Re: Simplify ptr - 0

[Marc Glisse]

On Thu, 23 Nov 2017, Richard Biener wrote:

What about 0 - ptr?  (ok, that's even more weird)

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

Regtested on gcc112.

--
Marc Glisse
Index: gcc/match.pd
===================================================================
--- gcc/match.pd	(revision 255118)
+++ gcc/match.pd	(working copy)
@@ -2449,23 +2449,27 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
     (minus @0 { tem; })))))
 
 /* Convert x+x into x*2.  */
 (simplify
  (plus @0 @0)
  (if (SCALAR_FLOAT_TYPE_P (type))
   (mult @0 { build_real (type, dconst2); })
   (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
    (-ARG1 + ARG0) reduces to -ARG1.  */
 (simplify
  (minus real_zerop@0 @1)
  (if (fold_real_zero_addition_p (type, @0, 0))
   (negate @1)))
 
 /* Transform x * -1 into -x.  */