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POTry-catch speeding up my code?
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copied!<p>I wrote some code for testing the impact of try-catch, but seeing some surprising results.</p> <pre><code>static void Main(string[] args) { Thread.CurrentThread.Priority = ThreadPriority.Highest; Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.RealTime; long start = 0, stop = 0, elapsed = 0; double avg = 0.0; long temp = Fibo(1); for (int i = 1; i < 100000000; i++) { start = Stopwatch.GetTimestamp(); temp = Fibo(100); stop = Stopwatch.GetTimestamp(); elapsed = stop - start; avg = avg + ((double)elapsed - avg) / i; } Console.WriteLine("Elapsed: " + avg); Console.ReadKey(); } static long Fibo(int n) { long n1 = 0, n2 = 1, fibo = 0; n++; for (int i = 1; i < n; i++) { n1 = n2; n2 = fibo; fibo = n1 + n2; } return fibo; } </code></pre> <p>On my computer, this consistently prints out a value around 0.96..</p> <p>When I wrap the for loop inside Fibo() with a try-catch block like this:</p> <pre><code>static long Fibo(int n) { long n1 = 0, n2 = 1, fibo = 0; n++; try { for (int i = 1; i < n; i++) { n1 = n2; n2 = fibo; fibo = n1 + n2; } } catch {} return fibo; } </code></pre> <p>Now it consistently prints out 0.69... -- it actually runs faster! But why?</p> <p>Note: I compiled this using the Release configuration and directly ran the EXE file (outside Visual Studio).</p> <p>EDIT: <a href="https://stackoverflow.com/a/8928476/282110">Jon Skeet's <em>excellent</em> analysis</a> shows that try-catch is somehow causing the x86 CLR to use the CPU registers in a more favorable way in this specific case (and I think we're yet to understand why). I confirmed Jon's finding that x64 CLR doesn't have this difference, and that it was faster than the x86 CLR. I also tested using <code>int</code> types inside the Fibo method instead of <code>long</code> types, and then the x86 CLR was as equally fast as the x64 CLR.</p> <hr> <p><strong>UPDATE:</strong> It looks like this issue has been fixed by Roslyn. Same machine, same CLR version -- the issue remains as above when compiled with VS 2013, but the problem goes away when compiled with VS 2015. </p>

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