[Webkit-unassigned] [Bug 24463] New: Do not detach/copy QString twice in WebCore::qstring

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=24463

           Summary: Do not detach/copy QString twice in WebCore::qstring
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKit Qt
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: treat at kde.org


Currently, WebCore::qstring is detaching and copying twice for every single
TextRun that is processed and drawn.  This is a very expensive operation and
profiling suggests this method is one of the top ten most expensive operations
in all of QtWebKit.  The patch attached minimizes the QString copying/detaching
to only those cases where it is necessary.

Even with this change this method is still a very expensive operation since
almost all TextRuns contain a character that needs special handling by the
QTextEngine.  A forthcoming patch will address this too, but it requires an
addition to Qt's API.


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