Definition vplub (v: aval) (p: aptr) : aptr :=
  match v with
  | Ptr q => plub q p
  | Ifptr q => plub q p
  | _ => p
  end.

Lemma vmatch_vplub_r: forall v x p, vmatch v (Ifptr p) -> vmatch v (Ifptr (vplub x p)).