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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/96793] __builtin_floor produces wrong result when
 rounding direction is FE_DOWNWARD
Date: Wed, 23 Dec 2020 08:20:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96793

--- Comment #21 from Uro=C5=A1 Bizjak <ubizjak at gmail dot com> ---


https://gcc.gnu.org/g:c40b640ebcef1aae78eaca56e04d204dda9e4cad

commit r9-9126-gc40b640ebcef1aae78eaca56e04d204dda9e4cad
Author: Uros Bizjak <ubizjak@gmail.com>
Date:   Wed Dec 23 09:09:29 2020 +0100

    i386: Fix __builtin_floor with FE_DOWNWARD rounding direction [PR96793]

    x86_expand_floorceil expander uses x86_sse_copysign_to_positive, which
    is unable to change the sign from - to +.  When FE_DOWNWARD rounding
    direction is in effect, the expanded sequence that involves subtraction
    can trigger x - x =3D -0.0 special rule.  x86_sse_copysign_to_positive
    fails to change the sign of the intermediate value, assumed to always
    be positive, back to positive.

    The patch adds one extra fabs that strips the sign from the intermediate
    value when flag_rounding_math is in effect.

    2020-12-22  Uro=C5=A1 Bizjak  <ubizjak@gmail.com>

    gcc/
            PR target/96793
            * config/i386/i386.c (ix86_expand_floorceil):
            Remove the sign of the intermediate value for flag_rounding_mat=
h.
            (ix86_expand_floorceildf_32): Ditto.

    gcc/testsuite/
            PR target/96793
            * gcc.target/i386/pr96793.c: New test.=