[SR-7391] CMake: Validate/add checks that all of our .a files depend on each other with interface dependencies

[gottesmm]

Previous ID	SR-7391
Radar	None
Original Reporter	@gottesmm
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, CMake
Assignee	None
Priority	Medium

md5: 1973f6e89dbe685aa987889bcc2b34ee

Issue Description:

I already found a couple of places (for instance libSILOptimizer's linkage against libSIL) where we are not doing this. We really should since this will:

1. Reduce the size of build products by not redundantly adding code to archives.
2. Reduce time spent building up said archives.
3. Reduce the work on the linker.

[gottesmm]

@swift-ci sync

[belkadan]

I'm pretty sure CMake doesn't build up archives in that way. Notice that libswiftSILOptimizer.a doesn't contain a definition for swift::getDeclLinkage but libswiftSIL.a does.

[gottesmm]

Then why did we run into the layering violation problem on Linux? Wasn't that using static libraries as well?

[gottesmm]

Also I verified that when we make the archive for swiftSILOptimizer, we aren't passing in anything but object files. So you are correct it isn't an issue on macOS at least.

[belkadan]

The issues occur when we go to link an executable or dynamic library. CMake builds up a list of libraries, transitively, that it needs to link, and puts them in an order that makes sense for an incremental linker (as opposed to ld64, which links everything all at once). That means our dependencies have to be correct, or that we cheat by specifying certain libraries multiple times.

[gottesmm]

Ok. It was that issue. Then nm. Lets close this.