[not for land yet] hacky fix for x.ndim followed by sub (#53120)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53120
Currently there is a pattern which is not handled correctly by
FX graph mode quantization:
```
def forward(self, x):
ndim = x.ndim
# or add, mul, div, etc
x = torch.sub(x, ndim)
return x
```
The reason this does not work is as follows:
1. x.ndim becomes a getattr node
2. the real world type of x.ndim is an integer, but this is not known from the graph (yet)
3. binary ops such as `torch.sub` require quantization of inputs
4. the framework inserts an observer to observe the output of `ndim`
5. the observer fails because `ndim` is not a Tensor
For now, we hack a bandaid to unblock some teams, none of this is for
land. We will have to think of a better fix which is landable (TBD).
Test Plan:
```
python test/test_quantization.py TestQuantizeFx.test_getattr_with_nontensor_result
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D26756180
fbshipit-source-id: c0e498766b22c23df74fbb5aaeaa237c4c944263
