re PR tree-optimization/57656 (Wrong constant folding)

2013-09-03  Richard Biener  <rguenther@suse.de>

	PR middle-end/57656
	* fold-const.c (negate_expr_p): Fix division case.
	(negate_expr): Likewise.

	* gcc.dg/torture/pr57656.c: New testcase.

From-SVN: r202204

1 files changed, 31 insertions, 14 deletions

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index f959f0a..9956b2c 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -483,11 +483,24 @@ negate_expr_p (tree t)
 	 and actually traps on some architectures.  But if overflow is
 	 undefined, we can negate, because - (INT_MIN / 1) is an
 	 overflow.  */
-      if (INTEGRAL_TYPE_P (TREE_TYPE (t))
-	  && !TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (t)))
-        break;
-      return negate_expr_p (TREE_OPERAND (t, 1))
-             || negate_expr_p (TREE_OPERAND (t, 0));
+      if (INTEGRAL_TYPE_P (TREE_TYPE (t)))
+	{
+	  if (!TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (t)))
+	    break;
+	  /* If overflow is undefined then we have to be careful because
+	     we ask whether it's ok to associate the negate with the
+	     division which is not ok for example for
+	     -((a - b) / c) where (-(a - b)) / c may invoke undefined
+	     overflow because of negating INT_MIN.  So do not use
+	     negate_expr_p here but open-code the two important cases.  */
+	  if (TREE_CODE (TREE_OPERAND (t, 0)) == NEGATE_EXPR
+	      || (TREE_CODE (TREE_OPERAND (t, 0)) == INTEGER_CST
+		  && may_negate_without_overflow_p (TREE_OPERAND (t, 0))))
+	    return true;
+	}
+      else if (negate_expr_p (TREE_OPERAND (t, 0)))
+	return true;
+      return negate_expr_p (TREE_OPERAND (t, 1));
 
     case NOP_EXPR:
       /* Negate -((double)float) as (double)(-float).  */
@@ -682,16 +695,20 @@ fold_negate_expr (location_t loc, tree t)
 	      return fold_build2_loc (loc, TREE_CODE (t), type,
 				  TREE_OPERAND (t, 0), negate_expr (tem));
 	    }
+	  /* If overflow is undefined then we have to be careful because
+	     we ask whether it's ok to associate the negate with the
+	     division which is not ok for example for
+	     -((a - b) / c) where (-(a - b)) / c may invoke undefined
+	     overflow because of negating INT_MIN.  So do not use
+	     negate_expr_p here but open-code the two important cases.  */
           tem = TREE_OPERAND (t, 0);
-          if (negate_expr_p (tem))
-	    {
-	      if (INTEGRAL_TYPE_P (type)
-		  && (TREE_CODE (tem) != INTEGER_CST
-		      || tree_int_cst_equal (tem, TYPE_MIN_VALUE (type))))
-		fold_overflow_warning (warnmsg, WARN_STRICT_OVERFLOW_MISC);
-	      return fold_build2_loc (loc, TREE_CODE (t), type,
-				  negate_expr (tem), TREE_OPERAND (t, 1));
-	    }
+	  if ((INTEGRAL_TYPE_P (type)
+	       && (TREE_CODE (tem) == NEGATE_EXPR
+		   || (TREE_CODE (tem) == INTEGER_CST
+		       && may_negate_without_overflow_p (tem))))
+	      || !INTEGRAL_TYPE_P (type))
+	    return fold_build2_loc (loc, TREE_CODE (t), type,
+				    negate_expr (tem), TREE_OPERAND (t, 1));
         }
       break;