Pre Compiled Headers are 1:1 perf wise identical to Clang modules for our 1 million Loc C++ project modulo system noise. There was no difference in compilation

Pre Compiled Headers are 1:1 perf wise identical to Clang modules for our 1 million Loc C++ project modulo system noise. There was no difference in compilation speed, neither for clean nor incremental builds. We supported them for a while (until 2015 or so; no perf difference over 3 years), but Clang modules gave the exact same perf and was easier to use, and unity builds were much faster for clean builds anyways, so there was no point in maintaining PCH in parallel to these two other options. For people that are not aware, PCH, modules, etc. bought us 20-40% compile time reduction. I expect 30% or so to be typical for projects that are using TUs correctly. A 30% compile time reduction or even a 2x compile time reduction is not “life changing”. It’s peanuts. Particularly compared with the 10-100x compile time reductions that Rust gives you. From 100min to 1 min, that’s a huge difference. From 100 min to 50-70min? That’s an irrelevant difference.