## Summary
Add three TFLite sequence recurrent operators to the Relax frontend, all
with
coupled input-forget gate (FULL kernel) and float32-only support.
- UNIDIRECTIONAL_SEQUENCE_LSTM
- BIDIRECTIONAL_SEQUENCE_RNN
- BIDIRECTIONAL_SEQUENCE_LSTM
From #19519.
## Changes
- **UNIDIRECTIONAL_SEQUENCE_LSTM**: same layout as single-step LSTM,
unrolls over
time and stacks per-step hidden states. Supports time_major, cell_clip,
proj_clip,
and fused activation.
- **BIDIRECTIONAL_SEQUENCE_RNN**: separate fw/bw RNN cells, backward
scans in
reverse. Supports merge_outputs (concat fw + bw) and split outputs via
Tuple.
- **BIDIRECTIONAL_SEQUENCE_LSTM**: 48-input operator with fw/bw LSTM
cells sharing
the same input tensor. States at indices 35-38.
- All converters propagate final states to exp_tab for multi-step
correctness.
- Peephole, projection, layer norm, and aux input are not supported
(raise
OpNotImplemented).
## Testing
- `test_unidirectional_sequence_lstm_none_activation` — output shape
[batch, time, num_units]
- `test_bidirectional_sequence_rnn_none_activation` —
merge_outputs=True, shape [batch, time, 2*num_units]
- `test_bidirectional_sequence_lstm_none_activation` —
merge_outputs=True, shape [batch, time, 2*num_units]
```bash
python -m pytest tests/python/relax/test_frontend_tflite.py -k "sequence_lstm or sequence_rnn" -v
```
YinHanke
e3933804ee