[E6300]

> The union ensures that the compiler doesn't move "u.lld = 0" above the first print statement, but usually writing from one type and reading from another is undefined behavior no matter how you accomplish it.

I know, but the only reason aliasing becomes an issue is because someone is trying to cast between unrelated pointer types to perform cheap type conversions. Yes, even with the union the behavior is undefined, but if you know the platform you're targeting the program may be well-behaved.

As for your snippets, yes, casting pointers across function boundaries will work. The problem is when you don't want to introduce a call, which is where unions come in.