From 2b6a60fb3a183a0195081e87343b4905fc5c9c35 Mon Sep 17 00:00:00 2001
From: Kartikaya Gupta <kgupta@mozilla.com>
Date: Tue, 30 Dec 2014 09:40:01 -0500
Subject: [PATCH] Bug 1098654 - Add a cache for animated geometry roots on the
 display list builder. r=roc

---
 layout/base/nsDisplayList.cpp | 26 ++++++++++++++++++++++++--
 layout/base/nsDisplayList.h   | 31 +++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index 9e021d45e3b..46e02da2242 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -1182,12 +1182,28 @@ nsDisplayListBuilder::IsAnimatedGeometryRoot(nsIFrame* aFrame, nsIFrame** aParen
   return false;
 }
 
+bool
+nsDisplayListBuilder::GetCachedAnimatedGeometryRoot(const nsIFrame* aFrame,
+                                                    const nsIFrame* aStopAtAncestor,
+                                                    nsIFrame** aOutResult)
+{
+  AnimatedGeometryRootLookup lookup(aFrame, aStopAtAncestor);
+  return mAnimatedGeometryRootCache.Get(lookup, aOutResult);
+}
+
 static nsIFrame*
 ComputeAnimatedGeometryRootFor(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
-                               const nsIFrame* aStopAtAncestor = nullptr)
+                               const nsIFrame* aStopAtAncestor = nullptr,
+                               bool aUseCache = false)
 {
   nsIFrame* cursor = aFrame;
   while (cursor != aStopAtAncestor) {
+    if (aUseCache) {
+      nsIFrame* result;
+      if (aBuilder->GetCachedAnimatedGeometryRoot(cursor, aStopAtAncestor, &result)) {
+        return result;
+      }
+    }
     nsIFrame* next;
     if (aBuilder->IsAnimatedGeometryRoot(cursor, &next))
       return cursor;
@@ -1202,13 +1218,19 @@ nsDisplayListBuilder::FindAnimatedGeometryRootFor(nsIFrame* aFrame, const nsIFra
   if (aFrame == mCurrentFrame) {
     return mCurrentAnimatedGeometryRoot;
   }
-  return ComputeAnimatedGeometryRootFor(this, aFrame, aStopAtAncestor);
+
+  nsIFrame* result = ComputeAnimatedGeometryRootFor(this, aFrame, aStopAtAncestor, true);
+  AnimatedGeometryRootLookup lookup(aFrame, aStopAtAncestor);
+  mAnimatedGeometryRootCache.Put(lookup, result);
+  return result;
 }
 
 void
 nsDisplayListBuilder::RecomputeCurrentAnimatedGeometryRoot()
 {
   mCurrentAnimatedGeometryRoot = ComputeAnimatedGeometryRootFor(this, const_cast<nsIFrame *>(mCurrentFrame));
+  AnimatedGeometryRootLookup lookup(mCurrentFrame, nullptr);
+  mAnimatedGeometryRootCache.Put(lookup, mCurrentAnimatedGeometryRoot);
 }
 
 void
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index e72544fdd31..123b6e04dc6 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -795,6 +795,15 @@ public:
 
   bool IsInWillChangeBudget(nsIFrame* aFrame) const;
 
+  /**
+   * Look up the cached animated geometry root for aFrame subject to
+   * aStopAtAncestor. Store the nsIFrame* result into *aOutResult, and return
+   * true if the cache was hit. Return false if the cache was not hit.
+   */
+  bool GetCachedAnimatedGeometryRoot(const nsIFrame* aFrame,
+                                     const nsIFrame* aStopAtAncestor,
+                                     nsIFrame** aOutResult);
+
 private:
   void MarkOutOfFlowFrameForDisplay(nsIFrame* aDirtyFrame, nsIFrame* aFrame,
                                     const nsRect& aDirtyRect);
@@ -840,6 +849,28 @@ private:
   nsPoint                        mCurrentOffsetToReferenceFrame;
   // The animated geometry root for mCurrentFrame.
   nsIFrame*                      mCurrentAnimatedGeometryRoot;
+
+  struct AnimatedGeometryRootLookup {
+    const nsIFrame* mFrame;
+    const nsIFrame* mStopAtFrame;
+
+    AnimatedGeometryRootLookup(const nsIFrame* aFrame, const nsIFrame* aStopAtFrame)
+      : mFrame(aFrame)
+      , mStopAtFrame(aStopAtFrame)
+    {
+    }
+
+    PLDHashNumber Hash() const {
+      return mozilla::HashBytes(this, sizeof(this));
+    }
+
+    bool operator==(const AnimatedGeometryRootLookup& aOther) const {
+      return mFrame == aOther.mFrame && mStopAtFrame == aOther.mStopAtFrame;
+    }
+  };
+  // Cache for storing animated geometry roots for arbitrary frames
+  nsDataHashtable<nsGenericHashKey<AnimatedGeometryRootLookup>, nsIFrame*>
+                                 mAnimatedGeometryRootCache;
   // will-change budget tracker
   nsDataHashtable<nsPtrHashKey<nsPresContext>, DocumentWillChangeBudget>
                                  mWillChangeBudget;