The Mill certainly raises a lot of interesting code generation and optimization issues. I'm sure there's plenty of scope for figuring out good optimization strategies, as a lot seems to depend on the ability of the compiler to make good choices about instruction scheduling and belt slot allocation. Sure, that's the case for traditional architectures as well, but there's more prior art there too. There may also be ingenious algorithms which work better on the Mill architecture specifically. I'd love to know if there's any theory on the hardness of allocating positions on the belt, compared to traditional register allocation.