if int(ID) < len(f.Cache.blocks) {
			b = &f.Cache.blocks[ID]
			b.ID = ID
		} else {
			b = &Block{ID: ID}
		}
	}
	b.Kind = kind
	b.Func = f
	b.Preds = b.predstorage[:0]
	b.Succs = b.succstorage[:0]
	b.Values = b.valstorage[:0]
	f.Blocks = append(f.Blocks, b)
	f.invalidateCFG()
	return b
}

func (f *Func) freeBlock(b *Block) {
	if b.Func == nil {

	var states map[string]bool
	for {
		change := false
		deadChange := false
		for _, b := range f.Blocks {
			var b0 *Block
			if debug > 1 {
				b0 = new(Block)
				*b0 = *b
				b0.Succs = append([]Edge{}, b.Succs...) // make a new copy, not aliasing
			}
			for i, c := range b.ControlValues() {
				for c.Op == OpCopy {
					c = c.Args[0]
					b.ReplaceControl(i, c)
				}
			}
			if rb(b) {

//  - auxint will be 0 if not specified.
//  - aux will be nil if not specified.

// blocks are specified using the following format:
// (kind controlvalue succ0 succ1 ...)
// controlvalue must be "nil" or a value expression
// succ* fields must be variables
// For now, the generated successors must be a permutation of the matched successors.

// constant folding
(Trunc16to8  (Const16  [c])) => (Const8   [int8(c)])