[Webkit-unassigned] [Bug 139651] New: Lazily recompute the nonFastScrollableRegion

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=139651

            Bug ID: 139651
           Summary: Lazily recompute the nonFastScrollableRegion
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: simon.fraser at apple.com

Profiling cssom/non-subpixel-scroll-top-left-values.html is very slow on Yosemite in debug shows 25% of time under:

Running Time    Self        Symbol Name
2310.0ms   28.0%    0.0                               WebCore::Element::setInnerHTML(WTF::String const&, int&)
2281.0ms   27.7%    0.0                                WebCore::replaceChildrenWithFragment(WebCore::ContainerNode&, WTF::PassRefPtr<WebCore::DocumentFragment>, int&)
2279.0ms   27.7%    0.0                                 WebCore::ContainerNode::removeChildren()
2277.0ms   27.6%    0.0                                  WebCore::ContainerNode::removeBetween(WebCore::Node*, WebCore::Node*, WebCore::Node&)
2277.0ms   27.6%    0.0                                   WebCore::destroyRenderTreeIfNeeded(WebCore::Node&)
2276.0ms   27.6%    0.0                                    WebCore::Style::detachRenderTree(WebCore::Element&)
2276.0ms   27.6%    0.0                                     WebCore::Style::detachRenderTree(WebCore::Element&, WebCore::Style::DetachType)
2228.0ms   27.1%    0.0                                      WebCore::RenderObject::destroyAndCleanupAnonymousWrappers()
2228.0ms   27.1%    0.0                                       WebCore::RenderObject::destroy()
2220.0ms   27.0%    0.0                                        WebCore::RenderBlockFlow::willBeDestroyed()
2220.0ms   27.0%    0.0                                         WebCore::RenderBoxModelObject::willBeDestroyed()
2220.0ms   27.0%    0.0                                          WebCore::RenderElement::willBeDestroyed()
2220.0ms   27.0%    0.0                                           WebCore::RenderObject::willBeDestroyed()
2195.0ms   26.6%    0.0                                            WebCore::RenderLayerModelObject::destroyLayer()
2195.0ms   26.6%    0.0                                             WebCore::RenderLayer::~RenderLayer()
2193.0ms   26.6%    0.0                                              WebCore::RenderLayer::~RenderLayer()
2193.0ms   26.6%    0.0                                               WebCore::RenderLayer::~RenderLayer()
2120.0ms   25.7%    0.0                                                WebCore::FrameView::removeScrollableArea(WebCore::ScrollableArea*)
2118.0ms   25.7%    0.0                                                 WebCore::FrameView::scrollableAreaSetChanged()
2118.0ms   25.7%    0.0                                                  WebCore::AsyncScrollingCoordinator::frameViewNonFastScrollableRegionChanged(WebCore::FrameView*)
2113.0ms   25.7%    4.0                                                   WebCore::ScrollingCoordinator::computeNonFastScrollableRegion(WebCore::Frame const*, WebCore::IntPoint const&) const
1543.0ms   18.7%    5.0                                                    WebCore::Region::unite(WebCore::Region const&)
1356.0ms   16.4%    2.0                                                     WebCore::Region::Shape::unionShapes(WebCore::Region::Shape const&, WebCore::Region::Shape const&)
1351.0ms   16.4%    15.0                                                      WebCore::Region::Shape WebCore::Region::Shape::shapeOperation<WebCore::Region::Shape::UnionOperation>(WebCore::Region::Shape const&, WebCore::Region::Shape const&)
658.0ms    8.0%    4.0                                                       WebCore::Region::Shape::appendSpan(int, int const*, int const*)

We should compute this region lazily.

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