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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/109011] missed optimization in presence of
 __builtin_ctz
Date: Thu, 20 Apr 2023 17:45:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109011

--- Comment #22 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:87c9bae4e32b54829dce0a93ff735412d5f684f8

commit r14-121-g87c9bae4e32b54829dce0a93ff735412d5f684f8
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Apr 20 19:44:27 2023 +0200

    tree-vect-patterns: One small vect_recog_ctz_ffs_pattern tweak [PR10901=
1]

    I've noticed I've made a typo, ifn in this function this late
    is always only IFN_CTZ or IFN_FFS, never IFN_CLZ.

    Due to this typo, we weren't using the originally intended
    .CTZ (X) =3D .POPCOUNT ((X - 1) & ~X)
    but
    .CTZ (X) =3D PREC - .POPCOUNT (X | -X)
    instead when we want to emit __builtin_ctz*/.CTZ using .POPCOUNT.
    Both compute the same value, both are defined at 0 with the
    same value (PREC), both have same number of GIMPLE statements,
    but I think the former ought to be preferred, because lots of targets
    have andn as a single operation rather than two, and also putting
    a -1 constant into a vector register is often cheaper than vector
    with broadcast PREC power of two value.

    2023-04-20  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/109011
            * tree-vect-patterns.cc (vect_recog_ctz_ffs_pattern): Use
            .CTZ (X) =3D .POPCOUNT ((X - 1) & ~X) in preference to
            .CTZ (X) =3D PREC - .POPCOUNT (X | -X).=