#438: M1393098

layout/generic/nsFrame.cpp

@@ -397,6 +397,7 @@ nsFrame::nsFrame(nsStyleContext* aContext)
 
   mState = NS_FRAME_FIRST_REFLOW | NS_FRAME_IS_DIRTY;
   mMayHaveRoundedCorners = false;
+  mReflowRequestedForCharDataChange = false;
   mStyleContext = aContext;
   mStyleContext->AddRef();
 #ifdef DEBUG

layout/generic/nsIFrame.h

@@ -3154,6 +3154,23 @@ protected:
 
   bool mMayHaveRoundedCorners : 1;
 
+  /**
+   * This bit is used in nsTextFrame::CharacterDataChanged() as an optimization
+   * to skip redundant reflow-requests when the character data changes multiple
+   * times between reflows. If this flag is set, then it implies that the
+   * NS_FRAME_IS_DIRTY state bit is also set (and that intrinsic sizes have
+   * been marked as dirty on our ancestor chain).
+   *
+   * XXXdholbert This bit is *only* used on nsTextFrame, but it lives here on
+   * nsIFrame simply because this is where we've got unused state bits
+   * available in a gap. If bits become more scarce, we should perhaps consider
+   * expanding the range of frame-specific state bits in nsFrameStateBits.h and
+   * moving this to be one of those (e.g. by swapping one of the adjacent
+   * general-purpose bits to take the place of this bool:1 here, so we can grow
+   * that range of frame-specific bits by 1).
+   */
+  bool mReflowRequestedForCharDataChange : 1;
+
   // Helpers
   /**
    * Can we stop inside this frame when we're skipping non-rendered whitespace?

layout/generic/nsTextFrame.cpp

@@ -4589,7 +4589,12 @@ nsTextFrame::CharacterDataChanged(CharacterDataChangeInfo* aInfo)
   }
 
   int32_t endOfChangedText = aInfo->mChangeStart + aInfo->mReplaceLength;
-  nsTextFrame* lastDirtiedFrame = nullptr;
+
+  // Parent of the last frame that we passed to FrameNeedsReflow (or noticed
+  // had already received an earlier FrameNeedsReflow call).
+  // (For subsequent frames with this same parent, we can just set their
+  // dirty bit without bothering to call FrameNeedsReflow again.)
+  nsIFrame* lastDirtiedFrameParent = nullptr;
 
   nsIPresShell* shell = PresContext()->GetPresShell();
   do {
@@ -4597,17 +4602,39 @@ nsTextFrame::CharacterDataChanged(CharacterDataChangeInfo* aInfo)
     // if this was a pure insertion).
     textFrame->mState &= ~TEXT_WHITESPACE_FLAGS;
     textFrame->ClearTextRuns();
-    if (!lastDirtiedFrame ||
-        lastDirtiedFrame->GetParent() != textFrame->GetParent()) {
-      // Ask the parent frame to reflow me.
-      shell->FrameNeedsReflow(textFrame, nsIPresShell::eStyleChange,
-                              NS_FRAME_IS_DIRTY);
-      lastDirtiedFrame = textFrame;
+
+    nsIFrame* parentOfTextFrame = textFrame->GetParent();
+    bool areAncestorsAwareOfReflowRequest = false;
+    if (lastDirtiedFrameParent == parentOfTextFrame) {
+      // An earlier iteration of this loop already called
+      // FrameNeedsReflow for a sibling of |textFrame|.
+      areAncestorsAwareOfReflowRequest = true;
     } else {
-      // if the parent is a block, we're cheating here because we should
-      // be marking our line dirty, but we're not. nsTextFrame::SetLength
-      // will do that when it gets called during reflow.
-      textFrame->AddStateBits(NS_FRAME_IS_DIRTY);
+      lastDirtiedFrameParent = parentOfTextFrame;
+    }
+
+    if (textFrame->mReflowRequestedForCharDataChange) {
+      // We already requested a reflow for this frame; nothing to do.
+      MOZ_ASSERT(textFrame->HasAnyStateBits(NS_FRAME_IS_DIRTY),
+                 "mReflowRequestedForCharDataChange should only be set "
+                 "on dirty frames");
+    } else {
+      // Make sure textFrame is queued up for a reflow.  Also set a flag so we
+      // don't waste time doing this again in repeated calls to this method.
+      textFrame->mReflowRequestedForCharDataChange = true;
+      if (!areAncestorsAwareOfReflowRequest) {
+        // Ask the parent frame to reflow me.
+        shell->FrameNeedsReflow(textFrame, nsIPresShell::eStyleChange,
+                                NS_FRAME_IS_DIRTY);
+      } else {
+        // We already called FrameNeedsReflow on behalf of an earlier sibling,
+        // so we can just mark this frame as dirty and don't need to bother
+        // telling its ancestors.
+        // Note: if the parent is a block, we're cheating here because we should
+        // be marking our line dirty, but we're not. nsTextFrame::SetLength will
+        // do that when it gets called during reflow.
+        textFrame->AddStateBits(NS_FRAME_IS_DIRTY);
+      }
     }
     textFrame->InvalidateFrame();
 
@@ -8514,8 +8541,10 @@ nsTextFrame::ReflowText(nsLineLayout& aLineLayout, nscoord aAvailableWidth,
 
   // Clear out the reflow state flags in mState. We also clear the whitespace
   // flags because this can change whether the frame maps whitespace-only text
-  // or not.
+  // or not. We also clear the flag that tracks whether we had a pending
+  // reflow request from CharacterDataChanged (since we're reflowing now).
   RemoveStateBits(TEXT_REFLOW_FLAGS | TEXT_WHITESPACE_FLAGS);
+  mReflowRequestedForCharDataChange = false;
 
   // Temporarily map all possible content while we construct our new textrun.
   // so that when doing reflow our styles prevail over any part of the