Proof with eauto with val_renamings.
intros.
destruct v...
destruct Hvalid as [b' Hf].
specialize (Hid _ _ Hf);
subst...
Qed.

Lemma val_obs_hiword:
forall f v v',
val_obs f v v' ->
val_obs f (Val.hiword v) (Val.hiword v').