GNU bug report logs - #15294
24.3.50; js2-mode parser is several times slower in lexical-binding mode

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#15294: closed (24.3.50; js2-mode parser is several times
 slower in lexical-binding mode)
Date: Sun, 14 Dec 2014 14:09:01 +0000

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Your message dated Sun, 14 Dec 2014 09:08:23 -0500
with message-id <jwv61denx6p.fsf-monnier+emacsbugs <at> gnu.org>
and subject line Re: bug#15294: 24.3.50; js2-mode parser is several times slower in lexical-binding mode
has caused the debbugs.gnu.org bug report #15294,
regarding 24.3.50; js2-mode parser is several times slower in lexical-binding mode
to be marked as done.

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From: Dmitry Gutov <dgutov <at> yandex.ru>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3.50;
 js2-mode parser is several times slower in lexical-binding mode
Date: Fri, 06 Sep 2013 23:59:20 +0300

If I append -*- lexical-binding: t -*- to the first line of js2-mode.el
and eval the buffer, parsing a file takes several (3 to 4) times longer.

To measure:

0. Install js2-mode, e.g. from GNU ELPA.
1. Save
http://mootools.net/download/get/mootools-core-1.4.5-full-nocompat.js to
some local directory, open it in Emacs.
2. If it opens in some other mode than js2-mode, M-x js2-mode.
3. Don't touch the keys, wait until the file is parsed (the parsing gets
interrupted and rescheduled on input). When redisplay works again, we
can re-parse the file again and measure the time it takes.
4. eval-expression (js2-time (js2-reparse t)), wait until the message
area displays the amount of seconds the process took.

To measure the performance in interpreted mode, open js2-mode.el, M-x
eval-buffer and go through the above scenario (1-4).
To measure the performance in compiled mode, M-x byte-compile-file, then
(load "js2-mode.elc"), then go through the scenario.

My measurements:

lexical-binding |       no |      yes |
Interpreted     |    1 sec | 4.26 sec |
Compiled        | 0.63 sec | 1.76 sec |

--
In GNU Emacs 24.3.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.6.4)
 of 2013-09-06 on axl
Bzr revision: 114159 dmantipov <at> yandex.ru-20130906164012-6j0s6otwkypj9s1z
Windowing system distributor `The X.Org Foundation', version 11.0.11303000
System Description:	Ubuntu 13.04

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Dmitry Gutov <dgutov <at> yandex.ru>
Cc: 15294-done <at> debbugs.gnu.org
Subject: Re: bug#15294: 24.3.50;
 js2-mode parser is several times slower in lexical-binding mode
Date: Sun, 14 Dec 2014 09:08:23 -0500

>>> Not sure if I should close this issue now or at least wait until
>>> byte-compile--use-old-handlers is nil by default.
>> won't run on older Emacsen.  I think I'd like to see 24.4 release before
>> making the change.  But please do set it in your .emacs ASAP so it gets
>> wider testing.
> Just a reminder: I've been running with that setting for a while now,

So have I.

> with no problems that I can remember.

Well, I fixed a bug in it a while ago (some issue with "volatile", fixed
before the 24.4 release), but other than that, indeed it works fine.

The default value has been changed in "master" a couple months ago, already.


        Stefan

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