pytorch

33530640 - Add option to automatically handle unsorted variable-length sequences in RNNs (#15225)

Add option to automatically handle unsorted variable-length sequences in RNNs (#15225) Summary: Fixes #3584. Motivation: manually sorting sequences, packing them, and then unsorting them is something a lot of users have complained about doing, especially when we can offer library support for them. Overview: we internally sort sequences before packing them and store a list of `unsorted_indices` that represent how to unsort the sequences inside PackedSequence. The packing helper functions return PackedSequence with the `permutation` field and the unpacking helper functions use it to unsort. To implement this, the following changes were made: - PackedSequence now keeps `sorted_indices` and `unsorted_indices`. These two can be thought of as permutations and are inverses of each other. `sorted_indices` is how the sequences were sorted; `unsorted_indices` is how to unsort the sequences. - Added an `enforce_sorted` argument to pack_sequence and pack_padded_sequence that maintains the legacy behavior of error-ing out on unsorted-sequences. When `enforce_sorted=True`, these functions maintain their ONNX exportability. - pack_sequence(sequences, enforce_sorted) takes in unsorted sequences. - pack_padded_sequence can take in a padded tensor that represents padded, unsorted sequences. - pad_packed_sequence unsorts the PackedSequence such that it is still the inverse operation of packed_padded_sequence. - RNNs apply `sort_indices` to their input hidden state and apply `unsort_indices` to their output hidden state. This is to ensure that the hidden state batches correspond to the user's ordering of input sequences. NOT BC-Breaking - The default for pack_sequence and pack_padded_sequence is `enforce_sorted=True` to avoid breaking ONNX export. To use the new functionality, pass in `enforce_sorted=False` Testing Plan - Modified TestNN.test_pack_sequence, TestNN.test_packed_padded_sequence, and TestNN.test_variable_sequence (RNN test) to check the behavior of unsorted sequences, sorted sequences, and sorted sequences with enforce_sorted=True - test/test_jit.py has a test to see if RNNs are exportable with enforce_sorted=True cc colesbury Pull Request resolved: https://github.com/pytorch/pytorch/pull/15225 Reviewed By: soumith Differential Revision: D13507138 Pulled By: zou3519 fbshipit-source-id: b871dccd6abefffca81bc4e3efef1873faa242ef