Do not add features to classes in rightmost compound selector.

Source/core/css/RuleFeature.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 91 matching lines @@
 
 bool RuleFeatureSet::updateClassInvalidationSets(const CSSSelector& selector)
 {
     if (!supportsClassDescendantInvalidation(selector))
         return false;
 
     Vector<AtomicString> classes;
     AtomicString id;
     AtomicString tagName;
 
-    const CSSSelector* lastSelector = &selector;
-    for (; lastSelector->relation() == CSSSelector::SubSelector; lastSelector = lastSelector->tagHistory()) {
-        extractClassIdOrTag(*lastSelector, classes, id, tagName);
-    }
-    extractClassIdOrTag(*lastSelector, classes, id, tagName);
-
-    for (const CSSSelector* current = &selector ; current; current = current->tagHistory()) {
+    bool rightmostCompoundSelector = true;
+    for (const CSSSelector* current = &selector; current; current = current->tagHistory()) {
+        if (rightmostCompoundSelector) {
+            extractClassIdOrTag(*current, classes, id, tagName);
+            if (current->m_match == CSSSelector::Class)
+                ensureClassInvalidationSet(current->value());
+            if (current->relation() != CSSSelector::SubSelector)
+                rightmostCompoundSelector = false;
+            continue;

[esprehn, 2014/02/21 04:33:46]

I think you want to do this as two loops like before. The first loop is over the
right most compound selector.

[rune, 2014/02/21 10:17:17]

Done that now. I did a break on !SubSelector instead of duplicating the code for
extract* and ensure*. I do a null check on the selector pointer now. If you
think it's safe enough to assume the leftmost selector will always be a
descendant combinator flag, I can change back to not checking and add an assert
instead.

+        }
         if (current->m_match == CSSSelector::Class) {
             DescendantInvalidationSet& invalidationSet = ensureClassInvalidationSet(current->value());
             if (!id.isEmpty())
                 invalidationSet.addId(id);
             if (!tagName.isEmpty())
                 invalidationSet.addTagName(tagName);
             for (Vector<AtomicString>::const_iterator it = classes.begin(); it != classes.end(); ++it) {
                 invalidationSet.addClass(*it);
             }
         }
@@ skipping 289 matching lines @@
     }
 
     invalidationClasses.remove(oldSize, invalidationClasses.size() - oldSize);
     element->clearChildNeedsStyleInvalidation();
     element->clearNeedsStyleInvalidation();
 
     return thisElementNeedsStyleRecalc;
 }
 
 } // namespace WebCore