* libguile/loader.c (scm_find_slot_map_unlocked): Rename from
  scm_find_dead_slot_map_unlocked.

* libguile/vm.c (struct slot_map_cache_entry, struct slot_map_cache)
  (find_slot_map): Rename, changing "dead_slot" to "slot".
  (enum slot_desc): New type.
  (scm_i_vm_mark_stack): Interpret slot maps as having two bits per
  slot, allowing us to indicate that a slot is live but not a pointer.

* module/language/cps/compile-bytecode.scm (compile-function): Adapt to
  emit-slot-map name change.

* module/system/vm/assembler.scm (<asm>): Rename dead-slot-maps field to
  slot-maps.
  (emit-slot-map): Rename from emit-dead-slot-map.
  (link-frame-maps): 2 bits per slot.

* module/language/cps/slot-allocation.scm (lookup-slot-map): Rename from
  lookup-dead-slot-map.
  (compute-var-representations): New function.
  (allocate-slots): Adapt to encode two-bit slot representations.