Bring back fast paths for HTMLTagCollection / ClassCollection's access

Source/core/html/HTMLCollection.cpp

Index: Source/core/html/HTMLCollection.cpp
diff --git a/Source/core/html/HTMLCollection.cpp b/Source/core/html/HTMLCollection.cpp
index 14023c7a3d6aeb227faccedbeddf67341e1de004..f600f26df3cd81e9cef7a790188af1e5dee25bcd 100644
--- a/Source/core/html/HTMLCollection.cpp
+++ b/Source/core/html/HTMLCollection.cpp
@@ -269,6 +269,16 @@ template <> inline bool isMatchingElement(const HTMLCollection& htmlCollection,
     return false;
 }
 
+template <> inline bool isMatchingElement(const ClassCollection& collection, const Element& element)
+{
+    return collection.elementMatches(element);
+}
+
+template <> inline bool isMatchingElement(const HTMLTagCollection& collection, const Element& element)
+{
+    return collection.elementMatches(element);
+}
+
 template <> inline bool isMatchingElement(const LiveNodeList& nodeList, const Element& element)
 {
     return nodeList.nodeMatches(element);
@@ -442,11 +452,18 @@ inline Element* nextMatchingChildElement(const HTMLCollection& nodeList, Element
 
 Element* HTMLCollection::traverseToFirstElement(const ContainerNode& root) const
 {
-    if (overridesItemAfter())
-        return virtualItemAfter(0);
-    if (shouldOnlyIncludeDirectChildren())
-        return firstMatchingChildElement(*this, root);
-    return firstMatchingElement(*this, root);
+    switch (type()) {

[arv (Not doing code reviews), 2014/02/04 15:12:36]

Would it make sense to use virtual dispatch instead of switch?

[Inactive, 2014/02/04 15:30:15]

As this is hot code, I think we should avoid virtual calls. A switch is what was
used before my CL that caused the regression so I am merely bringing it back.

+    case HTMLTagCollectionType:
+        return firstMatchingElement(static_cast<const HTMLTagCollection&>(*this), root);
+    case ClassCollectionType:
+        return firstMatchingElement(static_cast<const ClassCollection&>(*this), root);
+    default:
+        if (overridesItemAfter())
+            return virtualItemAfter(0);
+        if (shouldOnlyIncludeDirectChildren())
+            return firstMatchingChildElement(*this, root);
+        return firstMatchingElement(*this, root);
+    }
 }
 
 inline Element* HTMLCollection::traverseNextElement(Element& previous, const ContainerNode& root) const
@@ -461,23 +478,30 @@ inline Element* HTMLCollection::traverseNextElement(Element& previous, const Con
 Element* HTMLCollection::traverseForwardToOffset(unsigned offset, Node& currentElement, unsigned& currentOffset, const ContainerNode& root) const
 {
     ASSERT(currentOffset < offset);
-    if (overridesItemAfter()) {
-        Element* next = &toElement(currentElement);
-        while ((next = virtualItemAfter(next))) {
-            if (++currentOffset == offset)
-                return next;
+    switch (type()) {
+    case HTMLTagCollectionType:
+        return traverseMatchingElementsForwardToOffset(static_cast<const HTMLTagCollection&>(*this), offset, toElement(currentElement), currentOffset, root);
+    case ClassCollectionType:
+        return traverseMatchingElementsForwardToOffset(static_cast<const ClassCollection&>(*this), offset, toElement(currentElement), currentOffset, root);
+    default:
+        if (overridesItemAfter()) {
+            Element* next = &toElement(currentElement);
+            while ((next = virtualItemAfter(next))) {
+                if (++currentOffset == offset)
+                    return next;
+            }
+            return 0;
         }
-        return 0;
-    }
-    if (shouldOnlyIncludeDirectChildren()) {
-        Element* next = &toElement(currentElement);
-        while ((next = nextMatchingChildElement(*this, *next, root))) {
-            if (++currentOffset == offset)
-                return next;
+        if (shouldOnlyIncludeDirectChildren()) {
+            Element* next = &toElement(currentElement);
+            while ((next = nextMatchingChildElement(*this, *next, root))) {
+                if (++currentOffset == offset)
+                    return next;
+            }
+            return 0;
         }
-        return 0;
+        return traverseMatchingElementsForwardToOffset(*this, offset, toElement(currentElement), currentOffset, root);
     }
-    return traverseMatchingElementsForwardToOffset(*this, offset, toElement(currentElement), currentOffset, root);
 }
 
 Element* HTMLCollection::namedItem(const AtomicString& name) const