[Webkit-unassigned] [Bug 155551] New: Pathological performance on first execution of a function called with mismatched argument count

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=155551

            Bug ID: 155551
           Summary: Pathological performance on first execution of a
                    function called with mismatched argument count
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Keywords: NeedsRadar
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: oliver at apple.com
                CC: fpizlo at apple.com, mark.lam at apple.com,
                    msaboff at apple.com, sbarati at apple.com

So, i have a case of strange performance if i don’t pass an argument
function f(j) { for (var i = 0 ; i < 10000000; i++) j = (j ?  j * i : 1) ^ (i & j); }; var start = new Date; f(1); var end = new Date; print("1st: " + (end - start) + "ms"); var start = new Date; f(1); var end = new Date; print("2nd: " + (end - start) + "ms")
1st: 245ms
2nd: 223ms

If we do it again, without passing a parameter we get:
function f(j) { for (var i = 0 ; i < 10000000; i++) j = (j ?  j * i : 1) ^ (i & j); }; 
var start = new Date; f(); var end = new Date; print("1st: " + (end - start) + "ms"); 
var start = new Date; f(); var end = new Date; print("2nd: " + (end - start) + "ms")

1st: 11919ms
2nd: 29ms

I tried a couple of permutations, and in general it appears the first run through without passing a parameter never tiers up.

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