Because dereferencing a null pointer is undefined behavior, the compiler is free to assume it won&#x27;t ever happen. This, in turn, can lead to the compiler optimizing or reordering code in a counter-intuitive manner, completely changing the behavior of a program that you thought you understood.<p>The compiler might emit machine code that attempts to read the memory at location 0. It would also be perfectly within its rights to optimize away that branch of code (if it can prove that it always dereferences null). The code might even appear to work now, and completely break in the next version of the compiler.