if (subtypes.size() != 1) {
    return std::nullopt;
  }
  return subtypes[0].getElementType();
}

// Create an `ConstBytesAttr` which encodes the options
// for the `tf.custom` tensor list op to be created. If the given
// op is not a `tf.TensorList*` op, return empty, although this case
// should never be trigged in practice since patterns are only applied
// on `tf.TensorList*` ops.

  }

  auto dataset_while = builder.create<TF::WhileRegionOp>(
      reduce_dataset.getLoc(), while_input_types, /*input=*/while_input_values,
      /*parallel_iterations=*/10, false,
      /*shape_invariant=*/false);

  // `_lower_using_switch_merge` is the default for While ops created
  // in TensorFlow and allows lowering to V1 control flow for loop
  // parallelization.

        xla_tensor->AllocateShapedBuffer(device_tensor->dtype(), shape, client_,
                                         stream_->parent()->device_ordinal()));

    // The cpu_tensor and literal that we created here hold the data of host
    // tensor in descending layout. The layout could be different from layout in
    // device_tensor (but the logical shape has to be the same). The

    TF_DeleteStatus(status);
  }

  // 6. Read `var` using `ctx_1`. This read should succeed since `ctx_1` was
  // created with `isolate_session_state` set to false, and update should
  // preserve it.
  {
    // Create a handle to `var`, using `ctx_1`.
    TFE_TensorHandle* var_handle =
        CreateVarHandle(ctx_1, remote_device, /*variable_name=*/"var");

      moved_ops_list.push_back(new_if_op.getOperation());
    }
  }
}

// Create the Yield ops for both branches with merged results.
// `builder` is the OpBuilder.
// `if_op_segment` refers to the segment of IfRegions to be merged.
// `return_indices` refers to the return indices to be kept in merged IfRegion
// `new_if_op` refers to the created new IfRegion
void CreateYieldOps(

          attr_cst =
              builder.create<ConstOp>(op->getLoc(), output_type, attribute);
        } else {
          attr_cst = builder.create<mlir::arith::ConstantOp>(
              op->getLoc(), cast<TypedAttr>(attribute));
        }
        new_operands.push_back(attr_cst);
      }
    }

    // Create the TFR call op
    auto new_op = builder.create<CallOp>(

    std::string tmp_dir{};
    if (!env_->LocalTempFilename(&tmp_dir)) {
      return absl::InternalError("Failed to create temp file.");
    }

    TF_CHECK_OK(env_->CreateDir(tmp_dir));
    return tmp_dir;
  }

  // Parses `module_op_str` to create a `ModuleOp`. Checks whether the created
  // module op is valid.
  mlir::OwningOpRef<mlir::ModuleOp> ParseModuleOpString(
      const absl::string_view module_op_str) {

      absl::StrCat("device: ", DEVICE_TPU_SYSTEM, " device"));
  devices->push_back(std::make_unique<VirtualDevice>(options.env, attrs));
  VLOG(1) << "Created TPU_SYSTEM device. This host has " << device_count
          << " TPUs";

  return absl::OkStatus();
}

}  // namespace

void RegisterTpuDeviceToDeviceCopy() {
  static auto* const register_tpu_tpu_copy = new CopyTensor::Registration(

namespace mlir {
namespace TF {

namespace {

// Creates ConstOp for int32_t value.
ConstOp createI32ConstOp(int32_t value, Location loc,
                         PatternRewriter* rewriter) {
  auto int_attr = IntegerAttr::get(rewriter->getIntegerType(32), value);
  return rewriter->create<ConstOp>(loc, int_attr);
}

// Creates ConstantOp for array of int32_t.

}

// This is a basic test to make sure the C++ gradient code can handle while
// loops created by the C API (which calls the C++ API under the hood). There
// are more while loop gradient tests in cc/framework/while_gradients_test.cc.
TEST_F(CApiWhileLoopTest, Gradients) {
  Init(1);

  // Create loop: while (i < 10) i += 1
  TF_Operation* ten = ScalarConst(10, params_->cond_graph, s_);
  TF_Operation* less_than =