Re: [gomp4] Preserve NVPTX "reconvergence" points

[Bernd Schmidt <bernds at codesourcery dot com>]

On 06/19/2015 03:45 PM, Jakub Jelinek wrote:
> I actually believe having some optimization passes in between the ompexp
> and the lowering of the IR into the form PTX wants is highly desirable,
> the form with the worker-single or vector-single mode lowered will contain
> too complex CFG for many optimizations to be really effective, especially
> if it uses abnormal edges.  E.g. inlining supposedly would have harder job
> etc.  What exact unpredictable effects do you fear?

Mostly the ones I can't predict. But let's take one example, LICM: let's 
say you pull some assignment out of a loop, then you find yourself in 
one of two possible situations: either it's become not actually 
available inside the loop (because the data and control flow is not 
described correctly and the compiler doesn't know what's going on), or, 
to avoid that, you introduce additional broadcasting operations when 
entering the loop, which might be quite expensive.


Bernd