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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/95034] Failure to convert xor pattern (made
 out of or+and) to xor
Date: Tue, 12 Jan 2021 10:33:09 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95034

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
For
int
combine (int a, int b)
{
  return (a | b) & ~(a & b);
}
we do optimize it, for the ||s and &&s the problem is that it is split accr=
oss
multiple basic blocks, so match.pd is out of the picture, but on the other =
side
reassoc which can handle conditions split across multiple bbs will handle o=
nly
a single truth operation (so the && in this case) and so we'd need to look
through the |s from there manually.

Ah, an option could be to add some truth_{and,ior,*} rules in match.pd, lim=
ited
to GENERIC probably, as it won't trigger afterwards.
But of course that would handle only the above testcase and not e.g.
    bool t1 =3D a || b;
    bool t2 =3D !(a && b);
    return t1 && t2;
etc.

Richard, any ideas?=