From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings] Date: Wed, 03 Sep 2014 22:13:10 -0700 Organization: UCLA Computer Science Department Message-ID: <5407F4E6.2040809@cs.ucla.edu> References: <5405BE5D.1090003@yandex.ru> <5405DE8B.4050201@yandex.ru> <5406EC21.4060200@yandex.ru> <5407281C.3090302@cs.ucla.edu> <54073621.2040403@yandex.ru> <540744F5.2010804@cs.ucla.edu> <5407F1B7.6090704@yandex.ru> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1409828607 18770 80.91.229.3 (4 Sep 2014 11:03:27 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 4 Sep 2014 11:03:27 +0000 (UTC) Cc: Emacs development discussions To: Dmitry Antipov Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Thu Sep 04 07:13:49 2014 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XPPMj-0001nH-72 for ged-emacs-devel@m.gmane.org; Thu, 04 Sep 2014 07:13:49 +0200 Original-Received: from localhost ([::1]:48797 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPPMi-0003le-PP for ged-emacs-devel@m.gmane.org; Thu, 04 Sep 2014 01:13:48 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:37439) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPPMP-0003kw-PT for emacs-devel@gnu.org; Thu, 04 Sep 2014 01:13:37 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XPPMH-0001Qd-0E for emacs-devel@gnu.org; Thu, 04 Sep 2014 01:13:29 -0400 Original-Received: from smtp.cs.ucla.edu ([131.179.128.62]:49401) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPPMG-0001Ph-RY for emacs-devel@gnu.org; Thu, 04 Sep 2014 01:13:20 -0400 Original-Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp.cs.ucla.edu (Postfix) with ESMTP id C869939E8014; Wed, 3 Sep 2014 22:13:19 -0700 (PDT) X-Virus-Scanned: amavisd-new at smtp.cs.ucla.edu Original-Received: from smtp.cs.ucla.edu ([127.0.0.1]) by localhost (smtp.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id sQySanmTC9dW; Wed, 3 Sep 2014 22:13:11 -0700 (PDT) Original-Received: from [192.168.1.9] (pool-71-177-17-123.lsanca.dsl-w.verizon.net [71.177.17.123]) by smtp.cs.ucla.edu (Postfix) with ESMTPSA id 2110839E8012; Wed, 3 Sep 2014 22:13:11 -0700 (PDT) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 In-Reply-To: <5407F1B7.6090704@yandex.ru> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-Received-From: 131.179.128.62 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 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-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:174001 Dmitry Antipov wrote: > I don't see how to fold this snippet into a macro which can be used as > an rvalue, just like: How about something like this? The cool thing here is that GCC optimizes 'foo' away to a function that simply returns 0. typedef unsigned long uintptr_t; typedef uintptr_t Lisp_Object; struct __attribute__ ((aligned (8))) Lisp_Cons { Lisp_Object car; Lisp_Object cdr; }; #define BCONS(a, b) ((Lisp_Object) &(struct Lisp_Cons) { a, b } + 3) #define UNTAG(x) ((struct Lisp_Cons *) (uintptr_t) ((x) - 3)) int foo (void) { Lisp_Object a = BCONS (0, 0); Lisp_Object b = BCONS (0, a); return UNTAG (UNTAG (b) -> cdr) -> car; }