Make getComputedStyle optimization work for adjacent combinators.

Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 1879 matching lines @@
     ASSERT(!needsStyleRecalc());
     ASSERT(!childNeedsStyleRecalc());
     ASSERT(inStyleRecalc());
     m_lifecycle.advanceTo(DocumentLifecycle::StyleClean);
 }
 
 void Document::updateRenderTreeForNodeIfNeeded(Node* node)
 {
     bool needsRecalc = needsFullRenderTreeUpdate();
 
-    for (const Node* ancestor = node; ancestor && !needsRecalc; ancestor = NodeRenderingTraversal::parent(*ancestor))
-        needsRecalc = ancestor->needsStyleRecalc() || ancestor->needsStyleInvalidation();
+    for (const Node* ancestor = node; ancestor && !needsRecalc; ancestor = NodeRenderingTraversal::parent(*ancestor)) {
+        bool childrenAffectedByAdjacent = node != ancestor

[esprehn, 2014/12/05 09:52:36]

Can we hoist this out of the loop?

if (node->needsStyleRecalc() || node->needsStyleInvalidation())
  needsRecalc = true;

then do the loop starting from a real ancestor.

for (const ContainerNode* ancestor = NodeRenderingTraversal::parent(*node);
ancestor && !needsRecalc; ancestor = NodeRenderingTraversal::parent(*ancestor))
{
  ...

+            && ancestor->isContainerNode()

[esprehn, 2014/12/05 09:52:36]

this statement doesn't make sense, an ancestor must be a container node. (I get
what the code does, but it's confusing with these names)

+            && (toContainerNode(ancestor)->childrenAffectedByDirectAdjacentRules()
+                || toContainerNode(ancestor)->childrenAffectedByIndirectAdjacentRules());
+
+        needsRecalc = ancestor->needsStyleRecalc()
+            || ancestor->needsStyleInvalidation()
+            || (childrenAffectedByAdjacent && (ancestor->childNeedsStyleRecalc() || ancestor->childNeedsStyleInvalidation()));

[esprehn, 2014/12/05 09:52:36]

It seems like you can combine this with the above bit checks into a single
method like ancestor->needsAdjacentStyleRecalc() that checks

bool Node::needsAdjacentStyleRecalc() const {
  if (!childrenAffectedByDirectAdjacentRules() &&
!childrenAffectedByIndirectAdjacentRules())
    return false;
  return childNeedsStyleRecalc() || childNeedsStyleInvalidation();
}

then the loop is nicely

needsRecalc = ancestor->needsStyleRecalc() || ancestor->needsStyleInvalidation()
|| ancestor->needsAdjacentStyleRecalc();

+    }
 
     if (needsRecalc)
         updateRenderTreeIfNeeded();
 }
 
 void Document::updateLayout()
 {
     ASSERT(isMainThread());
 
     ScriptForbiddenScope forbidScript;
@@ skipping 3911 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif