Clustering algorithms have been used to improve the speed and quality of placement. Traditionally,
clustering focuses on the local connections between cells. In this paper, a new clustering algorithm
that is based on the estimated lengths of circuit interconnects and the connectivity is proposed. In
the proposed algorithm, first an a priori length estimation technique is used to estimate the lengths
of nets. Then, the estimated lengths are used in a clustering framework to modify a clustering
technique based on algebraic multigrid (AMG), that finds the cells with the highest connectivity.
Finally, based on the results from the AMG-based process, clusters are made. In addition, a
new physical unclustering technique is proposed. The results show a significant improvement,
reductions of up to 40%, in wire length can be achieved when using the proposed technique with
three academic placers on industry-based circuits. Moreover, the runtime is not significantly
degraded and can even be improved.
A New Length-Based Algebraic Multigrid Clustering Algorithm