code: def save_unet_if_not_exist(unet, cache_dir=None):
      """
      Saves an optimized UNet to local file system if it's not there
          Parameters:
              unet: the UNet2DConditionModel instance
              cache_dir: the model path to save the optimized UNet,
                  if None, will use the original UNet path
      """
      unet_attrs = unet_attributes(unet)
  
      # If the controlnet unet exists
      if cache_dir is None:
          cache_dir = unet_attrs["config"]._name_or_path
      exists, cache_path = try_load_existing_model(
          None,
          cache_dir,
          "openvino",
          ipex=False,
          precision="float16",
          additional_suffix="controlnet",
          return_model=False,
          low_memory=False,
          device="CPU",
      )
      if exists:
          unet_exists, unet_cache_path = try_load_existing_model(
              None,
              cache_dir,
              "openvino",
              ipex=False,
              precision="float16",
              return_model=False,
              low_memory=False,
              device="CPU",
          )
          if unet_exists:
              print(f"Deleting the deprecated unet...")
              shutil.rmtree(unet_cache_path)
          shutil.move(cache_path, unet_cache_path)
      else:
          opt_unet = optimize_unet(
              unet,
              unet_attrs,
              accelerator="openvino",
              ipex=False,
              precision="float16",
              cache=True,
              cache_dir=cache_dir,
              return_model=False,
          )
          del opt_unet
      del unet
  
imports: import os
  import time
  import torch
  import shutil
  from collections import OrderedDict
  from diffusers.models import ControlNetModel
  from huggingface_hub import snapshot_download
  from ..common.load import *
  from ..utils.paths import *
  from bigdl.nano.pytorch import InferenceOptimizer
  from bigdl.nano.utils.common import invalidInputError
label_desc: Use image node_id 5 for calling a global function with example usage: save_unet_if_not_exist(unet, cache_dir) without return types