Definition defined_by_instr (r': mreg) (i: instruction) :=
  match i with
  | Lgetstack sl ofs ty r => r' = r
  | Lop op args res => r' = res
  | Lload chunk addr args dst => r' = dst
  | Lbuiltin ef args res => In r' (params_of_builtin_res res) \/ In r' (destroyed_by_builtin ef)
  | _ => False
  end.

Lemma record_regs_of_function_ok: forall r i, In i f.(fn_code) -> defined_by_instr r i -> is_callee_save r = true -> RegSet.In r record_regs_of_function.