[masklinn]

> Hmm, it could be that once UB is encountered the entire program becomes invalid, then.

The UB doesn't actually need to be encountered, just guaranteed to be encountered eventually (in a non-statistical meaning), that is where the time travel comes from e.g. if you have

    if (condition) {
        printf("thing\n");
        1/0;
    } else {
        // other thing
    }

the compiler can turn this into

    if (condition) {
        // crash
    } else {
        // other thing
    }

as well as

    // other thing

In the first case you have "time travel" because the crash occurs before the print, even though in a sequentially consistent world where division by zero was defined as a crash (e.g. in python) you should see the print first.

[LoganDark]

> The UB doesn't actually need to be encountered, just guaranteed to be encountered eventually

That's what I meant. Anything that leads to UB itself has UB.