[pytorch] Add native support for segment reduce step1: API definition (#53727)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53727
This is first diff to add native support for segment reduction in PyTorch. It provides similar functionality like torch.scatter or "numpy.ufunc.reduceat".
This diff mainly focuses on API layer to make sure future improvements will not cause backward compatibility issues. Once API is settled, here are next steps I am planning:
- Add support for other major reduction types (e.g. min, sum) for 1D tensor
- Add Cuda support
- Backward support
- Documentation for the op
- Perf optimizations and benchmark util
- Support for multi dimensional tensors (on data and lengths) (not high priority)
- Support for 'indices' (not high priority)
Test Plan: Added unit test
Reviewed By: ngimel
Differential Revision: D26952075
fbshipit-source-id: 8040ec96def3013e7240cf675d499ee424437560
