Re: [Emacs-diffs] comment-cache 223d16f 2/3: Apply `comment-depth' text properties when calling `back_comment'.

[Dmitry Gutov]

On 03/14/2016 07:29 PM, Alan Mackenzie wrote:

> CC Mode doesn't use syntax-ppss.  It would be too much work to put it in,
> particularly as that function's future is unclear.

Could you please avoid FUD like that?

> > IIRC, Stefan posted a patch, which was like 10 lines long.
>
> Sorry, patch for what?  I've lost the context.

That one:

http://lists.gnu.org/archive/html/emacs-devel/2016-03/msg00593.html
http://lists.gnu.org/archive/html/emacs-devel/2016-03/msg00619.html

Any other grunt work I can assist with?

> > Could you please try it already, so we can move on to discussing the
> > actual performance problems of syntax-ppss, instead of theoretical ones?
>
> It would be a lot of work.  Perhaps you might like to undertake it.

Applying a patch and doing the measurements is a lot of work?

> > The approach X is out of the question, because my approach Y is usually
> > N times faster!
>
> > Why is it out of the question? Can I say "premature optimization"?
>
> You could, but it would sound a bit silly.

Considering the kind of arguments you provide, it's looking less and 
less silly with each message.

> > (parse-partial-sexp 1 (point)) on line 1661 takes ~0.002s here.
>
> > (parse-partial-sexp 1 (point-max)) takes just a little above that.
>
> > How do these timings translate into whole seconds of waiting after
> > pressing '/'?
>
> They don't.  It was CC Mode's indentation engine's scanning, not the raw
> parse-partial-sexp scanning.

I guess we found the problem, then. And the cache's performance is 
unlikely to change much.