From: Bastian Beischer <bastian.beischer@gmail.com>
To: Alan Mackenzie <acm@muc.de>
Cc: 30367@debbugs.gnu.org
Subject: bug#30367: 26.0.91; CC-Mode: Major slowdown when isearching big C++ file.
Date: Fri, 09 Feb 2018 10:16:53 +0100 [thread overview]
Message-ID: <87372a8quy.fsf@gmail.com> (raw)
In-Reply-To: <20180208184232.GB4335@ACM> (Alan Mackenzie's message of "Thu, 8 Feb 2018 18:42:32 +0000")
Hello Alan,
Alan Mackenzie <acm@muc.de> writes:
> On Thu, Feb 08, 2018 at 17:25:58 +0000, Alan Mackenzie wrote:
>> Hello, Bastian.
>
> [ .... ]
>
>> I think I understand what's happening, now.
>
>> c-looking-at-or-maybe-in-bracelist attempts to go back over the innards
>> of a brace list to the enclosing "{". At L+122, in new handling for a
>> comma, I rather rashly inserted a `c-go-up-list-backward' to test whether
>> the comma is inside a brace. This was in a loop, once for each sexp.
>
>> In your sample file there is, at L10,653 a construct at top level with
>> _lots_ of commas. My loop is trying to go to the non-existent containing
>> brace for each of these commas, so ends up scanning to BOB for each of
>> them. This entire activity will be being done several times.
>
>> I timed a single `c-go-up-list-backward' from one of these commas at
>> 0.033 seconds. 30 of these take about a second, and my machine is
>> anything but slow.
>
>> So, I just need to work out a way of fixing this, which may take some
>> while (sorry).
>
> Actually, that cond arm with the `c-go-up-list-backward' was merely an
> "optimisation". :-( If I simply remove it, the code goes ~30 times
> faster, without triggering any successes in the test suite.
>
> Would you please try out the following patch on real code, and either
> confirm to me that it fixes the bug, or tell me what it breaks. Thanks!
>
>
>
> diff -r e8b2c6141f97 cc-engine.el
> --- a/cc-engine.el Fri Feb 02 20:34:15 2018 +0000
> +++ b/cc-engine.el Thu Feb 08 18:39:40 2018 +0000
> @@ -10547,13 +10547,6 @@
> (looking-at c-return-key))
> (setq braceassignp t)
> nil)
> - ((and c-has-compound-literals
> - (eq (char-after) ?,))
> - (save-excursion
> - (when (and (c-go-up-list-backward nil lim)
> - (eq (char-after) ?\())
> - (setq braceassignp t)
> - nil)))
> ((eq (char-after) ?=)
> ;; We've seen a =, but must check earlier tokens so
> ;; that it isn't something that should be ignored.
>
>
>
> [ .... ]
>
Yes, this patch fixes the slowdown. But since I don't understand what
the original commit which introduced the slowdown tried to fix I cannot
comment on whether or not its the right thing to do within the context
of that commit.
I will run emacs with the patch included for a while and will let you
know in case I find any problems!
Thanks for tackling this so quickly!
>> > Cheers
>> > Bastian
next prev parent reply other threads:[~2018-02-09 9:16 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-06 10:34 bug#30367: 26.0.91; CC-Mode: Major slowdown when isearching big C++ file Bastian Beischer
2018-02-06 10:40 ` Bastian Beischer
[not found] ` <mailman.8662.1517913372.27995.bug-gnu-emacs@gnu.org>
2018-02-07 15:24 ` Alan Mackenzie
[not found] ` <20180207152435.72040.qmail@mail.muc.de>
2018-02-07 15:27 ` Bastian Beischer
2018-02-07 21:21 ` Alan Mackenzie
[not found] ` <20180207212145.GA3963@ACM>
2018-02-07 21:53 ` Bastian Beischer
2018-02-07 22:26 ` Alan Mackenzie
2018-02-07 22:45 ` Bastian Beischer
2018-02-08 17:25 ` Alan Mackenzie
[not found] ` <20180208172558.GA4335@ACM>
2018-02-08 18:42 ` Alan Mackenzie
[not found] ` <20180208184232.GB4335@ACM>
2018-02-09 9:16 ` Bastian Beischer [this message]
2018-03-20 18:49 ` Alan Mackenzie
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