Quality-Preserving Legalization for Analytical Floorplanning

Authors: Yunqi He, You Li, Ruofan Huang, Hai Zhou

Venue: International Conference on Computer-Aided Design (ICCAD), IEEE/ACM, 2026 — To appear

Floorplanning is a crucial step in VLSI physical design. Analytical floorplanning, which determines macro positions through electrostatic-based mixed-size placement, has become the most prevalent paradigm. However, the resulting floorplan contains inter-macro overlaps that must be resolved by a legalization step. Existing methods minimize displacement from the analytical floorplan without effective topological guidance, leading to inconsistent downstream quality. In this paper, we propose a new legalization workflow that preserves the high quality of analytical floorplanning. We leverage twin binary trees to capture the relation between adjacent blocks, and build a differentiable model to optimize their coordinates. Experiments on TILOS MacroPlacement benchmarks show that our method enables analytical floorplanning to match or surpass commercial and open-source macro placement tools in post-route timing and wirelength.