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..eb0d434633e5b44f33c252af34f610503f9ef663 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); }
+
+        inline bool compareEqualIndependent(const InheritedData& other) const
+        {
+            return (m_visibility == other.m_visibility)

[esprehn, 2016/07/19 03:46:26]

add a comment that these must match the .in file and only properties tagged
independent can be here?

[sashab, 2016/07/19 06:32:38]

Nice, yup done. Also added a TODO to generate this.. Haha :)

+                && (m_pointerEvents == other.m_pointerEvents);
+        }
+
+        inline 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 +297,35 @@ 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.
+    // Each bit in this struct corresponds to a single inherited property;
+    // eventually, all properties will have a bit in here to store whether they
+    // were inherited from their parent or not.
+    // Since two ComputedStyles are equal if their nonInheritedData is equal
+    // regardless of the isInherited flags, this struct is stored separately
+    // to avoid too many subset comparison functions.
+    // TODO(sashab): Move isInheritedFlags closer to inheritedData so that it's
+    // clear which inherited properties have a flag stored and which don't.
+    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;

[esprehn, 2016/07/19 03:46:26]

no m_ on public fields, ComputedStyle is a huge mess of bad naming, sorry it's
confusing :)

[sashab, 2016/07/19 06:32:39]

?? Oh, they are all called m_, so I just changed that... What is it meant to be
called? What style guide are you referring to? If that's the case I'll just
change them all in one go

+        unsigned m_isVisibilityInherited : 1;

[esprehn, 2016/07/19 03:46:26]

why can't we put this in NonInheritedFlags to avoid the bloat?

[sashab, 2016/07/19 06:32:38]

Yeah, that's a good point. Originally I didn't do that because I had to split
the compareEqual() function everywhere, but I've had to do that anyway so now
it's worth it. Thanks!!

P.S. This is a GREAT!!! idea. Makes the patch way smaller & takes up less space,
can't believe I didn't think of it before!! Although a little more confusing
with them all being in NonInheritedData, but this is getting generated anyway so
who cares. Awesome. :D

+    } m_isInheritedFlags;
+
 // !END SYNC!
 
 protected:
@@ -336,6 +375,10 @@ protected:
         m_nonInheritedData.m_affectedByDrag = false;
         m_nonInheritedData.m_isLink = false;
         m_nonInheritedData.m_hasRemUnits = false;
+
+        // All independently inherited properties default to being inherited.
+        m_isInheritedFlags.m_isPointerEventsInherited = true;
+        m_isInheritedFlags.m_isVisibilityInherited = true;
     }
 
 private:
@@ -365,6 +408,10 @@ 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 that are not explicitly set in child.
+    static void propagateIndependentInheritedProperties(const ComputedStyle& parent, ComputedStyle& child);

[Timothy Loh, 2016/07/19 01:29:32]

Why static?

[sashab, 2016/07/19 03:31:35]

Done.

+
     ContentPosition resolvedJustifyContentPosition(const StyleContentAlignmentData& normalValueBehavior) const;
     ContentDistributionType resolvedJustifyContentDistribution(const StyleContentAlignmentData& normalValueBehavior) const;
     ContentPosition resolvedAlignContentPosition(const StyleContentAlignmentData& normalValueBehavior) const;
@@ -1622,6 +1669,10 @@ public:
     bool inheritedEqual(const ComputedStyle&) const;
     bool nonInheritedEqual(const ComputedStyle&) const;
     bool loadingCustomFontsEqual(const ComputedStyle&) const;
+
+    inline bool independentInheritedEqual(const ComputedStyle&) const;
+    inline bool nonIndependentInheritedEqual(const ComputedStyle&) const;
+
     bool inheritedDataShared(const ComputedStyle&) const;
 
     bool isDisplayReplacedType() const { return isDisplayReplacedType(display()); }
@@ -1682,6 +1733,10 @@ 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; }