pytorch

1154a859 - Add instructional error message for cudnn RNN double backward workaround (#33884)

Add instructional error message for cudnn RNN double backward workaround (#33884) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/33884 Mitigates https://github.com/pytorch/pytorch/issues/5261. It's not possible for us to support cudnn RNN double backwards due to limitations in the cudnn API. This PR makes it so that we raise an error message if users try to get the double backward on a cudnn RNN; in the error message we suggest using the non-cudnn RNN. Test Plan: - added some tests to check the error message Reviewed By: albanD Differential Revision: D20143544 Pulled By: zou3519 fbshipit-source-id: c2e49b3d8bdb9b34b561f006150e4c7551a78fac