A single compiler can even seem inconsistent. A conforming compiler is allowed to completely remove undefined behavior like this: if((n << 64) == 0) {

A single compiler can even seem inconsistent. A conforming compiler is allowed to completely remove undefined behavior like this: if((n << 64) == 0) { println("Hi!\n"); } if((n << 64) != 0) { println("Hi!\n"); } If it were implementation-defined, it would have to compile it to the equivalent of println("Hi!\n");