AMD Am29000 family had exactly that. The problem is, you still have to be able to name registers indirectly, or you'll have to either give up on separate compil

AMD Am29000 family had exactly that. The problem is, you still have to be able to name registers indirectly, or you'll have to either give up on separate compilation or do link-time intra-procedural register allocation. Both of those things are, of course, feasible in small embedded environments... but not in general-purpose computing, especially if you want to bring in most of the pre-existing software in.