// backend_config of type StringAttr (if specified) should be legalized (i.e.
// considered to be illegal if still present after this pass is complete).
std::optional<bool> IsCustomCallLegal(mhlo::CustomCallOp op);

}  // namespace odml
}  // namespace mlir

    tfl_custom.setCustomOptionAttr(
        TFL::ConstBytesAttr::get(rewriter.getContext(), ""));
  }

  rewriter.replaceOp(mhlo_custom_call, tfl_custom);
  return success();
}

std::optional<bool> IsCustomCallLegal(mhlo::CustomCallOp op) {
  if (op.getCallTargetName().starts_with("custom_call.")) {
    auto bc = op.getBackendConfig();
    if (!bc || mlir::isa<mlir::StringAttr>(*bc)) {
      return false;
    }
  }

  target.addLegalDialect<TFL::TensorFlowLiteDialect, mhlo::MhloDialect>();
  target.addLegalOp<func::CallOp, func::ConstantOp, arith::ConstantOp>();
  target.addDynamicallyLegalOp<mhlo::CustomCallOp>(IsCustomCallLegal);
  target.addDynamicallyLegalOp<mhlo::ReduceOp>(IsReduceOpLegal);
  // Converted MHLO ops should be marked illegal here.
  // TODO: b/304003568 - Add TF_TransposeOp folding logic to tflite.