pytorch

12418a4f - Back out "Revert D28664514: [pytorch][PR] various TensorIterator speed improvements"

Back out "Revert D28664514: [pytorch][PR] various TensorIterator speed improvements" Summary: Original commit changeset: fcad039b7dc8 Test Plan: Existing tests Reviewed By: mruberry Differential Revision: D28720186 fbshipit-source-id: 14ac99ee2d7cafb86b20c979f8917beeefd616e1