Signoff Regression

[donn]

Description

The part that should as unaffected by OpenLane version updates as much as humanly possible is signoff.

DRC, LVS and STAPostPNR especially should return IDENTICAL results across OpenLane versions unless there is a documented and studied change to RCX behavior.

Proposal

We can have a couple of designs that go through just signoff to make sure the behavior is consistent.