rewriter.replaceOp(op, {nullptr, nullptr, lstm_result});
    return success();
  }
};

// Legalize unidirectional seqeucen rnn.
struct LegalizeUnidirectionalSequenceRnn : public RewritePattern {
  explicit LegalizeUnidirectionalSequenceRnn(MLIRContext* context)
      : RewritePattern(kUnidirectionalSequenceRnn, 1, context) {}

  LogicalResult matchAndRewrite(Operation* op,