> e.g. removing a check for for overflow is definitely NOT ignoring the behavior. Deleting write because it would be undefined behavior for a pointer to point at some location is also NOT ignoring the behavior.

Depending on how you look at it, this is ignoring the behavior.

For example, say you have this:

    int f(int a) {
        if (a + 1 < a) {
            // Handle error
        }
        // Do work
    }

You have 2 situations:

    1. a + 1 overflows
    2. a + 1 does not overflow

Situation 1 contains undefined behavior. If the compiler decides to "ignor[e] the situation completely", then Situation 1 can be dropped from consideration, leaving Situation 2. Since this is the only situation left, the compiler can then deduce that the condition is always false, and a later dead code elimination pass would result in the removal of the error handling code.

So the compiler is ignoring the behavior, but makes the decision to do so by not ignoring the behavior. It's slightly convoluted, but not unreasonable.