Comment by jcalvinowens

The "erroneous behavior" redefinition for reads of uninitialized variables is really interesting: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p27...

It does have a runtime cost. There's an attribute to force undefined behavior on read again and avoid the cost:

    int x [[indeterminate]];
    std::cin >> x;