If I were to reserve a fixed stack slot for a each temporary, however, there could be many more stack slots. Since some big functions can have thousands of temporaries, it is clearly essential to restrict the stack slot allocation so that only temporaries that are actually spilled have a stack slot allocated to them. Once the GC is in place, and I have function descriptors implemented, it should actually be fairly trivial to add information in there to support stack unwinding for exceptions.