bug#30367: 26.0.91; CC-Mode: Major slowdown when isearching big C++ file.

[Bastian Beischer]

Hello Alan,

On Wed, Feb 7, 2018 at 10:21 PM, Alan Mackenzie <acm@muc.de> wrote:
>
> Hello, Bastian.
>
> That was quick work.  :-)
>
> On Wed, Feb 07, 2018 at 16:27:35 +0100, Bastian Beischer wrote:
> > Hello Alan,
>
> > On Wed, Feb 7, 2018 at 4:24 PM, Alan Mackenzie <acm@muc.de> wrote:
>
> > > Hello, Bastian.
>
> > > In article <mailman.8662.1517913372.27995.bug-gnu-emacs@gnu.org> you
> > > wrote:
>
> > > > After updating CC-Mode to the latest version in the standalone mercurial
> > > > repository I noticed that searching large C++ files has become a lot
> > > > slower than before (factor 20 or so).
>
> > > Thanks for taking the trouble to report this bug.
>
> > > How large is large?  Any chance you could supply me with such a sample
> > > C++ file that is slow on searching.  Then, in case something else
> > > besides the size is slowing it down, I'll have a "working" file to
> > > diagnose the bug with.
>
>
> > Sure, but I will send you the file off-list, since I don't want it to
> > become public.
> >
>
> I've got the file you sent me, thanks very much, and I will treat it as
> confidential.
>
> Unfortunately, I cannot reproduce the slowdown in that file, at least,
> not starting from emacs-26.0.91 -Q.  I think you've got quite a lot of
> non-default minor modes active, and I've a suspicion that we're seeing
> some interaction between CC Mode and one of these minor modes, or
> possibly some other non-default setting you've got set.
>
> Would you please try to reproduce the problem with emacs -Q, and if you
> can't, try to pinpoint which one of your settings/minor modes is the one
> which CC Mode is working badly with.

Actually the profile runs I sent were done with 'emacs -Q'. It's just
that I used a different emacs instance to report the bug, which had
the usual modes loaded. Sorry about that. So I can reproduce the
problem from emacs -Q, but I _do_ load the latest cc-mode from it's
standalone repository. The actual command was:

emacs -Q --eval "(add-to-list 'load-path \"~/cc-mode\")" --eval
"(require 'cc-mode)" /path/to/file.C

then search for 'isinsha'.

~/cc-mode revision is as follows:

$ cd ~/cc-mode
$ hg summary
parent: 6256:e8b2c6141f97
Added tag 2018-01-29-mac-m for changeset 9785123a85b4
branch: default
commit: (clean)
update: (current)

emacs version is as in the original report (GNU Emacs 26.0.91 (build
1, x86_64-pc-linux-gnu, GTK+ Version 3.22.26) of 2018-02-06, commit
c787a4968273027960a20ced6d63bae0d1ffa87e)

>
>
> We'll crack this!

I'm sure :-)

>
>
> > Cheers
> > Bastian
>
> --
> Alan Mackenzie (Nuremberg, Germany).

Cheers
Bastian