Add a bitfield in LayoutObject for whether it corresponds to an effective root scroller.

This saves almost 4% of hit test time on some examples, and improves performance of
occlusion hit testing for IOv2 accordingly.

Bug: 831762

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I045e0414c84208b60796fe44ea023ebbb3fbe40a
Reviewed-on: https://chromium-review.googlesource.com/1152296
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578704}

third_party/blink/renderer/core/layout/layout_box.cc

@@ -63,7 +63,6 @@
 #include "third_party/blink/renderer/core/layout/shapes/shape_outside_info.h"
 #include "third_party/blink/renderer/core/page/autoscroll_controller.h"
 #include "third_party/blink/renderer/core/page/page.h"
-#include "third_party/blink/renderer/core/page/scrolling/root_scroller_util.h"
 #include "third_party/blink/renderer/core/page/scrolling/scrolling_coordinator.h"
 #include "third_party/blink/renderer/core/page/scrolling/snap_coordinator.h"
 #include "third_party/blink/renderer/core/paint/adjust_paint_offset_scope.h"
@@ -120,7 +119,7 @@ PaintLayerType LayoutBox::LayerTypeRequired() const {
       HasHiddenBackface() || HasReflection() || Style()->SpecifiesColumns() ||
       Style()->IsStackingContext() ||
       Style()->ShouldCompositeForCurrentAnimations() ||
-      RootScrollerUtil::IsEffective(*this))
+      IsEffectiveRootScroller())
     return kNormalPaintLayer;
 
   if (HasOverflowClip())
@@ -1512,7 +1511,7 @@ bool LayoutBox::HitTestAllPhases(HitTestResult& result,
   // Check if we need to do anything at all.
   // If we have clipping, then we can't have any spillout.
   // TODO(pdr): Why is this optimization not valid for the effective root?
-  if (!RootScrollerUtil::IsEffective(*this)) {
+  if (!IsEffectiveRootScroller()) {
     LayoutRect overflow_box =
         (HasOverflowClip() || ShouldApplyPaintContainment())
             ? BorderBoxRect()
@@ -1918,7 +1917,7 @@ LayoutRect LayoutBox::OverflowClipRect(
     OverlayScrollbarClipBehavior overlay_scrollbar_clip_behavior) const {
   LayoutRect clip_rect;
 
-  if (RootScrollerUtil::IsEffective(*this)) {
+  if (IsEffectiveRootScroller()) {
     // If this box is the effective root scroller, use the viewport clipping
     // rect since it will account for the URL bar correctly which the border
     // box does not. We can do this because the effective root scroller is

third_party/blink/renderer/core/layout/layout_embedded_content.cc

@@ -35,7 +35,6 @@
 #include "third_party/blink/renderer/core/layout/hit_test_result.h"
 #include "third_party/blink/renderer/core/layout/layout_analyzer.h"
 #include "third_party/blink/renderer/core/layout/layout_view.h"
-#include "third_party/blink/renderer/core/page/scrolling/root_scroller_util.h"
 #include "third_party/blink/renderer/core/paint/embedded_content_painter.h"
 
 namespace blink {
@@ -290,7 +289,7 @@ CursorDirective LayoutEmbeddedContent::GetCursor(const LayoutPoint& point,
 LayoutRect LayoutEmbeddedContent::ReplacedContentRect() const {
   LayoutRect content_rect = ContentBoxRect();
   // IFrames set as the root scroller should get their size from their parent.
-  if (ChildFrameView() && View() && RootScrollerUtil::IsEffective(*this))
+  if (ChildFrameView() && View() && IsEffectiveRootScroller())
     content_rect = LayoutRect(LayoutPoint(), View()->ViewRect().Size());
 
   // We don't propagate sub-pixel into sub-frame layout, in other words, the

third_party/blink/renderer/core/layout/layout_object.cc

@@ -178,6 +178,7 @@ struct SameSizeAsLayoutObject : DisplayItemClient {
 #endif
   unsigned bitfields_;
   unsigned bitfields2_;
+  unsigned bitfields3_;
   // The following fields are in FragmentData.
   LayoutRect visual_rect_;
   LayoutPoint paint_offset_;

third_party/blink/renderer/core/layout/layout_object.h

@@ -921,6 +921,16 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
 
   bool HasShapeOutside() const { return StyleRef().ShapeOutside(); }
 
+  // Return true if the given object is the effective root scroller in its
+  // Document. See |effective root scroller| in page/scrolling/README.md.
+  // Note: a root scroller always establishes a PaintLayer.
+  // This bit is updated in
+  // RootScrollerController::RecomputeEffectiveRootScroller in the LayoutClean
+  // document lifecycle phase.
+  bool IsEffectiveRootScroller() const {
+    return bitfields_.IsEffectiveRootScroller();
+  }
+
   // The pseudo element style can be cached or uncached.  Use the cached method
   // if the pseudo element doesn't respect any pseudo classes (and therefore
   // has no concept of changing state).
@@ -1139,6 +1149,9 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
   void SetCanContainFixedPositionObjects(bool can_contain_fixed_position) {
     bitfields_.SetCanContainFixedPositionObjects(can_contain_fixed_position);
   }
+  void SetIsEffectiveRootScroller(bool is_effective_root_scroller) {
+    bitfields_.SetIsEffectiveRootScroller(is_effective_root_scroller);
+  }
 
   virtual void Paint(const PaintInfo&) const;
 
@@ -2411,6 +2424,7 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
           inside_blocking_touch_event_handler_(false),
           effective_whitelisted_touch_action_changed_(true),
           descendant_effective_whitelisted_touch_action_changed_(false),
+          is_effective_root_scroller_(false),
           positioned_state_(kIsStaticallyPositioned),
           selection_state_(static_cast<unsigned>(SelectionState::kNone)),
           background_obscuration_state_(kBackgroundObscurationStatusInvalid),
@@ -2635,10 +2649,7 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
     ADD_BOOLEAN_BITFIELD(descendant_effective_whitelisted_touch_action_changed_,
                          DescendantEffectiveWhitelistedTouchActionChanged);
 
-   protected:
-    // Use protected to avoid warning about unused variable.
-    // Increment this to 63 if a new bit is added.
-    // unsigned unused_bits_ : 0;
+    ADD_BOOLEAN_BITFIELD(is_effective_root_scroller_, IsEffectiveRootScroller);
 
    private:
     // This is the cached 'position' value of this object

third_party/blink/renderer/core/layout/ng/layout_ng_mixin.cc

@@ -20,7 +20,6 @@
 #include "third_party/blink/renderer/core/layout/ng/ng_length_utils.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_physical_box_fragment.h"
 #include "third_party/blink/renderer/core/layout/ng/ng_relative_utils.h"
-#include "third_party/blink/renderer/core/page/scrolling/root_scroller_util.h"
 #include "third_party/blink/renderer/core/paint/adjust_paint_offset_scope.h"
 #include "third_party/blink/renderer/core/paint/ng/ng_block_flow_painter.h"
 #include "third_party/blink/renderer/core/paint/ng/ng_paint_fragment.h"
@@ -327,7 +326,7 @@ bool LayoutNGMixin<Base>::NodeAtPoint(
   // LayoutBox in the paint layer, regardless of writing mode or whether the box
   // was placed by NG or legacy.
   const LayoutPoint physical_offset = accumulated_offset + Base::Location();
-  if (!RootScrollerUtil::IsEffective(*this)) {
+  if (!this->IsEffectiveRootScroller()) {
     // Check if we need to do anything at all.
     // If we have clipping, then we can't have any spillout.
     LayoutRect overflow_box = Base::HasOverflowClip()

third_party/blink/renderer/core/page/scrolling/root_scroller_controller.cc

@@ -215,6 +215,11 @@ void RootScrollerController::RecomputeEffectiveRootScroller() {
         }
       }
     }
+    if (auto* object = old_effective_root_scroller->GetLayoutObject())
+      object->SetIsEffectiveRootScroller(false);
+
+    if (auto* object = new_effective_root_scroller->GetLayoutObject())
+      object->SetIsEffectiveRootScroller(true);
   }
 
   ApplyRootScrollerProperties(*old_effective_root_scroller);

third_party/blink/renderer/core/page/scrolling/root_scroller_util.cc

@@ -66,14 +66,6 @@ PaintLayer* PaintLayerForRootScroller(const Node* node) {
   return box->Layer();
 }
 
-bool IsEffective(const LayoutBox& box) {
-  if (!box.GetNode())
-    return false;
-
-  return box.GetNode() ==
-         &box.GetDocument().GetRootScrollerController().EffectiveRootScroller();
-}
-
 bool IsGlobal(const LayoutBox& box) {
   if (!box.GetNode() || !box.GetNode()->GetDocument().GetPage())
     return false;
@@ -84,13 +76,6 @@ bool IsGlobal(const LayoutBox& box) {
                               .GlobalRootScroller();
 }
 
-bool IsEffective(const PaintLayer& layer) {
-  if (!layer.GetLayoutBox())
-    return false;
-
-  return IsEffective(*layer.GetLayoutBox());
-}
-
 bool IsGlobal(const PaintLayer& layer) {
   if (!layer.GetLayoutBox())
     return false;

third_party/blink/renderer/core/page/scrolling/root_scroller_util.h

@@ -25,12 +25,6 @@ ScrollableArea* ScrollableAreaForRootScroller(const Node*);
 // rather than <html>'s since scrolling is handled by LayoutView.
 PaintLayer* PaintLayerForRootScroller(const Node*);
 
-// Return true if the given object is the effective root scroller in its
-// Document. See |effective root scroller| in README.md. Note: a root scroller
-// always establishes a PaintLayer.
-bool IsEffective(const LayoutBox&);
-bool IsEffective(const PaintLayer&);
-
 bool IsGlobal(const LayoutBox&);
 bool IsGlobal(const PaintLayer&);
 bool IsGlobal(const Element*);

third_party/blink/renderer/core/paint/paint_layer.cc

@@ -68,7 +68,6 @@
 #include "third_party/blink/renderer/core/layout/svg/layout_svg_resource_clipper.h"
 #include "third_party/blink/renderer/core/layout/svg/layout_svg_root.h"
 #include "third_party/blink/renderer/core/page/page.h"
-#include "third_party/blink/renderer/core/page/scrolling/root_scroller_util.h"
 #include "third_party/blink/renderer/core/page/scrolling/scrolling_coordinator.h"
 #include "third_party/blink/renderer/core/page/scrolling/sticky_position_scrolling_constraints.h"
 #include "third_party/blink/renderer/core/paint/box_reflection_utils.h"
@@ -2538,7 +2537,7 @@ bool PaintLayer::IntersectsDamageRect(
 LayoutRect PaintLayer::LogicalBoundingBox() const {
   LayoutRect rect = GetLayoutObject().VisualOverflowRect();
 
-  if (RootScrollerUtil::IsEffective(*this) || IsRootLayer()) {
+  if (GetLayoutObject().IsEffectiveRootScroller() || IsRootLayer()) {
     rect.Unite(LayoutRect(rect.Location(),
                           GetLayoutObject().View()->ViewRect().Size()));
   }
@@ -2659,7 +2658,7 @@ LayoutRect PaintLayer::BoundingBoxForCompositingInternal(
       !HasVisibleDescendant())
     return LayoutRect();
 
-  if (RootScrollerUtil::IsEffective(*this) || IsRootLayer()) {
+  if (GetLayoutObject().IsEffectiveRootScroller() || IsRootLayer()) {
     // In root layer scrolling mode, the main GraphicsLayer is the size of the
     // layout viewport. In non-RLS mode, it is the union of the layout viewport
     // and the document's layout overflow rect.