}
			if b.NumControls() != 1 {
				f.Fatalf("exit block %s has no control value", b)
			}
			if !b.Controls[0].Type.IsMemory() {
				f.Fatalf("exit block %s has non-memory control value %s", b, b.Controls[0].LongString())
			}
		case BlockRet:
			if len(b.Succs) != 0 {
				f.Fatalf("ret block %s has successors", b)
			}
			if b.NumControls() != 1 {
				f.Fatalf("ret block %s has nil control", b)

		}
	}
	switch b.Likely {
	case BranchUnlikely:
		s += " (unlikely)"
	case BranchLikely:
		s += " (likely)"
	}
	return s
}

// NumControls returns the number of non-nil control values the
// block has.
func (b *Block) NumControls() int {
	if b.Controls[0] == nil {
		return 0
	}
	if b.Controls[1] == nil {
		return 1
	}
	return 2
}