Buffered Steiner trees for difficult instances

Buffer insertion has become an increasingly critical optimization in high performance design. The problem of finding a delay-optimal buffered Steiner tree has been an active area of research, and excellent solutions exist for most instances. However, current approaches fail to adequately solve a particular class of real-world "difficult" instances which are characterized by a large number of sinks, variations in sink criticalities, and varying polarity requirements. We propose a new Steiner tree construction called C-Tree for these instance types. When combined with van Ginneken style buffer insertion, C-Tree achieves higher quality solutions with fewer resources compared to traditional approaches.