(** We need to show that, in the simulation diagram, we cannot
  take infinitely many Mach transitions that correspond to zero
  transitions on the ARM side.  Actually, all Mach transitions
  correspond to at least one ARM transition, except the
  transition from [Machsem.Returnstate] to [Machsem.State].
  So, the following integer measure will suffice to rule out
  the unwanted behaviour. *)

Definition measure (s: Mach.state) : nat :=
  match s with
  | Mach.State _ _ _ _ _ _ => 0%nat
  | Mach.Callstate _ _ _ _ => 0%nat
  | Mach.Returnstate _ _ _ => 1%nat
  end.Remark preg_of_not_R12: forall r, negb (mreg_eq r R12) = true -> IR IR12 <> preg_of r.

Theorem transf_program_correct: forward_simulation (Mach.semantics return_address_offset prog) (Asm.semantics tprog).