results: a list of futures.
    body_fn: input is [predicate_promise, arg0_future, arg0_promise, arg1_future, arg1_promise, ..., invariant_args] and has no returned results.
  }];

  let arguments = (ins TF_Tensor:$cond,
                       Variadic<TF_Tensor>:$arguments,
                       FlatSymbolRefAttr:$body_fn,
                       I32Attr:$invariant_size);