GNU bug report logs -
#25706
26.0.50; Slow C file fontification
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Reported by: Sujith <m.sujith <at> gmail.com>
Date: Mon, 13 Feb 2017 18:41:01 UTC
Severity: normal
Tags: moreinfo
Found in version 26.0.50
Done: Alan Mackenzie <acm <at> muc.de>
Bug is archived. No further changes may be made.
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30 nov. 2020 kl. 17.38 skrev Alan Mackenzie <acm <at> muc.de>:
> Yes. I've had a look at the file, and it's large and lacking in braces.
> There are functions in CC Mode which search backwards for opening braces
> to establish context. When there are none, the search goes back to BOB.
> Lots of these searches, not efficiently cached, take a long time.
>
> It's a problem with CC Mode, not with the source file. It's a known
> problem, and not easy to fix.
Actually, it's the underscores!
Demo: fill a file with the line pairs
#define abc_defg_hij_klm__nop_qrst_uvw_xyz_w__ooa_cin_e__aoi__uynv(s) \
0
repeated 1000 times, thus making it 2000 lines. Save as something.h. Slow!
Now replace each underscore with a letter. Save. Fast!
Fontifying the 2000 line file (with underscores) takes longer than the original 80000 line file.
I started going through c-find-decl-spots and c-find-decl-prefix-search (together there are while statements nested 4 deep) but am not sure exactly where the trouble is. A regexp? Something syntax-char related (since '_' has symbol syntax, not word)?
CC-mode in general thrashes the regexp cache; the miss rate is at 27 % for the original file, which is way too high. Enlarging the cache enough to eliminate misses helps, but not nearly enough.
This bug report was last modified 4 years and 213 days ago.
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