Bug 641341. Speed up CalculateHypotheticalBox for the case of a block containing a bunch of lines but absolutely no in-flows anywhere. r=roc

layout/generic/nsHTMLReflowState.cpp

@@ -55,6 +55,8 @@
 #include "nsIServiceManager.h"
 #include "nsIPercentHeightObserver.h"
 #include "nsLayoutUtils.h"
+#include "nsPlaceholderFrame.h"
+#include "nsFrameManager.h"
 #include "mozilla/Preferences.h"
 #ifdef IBMBIDI
 #include "nsBidiUtils.h"
@@ -847,7 +849,7 @@ static bool AreAllEarlierInFlowFramesEmpty(nsIFrame* aFrame,
 // cbrs->frame is the actual containing block
 void
 nsHTMLReflowState::CalculateHypotheticalBox(nsPresContext*    aPresContext,
-                                            nsIFrame*         aPlaceholderFrame,
+                                            nsPlaceholderFrame* aPlaceholderFrame,
                                             nsIFrame*         aContainingBlock,
                                             nscoord           aBlockLeftContentEdge,
                                             nscoord           aBlockContentWidth,
@@ -930,17 +932,12 @@ nsHTMLReflowState::CalculateHypotheticalBox(nsPresContext*    aPresContext,
     nsLayoutUtils::GetAsBlock(aContainingBlock->GetContentInsertionFrame());
   if (blockFrame) {
     nscoord blockYOffset = blockFrame->GetOffsetTo(aContainingBlock).y;
-    bool isValid;
-    nsBlockInFlowLineIterator iter(blockFrame, aPlaceholderFrame, &isValid);
-    if (!isValid) {
+    const nsLineBox* lineBox = aPlaceholderFrame->GetCachedLineBox();
+    if (!lineBox) {
       // Give up.  We're probably dealing with somebody using
       // position:absolute inside native-anonymous content anyway.
       aHypotheticalBox.mTop = placeholderOffset.y;
     } else {
-      NS_ASSERTION(iter.GetContainer() == blockFrame,
-                   "Found placeholder in wrong block!");
-      nsBlockFrame::line_iterator lineBox = iter.GetLine();
-
       // How we determine the hypothetical box depends on whether the element
       // would have been inline-level or block-level
       if (mStyleDisplay->IsOriginalDisplayInlineOutside()) {
@@ -954,10 +951,10 @@ nsHTMLReflowState::CalculateHypotheticalBox(nsPresContext*    aPresContext,
         // have been just before this line.
         // XXXbz the line box is not fully reflowed yet if our
         // containing block is relatively positioned...
-        if (lineBox != iter.End()) {
+        bool allEmpty = true;
+        if (!lineBox->IsValidCachedIsEmpty() || !lineBox->CachedIsEmpty()) {
           nsIFrame * firstFrame = lineBox->mFirstChild;
           bool found = false;
-          bool allEmpty = true;
           while (firstFrame) { // See bug 223064
             allEmpty = AreAllEarlierInFlowFramesEmpty(firstFrame,
               aPlaceholderFrame, &found);
@@ -966,20 +963,17 @@ nsHTMLReflowState::CalculateHypotheticalBox(nsPresContext*    aPresContext,
             firstFrame = firstFrame->GetNextSibling();
           }
           NS_ASSERTION(firstFrame, "Couldn't find placeholder!");
+        }
 
-          if (allEmpty) {
-            // The top of the hypothetical box is the top of the line
-            // containing the placeholder, since there is nothing in the
-            // line before our placeholder except empty frames.
-            aHypotheticalBox.mTop = lineBox->mBounds.y + blockYOffset;
-          } else {
-            // The top of the hypothetical box is just below the line
-            // containing the placeholder.
-            aHypotheticalBox.mTop = lineBox->mBounds.YMost() + blockYOffset;
-          }
+        if (allEmpty) {
+          // The top of the hypothetical box is the top of the line
+          // containing the placeholder, since there is nothing in the
+          // line before our placeholder except empty frames.
+          aHypotheticalBox.mTop = lineBox->mBounds.y + blockYOffset;
         } else {
-          // Just use the placeholder's y-offset wrt the containing block
-          aHypotheticalBox.mTop = placeholderOffset.y;
+          // The top of the hypothetical box is just below the line
+          // containing the placeholder.
+          aHypotheticalBox.mTop = lineBox->mBounds.YMost() + blockYOffset;
         }
       }
     }
@@ -1105,9 +1099,10 @@ nsHTMLReflowState::InitAbsoluteConstraints(nsPresContext* aPresContext,
                "Why are we here?");
 
   // Get the placeholder frame
-  nsIFrame*     placeholderFrame;
+  nsPlaceholderFrame*     placeholderFrame;
 
-  placeholderFrame = aPresContext->PresShell()->GetPlaceholderFrameFor(frame);
+  placeholderFrame =
+    aPresContext->PresShell()->FrameManager()->GetPlaceholderFrameFor(frame);
   NS_ASSERTION(nsnull != placeholderFrame, "no placeholder frame");
 
   // If both 'left' and 'right' are 'auto' or both 'top' and 'bottom' are

layout/generic/nsHTMLReflowState.h

@@ -49,6 +49,7 @@ class nsRenderingContext;
 class nsFloatManager;
 class nsLineLayout;
 class nsIPercentHeightObserver;
+class nsPlaceholderFrame;
 
 struct nsStyleDisplay;
 struct nsStyleVisibility;
@@ -511,7 +512,7 @@ protected:
                                         nscoord& aCBWidth);
 
   void CalculateHypotheticalBox(nsPresContext*    aPresContext,
-                                nsIFrame*         aPlaceholderFrame,
+                                nsPlaceholderFrame* aPlaceholderFrame,
                                 nsIFrame*         aContainingBlock,
                                 nscoord           aBlockLeftContentEdge,
                                 nscoord           aBlockContentWidth,

layout/generic/nsLineBox.cpp

@@ -289,7 +289,7 @@ nsLineBox::IsEmpty() const
 }
 
 bool
-nsLineBox::CachedIsEmpty()
+nsLineBox::CachedIsEmpty() const
 {
   if (mFlags.mDirty) {
     return IsEmpty();

layout/generic/nsLineBox.h

@@ -486,14 +486,14 @@ public:
   // Call this only while in Reflow() for the block the line belongs
   // to, only between reflowing the line (or sliding it, if we skip
   // reflowing it) and the end of reflowing the block.
-  bool CachedIsEmpty();
+  bool CachedIsEmpty() const;
 
   void InvalidateCachedIsEmpty() {
     mFlags.mEmptyCacheValid = PR_FALSE;
   }
 
   // For debugging purposes
-  bool IsValidCachedIsEmpty() {
+  bool IsValidCachedIsEmpty() const {
     return mFlags.mEmptyCacheValid;
   }
 
@@ -514,8 +514,8 @@ public:
     PRUint32 mLineWrapped: 1;
     PRUint32 mInvalidateTextRuns : 1;
     PRUint32 mResizeReflowOptimizationDisabled: 1;  // default 0 = means that the opt potentially applies to this line. 1 = never skip reflowing this line for a resize reflow
-    PRUint32 mEmptyCacheValid: 1;
-    PRUint32 mEmptyCacheState: 1;
+    mutable PRUint32 mEmptyCacheValid: 1;
+    mutable PRUint32 mEmptyCacheState: 1;
     // mHasBullet indicates that this is an inline line whose block's
     // bullet is adjacent to this line and non-empty.
     PRUint32 mHasBullet : 1;

layout/generic/nsPlaceholderFrame.cpp

@@ -145,6 +145,15 @@ nsPlaceholderFrame::Reflow(nsPresContext*          aPresContext,
   aDesiredSize.width = 0;
   aDesiredSize.height = 0;
 
+  // Cache our line box.
+  mCachedLineBox = nsnull;
+  if (aReflowState.mLineLayout) {
+    nsLineList::iterator* line = aReflowState.mLineLayout->GetLine();
+    if (line) {
+      mCachedLineBox = line->get();
+    }
+  }
+
   aStatus = NS_FRAME_COMPLETE;
   NS_FRAME_SET_TRUNCATION(aStatus, aReflowState, aDesiredSize);
   return NS_OK;

layout/generic/nsPlaceholderFrame.h

@@ -69,6 +69,8 @@
 #include "nsFrame.h"
 #include "nsGkAtoms.h"
 
+class nsLineBox;
+
 nsIFrame* NS_NewPlaceholderFrame(nsIPresShell* aPresShell,
                                  nsStyleContext* aContext,
                                  nsFrameState aTypeBit);
@@ -200,8 +202,17 @@ public:
     return outOfFlow;
   }
 
+  // GetCachedLineBox is only OK to call if you're sure this
+  // placeholder has has Reflow() called since any changes to the
+  // frame tree that could have affected which line box the
+  // placeholder is in.
+  const nsLineBox* GetCachedLineBox() const {
+    return mCachedLineBox;
+  }
+
 protected:
   nsIFrame* mOutOfFlowFrame;
+  nsLineBox* mCachedLineBox;
 };
 
 #endif /* nsPlaceholderFrame_h___ */