sure, that's exactly the point I am trying to make: if it takes 75 % time more to compile @ O1 than O0, it means that parsing takes at most ~ 60 % of compilatio

sure, that's exactly the point I am trying to make: if it takes 75 % time more to compile @ O1 than O0, it means that parsing takes at most ~ 60 % of compilation time for quite conservative optimization. I think it is quite common to compile above the lowest level of optimization. To have an accurate estimation, one could look at clang, and only run the tokenizer.