[Webkit-unassigned] [Bug 99118] New: JSC Should atomize constant strings before handing them to WebCore

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=99118

           Summary: JSC Should atomize constant strings before handing
                    them to WebCore
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: eric at webkit.org
                CC: ggaren at apple.com, oliver at apple.com,
                    barraclough at apple.com


JSC Should atomize constant strings before handing them to WebCore

The Dromaeo dom-query benchmark has the following subtest:

for ( var i = 0; i < num; i++ ) {
    var elems = document.getElementsByTagName("*");
    ret = elems[elems.length-1].nodeType;
}

That spends nearly 10% of total time in AtomicString hash lookups for "*".  "*" is of course already in the AtomicString hash (also a global called WTF::starAtom).

I suspect that JSC may already have code to identify "*" as a constant.  If it were to notice that it is a short string, and to do an AtomicString lookup for it, then it could pass WebCore an already atomized StringImpl, which would cause the AtomicString(const String&) constructor to go down the fast-path, and presumably drop 10% off this test!

I suspect variants of this may affect real world usage, but I don't know how much of a cost Atomizing constants in JSC would be on other benchmarks (or how complicated it would be).  I leave those up to you JSC experts.

I have not yet tested V8 to see if they already do this.

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