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').