[WIP]Relax some limitations of InferenceMode. (#54403)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54403
A few important points about InferenceMode behavior:
1. All tensors created in InferenceMode are inference tensors except for view ops.
- view ops produce output has the same is_inference_tensor property as their input.
Namely view of normal tensor inside InferenceMode produce a normal tensor, which is
exactly the same as creating a view inside NoGradMode. And view of
inference tensor outside InferenceMode produce inference tensor as output.
2. All ops are allowed inside InferenceMode, faster than normal mode.
3. Inference tensor cannot be saved for backward.
Test Plan: Imported from OSS
Reviewed By: ezyang
Differential Revision: D27316483
Pulled By: ailzhang
fbshipit-source-id: e03248a66d42e2d43cfe7ccb61e49cc4afb2923b
