[Webkit-unassigned] [Bug 92697] New: RenderObject needs a fast-path for removeAllChildren

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=92697

           Summary: RenderObject needs a fast-path for removeAllChildren
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: eric at webkit.org
                CC: jchaffraix at webkit.org, simon.fraser at apple.com,
                    jamesr at chromium.org, kling at webkit.org
            Blocks: 92258


RenderObject needs a fast-path for removeAllChildren

Looking at the sample of the benchmark attached to bug 92258.  We see nearly 10% of total time (on a 300x300 grid sample), spent under ContainerNode::removeChildren() tearing down the associated rendering tree.

Each renderer goes through and tell its ancestor chain that it's dying, and marks the view as needing repaint for its rect. We spend a bunch of time computing those repaint rects, and walking up/down the ancestor chain.

Just like how we have a "fast path" for removing subtrees in the DOM, we need some smarter logic for removing subtrees in the rendering tree.  At least in the non-positioned, flow cases, we should be able to have a single repaint rect instead of all this nonsense.

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