Not just traps... systems level code often relies on what is by the standard "Undefined Behavior" but is in fact well defined for that implementation, something the standard allows for very good reason. At the end of the day interacting with hardware sometimes requires doing things that "No Sane Programmer" would ever do normally. Most of undefined behavior is a nice way to say that the standard is not going to try to define something that is probably an artifact of the implementation. Compiler writers can however use and abuse the fact that there is no constraints. MSVC will prune code with undefined behavior. Clang may call the never-called (only if not static or in an anonymous namespace), etc. Undefined behavior is only undefined by the standard... in most cases it has very well defined results.. for a specific implementation and hardware set.