Comment by myrmidon
I would argue that these cases are pretty rare, and you could always get nominal performance with the __noinit hint, but I think this would seldomly even be needed.
If you have instances of zero-initialized structs where you set individual fields after the initialization, all modern compiler will elide the dead stores in the the typical cases already anyway, and data of relevant size that is supposed to stay uninitialized for long is rare and a bit of an anti-pattern in my opinion anyway.