
	* gcc.dg/torture/pr53501.c: New testcase.
	* c-c++-common/restrict-2.c: Adjust.

--- gcc-4.6.3/gcc/fold-const.c.~1~	2012-02-27 12:19:03.000000000 +0100
+++ gcc-4.6.3/gcc/fold-const.c	2012-06-09 22:14:21.000000000 +0200
@@ -9647,12 +9647,12 @@ fold_binary_loc (location_t loc,
       /* Handle (A1 * C1) + (A2 * C2) with A1, A2 or C1, C2 being the
 	 same or one.  Make sure type is not saturating.
 	 fold_plusminus_mult_expr will re-associate.  */
-      if ((TREE_CODE (arg0) == MULT_EXPR
-	   || TREE_CODE (arg1) == MULT_EXPR)
+      if ((TREE_CODE (op0) == MULT_EXPR
+	   || TREE_CODE (op1) == MULT_EXPR)
 	  && !TYPE_SATURATING (type)
 	  && (!FLOAT_TYPE_P (type) || flag_associative_math))
         {
-	  tree tem = fold_plusminus_mult_expr (loc, code, type, arg0, arg1);
+	  tree tem = fold_plusminus_mult_expr (loc, code, type, op0, op1);
 	  if (tem)
 	    return tem;
 	}
@@ -10266,12 +10266,12 @@ fold_binary_loc (location_t loc,
       /* Handle (A1 * C1) - (A2 * C2) with A1, A2 or C1, C2 being the
 	 same or one.  Make sure type is not saturating.
 	 fold_plusminus_mult_expr will re-associate.  */
-      if ((TREE_CODE (arg0) == MULT_EXPR
-	   || TREE_CODE (arg1) == MULT_EXPR)
+      if ((TREE_CODE (op0) == MULT_EXPR
+	   || TREE_CODE (op1) == MULT_EXPR)
 	  && !TYPE_SATURATING (type)
 	  && (!FLOAT_TYPE_P (type) || flag_associative_math))
         {
-	  tree tem = fold_plusminus_mult_expr (loc, code, type, arg0, arg1);
+	  tree tem = fold_plusminus_mult_expr (loc, code, type, op0, op1);
 	  if (tem)
 	    return tem;
 	}
--- gcc-4.6.3/gcc/testsuite/gcc.dg/torture/pr53501.c.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.6.3/gcc/testsuite/gcc.dg/torture/pr53501.c	2012-06-09 22:14:21.000000000 +0200
@@ -0,0 +1,22 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+int e[100], n, here;
+
+void __attribute__((noinline))
+foo(void)
+{
+  int i, k = 0;
+  for (i = 0; i < n; ++i) { e[k] = 10; ++k; e[k] = 10; ++k; }
+  for (i = 0; i < k; ++i) here = 1;
+  if (here != 1)
+    abort ();
+}
+
+int main(void)
+{
+  n = 10;
+  foo();
+  return 0;
+}