From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: Floating-point constant folding in Emacs byte compiler Date: Mon, 02 Apr 2018 14:22:27 +0300 Message-ID: <83370d7szw.fsf@gnu.org> References: <2ce39e5c-cd1b-65d6-b125-719caad67932@cs.ucla.edu> <83vadmgfbz.fsf@gnu.org> <87d0zr2n1u.fsf@gmail.com> <83h8p2g99p.fsf@gnu.org> <87370m3k4y.fsf@gmail.com> <838taeg6z5.fsf@gnu.org> <7a49cbdf-f2c3-0803-2ee8-3d9f55e405a5@cs.ucla.edu> <7a4f10ec-c1b9-953d-7a95-b2f1ff762735@cs.ucla.edu> Reply-To: Eli Zaretskii NNTP-Posting-Host: blaine.gmane.org X-Trace: blaine.gmane.org 1522668074 18549 195.159.176.226 (2 Apr 2018 11:21:14 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 2 Apr 2018 11:21:14 +0000 (UTC) Cc: rpluim@gmail.com, eggert@cs.ucla.edu, emacs-devel@gnu.org To: Pip Cet Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Mon Apr 02 13:21:10 2018 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1f2xWN-0004e7-NS for ged-emacs-devel@m.gmane.org; Mon, 02 Apr 2018 13:21:07 +0200 Original-Received: from localhost ([::1]:54349 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f2xYR-00034c-75 for ged-emacs-devel@m.gmane.org; Mon, 02 Apr 2018 07:23:15 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:43289) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f2xXg-00033z-Kb for emacs-devel@gnu.org; Mon, 02 Apr 2018 07:22:29 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f2xXb-0004ZK-Kw for emacs-devel@gnu.org; Mon, 02 Apr 2018 07:22:28 -0400 Original-Received: from fencepost.gnu.org ([2001:4830:134:3::e]:39269) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f2xXb-0004ZA-HG; Mon, 02 Apr 2018 07:22:23 -0400 Original-Received: from [176.228.60.248] (port=4927 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1f2xXa-0002iP-SG; Mon, 02 Apr 2018 07:22:23 -0400 In-reply-to: (message from Pip Cet on Mon, 2 Apr 2018 10:56:25 +0000) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2001:4830:134:3::e 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:224234 Archived-At: > From: Pip Cet > Date: Mon, 2 Apr 2018 10:56:25 +0000 > Cc: Robert Pluim , emacs-devel@gnu.org > > I believe the currently-documented behavior is that it's undefined; > however, merely leaving it undefined doesn't make bytecode compilation > reproducible. To do that, right now, I redefine EQ to be true for > same-value floats. I'd prefer the byte compiler to be fixed > (unfortunately, flet-binding eq around the invocation of the byte > compiler isn't an option since byte-compiled code won't let you > redefine eq), but there appear to be several places where the > assumption is built into it, and I haven't found them all. The > half-fixed compiler generates obviously-suboptimal bytecode sequences > like "const X; const X;". > > I think it makes sense to say that bytecode should be portable but not > necessarily identical between implementations, provided there's also a > way to canonicalize bytecode generation so the result is actually > target-independent (in the sense that if there are still bytecode > differences between targets, that's a bug in the Lisp code); I hope > redefining EQ is sufficient for that. Can you make a step back and explain what is it that you are trying to achieve, and why? Making potentially backward-incompatible changes without a very good reason is not something we should be enthusiastic about, IMO. E.g., the fact that two floats are never EQ is burned into too many muscle memories, and I expect subtle problems with at least C code that uses EQ. Thanks.