Ltac memval_lessdef_tac :=
match goal with
 | H: memval_lessdef ?a ?b |- _ => destruct a,b; inv H
 | H: list_forall2 _ ?a ?b |- _ => destruct a,b; inv H
 | H: proj_bytes ?a = Some _ |- _ => match a with context [nil] => inv H end
end;
 try discriminate;
 try solve [unfold decode_val; simpl; auto] .

Lemma mem_lessdef_decode_val: forall ch vl vl', list_forall2 memval_lessdef vl vl' -> Val.lessdef (decode_val ch vl) (decode_val ch vl').