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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/95034] Failure to convert xor pattern (made out of or+and) to xor
Date: Tue, 12 Jan 2021 10:56:41 +0000	[thread overview]
Message-ID: <bug-95034-4-iLHcQqa1s3@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-95034-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95034

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
On:
int
combine (int a, int b)
{
  int c = (a | b);
  int d = ~(a & b);
  return c & d;
}
it is the
/* (x | y) & ~(x & y) -> x ^ y */
(simplify
 (bit_and:c (bit_ior @0 @1) (bit_not (bit_and @0 @1)))
 (bit_xor @0 @1))
simplification (and there are similar around it).
So, if we go to doing this in GENERIC, we'd need
variants of this for truth_{and,ior} and truth_{and,ior}if (and for the latter
only under the !TREE_SIDE_EFFECTS and !generic_expr_could_trap_p conditions,
(though doesn't the more than one @1 already imply !TREE_SIDE_EFFECTS).
We do have truth_xor, but that will evaluate both arguments.

  parent reply	other threads:[~2021-01-12 10:56 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-10  9:48 [Bug tree-optimization/95034] New: Pattern for xor not converted " gabravier at gmail dot com
2020-05-13 12:38 ` [Bug tree-optimization/95034] Failure to convert xor pattern (made out of or+and) " pinskia at gcc dot gnu.org
2021-01-12 10:33 ` jakub at gcc dot gnu.org
2021-01-12 10:56 ` jakub at gcc dot gnu.org [this message]
2021-01-12 11:03 ` jakub at gcc dot gnu.org
2021-01-12 12:12 ` jakub at gcc dot gnu.org
2021-04-17 21:03 ` pinskia at gcc dot gnu.org
2023-08-23  2:16 ` pinskia at gcc dot gnu.org
2023-10-17  4:39 ` pinskia at gcc dot gnu.org

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