Joel de Guzman wrote:
Andy Little wrote:
There do seem to be limits to when the compiler will optimise a view though, It may have something to do with copying references(aka joint-view) as raw bytes, after which AFAICS the compiler will treat them as pointers. that said that is only an impression so far.
Ok, now I understand. You sent me an email about stacked fold of stacked joint_view created by push_back being difficult for the compiler to optimize. Here's why (and there's a solution):
joint_view is a prime example of a segmented sequence. The resulting iterators from it will have some overhead. That is inevitable. See joint_view_iterator so you'll know what I mean.
However, Eric Niebler did some work on segmented algorithms. His initial testing (for proto and early spirit-2 experiments) shows some exciting results. Basically, a segmented sequence is a sequence of sequences (for each segment). Instead of creating an iterator that "weaves" through each segment (like joint_view_iterator), segmented algorithms apply the algorithm recursively to each of the segments. For example, a fold of a joint_view will be 2 calls to fold, one for the left join and one for the right.
I know this is a bit hand-wavy, but once you see it in action, it really makes a lot of sense. I'm CCing Eric. I think now is the right time to incorporate his work into the fusion code base.
Thanks, Joel, I agree now would be a good time to integrate my work on segmented fusion. I haven't done any additional work on it since the "segmented fusion, a-ha!" days on spirit-devel. The latest version can be found in an attachment on the following message: http://article.gmane.org/gmane.comp.parsers.spirit.devel/2781 The next step would be to port this code to the latest Fusion-2 and add some tests. Perhaps we could check this in on a branch, or in an "experimental" sub-directory. And we can't make joint_view a segmented sequence until we have segmented versions of all the Fusion algorithms. Trouble is, I haven't had much time to work on this. :-( -- Eric Niebler Boost Consulting www.boost-consulting.com