re PR sanitizer/81065 (UBSAN: false positive as a result of distribution involving different types)

2017-06-13  Richard Biener  <rguenther@suse.de>

	PR middle-end/81065
	* fold-const.c (extract_muldiv_1): Remove bogus distribution
	case of C * (x * C2 + C3).
	(fold_addr_of_array_ref_difference): Properly fold index difference.

	* c-c++-common/ubsan/pr81065.c: New testcase.

From-SVN: r249144

gcc/ChangeLog

+2017-06-13  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81065
+	* fold-const.c (extract_muldiv_1): Remove bogus distribution
+	case of C * (x * C2 + C3).
+	(fold_addr_of_array_ref_difference): Properly fold index difference.
+
 2017-06-12  David S. Miller  <davem@davemloft.net>
 
 	PR target/80968

gcc/fold-const.c

@@ -6241,11 +6241,6 @@ extract_muldiv_1 (tree t, tree c, enum tree_code code, tree wide_type,
       if (TYPE_UNSIGNED (ctype) && ctype != type)
 	break;
 
-      /* If we were able to eliminate our operation from the first side,
-	 apply our operation to the second side and reform the PLUS.  */
-      if (t1 != 0 && (TREE_CODE (t1) != code || code == MULT_EXPR))
-	return fold_build2 (tcode, ctype, fold_convert (ctype, t1), op1);
-
       /* The last case is if we are a multiply.  In that case, we can
 	 apply the distributive law to commute the multiply and addition
 	 if the multiplication of the constants doesn't overflow
@@ -8908,7 +8903,7 @@ fold_addr_of_array_ref_difference (location_t loc, tree type,
       tree op0 = fold_convert_loc (loc, type, TREE_OPERAND (aref0, 1));
       tree op1 = fold_convert_loc (loc, type, TREE_OPERAND (aref1, 1));
       tree esz = fold_convert_loc (loc, type, array_ref_element_size (aref0));
-      tree diff = build2 (MINUS_EXPR, type, op0, op1);
+      tree diff = fold_build2_loc (loc, MINUS_EXPR, type, op0, op1);
       return fold_build2_loc (loc, PLUS_EXPR, type,
 			      base_offset,
 			      fold_build2_loc (loc, MULT_EXPR, type,

gcc/testsuite/ChangeLog

+2017-06-13  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/81065
+	* c-c++-common/ubsan/pr81065.c: New testcase.
+
 2017-06-12  Ian Lance Taylor  <iant@golang.org>
 
 	* gcc.dg/tree-prof/split-1.c: Require split_stack, don't require

gcc/testsuite/c-c++-common/ubsan/pr81065.c

+/* { dg-do run } */
+/* { dg-options "-fsanitize=undefined -fsanitize-undefined-trap-on-error" } */
+
+unsigned char x = 154;
+int foo() {
+  // 8575 * (254408 - 9057) = 8575 * 245351 = 2103884825 = 0x7d66bc19
+  return 8575 * (1652 * x - 9057);
+}
+
+int main() {
+  foo();
+  return 0;
+}