Despite the fact that the localizer's original motivation was to fix horrendous constant spilling at -O0, shortening live ranges still has net benefits even with optimizations enabled.
On an -Os build of CTMark, doing this improves code size by 0.5% geomean.
There are a few regressions, bullet increasing in size by 0.5%. One example from bullet where code size increased slightly was due to GlobalISel actually now generating the same code as SelectionDAG. So we actually have an opportunity in future to implement better heuristics for localization and therefore be *better* than SDAG in some cases. In relation to other optimizations though that one is relatively minor.