I do not see there a promise that the cast will produce an invalid pointer, nor anything prohibiting the compiler from rounding the pointer down, thus producing a valid one. “Converted” does not require bit copy. I don’t see how this interpretation is against any section of the spec.

I also do not see any requirement in the quoted text that the casted pointer be dereferenced before noting "the behavior is undefined".

In practice performing a cast doesn't really do much until you dereference, but without a carve out in the spec, it does really mean "the behavior is undefined".

> rounding the pointer down, thus producing a valid one

A "valid" pointer to the wrong object?

> Otherwise, when converted back again, the result shall compare equal to the original pointer.

Doesn't this part exclude the possibility of rounding down?