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Subject: [Bug tree-optimization/94026] combine missed opportunity to simplify
 comparisons with zero
Date: Mon, 27 Jun 2022 06:45:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94026

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:

https://gcc.gnu.org/g:f3f73e86ec8613f176db3e52bbfbfbb9636cb714

commit r13-1281-gf3f73e86ec8613f176db3e52bbfbfbb9636cb714
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Mon Jun 27 07:44:49 2022 +0100

    [PATCH] PR tree-optimization/94026: Simplify (X>>8)&6 !=3D 0 as X&1536 =
!=3D 0.

    This patch implements the missed optimization described in PR 94026,
    where a the shift can be eliminated from the sequence of a shift,
    followed by a bit-wise AND followed by an equality/inequality test.
    Specifically, ((X << C1) & C2) cmp C3 into (X & (C2 >> C1)) cmp (C3 >> =
C1)
    and likewise ((X >> C1) & C2) cmp C3 into (X & (C2 << C1)) cmp (C3 << C=
1)
    where cmp is =3D=3D or !=3D, and C1, C2 and C3 are integer constants.
    The example in the subject line is taken from the hot function
    self_atari from the Go program Leela (in SPEC CPU 2017).

    2022-06-27  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            PR tree-optimization/94026
            * match.pd (((X << C1) & C2) eq/ne C3): New simplification.
            (((X >> C1) & C2) eq/ne C3): Likewise.

    gcc/testsuite/ChangeLog
            PR tree-optimization/94026
            * gcc.dg/pr94026.c: New test case.=