[PATCH v2] match.pd: Canonicalize (X + (X >> (prec - 1))) ^ (X >> (prec - 1)) to abs (X) [PR94783]

[Richard Biener]

On May 7, 2020 4:34:59 PM GMT+02:00, Jakub Jelinek <jakub@redhat.com> wrote:
>On Thu, May 07, 2020 at 10:12:12AM +0200, Richard Biener wrote:
>> I think unconditionally using (abs @0) is simplifying things enough
>> (getting rid of one xor and one plus) to not worry about keeping
>> the (x >> (prec - 1))?
>
>Ok.
>
>> Do you really need the TYPE_OVERFLOW_UNDEFINED check?
>
>Probably not, if overflow isn't undefined, then ABS_EXPR will not be
>undefined on the type minimum either.
>
>So like this (including dropping :s from plus), or should there be
>single_use for it?  You've said that if the replacement is a simple
>stmt
>:s is ignored...
>
>2020-05-07  Jakub Jelinek  <jakub@redhat.com>
>
>	PR tree-optimization/94783
>	* match.pd ((X + (X >> (prec - 1))) ^ (X >> (prec - 1)) to abs (X)):
>	New simplification.
>
>	* gcc.dg/tree-ssa/pr94783.c: New test.
>
>--- gcc/match.pd.jj	2020-05-06 15:48:23.658858289 +0200
>+++ gcc/match.pd	2020-05-07 16:30:15.666817448 +0200
>@@ -120,6 +120,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>   (with { tree utype = unsigned_type_for (TREE_TYPE (@0)); }
>    (convert (absu:utype @0)))))
> 
>+#if GIMPLE
>+/* Optimize (X + (X >> (prec - 1))) ^ (X >> (prec - 1)) into abs (X). 
>*/
>+(simplify
>+ (bit_xor:c (plus:c @0 (rshift@2 @0 INTEGER_CST@1)) @2)
>+ (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
>+      && !TYPE_UNSIGNED (TREE_TYPE (@0))
>+      && wi::to_widest (@1) == element_precision (TREE_TYPE (@0)) - 1
>+      && TREE_CODE (@2) == SSA_NAME)

The SSA_NAME check is superfluous now. 

Otherwise OK. 

Thanks, 
Richard. 

>+  (abs @0)))
>+#endif
> 
> /* Simplifications of operations with one constant operand and
>    simplifications to constants or single values.  */
>--- gcc/testsuite/gcc.dg/tree-ssa/pr94783.c.jj	2020-05-06
>17:52:35.515323297 +0200
>+++ gcc/testsuite/gcc.dg/tree-ssa/pr94783.c	2020-05-06
>17:52:10.915693948 +0200
>@@ -0,0 +1,12 @@
>+/* PR tree-optimization/94783 */
>+/* { dg-do compile } */
>+/* { dg-options "-O2 -fdump-tree-optimized" } */
>+/* { dg-final { scan-tree-dump "ABS_EXPR" "optimized" } } */
>+/* { dg-final { scan-tree-dump-not " >> 31" "optimized" } } */
>+
>+int
>+foo (int v)
>+{
>+  int mask = v >> (__SIZEOF_INT__ * __CHAR_BIT__ - 1);
>+  return (v + mask) ^ mask;
>+}
>
>
>	Jakub