iterator_range<
      llvm::filter_iterator<SmallVector<MergedIsland>::const_iterator,
                            function_ref<bool(const MergedIsland&)>>>
  GetMergableIslands() const {
    function_ref<bool(const MergedIsland&)> filter_fn =
        [](const MergedIsland& merged_island) {
          return merged_island.islands.size() > 1;
        };