From: Richard Biener <rguenther@suse.de>
To: Jakub Jelinek <jakub@redhat.com>
Cc: "Joseph S. Myers" <joseph@codesourcery.com>,
Jason Merrill <jason@redhat.com>,
gcc-patches@gcc.gnu.org, roger@nextmovesoftware.com
Subject: Re: [PATCH] fold-const: Don't consider NaN non-negative [PR97965]
Date: Thu, 26 Nov 2020 10:03:50 +0000 (UTC) [thread overview]
Message-ID: <nycvar.YFH.7.77.849.2011261003140.7048@jbgna.fhfr.qr> (raw)
In-Reply-To: <20201126094903.GV3788@tucnak>
On Thu, 26 Nov 2020, Jakub Jelinek wrote:
> On Thu, Nov 26, 2020 at 09:16:29AM +0000, Richard Biener wrote:
> > > So, I really don't know if we want this or not, posting it for discussions.
> >
> > Is copysign (x, NaN) supposed to be well-defined? We'd stop folding
> > this then, no?
>
> Yes, we'd stop folding several cases with NaNs.
>
> > I think the ABS_EXPR<x> < 0 to false folding is
> > simply incomplete and should first check whether the operands are
> > ordered? That said, NaN is nonnegative but NaN < 0 isn't false(?)
> >
> > So I don't think the patch is good.
>
> Another possibility (if we have this optimization already in match.pd too)
> would be to only optimize the < 0 case in GENERIC if !HONOR_NANS like
> the >= 0 case is and only optimize it in GIMPLE. Though with the
> default -ftrapping-math I think even optimizing qNaN < 0 to 0 is incorrect,
> even that should raise invalid exception, shouldn't it?
> So perhaps add a defaulted argument to the *nonnegative* APIs that would
> say whether unordered is ok or not?
Roger recently added some exhaustive changes in related areas, so let's
see if he has anything to say here.
Richard.
next prev parent reply other threads:[~2020-11-26 10:03 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-26 8:31 Jakub Jelinek
2020-11-26 9:16 ` Richard Biener
2020-11-26 9:49 ` Jakub Jelinek
2020-11-26 10:03 ` Richard Biener [this message]
2020-11-26 13:56 ` Roger Sayle
2020-11-26 14:13 ` Jakub Jelinek
2020-11-26 14:20 ` Jakub Jelinek
2020-11-26 22:43 ` Jakub Jelinek
2020-11-27 10:51 ` Roger Sayle
2020-11-27 10:56 ` Roger Sayle
2020-11-27 20:39 ` Joseph Myers
2020-11-27 20:31 ` Joseph Myers
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=nycvar.YFH.7.77.849.2011261003140.7048@jbgna.fhfr.qr \
--to=rguenther@suse.de \
--cc=gcc-patches@gcc.gnu.org \
--cc=jakub@redhat.com \
--cc=jason@redhat.com \
--cc=joseph@codesourcery.com \
--cc=roger@nextmovesoftware.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.
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 read-only IMAP folder(s) and NNTP newsgroup(s).