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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 tree-optimization/110755] [13 Regression] Wrong optimization of
 fabs on ppc64el at -O1
Date: Thu, 27 Jul 2023 17:53:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110755

--- Comment #14 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:e684084a5fa9edaedb1a14e118b966a60e3449b9

commit r13-7615-ge684084a5fa9edaedb1a14e118b966a60e3449b9
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Jul 26 10:50:50 2023 +0200

    range-op-float: Fix up -frounding-math frange_arithmetic +- handling
[PR110755]

    IEEE754 says that x + (-x) and x - x result in +0 in all rounding modes
    but rounding towards negative infinity, in which case the result is -0
    for all finite x.  x + x and x - (-x) if it is zero retain sign of x.
    Now, range_arithmetic implements the normal rounds to even rounding,
    and as the addition or subtraction in those cases is exact, we don't do=
 any
    further rounding etc. and e.g. on the testcase below distilled from gli=
bc
    compute a range [+0, +INF], which is fine for -fno-rounding-math or
    if we'd have a guarantee that those statements aren't executed with
rounding
    towards negative infinity.

    I believe it is only +- which has this problematic behavior and I think
    it is best to deal with it in frange_arithmetic; if we know -frounding-=
math
    is on, it is x + (-x) or x - x and we are asked to round to negative
    infinity (i.e. want low bound rather than high bound), change +0 result=
 to
    -0.

    2023-07-26  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/110755
            * range-op-float.cc (frange_arithmetic): Change +0 result to -0
            for PLUS_EXPR or MINUS_EXPR if -frounding-math, inf is negative=
 and
            it is exact op1 + (-op1) or op1 - op1.

            * gcc.dg/pr110755.c: New test.

    (cherry picked from commit 21da32d995c8b574c929ec420cd3b0fcfe6fa4fe)=