Store :last/first-child state as restyle flags.

Source/core/dom/ContainerNode.cpp

Index: Source/core/dom/ContainerNode.cpp
diff --git a/Source/core/dom/ContainerNode.cpp b/Source/core/dom/ContainerNode.cpp
index d70e39e2f626376c4ac1739efc79423c41ab39f7..84f313231a43233e5e35d4e1b4f7d396b4e287a9 100644
--- a/Source/core/dom/ContainerNode.cpp
+++ b/Source/core/dom/ContainerNode.cpp
@@ -1289,20 +1289,18 @@ void ContainerNode::checkForSiblingStyleChanges(SiblingCheckType changeType, Nod
         ASSERT(changeType != FinishedParsingChildren);
         // Find our new first child element.
         Element* firstChildElement = ElementTraversal::firstChild(*this);
-        RenderStyle* firstChildElementStyle = firstChildElement ? firstChildElement->renderStyle() : nullptr;
 
         // Find the first element after the change.
         Element* elementAfterChange = nodeAfterChange->isElementNode() ? toElement(nodeAfterChange) : ElementTraversal::nextSibling(*nodeAfterChange);
-        RenderStyle* elementAfterChangeStyle = elementAfterChange ? elementAfterChange->renderStyle() : nullptr;
 
         // This is the element insertion as first child element case.
-        if (firstChildElement != elementAfterChange && elementAfterChangeStyle && elementAfterChangeStyle->firstChildState()) {
-            ASSERT(changeType == SiblingElementInserted);
+        if (changeType == SiblingElementInserted && elementAfterChange && firstChildElement != elementAfterChange
+            && (!nodeBeforeChange || !nodeBeforeChange->isElementNode()) && elementAfterChange->affectedByFirstChildRules()) {
             elementAfterChange->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::SiblingSelector));

[rune, 2014/11/26 15:14:05]

Since the flag is not cleared for every recalc, false positives may happen for
affectedByFirstChildRules(). That means the changeType may be different from
SiblingElementInserted at this point. I've moved it to the if-test instead. To
reduce the effect of false positives, I've added a check that if
nodeBeforeChange is a non-null element, the inserted child is not the new
firstChild, hence we don't need to update styles.

         }
 
         // This is the first child element removal case.
-        if (changeType == SiblingElementRemoved && firstChildElement == elementAfterChange && firstChildElement && (!firstChildElementStyle || !firstChildElementStyle->firstChildState()))
+        if (changeType == SiblingElementRemoved && firstChildElement == elementAfterChange && firstChildElement && firstChildElement->affectedByFirstChildRules())
             firstChildElement->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::SiblingSelector));
     }
 
@@ -1311,21 +1309,19 @@ void ContainerNode::checkForSiblingStyleChanges(SiblingCheckType changeType, Nod
     if (childrenAffectedByLastChildRules() && nodeBeforeChange) {
         // Find our new last child element.
         Element* lastChildElement = ElementTraversal::lastChild(*this);
-        RenderStyle* lastChildElementStyle = lastChildElement ? lastChildElement->renderStyle() : nullptr;
 
         // Find the last element before the change.
         Element* elementBeforeChange = nodeBeforeChange->isElementNode() ? toElement(nodeBeforeChange) : ElementTraversal::previousSibling(*nodeBeforeChange);
-        RenderStyle* elementBeforeChangeStyle = elementBeforeChange ? elementBeforeChange->renderStyle() : nullptr;
 
         // This is the element insertion as last child element case.
-        if (lastChildElement != elementBeforeChange && elementBeforeChangeStyle && elementBeforeChangeStyle->lastChildState()) {
-            ASSERT(SiblingElementInserted);
+        if (changeType == SiblingElementInserted && elementBeforeChange && lastChildElement != elementBeforeChange
+            && (!nodeAfterChange || !nodeAfterChange->isElementNode()) && elementBeforeChange->affectedByLastChildRules()) {

[rune, 2014/11/26 15:14:05]

Analogue to the other change, only for :last-child. The removed assert was bogus
(non-zero constant).

             elementBeforeChange->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::SiblingSelector));
         }
 
         // This is the last child element removal case. The parser callback case is similar to node removal as well in that we need to change the last child
         // to match now.
-        if ((changeType == SiblingElementRemoved || changeType == FinishedParsingChildren) && lastChildElement == elementBeforeChange && lastChildElement && (!lastChildElementStyle || !lastChildElementStyle->lastChildState()))
+        if ((changeType == SiblingElementRemoved || changeType == FinishedParsingChildren) && lastChildElement == elementBeforeChange && lastChildElement && lastChildElement->affectedByLastChildRules())
             lastChildElement->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::SiblingSelector));
     }