Re: auto vectorization in gcc

[Martin Brain <mjb at cs dot bath dot ac dot uk>]

Sorry about my previous out of thread posting - have now had a proper
chance to catch up on this discussion.

> Thanks very much for the responsiveness!
> 
> > The tree level is *more* capable than the rtl level at representing
> > vector types (and thus operations).  I think all we need is some
> > small amount of info from the target about vector widths and memory
> > blocking, and then the transformation should happen at the tree level.
> 
> I wonder if the target info that you suggest to expose to the tree level
> would suffice. In many cases code sequences that are perfectly
> parallelizable with respect to data dependences, will not benefit from
> vectorization. In order to avoid making really poor decisions, you want
> to have at least the following information exposed:
<snip>
> Bottom line is, if there's not enough information at the tree level, too
> much redundant code will be generated, requiring a lot of effort to
> undo it. I think we should either expose all vital target specific
> info to the tree-level, or perform only (target independent) analysis in
> the
> tree level, and do the actual vectorization transformation where we know if
> and how to do it.
This is very much along the same lines as I was envisaging.  Given we
currently have some time and resources that could be used on a project
like this would you be interested / able tocolaborate on this project?

Cheers,
 - Martin