public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/99405] Rotate with mask not optimized on x86 for QI/HImode rotates
Date: Fri, 05 Mar 2021 14:59:35 +0000	[thread overview]
Message-ID: <bug-99405-4-hOhiVslB9v@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-99405-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99405

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The valid C code if it is correct without UB and is pattern matched is
definitely better than some intrinsics, it is portable and can be optimized
generally sooner and better than the intrinsics.
Just be warned that there are many ways how to write not very good rotates,
e.g. (x << y) | (x >> (32 - y)) which has UB for y <= 0 or >= 32 etc.

  parent reply	other threads:[~2021-03-05 14:59 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-05 12:38 [Bug target/99405] New: " jakub at gcc dot gnu.org
2021-03-05 12:43 ` [Bug target/99405] " jakub at gcc dot gnu.org
2021-03-05 12:59 ` ubizjak at gmail dot com
2021-03-05 13:03 ` jakub at gcc dot gnu.org
2021-03-05 14:55 ` unlvsur at live dot com
2021-03-05 14:59 ` jakub at gcc dot gnu.org [this message]
2021-03-05 15:06 ` unlvsur at live dot com
2021-03-06 10:13 ` jakub at gcc dot gnu.org
2021-04-27  8:18 ` cvs-commit at gcc dot gnu.org
2022-05-27 18:43 ` roger at nextmovesoftware dot com

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=bug-99405-4-hOhiVslB9v@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@gcc.gnu.org \
    /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).