In general, most of the times when something "newly" becomes UB, it was already UB in practice. The most obvious case was the C11/C++11 definition of INT_MIN %

In general, most of the times when something "newly" becomes UB, it was already UB in practice. The most obvious case was the C11/C++11 definition of INT_MIN % -1 to be UB (as everyone tends to implement % as part of a combined / and % instruction, and INT_MIN / -1 is clearly UB).