Make getComputedStyle optimization work for adjacent combinators.

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 63cb1e518c441db49e3ef02308e29485cf4d1bf2..6f541e9fec97793ac051a56e69f1674fabf04d13 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -1897,8 +1897,16 @@ 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();