[Webkit-unassigned] [Bug 73754] New: Avoid calling calculateRects in RenderLayer::paintLayer when the rectangles are not needed

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=73754

           Summary: Avoid calling calculateRects in
                    RenderLayer::paintLayer when the rectangles are not
                    needed
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: jchaffraix at webkit.org
                CC: fishd at chromium.org, simon.fraser at apple.com,
                    dglazkov at chromium.org, jamesr at chromium.org
            Blocks: 73714


RenderLayer::paintLayer is called a lot in one of our benchmarks (I will link to it once it is available online) - easily in the order of 1.5 million calls on a sizable table with td { overflow: hidden } after scrolling for several seconds.

Currently we compute all the rectangles (clip rectangles, bounds, background...) even if we don't use them. Skipping this computation can save a lot of time due to the mere number of calls (it would be better to investigate limiting those calls in the first place but this is a separate issue).

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