Different calculation results between -Onone and -O with inout

optbug.swift

// import Foundation

struct S {
    var i: Int
}

func f(inout s: S) -> Int {
    s.i += 1
    return s.i
}

var s = S(i: 0)

// let d = NSDate()


let r1 = f(&s)
let r2 = f(&s)

println("r1 = \(r1), r2 = \(r2)")

~/src [3] % swiftc -Onone optbug.swift; ./optbug
r1 = 1, r2 = 2
~/src % swiftc -O optbug.swift; ./optbug
r1 = 1, r2 = 1

Incidentally, uncommenting that NSDate line makes the problem go away...