Definition setpair (p: rpair mreg) (v: val) (m: t) : t :=
match p with
| One r => set (R r) v m
| Twolong hi lo => set (R lo) (Val.loword  v) (set (R hi) (Val.hiword v) m)
end.

Lemma gpo:
forall p v m l,
forall_rpair (fun r => Loc.diff l (R r)) p -> setpair p v m l = m l.