re PR middle-end/67662 (-fsanitize=undefined cries wolf for X - 1 + X when X is 2**30)

2015-09-23   Richard Biener  <rguenther@suse.de>

	PR middle-end/67662
	* fold-const.c (fold_binary_loc): Do not reassociate two vars with
	undefined overflow unless they will cancel out.

	* gcc.dg/ubsan/pr67662.c: New testcase.

From-SVN: r228051

gcc/ChangeLog

+2015-09-23   Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/67662
+	* fold-const.c (fold_binary_loc): Do not reassociate two vars with
+	undefined overflow unless they will cancel out.
+
 2015-09-23  Kirill Yukhin  <kirill.yukhin@intel.com>
 
 	* config/i386/i386.md (define_insn "*<mshift><mode>3"): Fix

gcc/fold-const.c

@@ -9493,25 +9493,32 @@ fold_binary_loc (location_t loc,
 		{
 		  tree tmp0 = var0;
 		  tree tmp1 = var1;
+		  bool one_neg = false;
 
 		  if (TREE_CODE (tmp0) == NEGATE_EXPR)
-		    tmp0 = TREE_OPERAND (tmp0, 0);
+		    {
+		      tmp0 = TREE_OPERAND (tmp0, 0);
+		      one_neg = !one_neg;
+		    }
 		  if (CONVERT_EXPR_P (tmp0)
 		      && INTEGRAL_TYPE_P (TREE_TYPE (TREE_OPERAND (tmp0, 0)))
 		      && (TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (tmp0, 0)))
 			  <= TYPE_PRECISION (atype)))
 		    tmp0 = TREE_OPERAND (tmp0, 0);
 		  if (TREE_CODE (tmp1) == NEGATE_EXPR)
-		    tmp1 = TREE_OPERAND (tmp1, 0);
+		    {
+		      tmp1 = TREE_OPERAND (tmp1, 0);
+		      one_neg = !one_neg;
+		    }
 		  if (CONVERT_EXPR_P (tmp1)
 		      && INTEGRAL_TYPE_P (TREE_TYPE (TREE_OPERAND (tmp1, 0)))
 		      && (TYPE_PRECISION (TREE_TYPE (TREE_OPERAND (tmp1, 0)))
 			  <= TYPE_PRECISION (atype)))
 		    tmp1 = TREE_OPERAND (tmp1, 0);
 		  /* The only case we can still associate with two variables
-		     is if they are the same, modulo negation and bit-pattern
-		     preserving conversions.  */
-		  if (!operand_equal_p (tmp0, tmp1, 0))
+		     is if they cancel out.  */
+		  if (!one_neg
+		      || !operand_equal_p (tmp0, tmp1, 0))
 		    ok = false;
 		}
 	    }

gcc/testsuite/ChangeLog

+2015-09-23   Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/67662
+	* gcc.dg/ubsan/pr67662.c: New testcase.
+
 2015-09-23  Manuel López-Ibáñez  <manu@gcc.gnu.org>
 
 	PR c/49655

gcc/testsuite/gcc.dg/ubsan/pr67662.c

+/* { dg-do run } */
+/* { dg-options "-fsanitize=undefined" } */
+
+extern void abort (void);
+
+int
+main (void)
+{
+  int halfmaxval = __INT_MAX__ / 2 + 1;
+  int maxval = halfmaxval - 1 + halfmaxval;
+  if (maxval != __INT_MAX__)
+    abort ();
+  return 0;
+}