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_pair_match: forall ms sp rs m m' p v, agree ms sp rs -> Mem.extends m m' -> Mach.extcall_arg_pair ms m sp p v -> exists v', Asm.extcall_arg_pair rs m' p v' /\ Val.lessdef v v'.