Remark val_lessdef_normalize:
  forall v v' ty,
  Val.has_type v ty -> Val.lessdef v v' ->
  Val.lessdef v (Val.load_result (chunk_of_type ty) v').

Lemma match_stackframes_change_sig: forall s ts sg sg', match_stackframes s ts sg -> sg'.(sig_res) = sg.(sig_res) -> match_stackframes s ts sg'.