Re: [PATCH 0/5] OpenMP/PTX: improve correctness in SIMD regions

[Alexander Monakov <amonakov at ispras dot ru>]

On Wed, 18 Jan 2017, Jakub Jelinek wrote:
> > Inlining needs to do just like omp-low; if we take the current framework, it
> > would need to collect addressable locals into one struct, replace references to
> > those locals by field references in the inlined body.  Then it needs to
> > appropriately increase allocation size/alignment in SIMT_ENTER() call arguments.
> > And finally it would need to initialize the pointer to structure, either
> > immediately after SIMT_ENTER, or in a more fine-grained manner by a
> > __builtin_alloca_with_align-like function (__b_a_w_a is not usable for that
> > itself, because currently for known sizes gcc can make it a local variable).
> 
> One of the problems with that is that it means that you can't easily turn
> addressable private variables into non-addressable ones once you force them
> into such struct that can't be easily SRA split.
> In contrast, if you can get the variable flags/attributes work, if they
> become non-addressable (which is especially important to get rid of C++
> abstraction penalties), you simply don't add them into the specially
> allocated block.

I agree; I'd like to implement the approach with per-variable attributes once
it's clear how it ought to work (right now I'm not sure if placing CLOBBERs on
both entry and exit would be enough; if I understood correctly, Richard is
saying they might be moved, unless the middle-end is changed to prevent it).

Do you want me to pursue that during the early days of stage 4?  I think it
would be nice to have the issue addressed in some way for the upcoming release.

Thanks.
Alexander