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: Mon, 15 Apr 2019 20:42:56 -0700 Organization: UCLA Computer Science Department Message-ID: <4fa7885e-8c66-c7c4-ff71-a013505863af@cs.ucla.edu> References: <87a7gst973.fsf@gmail.com> <875zrgt12q.fsf@gmail.com> <6919a4c8-df76-ea1e-34db-1fa62a360e5a@cs.ucla.edu> <87h8aykdod.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="38835"; 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: Alex Gramiak Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Apr 16 05:43:11 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 1hGF02-0009x4-SZ for ged-emacs-devel@m.gmane.org; Tue, 16 Apr 2019 05:43:11 +0200 Original-Received: from localhost ([127.0.0.1]:58782 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hGF01-0001RS-8R for ged-emacs-devel@m.gmane.org; Mon, 15 Apr 2019 23:43:09 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:60002) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hGEzv-0001RM-IH for emacs-devel@gnu.org; Mon, 15 Apr 2019 23:43:04 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hGEzu-00069s-Jw for emacs-devel@gnu.org; Mon, 15 Apr 2019 23:43:03 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:36482) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hGEzu-000694-Bm for emacs-devel@gnu.org; Mon, 15 Apr 2019 23:43:02 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 5ACF0161648; Mon, 15 Apr 2019 20:43:00 -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 c36Ej1s-VaG9; Mon, 15 Apr 2019 20:42:59 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 9CA4E16175A; Mon, 15 Apr 2019 20:42:59 -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 uMFZt6EDqYOZ; Mon, 15 Apr 2019 20:42:59 -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 705C8161758; Mon, 15 Apr 2019 20:42:59 -0700 (PDT) In-Reply-To: <87h8aykdod.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:235505 Archived-At: Alex Gramiak wrote: >> These macro calls would not help near calls to emacs_abort, as it should already >> be obvious to a careful human reader that the jump to emacs_abort is the road >> less traveled. (That's also obvious to GCC, since emacs_abort is _Noreturn.) > To human readers, yes, but from what I can tell, GCC is mixed on this. Then we should fix GCC, if the code it generates has a performance problem (whatever it is, it's quite small). That'd be better than littering the Emacs source code with __builtin_expect or UNLIKELY calls. The GCC manual recommends against manually inserting such calls; performance nerds are supposed to use -fprofile-arcs instead. In my experience the calls are typically more trouble than they're worth.