Remark eval_shift_imm:
  forall (P: expr -> Prop) n a0 a1 a2 a3,
  (n = Int.zero -> P a0) ->
  (0 <= Int.unsigned n < Int.zwordsize ->
   Int.ltu n Int.iwordsize = true ->
   Int.ltu (Int.sub Int.iwordsize n) Int.iwordsize = true ->
   Int.ltu n Int64.iwordsize' = true ->
   P a1) ->
  (Int.zwordsize <= Int.unsigned n < Int64.zwordsize ->
   Int.ltu (Int.sub n Int.iwordsize) Int.iwordsize = true ->
   P a2) ->
  P a3 ->
  P (if Int.eq n Int.zero then a0
     else if Int.ltu n Int.iwordsize then a1
     else if Int.ltu n Int64.iwordsize' then a2
     else a3).

Theorem eval_modls_base: forall le a b x y z, eval_expr ge sp e m le a x -> eval_expr ge sp e m le b y -> Val.modls x y = Some z -> exists v, eval_expr ge sp e m le (modls_base a b) v /\ Val.lessdef z v.