re PR tree-optimization/83269 (Wrong constant folding)

	PR tree-optimization/83269
	* fold-const.c (fold_binary_loc): Perform (-A) - B -> (-B) - A
	subtraction in arg0's type if type is signed and arg0 is unsigned.
	Formatting fix.

	* gcc.c-torture/execute/pr83269.c: New test.

From-SVN: r255697

gcc/ChangeLog

 2017-12-15  Jakub Jelinek  <jakub@redhat.com>
 
+	PR tree-optimization/83269
+	* fold-const.c (fold_binary_loc): Perform (-A) - B -> (-B) - A
+	subtraction in arg0's type if type is signed and arg0 is unsigned.
+	Formatting fix.
+
 	PR sanitizer/81281
 	* match.pd ((T)(P + A) - (T)P -> (T) A): Use @@0 instead of @0 and
 	convert? on @0 instead of convert.  Check type of @1, not @0.

gcc/fold-const.c

@@ -9098,8 +9098,8 @@ expr_not_equal_to (tree t, const wide_int &w)
    return NULL_TREE.  */
 
 tree
-fold_binary_loc (location_t loc,
-	     enum tree_code code, tree type, tree op0, tree op1)
+fold_binary_loc (location_t loc, enum tree_code code, tree type,
+		 tree op0, tree op1)
 {
   enum tree_code_class kind = TREE_CODE_CLASS (code);
   tree arg0, arg1, tem;
@@ -9769,10 +9769,17 @@ fold_binary_loc (location_t loc,
 
       /* (-A) - B -> (-B) - A  where B is easily negated and we can swap.  */
       if (TREE_CODE (arg0) == NEGATE_EXPR
-	  && negate_expr_p (op1))
-	return fold_build2_loc (loc, MINUS_EXPR, type,
-				negate_expr (op1),
-				fold_convert_loc (loc, type,
+	  && negate_expr_p (op1)
+	  /* If arg0 is e.g. unsigned int and type is int, then this could
+	     introduce UB, because if A is INT_MIN at runtime, the original
+	     expression can be well defined while the latter is not.
+	     See PR83269.  */
+	  && !(ANY_INTEGRAL_TYPE_P (type)
+	       && TYPE_OVERFLOW_UNDEFINED (type)
+	       && ANY_INTEGRAL_TYPE_P (TREE_TYPE (arg0))
+	       && !TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (arg0))))
+	return fold_build2_loc (loc, MINUS_EXPR, type, negate_expr (op1),
+			        fold_convert_loc (loc, type,
 						  TREE_OPERAND (arg0, 0)));
 
       /* Fold __complex__ ( x, 0 ) - __complex__ ( 0, y ) to

gcc/testsuite/ChangeLog

 2017-12-15  Jakub Jelinek  <jakub@redhat.com>
 
+	PR tree-optimization/83269
+	* gcc.c-torture/execute/pr83269.c: New test.
+
 	PR sanitizer/81281
 	* gcc.dg/pr81281-3.c: New test.
 

gcc/testsuite/gcc.c-torture/execute/pr83269.c

+/* PR tree-optimization/83269 */
+
+int
+main ()
+{
+#if __SIZEOF_INT__ == 4 && __SIZEOF_LONG_LONG__ > 4 && __CHAR_BIT__ == 8
+  volatile unsigned char a = 1;
+  long long b = 0x80000000L;
+  int c = -((int)(-b) - (-0x7fffffff * a));
+  if (c != 1)
+    __builtin_abort ();
+#endif
+  return 0;
+}