well, this would mean you'd get feedback every time you declare a variable without giving it an initial value? (even if the value is never read from before bein

well, this would mean you'd get feedback every time you declare a variable without giving it an initial value? (even if the value is never read from before being written to - i.e is entirely safe to do?) or how about when you write a for loop? for(int i=0; i<LIMIT; i++) .. the compiler assumes that i cannot overflow in this case, because that would be undefined behaviour. on the most obvious level, it doesn't need to do an overflow check on each loop iteration, if it exploits undefined behaviour. and no, it simply can't check the value of LIMIT before the loop, because i may be changed in the loop body, or LIMIT itself may change. this also allows a myriad of other loop optimisations. pipelining, vectorization, unrolling.. i don't think you realise just how often undefined behaviour is used in compiler optimisations.