[SR-3725] Determine if struct data members are addressable or bit-packed

[ematejska]

Previous ID	SR-3725
Radar	rdar://problem/31411205
Original Reporter	@ematejska
Type	Sub-task
Status	Resolved
Resolution	Duplicate

Additional Detail from JIRA

Votes	0
Component/s
Labels	Sub-task, AffectsABI
Assignee	None
Priority	Medium

md5: 5a1de95d2cb7a398b3049ac4759aa21d

Parent-Task:

• SR-7809 Define layout algorithm for structs

duplicates:

• SR-5267 Optional layout is inefficient

Issue Description:

Ahead of ABI stability, consider if struct data members are addressable (i.e. byte-aligned) or if we'd rather do bit-packing to save space.

[bob-wilson]

@swift-ci create

[bob-wilson]

We do not plan to implement densely packed struct members for ABI stability. That is an important thing to do, but we can do it later. For resilient types, the fields are always accessed indirectly by accessors so we can change the layout later without affecting the ABI.

Since this issue was filed to track the work needed for ABI stability, I am going to resolve this as a duplicate of SR-5267, where we will track support for this in the future.