[Analemma_]

This might be less true now, but for a long time gcc's code was terrible and undocumented on purpose. rms wanted it that way, to make it harder for it to be forked or EEE'd by corporations.

Whether that was a good plan is up for debate, but there you go.

[WalterBright]

People say that dmd's backend is terrible and undocumented, but I don't know what they're talking about:

https://github.com/dlang/dmd/tree/master/src/dmd/backend