Fix reference cycle in sparse coalesce graph (#52874)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/52253
In the issue reproducer we can replace `torch.sparse.sum(S)` with `S.coalesce()` and get the same memory leak. The reason is that calling `coalesce()` on an already coalesced tensor returns `self`. With autograd, the result gets it's `grad_fn` set to a node that contains a reference to the input tensor, creating a reference cycle. Cloning the tensor fixes this, so `coalesce` always returns a new tensor.
As an aside, `torch.sparse.sum(S)` doesn't need to coalesce. The result should be the same either way.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52874
Reviewed By: bdhirsh
Differential Revision: D27246997
Pulled By: albanD
fbshipit-source-id: 0fe6c11043501a7874a50982afd42964f47470d3
