As a C++ compiler developer I don't think these features are what's causing long compilation times. Most of them don't even require any changes to llvm. AFAIK

As a C++ compiler developer I don't think these features are what's causing long compilation times. Most of them don't even require any changes to llvm. AFAIK ranges doesn't, and the changes necessary for coroutines are simpler than you may think. Next time you have a program that takes a while to compile, try profiling clang with perf! It's super interesting.