Also, at behavioural edges what you'll see on Godbolt is compiler bugs. So you learn nothing about what should happen. All popular modern C++ compilers have kn

Also, at behavioural edges what you'll see on Godbolt is compiler bugs. So you learn nothing about what should happen. All popular modern C++ compilers have known bugs and while I'm sure there are C compilers with no known bugs that will be because nobody tested very hard.