Answer by DJF for Swift optimization level 'Fastest' breaks sorting of array

This appears to be down to your naming convention within your sorted closure. Changing (p1, p2) to different names will resolve it. With -Ofastest, the compiler seems to be incorrectly doing 2 things:

1) causing p1 and p2 within the closure to refer to the NSDictionarys themselves rather than the closure parameters

2) cleaning up the references to the NSDictionary objects prematurely, given #1

Change the code so the last section shows:

let sortedPersons = persons.sorted { (d1, d2) -> Bool in    (d2["name"] as? String) > (d1["name"] as? String)}