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 <ja...@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)
+ (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
