pytorch

158b8bdc - Cleaning up DDP SPMD in reducer.cpp (#64113)

Cleaning up DDP SPMD in reducer.cpp (#64113) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/64113 Since there is only one model replica per process, `replicas` can be simplified from `std::vector<std::vector<at::Tensor>>` to `std::vector<at::Tensor>` in the Reducer class. Test Plan: All tests are passing `pytest test/distributed/test_c10d_gloo.py -vs` Imported from OSS Reviewed By: mrshenli Differential Revision: D30615965 fbshipit-source-id: d2ec809d99b788c200b01411333e7dbad1269b51