= do { initial_us <- getUs
; let initial_st = mkNatM_State initial_us 0
(new_tops, final_st) = initNat initial_st (cmmTopCodeGen cmm_top)
- final_us = natm_us final_st
final_delta = natm_delta final_st
final_imports = natm_imports final_st
; if final_delta == 0