Re: [gomp4 01/14] nvptx: emit kernels for 'omp target entrypoint' only for OpenACC

[Alexander Monakov <amonakov at ispras dot ru>]

On Wed, 21 Oct 2015, Jakub Jelinek wrote:

> On Tue, Oct 20, 2015 at 09:34:23PM +0300, Alexander Monakov wrote:
> > The NVPTX backend emits each functions either as .func (callable only from the
> > device code) or as .kernel (entry point for a parallel region).  OpenMP
> > lowering adds "omp target entrypoint" attribute to functions outlined from
> > target regions.  Unlike OpenACC offloading, OpenMP offloading does not invoke
> > such outlined functions directly, but instead passes their address to
> > 'gomp_nvptx_main'.  Restrict the special attribute treatment to OpenACC only.
> > 
> > 	* config/nvptx/nvptx.c (write_as_kernel): Additionally test
> > 	flag_openacc for "omp_target_entrypoint".
[...]

> This is certainly wrong.  People can use -fopenmp -fopenacc, whether
> flag_openacc is set does not mean whether the particular function is
> outlined openacc or openmp region.
> The question is, is .kernel actually harmful, even when you invoke it
> through a stub wrapper?  Like, does it not work at all, or is slower than it
> could be?

Taking the address of a .kernel function doesn't work (for some reason it's
restricted to sm_35+), and taking the address is necessary to pass it on to
gomp_nvptx_main.

> If it is harmful, you should use a different attribute for OpenMP and
> OpenACC target entrypoints, so perhaps "omp target entrypoint" for OpenMP
> ones and "acc target entrypoint" for OpenACC ones? create_omp_child_function
> that adds the attribute should have the stmt for which it is created in
> ctx->stmt, so you could e.g. use is_gimple_omp_oacc for that.

Thanks, that should resolve the issue nicely.

Alexander