Re: How can I predict which regions xdisp will present me for font-locking?

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 12 Mar 2012 13:47:00 -0400
> From: John Yates <john@yates-sheets.org>
> Cc: Alan Mackenzie <acm@muc.de>, emacs-devel@gnu.org
> 
> >  . every change in the buffer triggers a call to
> >    font-lock-extend-jit-lock-region-after-change (via
> >    jit-lock-after-change-extend-region-functions)
> >
> >  . font-lock-extend-jit-lock-region-after-change extends the region
> >    of the change according to the font-lock properties of the major
> >    mode, then marks that region unfontified by putting on it a
> >    `fontified' text property with the value nil
> >
> >  . the next redisplay cycle calls jit-lock-function (via
> >    fontification-functions) at the beginning of the region whose
> >    `fontified' property is nil, and refontifies the region from there
> >    in chunks of 500 characters (but every chunk is extended so that
> >    its start is at the beginning of a line and its end is at the end
> >    of a line)
> >
> > Does this explain what you see?
> 
> How does this strategy differ from 23.x?

It doesn't, not in the display engine.

> I am seeing a horrendous slowdown when editing atypical macros (though
> no more than 50 lines long).

Can you give more quantitative description of the slowdown?  E.g., how
much time does it take to move the cursor by one character or one
line, or to insert or delete a single character?

If you replace cc-mode Lisp files in v24 with those in v23, does the
problem go away?