llvm-project

e2ad5549 - [Flang][mlir] - Translation of delayed privatization for deferred target-tasks (#155348)

[Flang][mlir] - Translation of delayed privatization for deferred target-tasks (#155348) This PR adds support for translation of the private clause on deferred target tasks - that is `omp.target` operations with the `nowait` clause. An offloading call for a deferred target-task is not blocking - the offloading (target-generating) host task continues its execution after issuing the offloading call. Therefore, the key problem we need to solve is to ensure that the data needed for private variables to be initialized in the target task persists even after the host task has completed. We do this in a new pass called `PrepareForOMPOffloadPrivatizationPass`. For a privatized variable that needs its host counterpart for initialization (such as the shape of the data from the descriptor when an allocatable is privatized or the value of the data when an allocatable is firstprivatized), - the pass allocates memory on the heap. - it then initializes this memory by using the `init` and `copy` (for firstprivate) regions of the corresponding `omp::PrivateClauseOp`. - Finally the memory allocated on the heap is freed using the `dealloc` region of the same `omp::PrivateClauseOp` instance. This step is not straightforward though, because we cannot simply free the memory that's going to be used by another thread without any synchronization. So, for deallocation, we create a `omp.task` after the `omp.target` and synchronize the two with a dummy dependency (using the `depend` clause). In this newly created `omp.task` we do the deallocation.