Corollary agree_set_mreg_parallel:
  forall ms sp rs r v v',
  agree ms sp rs ->
  Val.lessdef v v' ->
  agree (Regmap.set r v ms) sp (Pregmap.set (preg_of r) v' rs).

Lemma extcall_arg_match: forall ms sp rs m m' l v, agree ms sp rs -> Mem.extends m m' -> Mach.extcall_arg ms m sp l v -> exists v', Asm.extcall_arg rs m' l v' /\ Val.lessdef v v'.