[Bug tree-optimization/94026] combine missed opportunity to simplify comparisons with zero
cvs-commit at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Mon Jun 27 06:45:48 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94026
--- 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 != 0 as X&1536 != 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 << C1)
where cmp is == or !=, 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.
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