From: "Stubbs, Andrew" <Andrew_Stubbs@mentor.com>
To: Richard Biener <rguenther@suse.de>,
"Burnus, Tobias" <Tobias_Burnus@mentor.com>
Cc: "Yeung, Kwok" <Kwok_Yeung@mentor.com>,
gcc-patches <gcc-patches@gcc.gnu.org>
Subject: RE: [PATCH] amdgcn: Add support for additional natively supported floating-point operations
Date: Fri, 9 Sep 2022 12:32:36 +0000 [thread overview]
Message-ID: <7a443bc59666477b8b57986cb8a3adf9@mentor.com> (raw)
In-Reply-To: <nycvar.YFH.7.77.849.2209091011440.20505@jbgna.fhfr.qr>
> -----Original Message-----
> I agree - for example powerpc has -mrecip= to control which instructions
> to use (float/double rsqrt or inverse) and -mrecip-precision to
> specify whether further iteration is done or not.
>
> x86 has similar but does always perform newton raphson iteration,
> documenting 2 ulp instead of 0.5 ulp precision.
>
> Your suggested huge reduction in precision isn't usually acceptable
> and should be always explicitely enabled.
There isn't a problem with *this* patch (although we do have existing accuracy issues thanks to previous documents lacking the information).
The "inaccurate" instructions are single-precision only, and therefore acceptable with -ffast-math.
Kwok intends to provide vectorized library calls for the double-precision and -fno-fast-math cases.
In general I want to avoid adding extra arch-specific options; partly because approximately no one will use them, and partly because the amdgcn compiler is almost always hidden behind an x86_64 compiler.
Andrew
next prev parent reply other threads:[~2022-09-09 12:32 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-08 20:38 Kwok Cheung Yeung
2022-09-09 8:10 ` Andrew Stubbs
2022-09-09 9:15 ` Tobias Burnus
2022-09-09 10:16 ` Richard Biener
2022-09-09 12:20 ` GCN: Add -mlow-precision-sqrt for double-precision sqrt [PR105246] (was: Re: [PATCH] amdgcn: Add support for additional natively supported floating-point operations) Tobias Burnus
2022-09-09 12:40 ` Andrew Stubbs
2022-09-09 12:32 ` Stubbs, Andrew [this message]
2022-09-09 17:57 ` [PATCH] amdgcn: Add support for additional natively supported floating-point operations 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=7a443bc59666477b8b57986cb8a3adf9@mentor.com \
--to=andrew_stubbs@mentor.com \
--cc=Kwok_Yeung@mentor.com \
--cc=Tobias_Burnus@mentor.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=rguenther@suse.de \
/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).