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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/110625] [14 Regression][AArch64] Vect: SLP fails to
 vectorize a loop as the reduction_latency calculated by new costs is too
 large
Date: Fri, 29 Dec 2023 15:59:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110625

--- Comment #24 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tamar Christina <tnfchris@gcc.gnu.org=
>:

https://gcc.gnu.org/g:984bdeaa39b6417b11736b2c167ef82119e272dc

commit r14-6865-g984bdeaa39b6417b11736b2c167ef82119e272dc
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Fri Dec 29 15:58:29 2023 +0000

    AArch64: Update costing for vector conversions [PR110625]

    In gimple the operation

    short _8;
    double _9;
    _9 =3D (double) _8;

    denotes two operations on AArch64.  First we have to widen from short to
    long and then convert this integer to a double.

    Currently however we only count the widen/truncate operations:

    (double) _5 6 times vec_promote_demote costs 12 in body
    (double) _5 12 times vec_promote_demote costs 24 in body

    but not the actual conversion operation, which needs an additional 12
    instructions in the attached testcase.   Without this the attached test=
case
ends
    up incorrectly thinking that it's beneficial to vectorize the loop at a
very
    high VF =3D 8 (4x unrolled).

    Because we can't change the mid-end to account for this the costing cod=
e in
the
    backend now keeps track of whether the previous operation was a
    promotion/demotion and ajdusts the expected number of instructions to:

    1. If it's the first FLOAT_EXPR and the precision of the lhs and rhs are
       different, double it, since we need to convert and promote.
    2. If it's the previous operation was a demonition/promotion then reduce
the
       cost of the current operation by the amount we added extra in the la=
st.

    with the patch we get:

    (double) _5 6 times vec_promote_demote costs 24 in body
    (double) _5 12 times vec_promote_demote costs 36 in body

    which correctly accounts for 30 operations.

    This fixes the 16% regression in imagick in SPECCPU 2017 reported on
Neoverse N2
    and using the new generic Armv9-a cost model.

    gcc/ChangeLog:

            PR target/110625
            * config/aarch64/aarch64.cc (aarch64_vector_costs::add_stmt_cos=
t):
            Adjust throughput and latency calculations for vector conversio=
ns.
            (class aarch64_vector_costs): Add m_num_last_promote_demote.

    gcc/testsuite/ChangeLog:

            PR target/110625
            * gcc.target/aarch64/pr110625_4.c: New test.
            * gcc.target/aarch64/sve/unpack_fcvt_signed_1.c: Add
            --param aarch64-sve-compare-costs=3D0.
            * gcc.target/aarch64/sve/unpack_fcvt_unsigned_1.c: Likewise=