Proof with eauto with val_erasure.
intros.
destruct v1,v2; simpl in *; inv Hval_erasure; auto;
unfold Val.cmplu, Val.cmplu_bool; simpl; eauto with val_erasure;
do 2 rewrite andb_if;
repeat match goal with
| [|- context[match ?Expr with | _ => _ end]] =>
destruct Expr eqn:?
end; simpl; eauto with val_erasure.
Qed.
Hint Resolve val_erasure_cmplu : val_erasure.

Lemma mem_erasure_idempotent:
forall m m',
mem_erasure m m' ->
mem_erasure m (erasePerm m').