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
next prev parent 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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