Keep it straight: teaching placement how to better handle designs with datapaths

As technology scales and frequency increases, a new design style is emerging, referred to as hybrid designs, which contain a mixture of random logic and datapath standard cell components. This work begins by demonstrating that conventional Half-Perimeter Wire Length (HPWL)-driven placers under-perform in terms of regularity and Steiner Wire Length (StWL) for such hybrid designs, and the quality gap between manual placement and automatic placers is more pronounced as the designs become more datapath-oriented. Then, a new unified placement flow that simultaneously handles random logic and datapath standard cells is proposed that significantly improves the placement quality of the datapath while leveraging the speed of modern state-of-the-art placement algorithms. The placement flow is built on top of a leading academic force-directed placer. It consists of a series of novel global and detailed placement techniques, collectively called Structure Aware Placement Techniques (SAPT). The techniques effectively integrate alignment constraints into placement, overcoming the deficiencies of the HPWL objective. Experimental results comparing our placement flow with six state-of-the-art placers on the ISPD 2011 Datapath Benchmark Suite show at least a 32% improvement in total StWL with over a 6x improvement in total routing overflow. In addition, the flow demonstrates an 8.25% improvement in total StWL on industrial hybrid designs.