OpBuilder builder(op);
  Operation *new_op = Operation::create(
      op->getLoc(), op->getName(), new_result_types, op->getOperands(),
      op->getAttrs(), op->getPropertiesStorage(), op->getSuccessors(),
      op->getNumRegions());
  builder.insert(new_op);

  // Move region bodies to the new operation.
  for (auto it : llvm::zip(op->getRegions(), new_op->getRegions())) {

  // Clone this old operation but with new result types.
  Operation* new_op = Operation::create(
      op_->getLoc(), op_->getName(), new_result_types, op_->getOperands(),
      op_->getAttrs(), op_->getPropertiesStorage(), op_->getSuccessors(),
      op_->getNumRegions());
  builder.insert(new_op);

  // Move regions to the new op.
  for (auto it : llvm::zip(op_->getRegions(), new_op->getRegions())) {

    return false;
  }

  SmallVector<Type, 4> inferred;
  LogicalResult res = infer_ti.inferReturnTypes(
      op->getContext(), op->getLoc(), op->getOperands(),
      op->getAttrDictionary(), op->getPropertiesStorage(), op->getRegions(),
      inferred);
  if (failed(res)) {
    op->emitOpError("failed to refine type as inference failed");
    return false;
  }

    Operation* op = while_op.getOperation();
    Operation* new_op = rewriter.insert(Operation::create(
        op->getLoc(), op->getName(), types, new_operands, op->getAttrs(),
        op->getPropertiesStorage(), {}, /*numRegions=*/2));

    for (int i = 0; i < 2; ++i) new_op->getRegion(i).takeBody(op->getRegion(i));
    int new_index = 0;
    for (int op_index = 0, e = op->getNumResults(); op_index < e; ++op_index) {