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From: "Dave.Love at manchester dot ac.uk" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/103008] poor inlined builtin_fmod on x86_64
Date: Sun, 13 Feb 2022 21:00:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103008

--- Comment #15 from Dave.Love at manchester dot ac.uk ---
"ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org> writes:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103008
>
> --- Comment #14 from Uro=C5=A1 Bizjak <ubizjak at gmail dot com> ---
> Created attachment 52428
>   --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52428&action=3Dedit
> Proposed patch
>
> The attached patch implements:
>
> fmod (a, p) =3D a - trunc (a/p) * p
> drem (a, p) =3D a - roundeven (a/p) * p
>
> using SSE4 round instruction (and uses fnma when available).
>
> Timings with Polyhedron ac.f90 on IvyBridge-E, Fedora-34, glibc 2.33-21.f=
c34
>
> -Ofast:
>        6,150082000 seconds user
>
> -Ofast -mno-80387:
>       18,354654000 seconds user
>
> -Ofast -msse4:
>        5,722511000 seconds user

I realize I never made a Fortran bug report about this, and should do.
(I think the gfortran intrinsic should avoid fmod anyway, and just use
the standard's arithmetical definition of MOD without having to bother
about errors.)=