In Doom async compute is vendor natural. It will run if the COMPUTE_BIT present in an independent queue.
But this won't help Pascal, because the post process overlap is a low latency implementation, and it will call the present from the COMPUTE_BIT. Pascal don't support this, so NV need a sync point first in the main queue with the GRAPHICS_BIT flag, and than they can do the present there. This will ad latency and minimize the performance gain. It doesn't really useful in the end, because you may gain 2-3% performance, but you get a lot ot additional latency with it.