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match.pd: Fold x == ~x to false [PR96782]

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x is never equal to ~x, so we can fold such comparisons to constants.

2021-01-04  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96782
	* match.pd (x == ~x -> false, x != ~x -> true): New simplifications.

	* gcc.dg/tree-ssa/pr96782.c: New test.
This commit is contained in:
Jakub Jelinek 2021-01-04 10:37:12 +01:00
parent 99dee82307
commit ad64e807ff
2 changed files with 24 additions and 0 deletions
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7
gcc/match.pd
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@ -4045,6 +4045,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(if (!flag_trapping_math)
{ constant_boolean_node (false, type); }))
/* x == ~x -> false */
/* x != ~x -> true */
(for cmp (eq ne)
(simplify
(cmp:c @0 (bit_not @0))
{ constant_boolean_node (cmp == NE_EXPR, type); }))
/* Fold ~X op ~Y as Y op X. */
(for cmp (simple_comparison)
(simplify

17
gcc/testsuite/gcc.dg/tree-ssa/pr96782.c Normal file
View file

@ -0,0 +1,17 @@
/* PR tree-optimization/96782 */
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-optimized" } */
/* { dg-final { scan-tree-dump-times "return 0;" 1 "optimized" } } */
/* { dg-final { scan-tree-dump-times "return 1;" 1 "optimized" } } */
int
foo (int a)
{
return a == ~a;
}
int
bar (int b)
{
return ~b != b;
}