Kefir C17/C23 Compiler (opens in new tab)

I think they provide enough information to take a reasonable guess. It seems likely to me that the author is the type of programmer who prefers to understand what their code is doing, with as little magic involved as possible. Using other people's compilers is very magical, all kinds of transformations are being applied to the code you wrote and you are relying entirely on abstractions without really knowing how your code translates to controlling the hardware. Some people prefer to know exactly that.

c-testsuite is amazing. i use it to test my compiler, but even after passing the test. my compiler still choke on some real world project. also the tests lack many of arcane preprocessor rules. so you still need to read https://www.spinellis.gr/blog/20060626/ in order to understand hideset and its macro expansion algorithm.