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From: Rich Felker <dalias@libc.org>
To: Ariadne Conill <ariadne@dereferenced.org>
Cc: musl@lists.openwall.com, Szabolcs Nagy <nsz@port70.net>
Subject: Re: [musl] [PATCH #2] Properly simplified nextafter()
Date: Sun, 15 Aug 2021 09:59:07 -0400	[thread overview]
Message-ID: <20210815135906.GF13220@brightrain.aerifal.cx> (raw)
In-Reply-To: <4272846f-eb89-2856-af9-38571037a924@dereferenced.org>

On Sun, Aug 15, 2021 at 02:46:58AM -0500, Ariadne Conill wrote:
> On Sun, 15 Aug 2021, Stefan Kanthak wrote:
> >[stefan@rome ~]$ gcc --version
> >gcc (GCC) 8.3.1 20190311 (Red Hat 8.3.1-3)
> >Copyright (C) 2018 Free Software Foundation, Inc.
> >This is free software; see the source for copying conditions.  There is NO
> >warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
> 
> gcc 8 is quite old at this point.  gcc 9 and 10 have much better
> optimizers that are much more capable.
> 
> Indeed, on my system with GCC 10.3.1, nextafter() is using SSE2
> instructions on Alpine x86_64, and if I rebuild musl with
> `-march=znver2` it uses AVX instructions for nextafter(), which
> seems more than sufficiently optimized to me.

As far as I can tell, the instructions used are not the issue here,
and there are no specialized instructions that help make it faster. If
GCC is doing a bad job, it's more a matter of the high level flow,
choice of how to load constants, how branches are implemented, etc.

Rich

  reply	other threads:[~2021-08-15 13:59 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-10  6:23 [musl] [PATCH] " Stefan Kanthak
2021-08-10 21:34 ` Szabolcs Nagy
2021-08-10 22:53   ` Stefan Kanthak
2021-08-11  2:40     ` Rich Felker
2021-08-11 15:44       ` Stefan Kanthak
2021-08-11 16:09         ` Rich Felker
2021-08-11 16:50           ` Stefan Kanthak
2021-08-11 17:57             ` Rich Felker
2021-08-11 22:16               ` Szabolcs Nagy
2021-08-11 22:43                 ` Stefan Kanthak
2021-08-12  0:59                   ` Rich Felker
2021-08-11  8:23     ` Szabolcs Nagy
2021-08-13 12:04   ` [musl] [PATCH #2] " Stefan Kanthak
2021-08-13 15:59     ` Rich Felker
2021-08-13 18:30       ` Stefan Kanthak
2021-08-14  4:07         ` Damian McGuckin
2021-08-14 22:45           ` Szabolcs Nagy
2021-08-14 23:46     ` Szabolcs Nagy
2021-08-15  7:04       ` Stefan Kanthak
2021-08-15  7:46         ` Ariadne Conill
2021-08-15 13:59           ` Rich Felker [this message]
2021-08-15 14:57             ` Ariadne Conill
2021-08-15  8:24         ` Damian McGuckin
2021-08-15 14:03           ` Rich Felker
2021-08-15 15:10             ` Damian McGuckin
2021-08-15 14:56         ` Szabolcs Nagy
2021-08-15 15:19           ` Stefan Kanthak
2021-08-15 15:48             ` Rich Felker
2021-08-15 16:29               ` Stefan Kanthak
2021-08-15 16:49                 ` Rich Felker
2021-08-15 20:52                   ` Stefan Kanthak
2021-08-15 21:48                     ` Rich Felker
2021-08-15 15:52             ` Ariadne Conill
2021-08-15 16:09               ` Rich Felker

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