GCC advances frequently break code exploiting undefined behavior that had been working in a certain way for years. "Works as you'd expect" is certainly one of t

GCC advances frequently break code exploiting undefined behavior that had been working in a certain way for years. "Works as you'd expect" is certainly one of the possibilities of undefined behavior, after all, but that's no guarantee the next compiler version will continue to work as you'd expect. In fact I'm pretty sure a GCC update broke this exact type of code in the Linux kernel, by effectively removing null pointer checks after the optimizer used its knowledge of a pointer use later in a function to assume that the pointer must be valid and non-null (after all, if it had been null, the behavior would be undefined, and the compiler is allowed to assume no undefined behavior happens, which means the earlier null pointer check had been redundant). I believe that got fixed in GCC to do what you'd expect, but that's just one example of the awesomeness of undefined behavior in C-based languages.