The Mill has 2 separate instuction streams that operate in sync. They are divided by functionality, one being the Exu-stream for computation and one being the Flow stream for control flow and memory access and address logic. Consequently there are two program counters, XPC and FPC. On control transfers both go to the same address and then diverge, XPC going down the address space, FPC going upward.
The main reason for this arrangement is simpler, cheaper and faster decoding of instructions and more efficient use of caches.