Proof with (try discriminate).
intros. unfold is_intconst in *.
destruct a... destruct o... inv H. inv H0. destruct vl; inv H5. auto.
Qed.

Theorem eval_modls:
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 a b) v /\ Val.lessdef z v.