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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/103008] poor inlined builtin_fmod on x86_64
Date: Mon, 14 Feb 2022 07:35:35 +0000	[thread overview]
Message-ID: <bug-103008-4-aZvO8StI6K@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-103008-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103008

--- Comment #17 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Uroš Bizjak from comment #14)
> Created attachment 52428 [details]
> Proposed patch
> 
> The attached patch implements:
> 
> fmod (a, p) = a - trunc (a/p) * p
> drem (a, p) = 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.fc34
> 
> -Ofast:
>        6,150082000 seconds user
> 
> -Ofast -mno-80387:
>       18,354654000 seconds user
> 
> -Ofast -msse4:
>        5,722511000 seconds user

I fear this is a bit too much on the "unsafe" side.  Maybe we can
go this way for float but use double arithmetic for the fmod to avoid
the exponent issue?  For double, can we do some cheap range checking
and fall back to fmod() when not safe?

That said, can we have a flag like -mrecip to control this?

      parent reply	other threads:[~2022-02-14  7:35 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-30 18:51 [Bug target/103008] New: " fx at gnu dot org
2021-10-30 18:52 ` [Bug target/103008] " fx at gnu dot org
2021-10-30 18:55 ` fx at gnu dot org
2021-10-30 18:56 ` fx at gnu dot org
2021-10-30 20:15 ` fx at gnu dot org
2021-10-30 20:39 ` anlauf at gcc dot gnu.org
2021-10-31 20:05 ` ubizjak at gmail dot com
2021-11-01  8:23 ` ubizjak at gmail dot com
2022-02-10 14:18 ` rguenth at gcc dot gnu.org
2022-02-10 14:22 ` rguenth at gcc dot gnu.org
2022-02-10 18:09 ` ubizjak at gmail dot com
2022-02-10 20:50 ` joseph at codesourcery dot com
2022-02-11  7:59 ` rguenth at gcc dot gnu.org
2022-02-11 15:47 ` ubizjak at gmail dot com
2022-02-12 22:07 ` ubizjak at gmail dot com
2022-02-13 21:00 ` Dave.Love at manchester dot ac.uk
2022-02-14  7:12 ` rguenther at suse dot de
2022-02-14  7:35 ` rguenth at gcc dot gnu.org [this message]

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