code: def testAddSubFallback(self):
      torch._lazy.config.set_force_fallback("aten::sub")
      device = get_test_device()
      x = torch.randn(2, 3, 4, device=device)
      y = torch.randn(2, 3, 4, device=device)
      z = torch.zeros(2, 3, 4, device=device)
  
      device = "lazy"
      x_lazy = x.detach().clone().to(device=device)
      y_lazy = y.detach().clone().to(device=device)
      z_lazy = z.detach().clone().to(device=device)
  
      for i in range(10):
          if i < 5:
              z += x + y
          else:
              z += x - y
  
      for i in range(10):
          if i < 5:
              z_lazy += x_lazy + y_lazy
          else:
              z_lazy += x_lazy - y_lazy
          torch._lazy.mark_step()
  
      torch.testing.assert_close(z.cpu(), z_lazy.cpu())
      assert (
          metrics.counter_value("IrNodeReused_torch::lazy::AddTensor")
          >= 8
      )
      metrics.reset()
      torch._lazy.ir_cache.reset()
      torch._lazy.config.set_force_fallback("")
  
file_path: pytorch/test/lazy/test_reuse_ir.py
imports: import torch
  import torch._lazy
  import torch._lazy.config
  import torch._lazy.ir_cache
  import torch._lazy.ts_backend
  import torch._lazy.metrics
  from torch.testing._internal.common_utils import IS_WINDOWS, run_tests, TestCase
  import os
  import unittest
label_desc: Use image node_id 3 for calling the TestLazyReuseIr obj's underlying member method code with example usage: obj.testAddSubFallback() without return types