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bug#42490: Emacs is very slow when navigating into a specific C++ file
From: |
Alan Mackenzie |
Subject: |
bug#42490: Emacs is very slow when navigating into a specific C++ file |
Date: |
Mon, 21 Sep 2020 09:06:39 +0000 |
Hello, Olivier.
Ping?
On Fri, Jul 24, 2020 at 21:34:51 +0200, Olivier Scalbert wrote:
> Hi,
> Thanks for your answer.
> Unfortunately, I am out of my home, with no PC, for the week-end.
> If I'll survive, I will test it next Monday. Very sorry !
> ;-)
Emacs 27.1 was released just a few weeks ago. Maybe you're already
using it.
I think CC Mode processes the test file fast enough on 27.1, so it's
probably time to close this bug. What do you say?
> Regards,
> Olivier
> On 7/24/20 9:24 PM, Alan Mackenzie wrote:
> > Hello, Mattias and Olivier.
> > Firstly Olivier, thanks for taking the trouble to report the bug.
> > On Fri, Jul 24, 2020 at 18:46:45 +0200, Mattias EngdegÄrd wrote:
> >> Hello Olivier,
> >> Thanks for the report! Could you try Emacs 27 (or git master), building
> >> from source if necessary? Those versions should be slightly faster,
> >> although the response time is probably well below acceptable.
> >> If we distill the essentials of your file to some sort of benchmark, we
> >> might end up with:
> >> (with-temp-buffer
> >> (c++-mode)
> >> (dotimes (_ 1000)
> >> (insert "OP(ed,b0) { ldir(); } /* LDIR */\n"))
> >> (garbage-collect)
> >> (let ((t0 (current-time)))
> >> (font-lock-ensure (point-min) (point-max))
> >> (time-to-seconds (time-since t0))))
> >> Emacs 26.3 runs it in 11.9 s on this old lappy, but Emacs 27 does it in
> >> 3.3 s. This is a clear improvement but we should be able to do better.
> >> Alan may have a feeling for where the cycles are spent.
> > I've bisected CC Mode to find the critical change, and it is:
> > commit cc80eeb4a43d2079963de3d181002a6a6b56560d
> > Author: Alan Mackenzie <acm@muc.de>
> > Date: Fri Apr 12 20:07:03 2019 +0000
> > Analyze C++ method with & or && ref-qualifier as defun, not brace list
> > Also firm up detection of beginning of brace list in
> > c-looking-at-or-maybe-in-bracelist.
> > I have a simple benchmark which scrolls through a file, fontifying it,
> > and my results from this benchmark are:
> > (i) Before applying that patch: 53.022s.
> > (ii) After applying that patch: 7.039s.
> > I don't understand at the moment why that patch sped up scrolling in your
> > (Olivier's) file, but it would seem the patch is most desirable.
> > Unfortunately, the patch won't apply cleanly to the Emacs 26.3 sources.
> > It might be possible to find a sequence of patches which would do the
> > job. I think (though I haven't checked) the patch will have been
> > included in the upcoming Emacs 27.1 release.
--
Alan Mackenzie (Nuremberg, Germany).
- bug#42490: Emacs is very slow when navigating into a specific C++ file,
Alan Mackenzie <=