Issue Description:

public enum RGB: Int, CaseIterable {
    case r, g, b
    
//    @inlinable
//    public static var allCases: [RGB] {
//        return [.r, .g, .b]
//    }
}

//@inlinable
public func test() -> Int {
    var result = 0
    for _ in 0..<100_000_000 {
        for c in RGB.allCases {
            result += c.rawValue
        }
    }
    return result
}

print(test())

I tested above code with time profiler in 3 cases.

• Case 1: `test` is not inlinable && use automatically implemented `allCases` -> 27ms

• Case 2: Make `test` inlinable && use automatically implemented `allCases` -> 480ms

• Case 3: Make `test` inlinable && use manually implemented inlinable `allCases` -> 29ms

In case 2, `RGB.allCases` is always allocating array.
It seems optimization is not working well.