On mismatches between incremental optimizers and instance perturbations in physical design tools

The incremental, "construct by correction" design methodology has become widespread in constraint-dominated DSM design. We study the problem of ECO for physical design domains in the general context of incremental optimization. We observe that an incremental design methodology is typically built from a full optimizer that generates a solution for an initial instance, and an incremental optimizer that generates a sequence of solutions corresponding to a sequence of perturbed instances. Our hypothesis is that in practice, there can be a mismatch between the strength of the incremental optimizer and the magnitude of the perturbation between successive instances. When such a mismatch occurs, the solution quality will degrade-perhaps to the point where the incremental optimizer should be replaced by the full optimizer. We document this phenomenon for three distinct domains-partitioning, placement and routing-using leading industry and academic tools. Our experiments show that current CAD tools may not be correctly designed for ECO-dominated design processes. Thus, compatibility between optimizer and instance perturbation merits attention both as a research question and as a matter of industry design practice.