Backward through sparse_coo_tensor (#50361)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/49683
This PR solves Backward through sparse_coo_tensor bug by implementing a `sparse_mask_helper` function for n-dimensional sparse tensor for CPU and CUDA which is used to reimplement `sparse_constructor_values_backward` function.
This `sparse_mask` function was implemented before for backward sparse-sparse matmul. However, the algorithm is little different because in this case it should be applyable not only for matrices but for n-dimensional tensors. Thankfully it was not quite hard to extend and now both share the same code base.
Note that no new tests are required because now the backward for sparse-sparse matmul now uses the new `sparse_mask_helper`.
ngimel, mruberry - kindly review this.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50361
Reviewed By: zhangguanheng66
Differential Revision: D26270483
Pulled By: ngimel
fbshipit-source-id: ee4bda49ff86e769342674b64d3c4bc34eae38ef
