Re: Unbearably slow editing in .h files

[Alan Mackenzie]

Hi, again!

On Thu, Apr 03, 2008 at 08:22:10AM -0700, Dan Nicolaescu wrote:
> Alan Mackenzie <address@hidden> writes:

>   > On Thu, Apr 03, 2008 at 06:10:40AM -0700, Dan Nicolaescu wrote:
>   > > Alan Mackenzie <address@hidden> writes:

>   > >   > On Wed, Apr 02, 2008 at 04:47:52PM -0700, Dan Nicolaescu wrote:

>   > > Note that `diff-add-change-log-entries-other-window'  is C-x 4 A not
>   > > C-x 4 a, it is the equivalent of:
>   > > FOR each hunk in a diff DO
>   > >     C-x 4 a

>   > Wow!  I've just tried this.  It's amazing!  There are one or two
>   > things in it which aren't quite right, though.

> Yep, it should not generate duplicate entries.  One possible
> improvement is that it should iterate at a lower granularity than a
> hunk, some hunks have changes ! + and - changes.  (but that's still not
> enough, a + hunk could be adding 5 functions...)

I tried it (with a window configuration I can't remember exactly) and
ChangeLog ended up in both the upper and lower windows.  But that's for
another thread.  ;-)

>   > > When used on a diff buffer with thousands of lines, it is a bit
>   > > slow.

>   > Hmmm.  I've only tried it on diffs with elisp files.  That was a
>   > little slow.  Do you mean it's _very_ slow with C file diffs?  Can
>   > you give some numbers here?  Processor speed, size of diff file,
>   > time it takes.  

> Unfortunately I don't have any massive patches handy, so I can't test
> now how much things have improved for exactly the things that had
> problems before.  But some quick tests with the diff for lisp.h
> revision 1.606 (i.e. something that had a long ChangeLog entry, 625
> lines unidiff) showed that things have improved quite a lot today vs a
> > 1 month old emacs (a few seconds vs > 2 minutes).  Which is great.
> Thanks!

:-)

> Trying C-x 4 A on a 4-5000 lines patch would be more interesting...

Yes.

>   > But then again, people are only going to be using it once or twice
>   > per patch (and then having to fill out the result by hand), so it
>   > is surely not that critical.  But if it were taking 20 minutes
>   > rather than 45 seconds, that would be too slow, I agree.

> Ideally in the future C-x 4 A should be done automatically when doing a
> checkin, that why it is important to be as fast as possible.

I'm not sure I agree, here.  That might make it far too easy for people
to forget (or even to "forget") to write commit comments.

>   > >   > To the extent that it's still slower than it might be, yes
>   > >   > it's the K&R stuff making it slow.  The function which takes
>   > >   > time is c-in-knr-argdecl (cc-engine.el, ~L6317).  Actually,
>   > >   > this function gets called twice.  It would take a lot of
>   > >   > refactoring to make it get called only once.

>   > > What if it's not called at all?  After all, the vast majority of
>   > > the users never edit K&R.  Just a thought...

>   > Well, one set of users who still use K&R is the Emacs development
>   > team.  ;-)  

> Yeah, and many people wish that would change at some point.  But that a
> separate discussion that we should get into now.

I'm not sure why we don't just change all the K&R declarations to ANSI
ones.  It could probably be done simply enough with a script (awk, perl,
python, Emacs Lisp, or anything else).

>   > It would be possible, and very easy, to make K&R a user option.
>   > But I don't think that's the right thing to do.

>   > The overhead that K&R imposes on C-M-a and C-x 4 a is not _that_
>   > high, and it will diminish as processors continue to get faster.  I
>   > recently put in a hard-coded limit to the number of parameter
>   > declarations in a K&R section.  That limit is currently 20. 

> Just exploring options here...
> Would simply ignoring K&R for the purpose of running C-x 4 a  work?

No.  You're at the opening brace of a C function/typedef/struct; you've
got, somehow, to get from there to the function name.  That involves
jumping backwards over the K&R region, should it be present.  Or, point
starts out _outside_ a brace block.  You've got to decide whether it's
inside a function/typedef/struct header, and this might be the K&R
region.

> Yes, it might generate the wrong name in the ChangeLog entry in some
> very limited cases (is that true?), .....

I doubt it.  I think it would foul up with _every_ K&R function
declaration.  To try it out, set the major mode to C++ mode, then try
C-M-a or C-x 4 a.  In fact, in xdisp.c, I've just done this, gone to EOB
and typed C-M-a 25 times.  It got BOD OK 8 times, failed 17 times.

> ...., but that's not very critical.

I think it would be.  It would only need to happen to a hacker once, and
he would lose all confidence in it.  He would then feel obliged to check
every entry by hand - and the complaints would find their way to
address@hidden  ;-(

-- 
Alan Mackenzie (Nuremberg, Germany).