$ cat z.swift 
protocol P {
    func foo() -> Self
}

class A: P {
    required init() {}
    func foo() -> Self { return self.dynamicType.init() }
}
class B: A {
    override func foo() -> B { return B() }
}
class C: B {
    func baz() { print("baz!") }
}

func f0<T: P>(t: T) -> T { return t.foo() }

let c: C = f0(C())
c.baz()

$ swiftc z.swift  && ./z
Segmentation fault: 11