It's a stupid convention of compiler writers and standards writers at the expense of common sense and engineering standards. In fact there are many thousands of lines of C code that depend on compilers doing something sensible with UB. For example 0 is a valid address in many cases (even in some versions of UNIX). The decision to allow compiler writers to make counter-factual assumptions on the basis of UB is the kind of decision one expects from petty bureaucrats.
>For example 0 is a valid address in many cases (even in some versions of UNIX).
0 may be a valid address at runtime, but a NULL pointer is always invalid.
On such platforms, the compiler should handle 0 pointer values correctly - and the NULL pointer may not have a 0 value, and must not compare equal to any valid pointer.
But 0 or NULL constant, when converted to a pointer type, MUST result in a NULL pointer value - which may be nonzero. Dereferencing such a pointer is an UB.
