Re: [gomp4 07/14] libgomp nvptx plugin: launch target functions via gomp_nvptx_main

[Alexander Monakov <amonakov@ispras.ru>]

On Tue, 20 Oct 2015, Bernd Schmidt wrote:

> On 10/20/2015 08:34 PM, Alexander Monakov wrote:
> > 2.  Make gomp_nvptx_main a device (.func) function.  To have that work, we'd
> > need to additionally emit a "trampoline" of sorts in the NVPTX backend.  For
> > each OpenMP target entrypoint foo$_omp_fn$0, we'd have to additionally emit
> >
> > __global__ void foo$_omp_fn$0$entry(void *args)
> > {
> >     gomp_nvptx_main(foo$_omp_fn$0, args);
> > }
> 
> Wouldn't it be simpler to generate a .kernel for every target region function
> (as OpenACC does)? That could be a small stub in each case which just calls
> gomp_nvptx_main with the right function pointer. We already have the machinery
> to look up the right kernel corresponding to a host address and invoke it, so
> I think we should just reuse that functionality.

As I see we are describing the same thing in different words.

In what you describe, and in my quoted paragraph, both gomp_nvptx_main and the
function originally outlined for a target region are device-only (.func)
functions.  The .kernel function that the plugin looks up and launches is a
small piece of code that calls gomp_nvptx_main, passing it a pointer to the
target region function.

Unless I didn't fully catch what you say?  Like I said in the email, I do like
this approach more.

Thanks.
Alexander