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

[Jakub Jelinek <jakub at redhat dot com>]

On Wed, Jan 18, 2017 at 06:34:05PM +0300, Alexander Monakov wrote:
> My main concern is that nothing indicates to optimization passes that after
> SIMT_EXIT(), underlying storage is unavailable.  What would prevent the compiler
> from transforming, say
> 
>   SIMT_ENTER();
>   // originally omp simd private(inner)
>   for (...)
>     { ... }
>   outer = inner;
>   SIMT_EXIT();
> 
> into
>   
>   SIMT_ENTER();
>   // omp simd private(inner)
>   for (...)
>     { ... }
>   SIMT_EXIT();
>   outer = inner; // too late
> 
> 
> Also, we'd need to ensure IPA-SRA propagates the magic flag when decomposing
> structs.

We are talking here about addressable vars, right (so if we turn it into
non-addressable, in the SIMT region we just use the normal PTX pseudos),
right?  We could emit inner ={v} {CLOBBER}; before SIMT_EXIT() to make it
clear it shouldn't be moved afterwards.  For the private vars used directly
in SIMD region, for the vars from inlined functions I assume if they are
addressable we emit clobbers for them too.  Or perhaps the alias oracle can
say that SIMT_EXIT ifn can clobber any addressable var with that
flag/attribute.  And yes, SRA would need to propagate it.

But I believe it is worth it, because inlining is essential for good
performance of the simd regions.

	Jakub