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[PATCH, i386]: Fix PR80723, ignore cost of adding/subtracting a carry flag for ADC/SBB insns

From: Uros Bizjak <ubizjak at gmail dot com>
To: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
Date: Fri, 12 May 2017 20:56:40 +0200
Subject: [PATCH, i386]: Fix PR80723, ignore cost of adding/subtracting a carry flag for ADC/SBB insns
Authentication-results: sourceware.org; auth=none

Hello!

Attached patch adjusts RTX costs to ignore addition or subtraction of
a carry flag for ADC or SBB instruction. These operations are
essentially free.

2017-05-12  Uros Bizjak  <ubizjak@gmail.com>

    PR target/80723
    * config/i386/i386.c (ix86_rtx_cost) [case PLUS]: Ignore the
    cost of adding a carry flag for ADC instruction.
    [case MINUS]: Ignore the cost of subtracting a carry flag
    for SBB instruction.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}, where
the patch fixes gcc.target/i386/cadd.c FAIL.

Committed to mainline SVN.

Uros.

Attachment: p.diff.txt
Description: Text document

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