message: add fixme for mutating operations
diff: @@ -318,7 +318,11 @@ public:
  void prepare() override { mtx_out_->copy_from(mtx_shuffled_.get()); }
  - void run() override { mtx_out_->sort_by_column_index(); }
  + void run() override
  + {
  + // FIXME: here, we are measuring sorted input except for the first run
  + mtx_out_->sort_by_column_index();
  + }
  private:
  std::unique_ptr<Mtx> mtx_shuffled_;
  