unsafe_split, unsafe_split_with_sizes, unsafe_chunk operations (#39299)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/36403
Copy-paste of the issue description:
* Escape hatch: Introduce unsafe_* version of the three functions above that have the current behavior (outputs not tracked as views). The documentation will explain in detail why they are unsafe and when it is safe to use them. (basically, only the outputs OR the input can be modified inplace but not both. Otherwise, you will get wrong gradients).
* Deprecation: Use the CreationMeta on views to track views created by these three ops and throw warning when any of the views is modified inplace saying that this is deprecated and will raise an error soon. For users that really need to modify these views inplace, they should look at the doc of the unsafe_* version to make sure their usecase is valid:
* If it is not, then pytorch is computing wrong gradients for their use case and they should not do inplace anymore.
* If it is, then they can use the unsafe_* version to keep the current behavior.
* Removal: Use the CreationMeta on view to prevent any inplace on these views (like we do for all other views coming from multi-output Nodes). The users will still be able to use the unsafe_ versions if they really need to do this.
Note about BC-breaking:
- This PR changes the behavior of the regular function by making them return proper views now. This is a modification that the user will be able to see.
- We skip all the view logic for these views and so the code should behave the same as before (except the change in the `._is_view()` value).
- Even though the view logic is not performed, we do raise deprecation warnings for the cases where doing these ops would throw an error.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39299
Differential Revision: D22432885
Pulled By: albanD
fbshipit-source-id: 324aef091b32ce69dd067fe9b13a3f17d85d0f12
