swift234

Teach escape analysis about the semantics of copy_addr instructions

If the copy_addr cannot release the destination then it behaves just like a load
followed by a store.

This allows us to stack promote protocol typed array literals.

  protocol Proto { func at() -> Int }

  func testStackAllocation(p: Proto) {
    var a = [p, p, p]

    for e in a {
      print(e.at())
    }
  }