Consider:

import QML

QtObject {
    function test() : int {
        var i = 0, x;
        while (i == 0) {
            x = 1;
            i = 1;
        }

        if (i == 1)
            return x;

        return 0
    }
}

This crashes the compiler because the register access on x in the "if" block is not correctly propagated. The type propagator still handles it via a second pass, but the basic blocks pass does not understand that x is indirectly propagated "backwards" through the "while". Turning off the life time analysis in QQmlJSBasicBlocks::adjustTypes() fixes the problem, but it's yet unclear at what cost.