From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: Using __builtin_expect (likely/unlikely macros) Date: Sat, 20 Apr 2019 08:57:57 -0700 Organization: UCLA Computer Science Department Message-ID: <9461246c-409b-15fd-943b-3d673c679870@cs.ucla.edu> References: <87a7gst973.fsf@gmail.com> <875zrgt12q.fsf@gmail.com> <6919a4c8-df76-ea1e-34db-1fa62a360e5a@cs.ucla.edu> <87h8aykdod.fsf@gmail.com> <4fa7885e-8c66-c7c4-ff71-a013505863af@cs.ucla.edu> <2dfb837d-989d-c736-b6e6-b20c0e940596@cs.ucla.edu> <87o956c4n4.fsf@gmail.com> <1fbd2fca-18f0-0a90-7a45-58419a9e11ee@cs.ucla.edu> <1555450070.23658.4@yandex.ru> <66b74701-012a-902e-4a5b-6bc30efa87c0@cs.ucla.edu> <87tveu85xt.fsf@gmail.com> <86ef5wd7az.fsf@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="51257"; mail-complaints-to="usenet@blaine.gmane.org" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 Cc: emacs-devel@gnu.org To: Andy Moreton Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Sat Apr 20 17:58:13 2019 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:256) (Exim 4.89) (envelope-from ) id 1hHsNY-000DEM-Qr for ged-emacs-devel@m.gmane.org; Sat, 20 Apr 2019 17:58:13 +0200 Original-Received: from localhost ([127.0.0.1]:42725 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hHsNX-0005H2-PC for ged-emacs-devel@m.gmane.org; Sat, 20 Apr 2019 11:58:11 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:54467) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hHsNP-0005Fp-1t for emacs-devel@gnu.org; Sat, 20 Apr 2019 11:58:04 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hHsNO-0007Fg-0q for emacs-devel@gnu.org; Sat, 20 Apr 2019 11:58:03 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:48610) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hHsNN-0007Et-RU for emacs-devel@gnu.org; Sat, 20 Apr 2019 11:58:01 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 3CA5D1616EA; Sat, 20 Apr 2019 08:58:00 -0700 (PDT) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id Fj89okQjn214; Sat, 20 Apr 2019 08:57:58 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id BB53316172F; Sat, 20 Apr 2019 08:57:58 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id nQY32cW2KOYW; Sat, 20 Apr 2019 08:57:58 -0700 (PDT) Original-Received: from [192.168.1.9] (cpe-23-242-74-103.socal.res.rr.com [23.242.74.103]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 790681616EA; Sat, 20 Apr 2019 08:57:58 -0700 (PDT) In-Reply-To: <86ef5wd7az.fsf@gmail.com> Content-Language: en-US X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 131.179.128.68 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 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.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:235695 Archived-At: Andy Moreton wrote: > If the patches from this discussion on marking code as cold or > liely/unlikely does not result in improved code generation and > measureable performance gains, then they should be dropped as needless > clutter in the source code. As I mentioned in the 'cold' changes that I installed into master improved overall performance on a largish practical benchmark (cd lisp && make compile-always) by 1.3% on my platform: Fedora 29, GCC 8.3.1 20190223 (Red Hat 8.3.1-2), AMD Phenom II X4 910e. The other changes proposed in this thread seem to not help performance (or even hurt it) and we have not installed them. I like to see significant benefits for performance-related changes where the effects are not obvious. For improvements where the generated code is "obviously" faster (fewer and simpler instructions, say), I typically don't bother with measurements as my own time is limited too.