From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.bugs Subject: bug#65051: internal_equal manipulates symbols with position without checking symbols-with-pos-enabled. Date: Mon, 7 Aug 2023 09:44:55 +0000 Message-ID: References: <2F680A0A-54B5-42C2-B27B-4E5C6332517A@gmail.com> <65A42652-DB4A-4FA6-8ADA-0D5BEB00F54C@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="40058"; mail-complaints-to="usenet@ciao.gmane.io" Cc: 65051@debbugs.gnu.org, Eli Zaretskii , Stefan Monnier To: Mattias =?UTF-8?Q?Engdeg=C3=A5rd?= Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Mon Aug 07 11:48:05 2023 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1qSwqB-000A3E-4K for geb-bug-gnu-emacs@m.gmane-mx.org; Mon, 07 Aug 2023 11:48:05 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qSwoV-000736-DH; Mon, 07 Aug 2023 05:46:11 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qSwoN-00071a-0O for bug-gnu-emacs@gnu.org; Mon, 07 Aug 2023 05:46:05 -0400 Original-Received: from debbugs.gnu.org ([2001:470:142:5::43]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1qSwoM-00031U-NU for bug-gnu-emacs@gnu.org; Mon, 07 Aug 2023 05:46:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1qSwoL-00005q-Sh for bug-gnu-emacs@gnu.org; Mon, 07 Aug 2023 05:46:01 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Alan Mackenzie Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Mon, 07 Aug 2023 09:46:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 65051 X-GNU-PR-Package: emacs Original-Received: via spool by 65051-submit@debbugs.gnu.org id=B65051.169140150532727 (code B ref 65051); Mon, 07 Aug 2023 09:46:01 +0000 Original-Received: (at 65051) by debbugs.gnu.org; 7 Aug 2023 09:45:05 +0000 Original-Received: from localhost ([127.0.0.1]:60613 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1qSwnQ-0008Vn-Sl for submit@debbugs.gnu.org; Mon, 07 Aug 2023 05:45:05 -0400 Original-Received: from mx3.muc.de ([193.149.48.5]:60991) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1qSwnN-0008Up-KA for 65051@debbugs.gnu.org; Mon, 07 Aug 2023 05:45:03 -0400 Original-Received: (qmail 73734 invoked by uid 3782); 7 Aug 2023 11:44:56 +0200 Original-Received: from acm.muc.de (pd953adbb.dip0.t-ipconnect.de [217.83.173.187]) (using STARTTLS) by colin.muc.de (tmda-ofmipd) with ESMTP; Mon, 07 Aug 2023 11:44:55 +0200 Original-Received: (qmail 3996 invoked by uid 1000); 7 Aug 2023 09:44:55 -0000 Content-Disposition: inline In-Reply-To: <65A42652-DB4A-4FA6-8ADA-0D5BEB00F54C@gmail.com> X-Submission-Agent: TMDA/1.3.x (Ph3nix) X-Primary-Address: acm@muc.de X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.bugs:266877 Archived-At: Hello, Mattias. On Mon, Aug 07, 2023 at 10:58:41 +0200, Mattias Engdegård wrote: > 6 aug. 2023 kl. 17.02 skrev Alan Mackenzie : > >>> together with an unsigned integer called the @dfn{position}. These > >>> -objects are intended for use by the byte compiler, which records in > >>> -them the position of each symbol occurrence and uses those positions > >>> -in warning and error messages. > >>> +objects are stored internally much like vectors > >> Not sure why we want to say how they are stored here. They can be > >> stored in bubble memory for all the user cares. > > The point is, they are _not_ stored in the obarray. Eli specifically > > asked me to clarify this point, yesterday. > Oh that part is perfectly fine (thank you), we just don't need to say > that the sympos objects are stored "like vectors" -- that just confuses > the reader. Why not? It's true, and I doubt it will cause confusion. I think we need to say something positive in that place (since we're following it with a negative). Perhaps you could suggest an alternative. > >>> +When @code{symbols-with-pos-enabled} is @code{nil}, any symbols with > >>> +position continue to exist, but do not behave as symbols, or have the > >>> +other useful properties outlined in the previous paragraph. @code{eq} > >>> +returns @code{t} when given identical arguments, and @code{equal} > >>> +returns @code{t} when given arguments with @code{equal} components. > >> Since the components are bare symbols and fixnums, equality and > >> identity for them are equivalent, right? > > No. If there are two distinct SWPs with the same bare symbol and the > > same position, they should be equal, but not eq. But the real point is > > to contrast how equal and eq work when symbols-with-pos-enabled is nil > > with when it is non-nil. > I meant that the components of equal sympos objects aren't merely equal > but identical. (This is a very minor quibble; you can keep the text if > you like.) The current proposed text has a more subtle intention. It says that eq and equal behave just like they always have done for everything when symbols-with-pos-enabled is nil. > >> OK. This reduces the number of branches in the hot path for ordinary > >> (non-sympos) code by one while adding one to sym-pos code, and that > >> should be a fair trade-off. The new branch should be well-predicted but > >> is still consuming resources. > > I did some simple timings on the old and new code, and the new code is > > not slower. > This is not easy to measure and details matter, but as I said -- there > is no reason to believe that your changes should be a regression in the > important measure, rather the opposite. Agreed. > >>> + if (SYMBOL_WITH_POS_P(o1)) /* symbols_with_pos_enabled is false. */ > >>> + return (internal_equal (XSYMBOL_WITH_POS (o1)->sym, > >>> + XSYMBOL_WITH_POS (o2)->sym, > >>> + equal_kind, depth + 1, ht) > >>> + && internal_equal (XSYMBOL_WITH_POS (o1)->pos, > >>> + XSYMBOL_WITH_POS (o2)->pos, > >>> + equal_kind, depth + 1, ht)); > >> Why recurse here if the components are a bare symbol and a fixnum, > >> respectively? > > Maybe in case they might somehow be something else? > No, we must be able to assume that internal invariants hold when we > offer no way for them to be violated. Let's just change the calls to > BASE_EQ and be done with it. OK, I think you're right, here, I'll change that. > >> However we should make an effort to prevent the compiler from > >> optimising (eq X X) -> t etc, which it is completely entitled to doing, > >> .... > > Why? (eq X X) is t in all circumstances, whether X is a symbol, a cons > > structure, or anything else. What am I missing, here? > If the compiler transforms (eq foo1 foo1) into t then the test won't > actually exercise the implementation of `eq`. Ah! You're talking about the tests. OK. In my tests, I timed (equal a b) where a and b were variables which were either equal or not. > >> .... and also test both the interpreted and compiled version of `eq` > >> and `equal`. > > They're the same code in both cases. I'm missing something here, too, I > > think. > Byte-code doesn't call Feq, it uses its own implementation. They should > work identically but as we are checking edge cases here we'd better be > sure about that. > >> The test bytecomp--eq-symbols-with-pos-enabled already does most of > >> this for a different reason. Perhaps it can be extended to cover > >> `equal` as well? > > I don't have such a test in my repository anywhere. Are you sure you > > wrote it right? > It was added in 44d7fd3805. OK. That commit is recent, then? If so, I'll see it soon. -- Alan Mackenzie (Nuremberg, Germany).