Add a fast-path for independent inherited properties

third_party/WebKit/Source/core/style/ComputedStyle.h

Index: third_party/WebKit/Source/core/style/ComputedStyle.h
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.h b/third_party/WebKit/Source/core/style/ComputedStyle.h
index 24caa7832faab720800d3a4962d6fdf33afcfbe8..d18257ccec5a0dcbd5b4bbf51378faa53a637886 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.h
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.h
@@ -163,11 +163,24 @@ protected:
     struct InheritedData {
         bool operator==(const InheritedData& other) const
         {
+            return compareEqualIndependent(other)
+                && compareEqualNonIndependent(other);
+        }
+
+        bool operator!=(const InheritedData& other) const { return !(*this == other); }
+
+        bool compareEqualIndependent(const InheritedData& other) const
+        {
+            return (m_visibility == other.m_visibility)
+                && (m_pointerEvents == other.m_pointerEvents);
+        }
+
+        bool compareEqualNonIndependent(const InheritedData& other) const
+        {
             return (m_emptyCells == other.m_emptyCells)
                 && (m_captionSide == other.m_captionSide)
                 && (m_listStyleType == other.m_listStyleType)
                 && (m_listStylePosition == other.m_listStylePosition)
-                && (m_visibility == other.m_visibility)
                 && (m_textAlign == other.m_textAlign)
                 && (m_textTransform == other.m_textTransform)
                 && (m_textUnderline == other.m_textUnderline)
@@ -178,13 +191,10 @@ protected:
                 && (m_boxDirection == other.m_boxDirection)
                 && (m_rtlOrdering == other.m_rtlOrdering)
                 && (m_printColorAdjust == other.m_printColorAdjust)
-                && (m_pointerEvents == other.m_pointerEvents)
                 && (m_insideLink == other.m_insideLink)
                 && (m_writingMode == other.m_writingMode);
         }
 
-        bool operator!=(const InheritedData& other) const { return !(*this == other); }
-
         unsigned m_emptyCells : 1; // EEmptyCells
         unsigned m_captionSide : 2; // ECaptionSide
         unsigned m_listStyleType : 7; // EListStyleType
@@ -287,6 +297,27 @@ protected:
         // 66 bits
     } m_nonInheritedData;
 
+    // For each inherited property, store a 1 if the stored value was inherited
+    // from its parent, or 0 if it is explicitly set on this element.
+    struct IsInheritedFlags {
+        bool operator==(const IsInheritedFlags& other) const
+        {
+            return m_isPointerEventsInherited == other.m_isPointerEventsInherited
+                && m_isVisibilityInherited == other.m_isVisibilityInherited;
+        }
+
+        bool operator!=(const IsInheritedFlags& other) const { return !(*this == other); }
+
+        // Keep this list of fields in sync with:
+        // - setBitDefaults()
+        // - The ComputedStyle setter, which must take an extra boolean parameter and set this
+        // - propagateIndependentInheritedProperties() in ComputedStyle.cpp
+        // - The compareEqual() methods in the corresponding class
+        // InheritedFlags
+        unsigned m_isPointerEventsInherited : 1;
+        unsigned m_isVisibilityInherited : 1;
+    } m_isInheritedFlags;

[meade_UTC10, 2016/07/13 07:29:13]

It's not clear to me how m_inheritedData and m_isInheritedFlags interact.

I think IsInheritedFlags are the independent properties that are inherited from
the parent style. If that's the case, would it be clearer to call it
m_IndependentlyInheritedData (or Flags?) or something else if I'm
misunderstanding??

[sashab, 2016/07/14 05:08:42]

Added a comment to explain the better way to implement this, as discussed :)

+
 // !END SYNC!
 
 protected:
@@ -336,6 +367,10 @@ protected:
         m_nonInheritedData.m_affectedByDrag = false;
         m_nonInheritedData.m_isLink = false;
         m_nonInheritedData.m_hasRemUnits = false;
+
+        // All properties default to being inherited.

[meade_UTC10, 2016/07/13 07:29:13]

All independently inherited properties?

[sashab, 2016/07/14 05:08:41]

Thanks!! Done.

[sashab, 2016/07/14 05:08:41]

Thanks!! Done.

+        m_isInheritedFlags.m_isPointerEventsInherited = true;
+        m_isInheritedFlags.m_isVisibilityInherited = true;
     }
 
 private:
@@ -365,6 +400,10 @@ public:
     // Computes how the style change should be propagated down the tree.
     static StyleRecalcChange stylePropagationDiff(const ComputedStyle* oldStyle, const ComputedStyle* newStyle);
 
+    // Copies the values of any independent inherited properties from parent to child
+    // child that are not explicitly set in child.

[meade_UTC10, 2016/07/13 07:29:13]

You have the word "child" twice :)

[sashab, 2016/07/14 05:08:41]

Haha thanks :) Nice find

+    static void propagateIndependentInheritedProperties(const ComputedStyle& parent, ComputedStyle& child);
+
     ContentPosition resolvedJustifyContentPosition(const StyleContentAlignmentData& normalValueBehavior) const;
     ContentDistributionType resolvedJustifyContentDistribution(const StyleContentAlignmentData& normalValueBehavior) const;
     ContentPosition resolvedAlignContentPosition(const StyleContentAlignmentData& normalValueBehavior) const;
@@ -1622,6 +1661,10 @@ public:
     bool inheritedEqual(const ComputedStyle&) const;
     bool nonInheritedEqual(const ComputedStyle&) const;
     bool loadingCustomFontsEqual(const ComputedStyle&) const;
+
+    bool independentInheritedEqual(const ComputedStyle&) const;
+    bool nonIndependentInheritedEqual(const ComputedStyle&) const;
+
     bool inheritedDataShared(const ComputedStyle&) const;
 
     bool isDisplayReplacedType() const { return isDisplayReplacedType(display()); }
@@ -1682,6 +1725,10 @@ public:
 
     void addPaintImage(StyleImage*);
 
+    // Inherited setters.
+    void setPointerEventsIsInherited(bool isInherited) { m_isInheritedFlags.m_isPointerEventsInherited = isInherited; }
+    void setVisibilityIsInherited(bool isInherited) { m_isInheritedFlags.m_isVisibilityInherited = isInherited; }
+
     // Initial values for all the properties
     static EBorderCollapse initialBorderCollapse() { return BorderCollapseSeparate; }
     static EBorderStyle initialBorderStyle() { return BorderStyleNone; }