//
// Remarks on other algorithms evaluated:
//  - GCC's 4.6.3 stable_sort with merge_without_buffer from libstdc++:
//    Not faster.
//  - GCC's __rotate for block rotations: Not faster.
//  - "Practical in-place mergesort" from  Jyrki Katajainen, Tomi A. Pasanen
//    and Jukka Teuhola; Nordic Journal of Computing 3,1 (1996), 27-40:
//    The given algorithms are in-place, number of Swap and Assignments

      %res = "tf.Print"(%add) { message = "add result 2" } : (tensor<*xi32>) -> (tensor<*xi32>)
      tf_executor.yield %add : tensor<*xi32>
    }
    %merge_out:3 = tf_executor.Merge %island1#0, %switch#1 : tensor<*xi32>
    tf_executor.fetch %merge_out#0, %merge_out#1 : tensor<*xi32>, tensor<i32>
  }
  func.return %graph#0, %graph#1 : tensor<*xi32>, tensor<i32>
}

// -----

      %res = "tf.Print"(%add) { message = "add result 2" } : (tensor<*xi32>) -> (tensor<*xi32>)
      tf_executor.yield %add : tensor<*xi32>
    }
    %merge_out:3 = tf_executor.Merge %island1#0, %switch#1 : tensor<*xi32>
    tf_executor.fetch %merge_out#0, %merge_out#1 : tensor<*xi32>, tensor<i32>
  }
  func.return %graph#0, %graph#1 : tensor<*xi32>, tensor<i32>
}

		if po.reaches(r, i, false) {
			return r
		}
	}
	panic("findroot didn't find any root")
}

// mergeroot merges two DAGs into one DAG by creating a new extra root
func (po *poset) mergeroot(r1, r2 uint32) uint32 {
	// Root #0 is special as it contains all constants. Since mergeroot
	// discards r2 as root and keeps r1, make sure that r2 is not root #0,
	// otherwise constants would move to a different root.

  @Override
  Iterator<C> createColumnKeyIterator() {
    Comparator<? super C> comparator = columnComparator();

    Iterator<C> merged =
        Iterators.mergeSorted(
            Iterables.transform(
                backingMap.values(), (Map<C, V> input) -> input.keySet().iterator()),
            comparator);

    return new AbstractIterator<C>() {

  @Override
  Iterator<C> createColumnKeyIterator() {
    Comparator<? super C> comparator = columnComparator();

    Iterator<C> merged =
        Iterators.mergeSorted(
            Iterables.transform(
                backingMap.values(), (Map<C, V> input) -> input.keySet().iterator()),
            comparator);

    return new AbstractIterator<C>() {

   * <p>For any equivalent elements across all {@code iterables}, it is undefined which element is
   * returned first.
   *
   * @since 11.0
   */
  public static <T extends @Nullable Object> Iterable<T> mergeSorted(
      final Iterable<? extends Iterable<? extends T>> iterables,
      final Comparator<? super T> comparator) {
    checkNotNull(iterables, "iterables");
    checkNotNull(comparator, "comparator");

   * <p>For any equivalent elements across all {@code iterables}, it is undefined which element is
   * returned first.
   *
   * @since 11.0
   */
  public static <T extends @Nullable Object> Iterable<T> mergeSorted(
      final Iterable<? extends Iterable<? extends T>> iterables,
      final Comparator<? super T> comparator) {
    checkNotNull(iterables, "iterables");
    checkNotNull(comparator, "comparator");

   * returned first.
   *
   * @since 11.0
   */
  public static <T extends @Nullable Object> UnmodifiableIterator<T> mergeSorted(
      Iterable<? extends Iterator<? extends T>> iterators, Comparator<? super T> comparator) {
    checkNotNull(iterators, "iterators");
    checkNotNull(comparator, "comparator");

   * returned first.
   *
   * @since 11.0
   */
  public static <T extends @Nullable Object> UnmodifiableIterator<T> mergeSorted(
      Iterable<? extends Iterator<? extends T>> iterators, Comparator<? super T> comparator) {
    checkNotNull(iterators, "iterators");
    checkNotNull(comparator, "comparator");