Changeset 107173 in webkit

Timestamp:

Feb 8, 2012 8:41:19 PM (12 years ago)

Author:

kling@webkit.org

Message:

Increased style sharing for elements with presentation attributes.
<​http://webkit.org/b/78199>

Reviewed by Antti Koivisto.

When determining whether two elements can share style, we can do a lot better.
Instead of comparing the attribute maps for exact equality, do a property-by-property
comparison of the attributeStyle() and the additionalAttributeStyle() (if any.)

This increases our style sharing hit rate and shaves 100ms off of each cycle on
Chromium's "Moz" page cycler test on my machine.

The function that compares attribute styles has O(n^{2) runtime in the worst case,
where n is the number of properties in the styles. However, given the low number of
properties found in attribute styles, this should be fine, and it doesn't seem to
heat up in profiles.}

• css/CSSStyleSelector.cpp:

(WebCore::attributeStylesEqual):
(WebCore::CSSStyleSelector::canShareStyleWithElement):

Location:

trunk/Source/WebCore

Files:

• ChangeLog (modified) (1 diff)
• css/CSSStyleSelector.cpp (modified) (3 diffs)

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2012-02-08  Andreas Kling  <awesomekling@apple.com>
+
+        Increased style sharing for elements with presentation attributes.
+        <http://webkit.org/b/78199>
+
+        Reviewed by Antti Koivisto.
+
+        When determining whether two elements can share style, we can do a lot better.
+        Instead of comparing the attribute maps for exact equality, do a property-by-property
+        comparison of the attributeStyle() and the additionalAttributeStyle() (if any.)
+
+        This increases our style sharing hit rate and shaves 100ms off of each cycle on
+        Chromium's "Moz" page cycler test on my machine.
+
+        The function that compares attribute styles has O(n^2) runtime in the worst case,
+        where n is the number of properties in the styles. However, given the low number of
+        properties found in attribute styles, this should be fine, and it doesn't seem to
+        heat up in profiles.
+
+        * css/CSSStyleSelector.cpp:
+        (WebCore::attributeStylesEqual):
+        (WebCore::CSSStyleSelector::canShareStyleWithElement):
+
 2012-02-08  Raymond Liu  <raymond.liu@intel.com>
 

trunk/Source/WebCore/css/CSSStyleSelector.cpp

@@ -1195 +1195 @@
 }
 
+// This function makes some assumptions that only make sense for attribute styles (we only compare CSSProperty::id() and CSSProperty::value().)
+static inline bool attributeStylesEqual(StylePropertySet* a, StylePropertySet* b)
+{
+    if (a == b)
+        return true;
+    if (a->propertyCount() != b->propertyCount())
+        return false;
+    unsigned propertyCount = a->propertyCount();
+    for (unsigned i = 0; i < propertyCount; ++i) {
+        const CSSProperty& aProperty = a->propertyAt(i);
+        unsigned j;
+        for (j = 0; j < propertyCount; ++j) {
+            const CSSProperty& bProperty = b->propertyAt(j);
+            if (aProperty.id() != bProperty.id())
+                continue;
+            // We could get a few more hits by comparing cssText() here, but that gets expensive quickly.
+            if (aProperty.value() != bProperty.value())
+                return false;
+            break;
+        }
+        if (j == propertyCount)
+            return false;
+    }
+    return true;
+}
+
 bool CSSStyleSelector::canShareStyleWithElement(StyledElement* element) const
 {
@@ -1210 +1236 @@
         return false;
     if (!!element->attributeStyle() != !!m_styledElement->attributeStyle())
+        return false;
+    StylePropertySet* additionalAttributeStyleA = element->additionalAttributeStyle().get();
+    StylePropertySet* additionalAttributeStyleB = m_styledElement->additionalAttributeStyle().get();
+    if (!additionalAttributeStyleA != !additionalAttributeStyleB)
         return false;
     if (element->isLink() != m_element->isLink())
@@ -1275 +1305 @@
         return false;
 
-    if (element->attributeStyle() && !element->attributeMap()->mapsEquivalent(m_styledElement->attributeMap()))
+    if (element->attributeStyle() && !attributeStylesEqual(element->attributeStyle(), m_styledElement->attributeStyle()))
+        return false;
+
+    if (additionalAttributeStyleA && !attributeStylesEqual(additionalAttributeStyleA, additionalAttributeStyleB))
         return false;