That happens once in a while when you try to exploit undefined behavior. I don't do that in my code. I use undefined behavior sanitizer to prove that statement (without that tool I make mistakes)
But it's not the programmer trying to exploit undefined behavior, it's the compiler. That's just wrong. How would you check for a null pointer in a way that the compiler can't optimize away?
I sort-of agree with you that 'exploiting' undefined behaviour is a bad thing. But that's what C (and C++) are all about: the undefined behaviour everywhere allows the compiler to make lots of optimizations without having laboriously to prove that they are safe. And those languages are all about speed at the expense of safety.
If you want (more) safety, there are languages for that.
Including C dialects you get via various compiler flags. Eg the Linux kernel uses a special gcc compiler flag to keep all null checks. For this very reason.
