Bug 931668 - Part 3: Add a style context bit to represent whether it depends on style data from its grandparent or higher ancestor. r=dbaron

--HG--
extra : rebase_source : 64deabb466cfaaeae220a00024cd05d8e87832bc

layout/style/nsRuleNode.cpp

@@ -1630,6 +1630,38 @@ nsRuleNode::PropagateDependentBit(nsStyleStructID aSID, nsRuleNode* aHighestNode
   }
 }
 
+/* static */ void
+nsRuleNode::PropagateGrandancestorBit(nsStyleContext* aContext,
+                                      nsStyleContext* aContextInheritedFrom)
+{
+  MOZ_ASSERT(aContext);
+  MOZ_ASSERT(aContextInheritedFrom &&
+             aContextInheritedFrom != aContext &&
+             aContextInheritedFrom != aContext->GetParent(),
+             "aContextInheritedFrom must be an ancestor of aContext's parent");
+
+  aContext->AddStyleBit(NS_STYLE_USES_GRANDANCESTOR_STYLE);
+
+  nsStyleContext* context = aContext->GetParent();
+  if (!context) {
+    return;
+  }
+
+  for (;;) {
+    nsStyleContext* parent = context->GetParent();
+    if (!parent) {
+      MOZ_ASSERT(false, "aContextInheritedFrom must be an ancestor of "
+                        "aContext's parent");
+      break;
+    }
+    if (parent == aContextInheritedFrom) {
+      break;
+    }
+    context->AddStyleBit(NS_STYLE_USES_GRANDANCESTOR_STYLE);
+    context = parent;
+  }
+}
+
 /*
  * The following "Check" functions are used for determining what type of
  * sharing can be used for the data on this rule node.  MORE HERE...
@@ -2308,6 +2340,9 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
              parentContext->GetPseudo() == nsCSSPseudoElements::firstLine) {
         parentContext = parentContext->GetParent();
       }
+      if (parentContext && parentContext != aContext->GetParent()) {
+        PropagateGrandancestorBit(aContext, parentContext);
+      }
     }
     if (parentContext) {
       // We have a parent, and so we should just inherit from the parent.
@@ -3893,6 +3928,13 @@ nsRuleNode::SetGenericFont(nsPresContext* aPresContext,
 
     parentFont = *aFont;
   }
+
+  if (higherContext && contextPath.Length() > 1) {
+    // contextPath is a list of all ancestor style contexts, so it must have
+    // at least two elements for it to result in a dependency on grandancestor
+    // styles.
+    PropagateGrandancestorBit(aContext, higherContext);
+  }
 }
 
 const void*
@@ -7535,6 +7577,7 @@ nsRuleNode::ComputePositionData(void* aStartStruct,
           const nsStylePosition* grandparentPos =
             grandparentContext->StylePosition();
           inheritedAlignSelf = grandparentPos->mAlignItems;
+          aContext->AddStyleBit(NS_STYLE_USES_GRANDANCESTOR_STYLE);
         }
       }
     }

layout/style/nsRuleNode.h

@@ -426,6 +426,8 @@ protected:
   void PropagateDependentBit(nsStyleStructID aSID, nsRuleNode* aHighestNode,
                              void* aStruct);
   void PropagateNoneBit(uint32_t aBit, nsRuleNode* aHighestNode);
+  static void PropagateGrandancestorBit(nsStyleContext* aContext,
+                                        nsStyleContext* aContextInheritedFrom);
 
   const void* SetDefaultOnRoot(const nsStyleStructID aSID,
                                nsStyleContext* aContext);

layout/style/nsStyleContext.h

@@ -193,6 +193,12 @@ public:
     }
   }
 
+  // Does this style context, or any of its descendants, have any style values
+  // that were computed based on this style context's grandparent style context
+  // or any of the grandparent's ancestors?
+  bool UsesGrandancestorStyle() const
+    { return !!(mBits & NS_STYLE_USES_GRANDANCESTOR_STYLE); }
+
   // Tell this style context to cache aStruct as the struct for aSID
   void SetStyle(nsStyleStructID aSID, void* aStruct);
 

layout/style/nsStyleStruct.h

@@ -49,9 +49,11 @@ class imgIContainer;
 #define NS_STYLE_RELEVANT_LINK_VISITED     0x004000000
 // See nsStyleContext::IsStyleIfVisited
 #define NS_STYLE_IS_STYLE_IF_VISITED       0x008000000
+// See nsStyleContext::UsesGrandancestorStyle
+#define NS_STYLE_USES_GRANDANCESTOR_STYLE  0x010000000
 // See nsStyleContext::GetPseudoEnum
-#define NS_STYLE_CONTEXT_TYPE_MASK         0x1f0000000
-#define NS_STYLE_CONTEXT_TYPE_SHIFT        28
+#define NS_STYLE_CONTEXT_TYPE_MASK         0x3e0000000
+#define NS_STYLE_CONTEXT_TYPE_SHIFT        29
 
 // Additional bits for nsRuleNode's mDependentBits:
 #define NS_RULE_NODE_GC_MARK                0x02000000