continue
		}
		m := module.Version{Path: path, Version: max[path]}
		min = append(min, m)
		walk(m)
		haveBase[path] = true
	}
	// Now the reverse postorder to bring in anything else.
	for i := len(postorder) - 1; i >= 0; i-- {
		m := postorder[i]
		if max[m.Path] != m.Version {
			// Older version.
			continue
		}
		if !have[m] {
			min = append(min, m)
			walk(m)
		}
	}

// Comment assignment.
// We build two lists of all subexpressions, preorder and postorder.
// The preorder list is ordered by start location, with outer expressions first.
// The postorder list is ordered by end location, with outer expressions last.
// We use the preorder list to assign each whole-line comment to the syntax
// immediately following it, and we use the postorder list to assign each
// end-of-line comment to the syntax immediately preceding it.

	}
	f.fe.Fatalf(f.Entry.Pos, msg, args...)
}

// postorder returns the reachable blocks in f in a postorder traversal.
func (f *Func) postorder() []*Block {
	if f.cachedPostorder == nil {
		f.cachedPostorder = postorder(f)
	}
	return f.cachedPostorder
}

func (f *Func) Postorder() []*Block {
	return f.postorder()
}

	defer f.Cache.freeInt8Slice(certain)
	local := f.Cache.allocInt8Slice(f.NumBlocks()) // for our immediate predecessors.
	defer f.Cache.freeInt8Slice(local)

	po := f.postorder()
	nest := f.loopnest()
	b2l := nest.b2l

	for _, b := range po {
		switch b.Kind {
		case BlockExit:
			// Very unlikely.
			local[b.ID] = blEXIT
			certain[b.ID] = blEXIT

    ImmutableSet<N> validated = validate(startNodes);
    return new Iterable<N>() {
      @Override
      public Iterator<N> iterator() {
        return newTraversal().postOrder(validated.iterator());
      }
    };
  }

  abstract Traversal<N> newTraversal();

  @SuppressWarnings("CheckReturnValue")
  private ImmutableSet<N> validate(Iterable<? extends N> startNodes) {

    ImmutableSet<N> validated = validate(startNodes);
    return new Iterable<N>() {
      @Override
      public Iterator<N> iterator() {
        return newTraversal().postOrder(validated.iterator());
      }
    };
  }

  abstract Traversal<N> newTraversal();

  @SuppressWarnings("CheckReturnValue")
  private ImmutableSet<N> validate(Iterable<? extends N> startNodes) {

		return
	}

	backedges := backedges(f)
	if len(backedges) == 0 { // no backedges means no rescheduling checks.
		return
	}

	lastMems := findLastMems(f)

	idom := f.Idom()
	po := f.postorder()
	// The ordering in the dominator tree matters; it's important that
	// the walk of the dominator tree also be a preorder (i.e., a node is
	// visited only after all its non-backedge predecessors have been visited).

	// Instead of iterating over f.Blocks, iterate over their postordering.
	// Liveness information flows backward, so starting at the end
	// increases the probability that we will stabilize quickly.
	po := s.f.postorder()
	for {
		changed := false
		for _, b := range po {
			// Start with known live values at the end of the block
			live.clear()
			live.addAll(s.live[b.ID])

			case OpLoad, OpAtomicLoad8, OpAtomicLoad32, OpAtomicLoad64, OpAtomicLoadPtr, OpAtomicLoadAcq32, OpAtomicLoadAcq64:
				loadAddr.add(v.Args[0].ID)
			case OpMove:
				loadAddr.add(v.Args[1].ID)
			}
		}
	}
	po := f.postorder()
	for {
		n := loadAddr.size()
		for _, b := range po {
			for i := len(b.Values) - 1; i >= 0; i-- {
				v := b.Values[i]
				if !loadAddr.contains(v.ID) {
					continue
				}
				for _, a := range v.Args {

				}
			}
		}
	}

	// Check loop construction
	if f.RegAlloc == nil && f.pass != nil { // non-nil pass allows better-targeted debug printing
		ln := f.loopnest()
		if !ln.hasIrreducible {
			po := f.postorder() // use po to avoid unreachable blocks.
			for _, b := range po {
				for _, s := range b.Succs {
					bb := s.Block()
					if ln.b2l[b.ID] == nil && ln.b2l[bb.ID] != nil && bb != ln.b2l[bb.ID].header {