Actually, the Mill uses just the forwarding network which I completely ignored in this explanation. The really short explanation about the forwarding network i

Actually, the Mill uses just the forwarding network which I completely ignored in this explanation. The really short explanation about the forwarding network is that writing/reading the PRF takes too much time for you to read it and do work on the same cycle. If you operated on it alone, all operations that were dependent on each other would have multi-cycle latencies. Since this sucks, in addition to the PRF the machines have a forwarding network, where the result of every instruction is broadcast to all the execution units of a similar type. If the broadcasted PRF number matches the register you want, it's read from the forwarding network instead of the PRF. AFAICT, the Mill works by completely eschewing the final register file, and exclusively using the forwarding network with some local storage at each execution unit for the past values on the network.