[PATCH] D120353: [OpenMP] Add option to make offloading mandatory

[Joseph Huber via Phabricator via cfe-commits]

jhuber6 added a comment.

In D120353#3338718 <https://reviews.llvm.org/D120353#3338718>, @ABataev wrote:

> In D120353#3338647 <https://reviews.llvm.org/D120353#3338647>, @jhuber6 wrote:
>
>> But the main reason I made this patch is for interoperability. Without this if you want to call a CUDA function from the OpenMP device you'd need a variant and a dummy implementation. If you don't write a dummy implementation you'll get a linker error, if you don't use a variant you'll override the CUDA function.
>
> Ah, ok, I see. How is supposed to be used? In Cuda code or in plain C/C++ code?

I haven't finalized the implementation, but the basic support I've tested was calling a `__device__` function compiled from another file with OpenMP, with this patch the source files would look like this for example. I think the inverse would also be possible given some code on the CUDA side. Calling CUDA kernels would take some extra work.

  __device__ int cuda() { return 0; }



  int cuda(void);
  #pragma omp declare target device_type(nohost) to(cuda)
  
  int main() {
    int x = 1;
  #pragma omp target map(from : x)
    x = cuda();
  
    return x;
  }


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