Faster by removing variables - Original and optimised Swift (optimised is 30-40% faster

pointless swift benchmarks

import Foundation

private let testSize = 100_000_000
private var testTime:CFAbsoluteTime = 0
private var optimisedTestTime:CFAbsoluteTime = 0

class Test
{
    func testing2(var x : Int) -> Int
    {
        if x % 3 == 0 {
            x += 10
        }
        x++
        return x
    }
    
    func test()
    {
        var time = NSDate.timeIntervalSinceReferenceDate();
        var x = 0;
        for (var i = 0; i < testSize; i++)
        {
            x = testing2(x)
        }
        let time2 = NSDate.timeIntervalSinceReferenceDate() - time
        NSLog("Original: %i in %f seconds", x, time2)
        testTime = time2
    }
}

Test().test()


final class OptimisedTest
{
    func testing2(x : Int) -> Int
    {
        return x % 3 == 0 ? x + 11 : x + 1
    }
    
    func test()
    {
        let time = CFAbsoluteTimeGetCurrent()
        var x = 0;
        for _ in 0..<testSize {
            x = testing2(x)
        }
        let time2 = CFAbsoluteTimeGetCurrent() - time
        print("Optimised: \(x) in \(time2) seconds")
        optimisedTestTime = time2
    }
}

OptimisedTest().test()

print((testTime / optimisedTestTime) - 1)

I'm slightly surprised that the Swift compiler wasn't eliminating test2 completely before the print out of the result was added or at least identifiying these improvements and making them equivalent.

It is notable that the changes make the code more functional (less vars, more constants).

Unless you built with whole module optimization, we can't devirtualize testing2 because Test may have subclasses in other files. Making Test private or final, or enabling -Owholemodule, should be sufficient to enable that.