Bug 1288938: layout: Move the GlyphObserver to the text run instead of the frame. r=jfkthame

MozReview-Commit-ID: KphTCkcZeid
2024-10-09 03:15:11 +00:00 · 2016-07-24 02:40:01 -07:00 · 2016-07-24 02:40:01 -07:00 · e1e6b574d9
commit e1e6b574d9
parent 9a11ee24d8
3 changed files with 236 additions and 103 deletions
--- a/gfx/thebes/gfxFont.h
+++ b/gfx/thebes/gfxFont.h
@ -568,8 +568,6 @@ public:

        // Set if the textrun should use the OpenType 'math' script.
        TEXT_USE_MATH_SCRIPT = 0x80000000,
-
-        TEXT_UNUSED_FLAGS = 0x10000000
    };

    /**
--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@ -180,24 +180,22 @@ NS_DECLARE_FRAME_PROPERTY_WITHOUT_DTOR(UninflatedTextRunProperty, gfxTextRun)

 NS_DECLARE_FRAME_PROPERTY_SMALL_VALUE(FontSizeInflationProperty, float)

+/**
+ * A glyph observer for the change of a font glyph in a text run.
+ *
+ * This is stored in {Simple, Complex}TextRunUserData.
+ */
 class GlyphObserver : public gfxFont::GlyphChangeObserver {
 public:
-  GlyphObserver(gfxFont* aFont, nsTextFrame* aFrame)
-    : gfxFont::GlyphChangeObserver(aFont), mFrame(aFrame) {}
+  GlyphObserver(gfxFont* aFont, gfxTextRun* aTextRun)
+    : gfxFont::GlyphChangeObserver(aFont), mTextRun(aTextRun) {
+    MOZ_ASSERT(aTextRun->GetUserData());
+  }
  virtual void NotifyGlyphsChanged() override;
 private:
-  nsTextFrame* mFrame;
+  gfxTextRun* mTextRun;
 };

-/**
- * This property is set on text frames with TEXT_IN_TEXTRUN_USER_DATA set that
- * have potentially-animated glyphs.
- * The only reason this list is in a property is to automatically destroy the
- * list when the frame is deleted, unregistering the observers.
- */
-NS_DECLARE_FRAME_PROPERTY_DELETABLE(TextFrameGlyphObservers,
-                                    nsTArray<UniquePtr<GlyphObserver>>)
-
 static const nsFrameState TEXT_REFLOW_FLAGS =
   TEXT_FIRST_LETTER |
   TEXT_START_OF_LINE |
@ -223,21 +221,55 @@ static const nsFrameState TEXT_WHITESPACE_FLAGS =
 * 
 * A gfxTextRun can cover more than one DOM text node. This is necessary to
 * get kerning, ligatures and shaping for text that spans multiple text nodes
- * but is all the same font. The userdata for a gfxTextRun object is a
- * TextRunUserData* or an nsIFrame*.
- * 
+ * but is all the same font.
+ *
+ * The userdata for a gfxTextRun object can be:
+ *
+ *   - A nsTextFrame* in the case a text run maps to only one flow. In this
+ *   case, the textrun's user data pointer is a pointer to mStartFrame for that
+ *   flow, mDOMOffsetToBeforeTransformOffset is zero, and mContentLength is the
+ *   length of the text node.
+ *
+ *   - A SimpleTextRunUserData in the case a text run maps to one flow, but we
+ *   still have to keep a list of glyph observers.
+ *
+ *   - A ComplexTextRunUserData in the case a text run maps to multiple flows,
+ *   but we need to keep a list of glyph observers.
+ *
+ *   - A TextRunUserData in the case a text run maps multiple flows, but it
+ *   doesn't have any glyph observer for changes in SVG fonts.
+ *
+ * You can differentiate between the four different cases with the
+ * TEXT_IS_SIMPLE_FLOW and TEXT_MIGHT_HAVE_GLYPH_CHANGES flags.
+ *
 * We go to considerable effort to make sure things work even if in-flow
 * siblings have different style contexts (i.e., first-letter and first-line).
- * 
+ *
 * Our convention is that unsigned integer character offsets are offsets into
 * the transformed string. Signed integer character offsets are offsets into
 * the DOM string.
- * 
+ *
 * XXX currently we don't handle hyphenated breaks between text frames where the
 * hyphen occurs at the end of the first text frame, e.g.
 *   <b>Kit&shy;</b>ty
 */

+/**
+ * This is our user data for the textrun, when textRun->GetFlags() has
+ * TEXT_IS_SIMPLE_FLOW set, and also TEXT_MIGHT_HAVE_GLYPH_CHANGES.
+ *
+ * This allows having an array of observers if there are fonts whose glyphs
+ * might change, but also avoid allocation in the simple case that there aren't.
+ */
+struct SimpleTextRunUserData {
+  nsTArray<UniquePtr<GlyphObserver>> mGlyphObservers;
+  nsTextFrame* mFrame;
+  explicit SimpleTextRunUserData(nsTextFrame* aFrame)
+    : mFrame(aFrame)
+  {
+  }
+};
+
 /**
 * We use an array of these objects to record which text frames
 * are associated with the textrun. mStartFrame is the start of a list of
@ -259,11 +291,11 @@ struct TextRunMappedFlow {
 };

 /**
- * This is our user data for the textrun, when textRun->GetFlags() does not
- * have TEXT_IS_SIMPLE_FLOW set. When TEXT_IS_SIMPLE_FLOW is set, there is
- * just one flow, the textrun's user data pointer is a pointer to mStartFrame
- * for that flow, mDOMOffsetToBeforeTransformOffset is zero, and mContentLength
- * is the length of the text node.
+ * This is the type in the gfxTextRun's userdata field in the common case that
+ * the text run maps to multiple flows, but no fonts have been found with
+ * animatable glyphs.
+ *
+ * This way, we avoid allocating and constructing the extra nsTArray.
 */
 struct TextRunUserData {
  TextRunMappedFlow* mMappedFlows;
@ -271,6 +303,14 @@ struct TextRunUserData {
  uint32_t           mLastFlowIndex;
 };

+/**
+ * This is our user data for the textrun, when textRun->GetFlags() does not
+ * have TEXT_IS_SIMPLE_FLOW set and has the TEXT_MIGHT HAVE_GLYPH_CHANGES flag.
+ */
+struct ComplexTextRunUserData : public TextRunUserData {
+  nsTArray<UniquePtr<GlyphObserver>> mGlyphObservers;
+};
+
 /**
 * This helper object computes colors used for painting, and also IME
 * underline information. The data is computed lazily and cached as necessary.
@ -413,15 +453,85 @@ protected:
                               nscolor aBackColor);
 };

-static void
-DestroyUserData(void* aUserData)
+static TextRunUserData*
+CreateUserData(uint32_t aMappedFlowCount)
 {
-  TextRunUserData* userData = static_cast<TextRunUserData*>(aUserData);
-  if (userData) {
-    free(userData);
+  TextRunUserData* data = static_cast<TextRunUserData*>
+      (moz_xmalloc(sizeof(TextRunUserData) +
+       aMappedFlowCount * sizeof(TextRunMappedFlow)));
+  data->mMappedFlows = reinterpret_cast<TextRunMappedFlow*>(data + 1);
+  data->mMappedFlowCount = aMappedFlowCount;
+  data->mLastFlowIndex = 0;
+  return data;
+}
+
+static void
+DestroyUserData(TextRunUserData* aUserData)
+{
+  if (aUserData) {
+    free(aUserData);
  }
 }

+static ComplexTextRunUserData*
+CreateComplexUserData(uint32_t aMappedFlowCount)
+{
+  ComplexTextRunUserData* data = static_cast<ComplexTextRunUserData*>
+      (moz_xmalloc(sizeof(ComplexTextRunUserData) +
+       aMappedFlowCount * sizeof(TextRunMappedFlow)));
+  new (data) ComplexTextRunUserData();
+  data->mMappedFlows = reinterpret_cast<TextRunMappedFlow*>(data + 1);
+  data->mMappedFlowCount = aMappedFlowCount;
+  data->mLastFlowIndex = 0;
+  return data;
+}
+
+static void
+DestroyComplexUserData(ComplexTextRunUserData* aUserData)
+{
+  if (aUserData) {
+    aUserData->~ComplexTextRunUserData();
+    free(aUserData);
+  }
+}
+
+static void
+DestroyTextRunUserData(gfxTextRun* aTextRun)
+{
+  MOZ_ASSERT(aTextRun->GetUserData());
+  if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
+    if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES) {
+      delete static_cast<SimpleTextRunUserData*>(aTextRun->GetUserData());
+    }
+  } else {
+    if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES) {
+      DestroyComplexUserData(
+        static_cast<ComplexTextRunUserData*>(aTextRun->GetUserData()));
+    } else {
+      DestroyUserData(
+        static_cast<TextRunUserData*>(aTextRun->GetUserData()));
+    }
+  }
+  aTextRun->ClearFlagBits(nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES);
+  aTextRun->SetUserData(nullptr);
+}
+
+/**
+ * These are utility functions just for helping with the complexity related with
+ * the text runs user data.
+ */
+static nsTextFrame*
+GetFrameForSimpleFlow(gfxTextRun* aTextRun)
+{
+  MOZ_ASSERT(aTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW,
+             "Not so simple flow?");
+  if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES) {
+    return static_cast<SimpleTextRunUserData*>(aTextRun->GetUserData())->mFrame;
+  }
+
+  return static_cast<nsTextFrame*>(aTextRun->GetUserData());
+}
+
 /**
 * Remove |aTextRun| from the frame continuation chain starting at
 * |aStartContinuation| if non-null, otherwise starting at |aFrame|.
@ -475,12 +585,12 @@ ClearAllTextRunReferences(nsTextFrame* aFrame, gfxTextRun* aTextRun,
 static void
 UnhookTextRunFromFrames(gfxTextRun* aTextRun, nsTextFrame* aStartContinuation)
 {
-  if (!aTextRun->GetUserData())
+  if (!aTextRun->GetUserData()) {
    return;
+  }

  if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
-    nsTextFrame* userDataFrame = static_cast<nsTextFrame*>(
-      static_cast<nsIFrame*>(aTextRun->GetUserData()));
+    nsTextFrame* userDataFrame = GetFrameForSimpleFlow(aTextRun);
    nsFrameState whichTextRunState =
      userDataFrame->GetTextRun(nsTextFrame::eInflated) == aTextRun
        ? TEXT_IN_TEXTRUN_USER_DATA
@ -491,11 +601,10 @@ UnhookTextRunFromFrames(gfxTextRun* aTextRun, nsTextFrame* aStartContinuation)
    NS_ASSERTION(!aStartContinuation || found,
                 "aStartContinuation wasn't found in simple flow text run");
    if (!(userDataFrame->GetStateBits() & whichTextRunState)) {
-      aTextRun->SetUserData(nullptr);
+      DestroyTextRunUserData(aTextRun);
    }
  } else {
-    TextRunUserData* userData =
-      static_cast<TextRunUserData*>(aTextRun->GetUserData());
+    auto userData = static_cast<TextRunUserData*>(aTextRun->GetUserData());
    int32_t destroyFromIndex = aStartContinuation ? -1 : 0;
    for (uint32_t i = 0; i < userData->mMappedFlowCount; ++i) {
      nsTextFrame* userDataFrame = userData->mMappedFlows[i].mStartFrame;
@ -509,8 +618,7 @@ UnhookTextRunFromFrames(gfxTextRun* aTextRun, nsTextFrame* aStartContinuation)
      if (found) {
        if (userDataFrame->GetStateBits() & whichTextRunState) {
          destroyFromIndex = i + 1;
-        }
-        else {
+        } else {
          destroyFromIndex = i;
        }
        aStartContinuation = nullptr;
@ -519,10 +627,8 @@ UnhookTextRunFromFrames(gfxTextRun* aTextRun, nsTextFrame* aStartContinuation)
    NS_ASSERTION(destroyFromIndex >= 0,
                 "aStartContinuation wasn't found in multi flow text run");
    if (destroyFromIndex == 0) {
-      DestroyUserData(userData);
-      aTextRun->SetUserData(nullptr);
-    }
-    else {
+      DestroyTextRunUserData(aTextRun);
+    } else {
      userData->mMappedFlowCount = uint32_t(destroyFromIndex);
      if (userData->mLastFlowIndex >= uint32_t(destroyFromIndex)) {
        userData->mLastFlowIndex = uint32_t(destroyFromIndex) - 1;
@ -531,16 +637,14 @@ UnhookTextRunFromFrames(gfxTextRun* aTextRun, nsTextFrame* aStartContinuation)
  }
 }

-void
-GlyphObserver::NotifyGlyphsChanged()
+static void
+InvalidateFrameDueToGlyphsChanged(nsIFrame* aFrame)
 {
-  nsIPresShell* shell = mFrame->PresContext()->PresShell();
-  for (nsIFrame* f = mFrame; f;
+  MOZ_ASSERT(aFrame);
+
+  nsIPresShell* shell = aFrame->PresContext()->PresShell();
+  for (nsIFrame* f = aFrame; f;
       f = nsLayoutUtils::GetNextContinuationOrIBSplitSibling(f)) {
-    if (f != mFrame && f->HasAnyStateBits(TEXT_IN_TEXTRUN_USER_DATA)) {
-      // f will have its own GlyphObserver (if needed) so we can stop here.
-      break;
-    }
    f->InvalidateFrame();

    // If this is a non-display text frame within SVG <text>, we need
@ -563,6 +667,20 @@ GlyphObserver::NotifyGlyphsChanged()
  }
 }

+void
+GlyphObserver::NotifyGlyphsChanged()
+{
+  if (mTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
+    InvalidateFrameDueToGlyphsChanged(GetFrameForSimpleFlow(mTextRun));
+    return;
+  }
+
+  auto data = static_cast<TextRunUserData*>(mTextRun->GetUserData());
+  for (uint32_t i = 0; i < data->mMappedFlowCount; ++i) {
+    InvalidateFrameDueToGlyphsChanged(data->mMappedFlows[i].mStartFrame);
+  }
+}
+
 int32_t nsTextFrame::GetContentEnd() const {
  nsTextFrame* next = static_cast<nsTextFrame*>(GetNextContinuation());
  return next ? next->GetContentOffset() : mContent->GetText()->GetLength();
@ -744,27 +862,19 @@ IsAllWhitespace(const nsTextFragment* aFrag, bool aAllowNewline)
 }

 static void
-CreateObserverForAnimatedGlyphs(nsTextFrame* aFrame, const nsTArray<gfxFont*>& aFonts)
+ClearObserversFromTextRun(gfxTextRun* aTextRun)
 {
-  if (!(aFrame->GetStateBits() & TEXT_IN_TEXTRUN_USER_DATA)) {
-    // Maybe the textrun was created for uninflated text.
+  if (!(aTextRun->GetFlags() & nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES)) {
    return;
  }

-  nsTArray<UniquePtr<GlyphObserver>>* observers =
-    new nsTArray<UniquePtr<GlyphObserver>>();
-  for (uint32_t i = 0, count = aFonts.Length(); i < count; ++i) {
-    observers->AppendElement(new GlyphObserver(aFonts[i], aFrame));
+  if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
+    static_cast<SimpleTextRunUserData*>(aTextRun->GetUserData())
+      ->mGlyphObservers.Clear();
+  } else {
+    static_cast<ComplexTextRunUserData*>(aTextRun->GetUserData())
+      ->mGlyphObservers.Clear();
  }
-  aFrame->Properties().Set(TextFrameGlyphObservers(), observers);
-  // We are lazy and don't try to remove a property value that might be
-  // obsolete due to style changes or font selection changes. That is
-  // likely to be rarely needed, and we don't want to eat the overhead of
-  // doing it for the overwhelmingly common case of no property existing.
-  // (And we're out of state bits to conveniently use for a fast property
-  // existence check.) The only downside is that in some rare cases we might
-  // keep fonts alive for longer than necessary, or unnecessarily invalidate
-  // frames.
 }

 static void
@ -773,6 +883,9 @@ CreateObserversForAnimatedGlyphs(gfxTextRun* aTextRun)
  if (!aTextRun->GetUserData()) {
    return;
  }
+
+  ClearObserversFromTextRun(aTextRun);
+
  nsTArray<gfxFont*> fontsWithAnimatedGlyphs;
  uint32_t numGlyphRuns;
  const gfxTextRun::GlyphRun* glyphRuns =
@ -784,19 +897,46 @@ CreateObserversForAnimatedGlyphs(gfxTextRun* aTextRun)
    }
  }
  if (fontsWithAnimatedGlyphs.IsEmpty()) {
+    // NB: Theoretically, we should clear the TEXT_MIGHT_HAVE_GLYPH_CHANGES
+    // here. That would involve de-allocating the simple user data struct if
+    // present too, and resetting the pointer to the frame. In practice, I
+    // don't think worth doing that work here, given the flag's only purpose is
+    // to distinguish what kind of user data is there.
    return;
  }

+  nsTArray<UniquePtr<GlyphObserver>>* observers;
+
  if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
-    CreateObserverForAnimatedGlyphs(static_cast<nsTextFrame*>(
-      static_cast<nsIFrame*>(aTextRun->GetUserData())), fontsWithAnimatedGlyphs);
-  } else {
-    TextRunUserData* userData =
-      static_cast<TextRunUserData*>(aTextRun->GetUserData());
-    for (uint32_t i = 0; i < userData->mMappedFlowCount; ++i) {
-      CreateObserverForAnimatedGlyphs(userData->mMappedFlows[i].mStartFrame,
-                                      fontsWithAnimatedGlyphs);
+    // Swap the frame pointer for a just-allocated SimpleTextRunUserData if
+    // appropriate.
+    if (!(aTextRun->GetFlags() & nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES)) {
+      auto frame = static_cast<nsTextFrame*>(aTextRun->GetUserData());
+      aTextRun->SetUserData(new SimpleTextRunUserData(frame));
    }
+
+    auto data =
+      static_cast<SimpleTextRunUserData*>(aTextRun->GetUserData());
+    observers = &data->mGlyphObservers;
+  } else {
+    if (!(aTextRun->GetFlags() & nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES)) {
+      auto oldData = static_cast<TextRunUserData*>(aTextRun->GetUserData());
+      auto data = CreateComplexUserData(oldData->mMappedFlowCount);
+      data->mLastFlowIndex = oldData->mLastFlowIndex;
+      for (uint32_t i = 0; i < oldData->mMappedFlowCount; ++i) {
+        data->mMappedFlows[i] = oldData->mMappedFlows[i];
+      }
+      DestroyUserData(oldData);
+      aTextRun->SetUserData(data);
+    }
+    auto data = static_cast<ComplexTextRunUserData*>(aTextRun->GetUserData());
+    observers = &data->mGlyphObservers;
+  }
+
+  aTextRun->SetFlagBits(nsTextFrameUtils::TEXT_MIGHT_HAVE_GLYPH_CHANGES);
+
+  for (auto font : fontsWithAnimatedGlyphs) {
+    observers->AppendElement(new GlyphObserver(font, aTextRun));
  }
 }

@ -945,9 +1085,7 @@ public:
    }

    void Finish(gfxMissingFontRecorder* aMFR) {
-      MOZ_ASSERT(!(mTextRun->GetFlags() &
-                   (gfxTextRunFactory::TEXT_UNUSED_FLAGS |
-                    nsTextFrameUtils::TEXT_UNUSED_FLAG)),
+      MOZ_ASSERT(!(mTextRun->GetFlags() & nsTextFrameUtils::TEXT_UNUSED_FLAG),
                   "Flag set that should never be set! (memory safety error?)");
      if (mTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_TRANSFORMED) {
        nsTransformedTextRun* transformedTextRun =
@ -1400,12 +1538,13 @@ ExpandBuffer(char16_t* aDest, uint8_t* aSrc, uint32_t aCount)

 bool BuildTextRunsScanner::IsTextRunValidForMappedFlows(gfxTextRun* aTextRun)
 {
-  if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW)
+  if (aTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
    return mMappedFlows.Length() == 1 &&
-      mMappedFlows[0].mStartFrame == static_cast<nsTextFrame*>(aTextRun->GetUserData()) &&
+      mMappedFlows[0].mStartFrame == GetFrameForSimpleFlow(aTextRun) &&
      mMappedFlows[0].mEndFrame == nullptr;
+  }

-  TextRunUserData* userData = static_cast<TextRunUserData*>(aTextRun->GetUserData());
+  auto userData = static_cast<TextRunUserData*>(aTextRun->GetUserData());
  if (userData->mMappedFlowCount != mMappedFlows.Length())
    return false;
  for (uint32_t i = 0; i < mMappedFlows.Length(); ++i) {
@ -1875,14 +2014,12 @@ BuildTextRunsScanner::BuildTextRunForFrames(void* aTextBuffer)
    userData = &dummyData;
    userDataToDestroy = nullptr;
    dummyData.mMappedFlows = &dummyMappedFlow;
+    dummyData.mMappedFlowCount = mMappedFlows.Length();
+    dummyData.mLastFlowIndex = 0;
  } else {
-    userData = static_cast<TextRunUserData*>
-      (moz_xmalloc(sizeof(TextRunUserData) + mMappedFlows.Length()*sizeof(TextRunMappedFlow)));
+    userData = CreateUserData(mMappedFlows.Length());
    userDataToDestroy = userData;
-    userData->mMappedFlows = reinterpret_cast<TextRunMappedFlow*>(userData + 1);
  }
-  userData->mMappedFlowCount = mMappedFlows.Length();
-  userData->mLastFlowIndex = 0;

  uint32_t currentTransformedTextOffset = 0;

@ -2280,14 +2417,12 @@ BuildTextRunsScanner::SetupLineBreakerContext(gfxTextRun *aTextRun)
    userData = &dummyData;
    userDataToDestroy = nullptr;
    dummyData.mMappedFlows = &dummyMappedFlow;
+    dummyData.mMappedFlowCount = mMappedFlows.Length();
+    dummyData.mLastFlowIndex = 0;
  } else {
-    userData = static_cast<TextRunUserData*>
-      (moz_xmalloc(sizeof(TextRunUserData) + mMappedFlows.Length()*sizeof(TextRunMappedFlow)));
+    userData = CreateUserData(mMappedFlows.Length());
    userDataToDestroy = userData;
-    userData->mMappedFlows = reinterpret_cast<TextRunMappedFlow*>(userData + 1);
  }
-  userData->mMappedFlowCount = mMappedFlows.Length();
-  userData->mLastFlowIndex = 0;

  uint32_t nextBreakIndex = 0;
  nsTextFrame* nextBreakBeforeFrame = GetNextBreakBeforeFrame(&nextBreakIndex);
@ -2576,16 +2711,14 @@ BuildTextRunsScanner::AssignTextRun(gfxTextRun* aTextRun, float aInflation)
      if (f->GetTextRun(mWhichTextRun)) {
        gfxTextRun* textRun = f->GetTextRun(mWhichTextRun);
        if (textRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
-          if (mMappedFlows[0].mStartFrame != static_cast<nsTextFrame*>(textRun->GetUserData())) {
+          if (mMappedFlows[0].mStartFrame != GetFrameForSimpleFlow(textRun)) {
            NS_WARNING("REASSIGNING SIMPLE FLOW TEXT RUN!");
          }
        } else {
-          TextRunUserData* userData =
-            static_cast<TextRunUserData*>(textRun->GetUserData());
-         
+          auto userData = static_cast<TextRunUserData*>(aTextRun->GetUserData());
          if (userData->mMappedFlowCount >= mMappedFlows.Length() ||
              userData->mMappedFlows[userData->mMappedFlowCount - 1].mStartFrame !=
-              mMappedFlows[userData->mMappedFlowCount - 1].mStartFrame) {
+              mMappedFlows[userdata->mMappedFlowCount - 1].mStartFrame) {
            NS_WARNING("REASSIGNING MULTIFLOW TEXT RUN (not append)!");
          }
        }
@ -2597,17 +2730,16 @@ BuildTextRunsScanner::AssignTextRun(gfxTextRun* aTextRun, float aInflation)
        nsTextFrame* firstFrame = nullptr;
        uint32_t startOffset = 0;
        if (oldTextRun->GetFlags() & nsTextFrameUtils::TEXT_IS_SIMPLE_FLOW) {
-          firstFrame = static_cast<nsTextFrame*>(oldTextRun->GetUserData());
-        }
-        else {
-          TextRunUserData* userData = static_cast<TextRunUserData*>(oldTextRun->GetUserData());
+          firstFrame = GetFrameForSimpleFlow(oldTextRun);
+        } else {
+          auto userData = static_cast<TextRunUserData*>(oldTextRun->GetUserData());
          firstFrame = userData->mMappedFlows[0].mStartFrame;
          if (MOZ_UNLIKELY(f != firstFrame)) {
-            TextRunMappedFlow* flow = FindFlowForContent(userData, f->GetContent());
+            TextRunMappedFlow* flow = FindFlowForContent(userData,
+                                                         f->GetContent());
            if (flow) {
              startOffset = flow->mDOMOffsetToBeforeTransformOffset;
-            }
-            else {
+            } else {
              NS_ERROR("Can't find flow containing frame 'f'");
            }
          }
@ -2687,7 +2819,7 @@ nsTextFrame::EnsureTextRun(TextRunType aWhichTextRun,
    return gfxSkipCharsIterator(textRun->GetSkipChars(), 0, mContentOffset);
  }

-  TextRunUserData* userData = static_cast<TextRunUserData*>(textRun->GetUserData());
+  auto userData = static_cast<TextRunUserData*>(textRun->GetUserData());
  TextRunMappedFlow* flow = FindFlowForContent(userData, mContent);
  if (flow) {
    // Since textruns can only contain one flow for a given content element,
--- a/layout/generic/nsTextFrameUtils.h
+++ b/layout/generic/nsTextFrameUtils.h
@ -50,7 +50,10 @@ public:
    // NS_FRAME_IS_IN_SINGLE_CHAR_MI flag is set.  This occurs if the textframe
    // belongs to a MathML <mi> element whose embedded text consists of a
    // single character.
-    TEXT_IS_SINGLE_CHAR_MI   = 0x8000000
+    TEXT_IS_SINGLE_CHAR_MI   = 0x8000000,
+
+    // This is set if the text run might be observing for glyph changes.
+    TEXT_MIGHT_HAVE_GLYPH_CHANGES = 0x10000000,

    // The following are defined by gfxTextRunWordCache rather than here,
    // so that it also has access to the _INCOMING flag