[lldb] [llvm] Emit DIE's size in bits when size is not a multiple of 8 (PR #69741)

[David Blaikie via llvm-commits]

dwblaikie wrote:

> > I'm arguing it doesn't fit it particularly well. We use it for bit fields - which are pretty special, for instance, but it seems like this thing isn't quite like that - it does have a whole byte size (if you allocated an array of them, for instance, I'm guessing they're a byte each, right?) but then has some padding bits that can be reused in some circumstances? That's why I'm saying it seems like it fits more closely to the struct padding representation.
> 
> Swift is really clever at packing at packing aggregate types. For example, the discriminator bits for enums are always stored in unused bits of the payload type. For a contrived example, the type Optional<Optional> has a size of 3 bits.

Sure enough - C++ tail padding does similar things: https://godbolt.org/z/4jsYWK6ev - where t2's member is packed into the tail padding of t1, but still leaves more tail padding for t3. (it's not identical, of course - it's somewhere between C++ tail padding and the ad-hoc stuff we have in LLVM for PointerIntPair, where multiple of those can be nested together and use the remaining bits for another element)

https://github.com/llvm/llvm-project/pull/69741