Simplify 0 - ptr.

2017-11-24  Marc Glisse  <marc.glisse@inria.fr>

	* match.pd (0-ptr): New transformation.

From-SVN: r255139

gcc/ChangeLog

+2017-11-24  Marc Glisse  <marc.glisse@inria.fr>
+
+	* match.pd (0-ptr): New transformation.
+
 2017-11-24  Jan Hubicka  <hubicka@ucw.cz>
 
 	PR bootstrap/83015

gcc/match.pd

@@ -2456,9 +2456,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (if (INTEGRAL_TYPE_P (type))
    (mult @0 { build_int_cst (type, 2); }))))
 
+/* 0 - X  ->  -X.  */
 (simplify
  (minus integer_zerop @1)
  (negate @1))
+(simplify
+ (pointer_diff integer_zerop @1)
+ (negate (convert @1)))
 
 /* (ARG0 - ARG1) is the same as (-ARG1 + ARG0).  So check whether
    ARG0 is zero and X + ARG0 reduces to X, since that would mean