Remark find_label_add_delta_ranges:
forall lbl c before after, find_label lbl (add_delta_ranges before after c) = find_label lbl c.

Lemma find_label_match:
forall f tf lbl c,
match_function f tf ->
find_label lbl f.(fn_code) = Some c ->
exists before after tc, find_label lbl tf.(fn_code) = Some (add_delta_ranges before after tc) /\ match_code c tc.