// come right after it.
	after := map[ID][]*Block{}

	// Check each loop header and decide if we want to move it.
	for _, loop := range loopnest.loops {
		b := loop.header
		var p *Block // b's in-loop predecessor
		for _, e := range b.Preds {
			if e.b.Kind != BlockPlain {
				continue
			}
			if loopnest.b2l[e.b.ID] != loop {
				continue
			}
			p = e.b
		}
		if p == nil {
			continue
		}

	}
	for _, r := range rules {
		if r.op == "!<" {
			disallowed = append(disallowed, r)
			continue
		}
		for _, def := range r.def {
			if def == "NONE" {
				errorf("NONE cannot be a predecessor")
				continue
			}
			if !g.addNode(def) {
				errorf("multiple definitions for %s", def)
			}
			for _, less := range r.less {
				if less == "NONE" {
					continue
				}