Postplacement rewiring by exhaustive search for functional symmetries

Abstract

We propose two new algorithms for rewiring: a postplacement optimization that reconnects pins of a given netlist without changing the logic function and gate locations. In the first algorithm, we extract small subcircuits consisting of several gates from the design and reconnect pins according to the symmetries of the subcircuits. To enhance the power of symmetry detection, we also propose a graph-based symmetry detector that can identify permutational and phase-shift symmetries on multiple input and output wires, as well as hybrid symmetries, creating abundant opportunities for rewiring. Our second algorithm, called long-range rewiring, is based on reconnecting equivalent pins and can augment the first approach for further optimization. We apply our techniques for wirelength optimization and observe that they provide wirelength reduction comparable to that achieved by detailed placement.