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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/113295] [14 Regression] SPEC 2006 416.gamess miscompares
 on Aarch64 when built with -Ofast -mcpu=native since
 g:2f46e3578d45ff060a0a329cb39d4f52878f9d5a
Date: Fri, 23 Feb 2024 14:13:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113295

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.or=
g>:

https://gcc.gnu.org/g:8a16e06da97f51574cfad17e2cece2e58571305d

commit r14-9155-g8a16e06da97f51574cfad17e2cece2e58571305d
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Fri Feb 23 14:12:54 2024 +0000

    aarch64: Add missing early-ra bookkeeping [PR113295]

    416.gamess showed up two wrong-code bugs in early-ra.  This patch
    fixes the first of them.  It was difficult to reduce the source code
    to something that would meaningfully show the situation, so the
    testcase uses a direct RTL sequence instead.

    In the sequence:

    (a) register <2> is set more than once
    (b) register <2> is copied to a temporary (<4>)
    (c) register <2> is the destination of an FCSEL between <4> and
        another value (<5>)
    (d) <4> and <2> are equivalent for <4>'s live range
    (e) <5>'s and <2>'s live ranges do not intersect, and there is
        a pseudo-copy between <5> and <2>

    On its own, (d) implies that <4> can be treated as equivalent to <2>.
    And on its own, (e) implies that <5> can share <2>'s register.  But
    <4>'s and <5>'s live ranges conflict, meaning that they cannot both
    share the register together.  A bit of missing bookkeeping meant that
    the mechanism for detecting this didn't fire.  We therefore ended up
    with an FCSEL in which both inputs were the same register.

    gcc/
            PR target/113295
            * config/aarch64/aarch64-early-ra.cc
            (early_ra::find_related_start): Account for definitions by shar=
ed
            registers when testing for a single register definition.
            (early_ra::accumulate_defs): New function.
            (early_ra::record_copy): If A shares B's register, fold A's
            definition information into B's.  Fold A's use information into
B's.

    gcc/testsuite/
            PR target/113295
            * gcc.dg/rtl/aarch64/pr113295-1.c: New test.=