re PR middle-end/68067 (Wrong constant folding)

2015-10-28  Richard Biener  <rguenther@suse.de>

	PR middle-end/68067
	* fold-const.c (negate_expr_p): We cannot negate plus or minus
	if overflow is not wrapping.  Likewise multiplication unless
	one operand is constant and not power of two.
	(fold_negate_expr): Adjust accordingly.

	* gcc.dg/torture/pr68067-1.c: New testcase.
	* gcc.dg/torture/pr68067-2.c: Likewise.

From-SVN: r229479

gcc/ChangeLog

+2015-10-28  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/68067
+	* fold-const.c (negate_expr_p): We cannot negate plus or minus
+	if overflow is not wrapping.  Likewise multiplication unless
+	one operand is constant and not power of two.
+	(fold_negate_expr): Adjust accordingly.
+
 2015-10-27  Nathan Sidwell  <nathan@codesourcery.com>
 
 	* omp-low.c (struct omp_context): Remove gwv_below, gwv_this

gcc/fold-const.c

@@ -443,7 +443,9 @@ negate_expr_p (tree t)
 
     case PLUS_EXPR:
       if (HONOR_SIGN_DEPENDENT_ROUNDING (element_mode (type))
-	  || HONOR_SIGNED_ZEROS (element_mode (type)))
+	  || HONOR_SIGNED_ZEROS (element_mode (type))
+	  || (INTEGRAL_TYPE_P (type)
+	      && ! TYPE_OVERFLOW_WRAPS (type)))
 	return false;
       /* -(A + B) -> (-B) - A.  */
       if (negate_expr_p (TREE_OPERAND (t, 1))
@@ -457,12 +459,23 @@ negate_expr_p (tree t)
       /* We can't turn -(A-B) into B-A when we honor signed zeros.  */
       return !HONOR_SIGN_DEPENDENT_ROUNDING (element_mode (type))
 	     && !HONOR_SIGNED_ZEROS (element_mode (type))
+	     && (! INTEGRAL_TYPE_P (type)
+		 || TYPE_OVERFLOW_WRAPS (type))
 	     && reorder_operands_p (TREE_OPERAND (t, 0),
 				    TREE_OPERAND (t, 1));
 
     case MULT_EXPR:
-      if (TYPE_UNSIGNED (TREE_TYPE (t)))
-        break;
+      if (TYPE_UNSIGNED (type))
+	break;
+      /* INT_MIN/n * n doesn't overflow while negating one operand it does
+         if n is a power of two.  */
+      if (INTEGRAL_TYPE_P (TREE_TYPE (t))
+	  && ! TYPE_OVERFLOW_WRAPS (TREE_TYPE (t))
+	  && ! ((TREE_CODE (TREE_OPERAND (t, 0)) == INTEGER_CST
+		 && ! integer_pow2p (TREE_OPERAND (t, 0)))
+		|| (TREE_CODE (TREE_OPERAND (t, 1)) == INTEGER_CST
+		    && ! integer_pow2p (TREE_OPERAND (t, 1)))))
+	break;
 
       /* Fall through.  */
 

gcc/testsuite/ChangeLog

+2015-10-28  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/68067
+	* gcc.dg/torture/pr68067-1.c: New testcase.
+	* gcc.dg/torture/pr68067-2.c: Likewise.
+
 2015-10-28  Segher Boessenkool  <segher@kernel.crashing.org>
 
 	* gcc.target/powerpc/p8vector-builtin-8.c: Add "target int128".

gcc/testsuite/gcc.dg/torture/pr68067-1.c

+/* { dg-do run } */
+
+int main()
+{
+  int a = -1;
+  static int b = -2147483647 - 1;
+  static int c = 0;
+  int t = a - (b - c);
+  if (t != 2147483647)
+    __builtin_abort();
+  return 0;
+}

gcc/testsuite/gcc.dg/torture/pr68067-2.c

+/* { dg-do run } */
+
+int main()
+{
+  int a = -1;
+  static int b = -2147483647 - 1;
+  static int c = 0;
+  int t = a - (b + c*-2);
+  if (t != 2147483647)
+    __builtin_abort();
+  return 0;
+}
+