rewrite C++ __torch_function__ handling to work with TensorList operands (#34725)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/34294
This updates the C++ argument parser to correctly handle `TensorList` operands. I've also included a number of updates to the testing infrastructure, this is because we're now doing a much more careful job of testing the signatures of aten kernels, using the type information about the arguments as read in from `Declarations.yaml`. The changes to the tests are required because we're now only checking for `__torch_function__` attributes on `Tensor`, `Optional[Tensor]` and elements of `TensorList` operands, whereas before we were checking for `__torch_function__` on all operands, so the relatively simplistic approach the tests were using before -- assuming all positional arguments might be tensors -- doesn't work anymore. I now think that checking for `__torch_function__` on all operands was a mistake in the original design.
The updates to the signatures of the `lambda` functions are to handle this new, more stringent checking of signatures.
I also added override support for `torch.nn.functional.threshold` `torch.nn.functional.layer_norm`, which did not yet have python-level support.
Benchmarks are still WIP.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34725
Reviewed By: mruberry
Differential Revision: D22357738
Pulled By: ezyang
