(* Move elsewhere? *)
Remark fold_left_preserves:
forall (A B: Type) (f: A -> B -> A) (P: A -> Prop),
(forall a b, P a -> P (f a b)) ->
forall l a, P a -> P (fold_left f l a).
Remark fold_left_ensures:
forall (A B: Type) (f: A -> B -> A) (P: A -> Prop) b0,
(forall a b, P a -> P (f a b)) ->
(forall a, P (f a b0)) ->
forall l a, In b0 l -> P (fold_left f l a).
Definition only_callee_saves (u: RegSet.t) : Prop :=
forall r, RegSet.In r u -> is_callee_save r = true.

Lemma record_reg_only: forall u r, only_callee_saves u -> only_callee_saves (record_reg u r).