Does an expression with undefined behaviour that is never actually executed make a program erroneous?

Question

In many discussions about undefined behavior (UB), the point of view has been put forward that in the mere presence in a program of any construct that has UB in a p

Answer 1

Deciding whether a program will perform an integer division by 0 (which is UB) is in general equivalent the halting problem. There is no way a compiler can determine that, in general. And so the mere presence of possible UB can not logically affect the rest of the program: a requirement to that effect in the standard, would require each compiler vendor to provide a halting problem solver in the compiler.

Even simpler, the following program has UB only if the user inputs 0:

#include 
using namespace std;

auto main() -> int
{
    int x;
    if( cin >> x ) cout << 100/x << endl;
}

It would be absurd to maintain that this program in itself has UB.

Once the undefined behavior occurs, however, then anything can happen: the further execution of code in the program is then compromised (e.g. the stack might have been fouled up).