From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: HAVE_FAST_UNALIGNED_ACCESS Date: Sat, 01 Apr 2023 16:33:15 +0300 Message-ID: <83zg7rybfo.fsf@gnu.org> References: <87sfdmlgzx.fsf@gmail.com> <94d3de92c50a96d9172f88462bf3bc9c2792600c.camel@gmail.com> <83mt3s244o.fsf@gnu.org> <875yagtopn.fsf@yahoo.com> <838rfc17ja.fsf@gnu.org> <871ql4t8ph.fsf@yahoo.com> <83wn2wyuli.fsf@gnu.org> <63A29442-4C0C-4C3C-B40E-4A3DB91E3009@gmail.com> <83lejcypyw.fsf@gnu.org> <87wn2wrmgc.fsf@yahoo.com> <83bkk7zvxl.fsf@gnu.org> <87lejbpxkm.fsf@aarsen.me> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="34823"; mail-complaints-to="usenet@ciao.gmane.io" Cc: luangruo@yahoo.com, mattias.engdegard@gmail.com, vibhavp@gmail.com, rpluim@gmail.com, emacs-devel@gnu.org To: Arsen =?utf-8?Q?Arsenovi=C4=87?= Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sat Apr 01 15:33:47 2023 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1pibMY-0008pc-Ti for ged-emacs-devel@m.gmane-mx.org; Sat, 01 Apr 2023 15:33:46 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pibLp-00077w-EL; Sat, 01 Apr 2023 09:33:01 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pibLo-00077e-Am for emacs-devel@gnu.org; Sat, 01 Apr 2023 09:33:00 -0400 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pibLn-0002lK-Uc; Sat, 01 Apr 2023 09:32:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=gnu.org; s=fencepost-gnu-org; h=MIME-version:References:Subject:In-Reply-To:To:From: Date; bh=e/JZ3oPB8pLcYPcC+2SkMJVIrxZaqiSYf47jE18pO04=; b=bdO1ZkaNnyxZiVlzKJTf LIhJhg3hblsEDUmRg947q3j1FhI/RXzE6NHhMGf5002Kp7GEZk5bfR5w3Fqt89co5yNCAxjBFdBKu LaGc/R2nxB8Elu5ZZDCnVLMJRqKTBhnkGX0ofa233fWFRaqPcVyDuA0gMrWUr2p/rn+/ZJGOPqzt+ R9Tr7SQiBbqfjHlxytYz7aAxlQ04jpqY1bJCA56bFTSwh5Ua1IVw077ponK+8r1/Ncmv3YkoBK+xS O7/M4ZEw3p6XH+8tNjm+D8P3K679VgYHGjPUd2NB62e01L6Pjb6GUNeFyK2xdumGGz9J1bgooz7qF Vw6adq8eZzbKKQ==; Original-Received: from [87.69.77.57] (helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pibLn-00025Z-BY; Sat, 01 Apr 2023 09:32:59 -0400 In-Reply-To: <87lejbpxkm.fsf@aarsen.me> (message from Arsen =?utf-8?Q?Arse?= =?utf-8?Q?novi=C4=87?= on Sat, 01 Apr 2023 14:59:53 +0200) X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:305005 Archived-At: > From: Arsen Arsenović > Cc: Po Lu , mattias.engdegard@gmail.com, > vibhavp@gmail.com, rpluim@gmail.com, emacs-devel@gnu.org > Date: Sat, 01 Apr 2023 14:59:53 +0200 > > Eli Zaretskii writes: > > > I'm still unconvinced, and I said already what will have a chance of > > convincing me: a specific report about a problem this particular code > > causes on a specific existing platform we support in Emacs 29 and with > > a specific compiler. > > Similar (but not exactly the same) loops as this one have been shown to > generate incorrect code in this thread. It's not a large leap for it to > happen to this one, introducing subtle errors for a bit of code that is > completely unnecessary (as demonstrated by it being optional), > especially at higher optimization levels, where the compiler could > easily produce better code than the assumption of a 'mov' would. > > Is the following trivial enough for 29? You are again trying to push for a change without showing any actual bug with the existing code. Please humor me, and please show me an actual bug due to the existing code before suggesting a solution. See above for the description of the details I'd like to know about such actual bug. > .. or something similar to it, assuming I made an error, which is likely > given the circumstances. This does pass the testsuite, anyway. It > should just expand deferences into explicit memcpys. > > No actual memcpy calls are produced, and this is at least functional on > a superset of compilers, and I suspect replacing the whole thing with a > naive-looking while (*(w1++) != *(w2++)); loop would be even better (but > I can settle for that being too experimental). Sorry, I don't want to risk any errors, and I would like to avoid any experiments with the release branch. Which is why I'm asking for hard evidence. It isn't that I don't understand what you and others are saying, or don't believe you. It's just that we need to see the problems before we can judge the solutions that must be safe on this branch.