Re: Fusion-ifying proto parse trees

Eric Niebler wrote:
> Joel de Guzman wrote:
> > Eric Niebler wrote:
> >
> > > OK, you're saying the problem is the performance of creating a view. 
> > > You agree, though, that there's no sense redesigning proto until we 
> > > do the performance testing that shows there is a problem that is best 
> > > addressed that way. Otherwise, it's just premature optimization.
> >
> > Fair enough. Let me remind you though that the competition is tough.
> > What we are up against (flattening the sequence up front in the
> > proto-ET stage) is zero-overhead. When you flatten the sequence
> > up front, you do as much as you can in a single stage, such that
> > the stage is already prepared when you go to the second; i.e. parsing.
> > I still believe that that's the way to go.
>
>
> Here's why I think segmented Fusion algorithms will be as fast, or even 
> faster, than flattening the sequence up front. Fusion algorithms are 
> recursive, right? You process the current node and then recurse on the 
> sequence [next(begin), end). But imagine how you would write the Fusion 
> algorithms to handle binary trees specially. Instead of recursing once 
> on next(begin), you would recurse *twice* on left(begin) and 
> right(begin). Now generalize. :-) That's what the segmented algorithms are.
>
> Once we have the segmented algorithms, I can write segmented iterators 
> for proto trees, and the algorithms will Just Work with zero additional 
> overhead. Do you believe me? :-)

Yes, sir! :)

> > Anyway, out of curiosity, how do you intend to do performance testing?
> > What will be your benchmark?
>
>
> Good question. Care to write a proto-lite that pre-flattens so we can 
> benchmark against it?

We have code that flattens alright. It does not use proto, which is
also a good thing because we can also test the impact of proto on
perf. The one in the Spirit CVS at branch SPIRIT_2 is it.

> > > I'm going to spend some time thinking about segmented Fusion 
> > > algorithms, because I think that's where we'll get the most bang for 
> > > our buck.
> >
> > That would be awesome!
>
> Working on it.

Double awesome! This is exciting!

Regards,
--
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net



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