Swift's compiler elides obviously useless RC operations at compile time. It doesn't do anything at runtime though.
> When receiving a return result from such a function or method, ARC releases the value at the end of the full-expression it is contained within, subject to the usual optimizations for local values.
Quote from [2] (section 6 has the full details about optimizations). I believe [3] might be the compiler pass.
There actually is some elision that happens at runtime if you install an autoreleasepool if I recall correctly.
I did actually work at Apple so that’s where my recollection comes from although it’s been 8 years since then and I didn’t work on the compiler side of things so my memory could be faulty.
[1] https://github.com/apple/swift/pull/32233
[2] https://opensource.apple.com/source/lldb/lldb-112/llvm/tools...
I'm not sure Swift supports "static library modules" so in practice any linked object consists of a single module.
> There actually is some elision that happens at runtime if you install an autoreleasepool if I recall correctly.
There is a trick in the ObjC ABI that elides autorelease-returns, but it's deterministic after compilation time so I wouldn't call it a runtime optimization.
> but it's deterministic after compilation time so I wouldn't call it a runtime optimization.
What do you mean? My understanding is that autoreleasepool is 100% at runtime. The compiler is not involved afaik except to know to register autorelease with the currently installed pool.
The compiler emits calls that always put something in the autorelease pool or always don't; there's no smart decisions at runtime that skips it or make the ordering of releases nondeterministic. A garbage collector runs whenever it feels like and so the ordering of finalizations changes.