dynamo stack trace

  /workspace/pytorch/xla/test/dynamo/test_dynamo.py(37)test_simple_model()
-> res_xla_dynamo = self.fn_simple_dynamo(xla_x, xla_y)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/eval_frame.py(212)_fn()
-> return fn(*args, **kwargs)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/eval_frame.py(333)catch_errors()
-> return callback(frame, cache_size, hooks)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/convert_frame.py(480)_convert_frame()
-> result = inner_convert(frame, cache_size, hooks)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/convert_frame.py(103)_fn()
-> return fn(*args, **kwargs)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/utils.py(88)time_wrapper()
-> r = func(*args, **kwargs)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/convert_frame.py(348)_convert_frame_assert()
-> frame,
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/convert_frame.py(400)_compile()
-> out_code = transform_code_object(code, transform)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/bytecode_transformation.py(341)transform_code_object()
-> transformations(instructions, code_options)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/convert_frame.py(385)transform()
-> mutated_closure_cell_contents,
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/symbolic_convert.py(1638)__init__()
-> for k in vars
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/symbolic_convert.py(1639)<genexpr>()
-> if k in f_locals
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/variables/builder.py(170)__call__()
-> return self._wrap(value).clone(**self.options())
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/variables/builder.py(236)_wrap()
-> return self.wrap_tensor(value)
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/variables/builder.py(624)wrap_tensor()
-> source=self.get_source(),
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/variables/builder.py(745)wrap_fx_proxy()
-> **options,
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/variables/builder.py(801)wrap_fx_proxy_cls()
-> example_value, tx=tx, **kwargs
  /opt/conda/lib/python3.7/site-packages/torch/_dynamo/variables/builder.py(952)wrap_to_fake_tensor_and_record()
-> fake_e = wrap_fake_exception(
> /opt/conda/lib/python3.7/site-packages/torch/_dynamo/utils.py(702)wrap_fake_exception()
-> try: