pytorch

b03b45af - [DDP Comm Hook] Use a single tensor instead of a tensor list as the comm hook result (#62074)

[DDP Comm Hook] Use a single tensor instead of a tensor list as the comm hook result (#62074) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/62074 Since SPMD mode is retired, the comm hook result will always be a single tensor. This can improve comm hook developer experience, as no need to add an extra `[0]` to the precursor future result. #Closes: https://github.com/pytorch/pytorch/issues/61914 ghstack-source-id: 134164593 Test Plan: buck test mode/dev-nosan caffe2/test/distributed:c10d buck test mode/dev-nosan caffe2/test/distributed:distributed_nccl_fork Reviewed By: rohan-varma Differential Revision: D29864732 fbshipit-source-id: 59fe6dd78b66214b1788514ad4d236039d9bda31