Embedded KeyPath Optimization Limited to Types Internal to the Module

[filip-sakel]

Description

This PR added support for optimizing key paths out of Embedded code, but it seems to work solely on types declared in the current module. Trying something like Box<String>().count fails for example.

Reproduction

Building with the following flags: -Xfrontend -enable-experimental-feature -Xfrontend Embedded -wmo -Xfrontend -enable-experimental-feature -Xfrontend SymbolLinkageMarkers:

@dynamicMemberLookup
public struct MyBox<T>: ~Copyable {
    init() {
        self.value = UnsafeMutablePointer<T>.allocate(capacity: 1)
    }

    subscript<U>(dynamicMember member: WritableKeyPath<T, U>) -> U {
        @_transparent
        get { return self.value.pointer(to: member)!.pointee }

        @_transparent
        set { self.value.pointer(to: member)!.pointee = newValue }
    }

    subscript<U>(dynamicMember member: KeyPath<T, U>) -> U {
        @_transparent
        get { return self.value.pointer(to: member)!.pointee }
    }

    var value: UnsafeMutablePointer<T>
}

struct MyType {
    var computedProp: Int { 0 }
}

@_used
func useVector() -> Int {
    let myBox = MyBox<MyType>()

    // Works fine :)
    return myBox.computedProp
}


@_used
func useString() -> Int {
    let myBox = MyBox<MyType>()

    // Error: cannot use key path in embedded Swift
    return myBox.count
}

Or see live in Godbolt

Expected behavior

I would expect key paths to external types to also get optimized out.

Environment

Swift version 6.1-dev (LLVM 83bb915697f5992, Swift 1e211b4)
Target: x86_64-unknown-linux-gnu

Additional information

No response