As a C++ developer, stuff like that is what keeps me up at night. Undefined behaviour optimizations, i.e. optimizations which are undertaken because the compile

As a C++ developer, stuff like that is what keeps me up at night. Undefined behaviour optimizations, i.e. optimizations which are undertaken because the compiler proves that a variable cannot have a specific value, since if it did, that would be undefined behaviour, should probably only be undertaken within the scope of a single expression. Reason being that first, I shouldn't be afraid that editing code in one end of the function can change the semantics of unrelated code somewhere else and second, the code is always written with a specific physical architecture in mind and being unable to reason what it would actually do is very problematic. Said undefined behaviour is also always only undefined within the scope of the C++ language, the machine defines the behaviour perfectly fine. I can, for instance, install a segmentation fault handler and catch places where I dereference a null pointer. In fact, the null page could even be mapped to some hardware device, making null pointers valid. Right now I don't have a way to communicate that fact to the compiler. Worse, we don't have tools that can tell us when code changes semantics from what a trivial -O0 compilation would produce.