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

[Jakub Jelinek <jakub at redhat dot com>]

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".
> ---
>  gcc/config/nvptx/nvptx.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/gcc/config/nvptx/nvptx.c b/gcc/config/nvptx/nvptx.c
> index 21c59ef..df7b61f 100644
> --- a/gcc/config/nvptx/nvptx.c
> +++ b/gcc/config/nvptx/nvptx.c
> @@ -401,8 +401,10 @@ write_one_arg (std::stringstream &s, tree type, int i, machine_mode mode,
>  static bool
>  write_as_kernel (tree attrs)
>  {
> -  return (lookup_attribute ("kernel", attrs) != NULL_TREE
> -	  || lookup_attribute ("omp target entrypoint", attrs) != NULL_TREE);
> +  if (flag_openacc
> +      && lookup_attribute ("omp target entrypoint", attrs) != NULL_TREE)
> +    return true;
> +  return lookup_attribute ("kernel", attrs) != NULL_TREE;
>  }
>  
>  /* Write a function decl for DECL to S, where NAME is the name to be used.

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?  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.

	Jakub