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Subject: [Bug target/97503] Suboptimal use of cntlzw and cntlzd
Date: Wed, 21 Oct 2020 08:54:54 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97503

--- Comment #3 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:5244b4af5e47bc98a2a9cf36f048981583a1b163

commit r11-4183-g5244b4af5e47bc98a2a9cf36f048981583a1b163
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Oct 21 10:51:33 2020 +0200

    phiopt: Optimize x ? __builtin_clz (x) : 32 in GIMPLE [PR97503]

    While we have at the RTL level noce_try_ifelse_collapse combined with
    simplify_cond_clz_ctz, that optimization doesn't always trigger because
    e.g. on powerpc there is an define_insn to compare a reg against zero a=
nd
    copy that register to another one and so we end up with a different pse=
udo
    in the simplify_cond_clz_ctz test and punt.

    For targets that define C?Z_DEFINED_VALUE_AT_ZERO to 2 for certain mode=
s,
    we can optimize it already in phiopt though, just need to ensure that
    we transform the __builtin_c?z* calls into .C?Z ifns because my recent
    VRP changes codified that the builtin calls are always undefined at zer=
o,
    while ifns honor C?Z_DEFINED_VALUE_AT_ZERO equal to 2.
    And, in phiopt we already have popcount handling that does pretty much =
the
    same thing, except for always using a zero value rather than the one set
    by C?Z_DEFINED_VALUE_AT_ZERO.

    So, this patch extends that function to handle not just popcount, but a=
lso
    clz and ctz.

    2020-10-21  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/97503
            * tree-ssa-phiopt.c: Include internal-fn.h.
            (cond_removal_in_popcount_pattern): Rename to ...
            (cond_removal_in_popcount_clz_ctz_pattern): ... this.  Handle n=
ot
just
            popcount, but also clz and ctz if it has C?Z_DEFINED_VALUE_AT_Z=
ERO
2.

            * gcc.dg/tree-ssa/pr97503.c: New test.=