[PATCH] D106509: [OpenMP][OpenACC] Implement `ompx_hold` map type modifier extension in Clang (1/2)

[Joachim Protze via Phabricator via cfe-commits]

protze.joachim added a comment.

I was wondering about the connection to OpenACC, so I had a quick look into the OpenACC spec to try and understand the background.
OpenACC uses two separate reference counters for structured and unstructured map. If one of them is >0, the data is present. If both become 0, data is deleted.

I think, the `hold` modifier is not sufficient to replicate OpenACC behavior. Consider the following example:

  #pragma acc data copy(a)  // structured ref := 1
  {
  #pragma acc exit data delete(a) // dynamic ref := 0
  #pragma acc enter data copyin(a) // dynamic ref := 1
  } // structured ref := 0 // no copyout because dynamic ref >0

As I understand this will be translated to the following OpenMP:

  #pragma omp target data map(ompx_hold, tofrom:a)  // ref := 1
  {
  #pragma omp exit data map(delete:a) // ref := 0  // no action because of hold
  #pragma omp enter data map(to:a) // ref := 1
  } // ref := 0 // perform map from

I don't think, that trying to map the two openacc reference count to a single openmp reference count will work in general.


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