https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96550
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> --- The compiler can't diagnose this as an error (unless -Werror* is used), because it is only an error if such code is ever called at runtime, which the compiler can't determine at compile time. That is why it is just a warning. And, as an optimizing compiler, the compiler can and does optimize anything that would be only reachable through that statement with UB. This isn't an attempt to punish those who write broken code, but it actually helps a lot in real-world code, something like that can happen frequently, but usually in code that will not be actually encountered at runtime, just the compiler can't prove that.
