on legalization of row-based placements
Cell overlaps in the results of global placement are guaranteed to prevent successful routing. However, common techniques for fixing these problems may endanger routing in a different way --- through increased wirelength and congestion. We evaluate several such techniques with routability of row-based placements in mind, and propose new ones that, in conjunction with our detail placer, improve overall routability and routed wirelength. Our generic two-phase approach for resolving illegal placements calls for (i) balancing the numbers of cells in rows, (ii) removing overlaps within rows through a generic dynamic programming procedure. Relevant objectives include minimum total perturbation, minimum wirelength increase and minimum maximum movement. Additionally, we trace cell overlaps in min-cut placement to vertical cuts and show that, if bisection cut directions are varied, overlaps anti-correlate with improved wirelength.Empirical validation is performed using placers Capo and Cadence QPlace, followed by various legalizers and detail placers, with subsequent routing by Cadence WarpRoute. We use a number of IBMv2 benchmarks with routing information. Our legalizer reduces both Capo and QPlace placements' wirelength by up to 4\% compared to results of Capo legalized by Cadence's QPlace in the ECO mode.
legalization placement global routing congestion evaluation generic dynamic programming relevance object movement traces min-cut placement direct use benchmark informal detailed placement