canBeMovedDownwards checks if the "wait" counterpart of __tgt_target_data_begin_mapper can be moved downwards, returning a pointer to the instruction that might require/modify the data transferred, and returning null it the movement is not possible or not worth it. The function splitTargetDataBeginRTC receives that returned instruction and instead of moving the "wait" it creates it at that point.
Differential Revision: https://reviews.llvm.org/D86155
WIP that tries to hide the latency of runtime calls that involve host to
device memory transfers by splitting them into their "issue" and "wait"
versions. The "issue" is moved upwards as much as possible. The "wait" is
moved downards as much as possible. The "issue" issues the memory transfer
asynchronously, returning a handle. The "wait" waits in the returned
handle for the memory transfer to finish. We still lack of the movement.
Hamilton Tobon Mosquera