// pair has matching devices or no devices.
  if (auto source = llvm::dyn_cast<tf_executor::NextIterationSourceOp>(op)) {
    return ops_have_same_device(source, source.GetSink());
  } else if (auto sink = llvm::dyn_cast<tf_executor::NextIterationSinkOp>(op)) {
    return ops_have_same_device(sink.GetSource(), sink);
  }

  return llvm::isa<tf_executor::EnterOp, tf_executor::ExitOp,