func layoutOrder(f *Func) []*Block {
	order := make([]*Block, 0, f.NumBlocks())
	scheduled := f.Cache.allocBoolSlice(f.NumBlocks())
	defer f.Cache.freeBoolSlice(scheduled)
	idToBlock := f.Cache.allocBlockSlice(f.NumBlocks())
	defer f.Cache.freeBlockSlice(idToBlock)
	indegree := f.Cache.allocIntSlice(f.NumBlocks())
	defer f.Cache.freeIntSlice(indegree)
	posdegree := f.newSparseSet(f.NumBlocks()) // blocks with positive remaining degree

	// is less likely. It's possible to assign a negative
	// unlikeliness (though not currently the case).
	certain := f.Cache.allocInt8Slice(f.NumBlocks()) // In the long run, all outcomes are at least this bad. Mainly for Exit
	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

func dominatorsSimple(f *Func) []*Block {
	// A simple algorithm for now
	// Cooper, Harvey, Kennedy
	idom := make([]*Block, f.NumBlocks())

	// Compute postorder walk
	post := f.postorder()

	// Make map from block id to order index (for intersect call)
	postnum := f.Cache.allocIntSlice(f.NumBlocks())
	defer f.Cache.freeIntSlice(postnum)
	for i, b := range post {
		postnum[b.ID] = i
	}

	// not to generate any more output after the buffer is drained.
	numBlocks := (uint64(len(src)) + blockSize - 1) / blockSize
	if s.overflow || uint64(s.counter)+numBlocks > 1<<32 {
		panic("chacha20: counter overflow")
	} else if uint64(s.counter)+numBlocks == 1<<32 {
		s.overflow = true
	}

	// xorKeyStreamBlocks implementations expect input lengths that are a

	depth      int32 // depth in dominator tree (root=0, its children=1, etc.)
}

func makeLCArange(f *Func) *lcaRange {
	dom := f.Idom()

	// Build tree
	blocks := make([]lcaRangeBlock, f.NumBlocks())
	for _, b := range f.Blocks {
		blocks[b.ID].b = b
		if dom[b.ID] == nil {
			continue // entry or unreachable
		}
		parent := dom[b.ID].ID
		blocks[b.ID].parent = parent

				break levels
			}
		}
	}

	// Allocate scratch locations.
	s.priq.level = s.level
	s.q = make([]*ssa.Block, 0, s.f.NumBlocks())
	s.queued = newSparseSet(s.f.NumBlocks())
	s.hasPhi = newSparseSet(s.f.NumBlocks())
	s.hasDef = newSparseSet(s.f.NumBlocks())
	s.placeholder = s.s.entryNewValue0(ssa.OpUnknown, types.TypeInvalid)

	// Generate phi ops for each variable.
	for n := range vartypes {

	canMove := f.Cache.allocBoolSlice(f.NumValues())
	defer f.Cache.freeBoolSlice(canMove)

	// Compute the memory states of each block.
	startMem := f.Cache.allocValueSlice(f.NumBlocks())
	defer f.Cache.freeValueSlice(startMem)
	endMem := f.Cache.allocValueSlice(f.NumBlocks())
	defer f.Cache.freeValueSlice(endMem)
	memState(f, startMem, endMem)

	for _, b := range f.Blocks {
		for _, v := range b.Values {
			if v.Op.isLoweredGetClosurePtr() {

	// Compute the in-register flag value we want at the end of
	// each block. This is basically a best-effort live variable
	// analysis, so it can be much simpler than a full analysis.
	end := f.Cache.allocValueSlice(f.NumBlocks())
	defer f.Cache.freeValueSlice(end)
	po := f.postorder()
	for n := 0; n < 2; n++ {
		for _, b := range po {
			// Walk values backwards to figure out what flag
			// value we want in the flag register at the start

type SparseTree []SparseTreeNode

// newSparseTree creates a SparseTree from a block-to-parent map (array indexed by Block.ID).
func newSparseTree(f *Func, parentOf []*Block) SparseTree {
	t := make(SparseTree, f.NumBlocks())
	for _, b := range f.Blocks {
		n := &t[b.ID]
		if p := parentOf[b.ID]; p != nil {
			n.parent = p
			n.sibling = t[p.ID].child
			t[p.ID].child = b
		}
	}
	t.numberBlock(f.Entry, 1)
	return t
}

	if lastMems[f.Entry.ID] == nil {
		lastMems[f.Entry.ID] = f.Entry.NewValue0(f.Entry.Pos, OpInitMem, types.TypeMem)
	}

	memDefsAtBlockEnds := f.Cache.allocValueSlice(f.NumBlocks()) // For each block, the mem def seen at its bottom. Could be from earlier block.
	defer f.Cache.freeValueSlice(memDefsAtBlockEnds)

	// Propagate last mem definitions forward through successor blocks.