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Subject: [Bug target/101044] -ABS(A) produces two neg instructions
Date: Thu, 01 Jul 2021 09:21:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101044

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Uros Bizjak <uros@gcc.gnu.org>:

https://gcc.gnu.org/g:9f6aeb85ee87c6b4e580b6b71e26cbe99e1dab70

commit r12-1950-g9f6aeb85ee87c6b4e580b6b71e26cbe99e1dab70
Author: Uros Bizjak <ubizjak@gmail.com>
Date:   Thu Jul 1 10:56:32 2021 +0200

    i386: Add integer nabs instructions [PR101044]

    The patch adds integer nabs "(NEG (ABS (...)))" instructions, adds STV
    conversion and adjusts STV cost calculations accordingly.  When CMOV
    instruction is used to implement abs, the sign is determined from the
    preceeding operand negation, and CMOVS is used to select between
    negated and non-negated value.

    To implement nabs, just reverse the condition and emit CMOVNS instead.

    The STV costs are adjusted for inherent NOT of nabs insn. V2DI NOT is
    somehow costly operation, since it is implemented as a load of zero,
    followed by a SUB insn. OTOH, integer nabs with inherent NOT is relativ=
ely
    cheap, so some STV chains became less profitable for conversion.

    The patch rewrites operand scanner in compute_convert_gain to a switch
    and reorders case instances in general_scalar_to_vector_candidate_p
    to benefit from fallthroughs, and to remove special processing of
    andnot in the later case.

    gcc/

    2021-07-01  Uro=C3=85=C2=A1 Bizjak  <ubizjak@gmail.com>

            PR target/101044
            * config/i386/i386.md (*nabs<dwi>2_doubleword):
            New insn_and_split pattern.
            (*nabs<dwi>2_1): Ditto.
            * config/i386/i386-features.c
            (general_scalar_chain::compute_convert_gain):
            Handle (NEG (ABS (...))) RTX.  Rewrite src code
            scanner as switch statement.
            (general_scalar_chain::convert_insn):
            Handle (NEG (ABS (...))) RTX.
            (general_scalar_to_vector_candidate_p):
            Detect  (NEG (ABS (...))) RTX.  Reorder case statements
            for (AND (NOT (...) ...)) fallthrough.

    gcc/testsuite/

    2021-07-01  Uro=C3=85=C2=A1 Bizjak  <ubizjak@gmail.com>

            PR target/101044
            * gcc.target/i386/pr101044.c: New test.=