Both of those programs are playing with C's infamously broad undefined behavior rules, the first for a non-terminating loop and the second for using too much st

Both of those programs are playing with C's infamously broad undefined behavior rules, the first for a non-terminating loop and the second for using too much stack (when called with a sufficiently large number). -O2 being nice to you is a coincidence, not something you should rely on. In a language which prefers diagnosing programmer error over punting both should be errors.