Definition subl (v w: aval) :=
match v, w with
| L i1, L i2 => L (Int64.sub i1 i2)
| Ptr p, L i => if Archi.ptr64 then Ptr (psub p (Ptrofs.of_int64 i)) else Ifptr (poffset p)
| Ptr p, _   => Ifptr (poffset p)
| Ifptr p, L i => if Archi.ptr64 then Ifptr (psub p (Ptrofs.of_int64 i)) else Ifptr (plub (poffset p) (provenance w))
| Ifptr p, _ => Ifptr (plub (poffset p) (provenance w))
| _, _ => ntop2 v w
end.

Lemma subl_sound:
forall v w x y, vmatch v x -> vmatch w y -> vmatch (Val.subl v w) (subl x y).