if (!func) {
    return emitError("'f' attribute refers to an undefined function: ")
           << func_name;
  }

  FunctionType func_ty = func.getFunctionType();
  int func_arg_count = func_ty.getNumInputs();
  int arg_count = getArgs().size();

  if (arg_count != func_arg_count) {
    return emitError() << "argument count mismatch: 'args' has " << arg_count