bug#25706: 26.0.50; Slow C file fontification

[Mattias Engdegård]

3 dec. 2020 kl. 11.48 skrev Alan Mackenzie <acm@muc.de>:

> I've found it.  There was a "harmless" c-backward-syntactic-ws invocation
> in c-determine-limit.  This macro moves back over syntactic whitespace,
> which includes macros.  So this was going back all the way to BOB, from
> which we scanned forward again.

Not bad. Now Emacs starts becoming usable for real code!
I can confirm a big subjective improvement on several big preprocessor-heavy 
files, and measurements agree.

> It now takes me just under 6 minutes to (time-scroll) through the entire
> buffer, compared with a previous hour.  As already mentioned, it is still
> slightly more sluggish near the end of the buffer than near the start.

Is that with or without my regexp patch?

It looks like there may be more regexp improvements possible. We can take a 
closer look later on, when the running time is less dominated by other issues.