The compiler is not removing or killing invalid code, you can still find it in the source file. What is doing, in the extreme case, is ignoring it and not gen

The compiler is not removing or killing invalid code, you can still find it in the source file. What is doing, in the extreme case, is ignoring it and not generating asm statements for it. Then again, how it could? Code that will trigger UB has no meaning so the compiler wouldn't know what code to generate. Of course a compiler could assign meaning to some instance to UB. For example I'm pretty sure that in GCC dereferencing a null pointer is not UB, but it is expected to trap (because POSIX) and the execution not to continue except via abnormal edges (exceptions or longjmp). This means that any code that can be proven to be reachable only through a nullpter dereference is effectively dead code, so in practice it can still introduce bugs if it didn't trap.