Earlier quoted context omitted.
I don't have a source, and maybe I'm misremembering, but I think compilers (for software) and CPU production tooling (for hardware) both bootstrap off their own performance. A better compiler can compile itself more efficiently, same for CPU/chip layout systems.
The original version of the C# compiler was written in C and C++, but today's version is indeed itself written in C#! https://stackoverflow.com/questions/27513234/in-which-langua...
Its been a while, and I think it was gcc 7.x timeframe, and IIRC, you had to have at a min, gcc 4.x available to bootstrap, and it took something like 3 separate bootstrap iterations to get the final compilers was like 4-6 hours if memory serves.