Re: Fusion-ifying proto parse trees

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? :-)


> 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?


> > 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.


--
Eric Niebler
Boost Consulting
www.boost-consulting.com


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