re PR middle-end/81705 (UBSAN: yet another false positive)

2017-08-04  Richard Biener  <rguenther@suse.de>

	PR middle-end/81705
	* fold-const.c (fold_binary_loc): Properly restrict
	minus_var0 && minus_var1 case when associating undefined overflow
	entities.

	* c-c++-common/ubsan/pr81705.c: New testcase.

From-SVN: r250866

gcc/ChangeLog

+2017-08-04  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81705
+	* fold-const.c (fold_binary_loc): Properly restrict
+	minus_var0 && minus_var1 case when associating undefined overflow
+	entities.
+
 2017-08-04  Tom de Vries  <tom@codesourcery.com>
 
 	* omp-simd-clone.c (simd_clone_adjust): Add missing edge probability.

gcc/fold-const.c

@@ -9592,12 +9592,13 @@ fold_binary_loc (location_t loc,
 	  if (POINTER_TYPE_P (atype)
 	      || (INTEGRAL_TYPE_P (atype) && !TYPE_OVERFLOW_WRAPS (atype)))
 	    {
-	      if (var0 && var1)
+	      if ((var0 && var1) || (minus_var0 && minus_var1))
 		{
 		  /* ???  If split_tree would handle NEGATE_EXPR we could
-		     simplify this down to the var0/minus_var1 cases.  */
-		  tree tmp0 = var0;
-		  tree tmp1 = var1;
+		     simply reject these cases and the allowed cases would
+		     be the var0/minus_var1 ones.  */
+		  tree tmp0 = var0 ? var0 : minus_var0;
+		  tree tmp1 = var1 ? var1 : minus_var1;
 		  bool one_neg = false;
 
 		  if (TREE_CODE (tmp0) == NEGATE_EXPR)

gcc/testsuite/ChangeLog

+2017-08-04  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81705
+	* c-c++-common/ubsan/pr81705.c: New testcase.
+
 2017-08-03  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	* gcc.target/powerpc/bfp/scalar-cmp-exp-eq-2.c: Adjust for error

gcc/testsuite/c-c++-common/ubsan/pr81705.c

+/* { dg-do run } */
+/* { dg-options "-fsanitize=undefined -fsanitize-undefined-trap-on-error" } */
+
+int var_4 = -1716607962;
+int var_14 = 943738830;
+volatile int a;
+int main()
+{
+  //  (-(-1716607962) - 516151698) - -(9403738830)
+  a = (-var_4 - 516151698) - -var_14;
+  return 0;
+}