// returns `std::nullopt`.
std::optional<llvm::StringRef> GetTpuClusterName(Operation* op) {
  if (auto tpu_status = op->getAttrOfType<StringAttr>(kTpuStatusAttr)) {
    // Borrow cluster name from TPU status (for `TPUCompilationResult` op).
    return tpu_status.getValue();
  }
  auto device_type = op->getAttrOfType<StringAttr>(TF::kCompileDeviceTypeAttr);
  if (!device_type || device_type.getValue() != TF::kTpuDevice) {