Definition shrxl (v w: aval) :=
  match v, w with
  | L i, I j => if Int.ltu j (Int.repr 63) then L(Int64.shrx' i j) else ntop
  | _, _ => ntop1 v
  end.

Lemma shrxl_sound: forall v w u x y, vmatch v x -> vmatch w y -> Val.shrxl v w = Some u -> vmatch u (shrxl x y).