(** Reverse sub immediate *)

Lemma rsubimm_correct:
forall r1 r2 n k rs m,
exists rs',
exec_straight ge fn (rsubimm r1 r2 n k) rs m  k rs' m
/\ rs'#r1 = Val.sub (Vint n) rs#r2
/\ forall r': preg, r' <> r1 -> if_preg r' = true -> rs'#r' = rs#r'.