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

[Augusto Noronha via lldb-commits]

augusto2112 wrote:

> I guess one question that might be relevant - does Swift have something like sizeof and what result does it give for these sort of types with bits to spare?

You can't actually use that with these types as these are special compiler builtin types which aren't actually accessible in source code.

> But like I said - it seems like structs with tail padding are similar to this situation - we still describe the whole size of the struct, because that's used for creating arrays of instances, ABI passing, etc. But the tail padding can still be used, in certain circumstances, when laying out a derived class. We encode this as the POD-ness of the type, and so if you wanted to create a class that derived from one described in DWARF you could do so & would know whether or not to put the derived class's members into the tail padding of the base or not.

I understand the rationale of basing this on precedent, but in this case in this case we should break from it for two reasons:

- DW_AT_BIT_SIZE is already a standardized attribute in Dwarf that fits this use case.
- Round up to the nearest byte would lose information, which can be kept with fairly minimal downsides in my opinion.

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