From: Alexander Monakov <amonakov@ispras.ru>
To: musl@lists.openwall.com
Subject: Re: FE Exception triggered by comparison
Date: Wed, 27 Feb 2019 19:32:01 +0300 (MSK) [thread overview]
Message-ID: <alpine.LNX.2.20.13.1902271917310.30425@monopod.intra.ispras.ru> (raw)
In-Reply-To: <alpine.LRH.2.02.1902280305570.11194@key0.esi.com.au>
On Thu, 28 Feb 2019, Damian McGuckin wrote:
> > Hm, no, for x86 with GCC you should not see that: the compiler knows how to
> > expand isnan efficiently. Are you perhaps on OS X and the 'gcc' command
> > actually invokes Clang/LLVM?
>
> No.
>
> > If not, can you show output of 'gcc -v', command-line flags you used, and
> > the assembly you're seeing?
>
> gcc -O3 -S -msse4.2 -mfma mynan.c
Ah, in this case you're falling victim of a problem in your Glibc version:
while GCC is sufficiently new to know how to expand isnan efficiently,
Glibc math.h defines isnan as a macro that redirects to __isnan that GCC
does not recognize. Newer Glibc versions use __builtin_isnan where suitable,
which leads to optimal assembly.
(musl does not use this builtin, expanding the macro to a bit test instead)
Alexander
next prev parent reply other threads:[~2019-02-27 16:32 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-24 13:28 Damian McGuckin
2019-02-24 17:12 ` Markus Wichmann
2019-02-24 19:25 ` Szabolcs Nagy
2019-02-24 20:04 ` Jens Gustedt
2019-02-24 21:50 ` Damian McGuckin
2019-02-25 5:21 ` Damian McGuckin
2019-02-25 15:51 ` Markus Wichmann
2019-02-26 3:55 ` Damian McGuckin
2019-02-27 14:14 ` Alexander Monakov
2019-02-27 15:38 ` Damian McGuckin
2019-02-27 16:00 ` Alexander Monakov
2019-02-27 16:09 ` Damian McGuckin
2019-02-27 16:14 ` Markus Wichmann
2019-02-27 16:20 ` Damian McGuckin
2019-02-28 1:07 ` Damian McGuckin
2019-02-28 1:27 ` Rich Felker
2019-02-28 2:28 ` Damian McGuckin
2019-02-27 16:32 ` Alexander Monakov [this message]
2019-02-27 16:42 ` Rich Felker
2019-02-27 17:08 ` Szabolcs Nagy
2019-02-27 17:14 ` Alexander Monakov
2019-02-27 17:26 ` Rich Felker
2019-02-27 19:36 ` Szabolcs Nagy
2019-02-27 19:48 ` Alexander Monakov
2019-02-27 20:16 ` Szabolcs Nagy
2019-02-27 20:35 ` Rich Felker
2019-02-27 21:03 ` Szabolcs Nagy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.LNX.2.20.13.1902271917310.30425@monopod.intra.ispras.ru \
--to=amonakov@ispras.ru \
--cc=musl@lists.openwall.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).