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

George Rokos via Phabricator via Openmp-commits openmp-commits at lists.llvm.org
Fri Aug 13 02:09:29 PDT 2021

grokos added a comment.

In D106509#2943239 <https://reviews.llvm.org/D106509#2943239>, @protze.joachim wrote:

> 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.

The next patch in this series (D106510 <https://reviews.llvm.org/D106510>) modifies libomptarget and introduces a second reference count for ompx_hold. There won't be a singe RefCount anymore. I will review that patch once this one has been finalized.



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