auto function = dyn_cast_or_null<mlir::func::FuncOp>(
      SymbolTable::lookupSymbolIn(module, op.getReducer()));
  if (!function) return op.emitOpError() << "No reducer";
  if (!function.getBody().hasOneBlock())
    return op.emitOpError() << "reducer has more than one block";

  return success();
}

//===----------------------------------------------------------------------===//
// XlaVariadicSortOp

        start_indices_tensor);
    return success();
  };
};

template <typename ReturnOpType>
bool MatchTopKComparator(Region& comparator) {
  if (!comparator.hasOneBlock()) return false;
  Block& comparator_blk = comparator.front();
  using OpListType = llvm::iplist<Operation>;
  OpListType& operations = comparator_blk.getOperations();
  if (operations.size() != 2) return false;