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 09:42:29 -0700 Organization: UCLA Computer Science Department Message-ID: <540744F5.2010804@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> 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 1409762594 30085 80.91.229.3 (3 Sep 2014 16:43:14 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 3 Sep 2014 16:43:14 +0000 (UTC) Cc: Emacs development discussions To: Dmitry Antipov Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Wed Sep 03 18:43:07 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 1XPDeF-0005cF-5c for ged-emacs-devel@m.gmane.org; Wed, 03 Sep 2014 18:43:07 +0200 Original-Received: from localhost ([::1]:46620 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPDeE-0007kb-NZ for ged-emacs-devel@m.gmane.org; Wed, 03 Sep 2014 12:43:06 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:49745) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPDdv-0007kL-7a for emacs-devel@gnu.org; Wed, 03 Sep 2014 12:42:54 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XPDdn-0005fj-Nj for emacs-devel@gnu.org; Wed, 03 Sep 2014 12:42:47 -0400 Original-Received: from smtp.cs.ucla.edu ([131.179.128.62]:45732) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XPDdn-0005fd-Hl for emacs-devel@gnu.org; Wed, 03 Sep 2014 12:42:39 -0400 Original-Received: from localhost (localhost.localdomain [127.0.0.1]) by smtp.cs.ucla.edu (Postfix) with ESMTP id 6613039E8016; Wed, 3 Sep 2014 09:42:38 -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 58sm7RxpzyKg; Wed, 3 Sep 2014 09:42:29 -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 B4024A60006; Wed, 3 Sep 2014 09:42:29 -0700 (PDT) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 In-Reply-To: <54073621.2040403@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:173988 Archived-At: Dmitry Antipov wrote: > 1) Function-scoped version using alloca (assuming statement expressions): > ... > 2) Block-scoped version using implicit stack allocation (assuming > statement expressions): > ... > 3) Block-scoped version assuming no statement expression but compound > literals: > ... > If we have 2), why we need 1) at all? 2) in a top-level function scope > is an equivalent to 1), isn't it? Correct. We'd need (1) e.g. to build up a list in a loop, and have the list survive until function exit. But on further thought this is probably a dangerous feature, since it'll be too tempting to write unbounded loops. So let's not do (1). > In 3), how we can be sure that Lisp_Cons is properly aligned on stack? For GCC, we can define struct Lisp_Cons via 'struct __attribute__ ((aligned (GCALIGNMENT))) Lisp_Cons { ... };'. For compilers that don't support this syntax we can align the struct by hand, by using a character-array compound literal that's a bit too large, aligning the resulting pointer by hand, and then using the aligned pointer.