Bug 1554461 - Use an array to store nsContinuationStates when the number of them is low. r=jfkthame

Differential Revision: https://phabricator.services.mozilla.com/D32617

--HG--
extra : moz-landing-system : lando

layout/base/nsBidiPresUtils.cpp

@@ -1356,10 +1356,11 @@ nsBidiLevel nsBidiPresUtils::GetFrameBaseLevel(nsIFrame* aFrame) {
   return firstLeaf->GetBaseLevel();
 }
 
-void nsBidiPresUtils::IsFirstOrLast(
-    nsIFrame* aFrame, const nsContinuationStates* aContinuationStates,
-    bool aSpanDirMatchesLineDir, bool& aIsFirst /* out */,
-    bool& aIsLast /* out */) {
+void nsBidiPresUtils::IsFirstOrLast(nsIFrame* aFrame,
+                                    nsContinuationStates* aContinuationStates,
+                                    bool aSpanDirMatchesLineDir,
+                                    bool& aIsFirst /* out */,
+                                    bool& aIsLast /* out */) {
   /*
    * Since we lay out frames in the line's direction, visiting a frame with
    * 'mFirstVisualFrame == nullptr', means it's the first appearance of one
@@ -1372,7 +1373,7 @@ void nsBidiPresUtils::IsFirstOrLast(
    */
 
   bool firstInLineOrder, lastInLineOrder;
-  nsFrameContinuationState* frameState = aContinuationStates->GetEntry(aFrame);
+  nsFrameContinuationState* frameState = aContinuationStates->Get(aFrame);
   nsFrameContinuationState* firstFrameState;
 
   if (!frameState->mFirstVisualFrame) {
@@ -1390,7 +1391,7 @@ void nsBidiPresUtils::IsFirstOrLast(
      */
     // Traverse continuation chain backward
     for (frame = aFrame->GetPrevContinuation();
-         frame && (contState = aContinuationStates->GetEntry(frame));
+         frame && (contState = aContinuationStates->Get(frame));
          frame = frame->GetPrevContinuation()) {
       frameState->mFrameCount++;
       contState->mFirstVisualFrame = aFrame;
@@ -1399,7 +1400,7 @@ void nsBidiPresUtils::IsFirstOrLast(
 
     // Traverse continuation chain forward
     for (frame = aFrame->GetNextContinuation();
-         frame && (contState = aContinuationStates->GetEntry(frame));
+         frame && (contState = aContinuationStates->Get(frame));
          frame = frame->GetNextContinuation()) {
       frameState->mFrameCount++;
       contState->mFirstVisualFrame = aFrame;
@@ -1411,8 +1412,7 @@ void nsBidiPresUtils::IsFirstOrLast(
   } else {
     // aFrame is not the first visual frame of its continuation chain
     firstInLineOrder = false;
-    firstFrameState =
-        aContinuationStates->GetEntry(frameState->mFirstVisualFrame);
+    firstFrameState = aContinuationStates->Get(frameState->mFirstVisualFrame);
   }
 
   lastInLineOrder = (firstFrameState->mFrameCount == 1);
@@ -1507,7 +1507,7 @@ void nsBidiPresUtils::RepositionRubyContentFrame(
 
 /* static */
 nscoord nsBidiPresUtils::RepositionRubyFrame(
-    nsIFrame* aFrame, const nsContinuationStates* aContinuationStates,
+    nsIFrame* aFrame, nsContinuationStates* aContinuationStates,
     const WritingMode aContainerWM, const LogicalMargin& aBorderPadding) {
   LayoutFrameType frameType = aFrame->Type();
   MOZ_ASSERT(RubyUtils::IsRubyBox(frameType));
@@ -1570,7 +1570,7 @@ nscoord nsBidiPresUtils::RepositionRubyFrame(
 /* static */
 nscoord nsBidiPresUtils::RepositionFrame(
     nsIFrame* aFrame, bool aIsEvenLevel, nscoord aStartOrEnd,
-    const nsContinuationStates* aContinuationStates, WritingMode aContainerWM,
+    nsContinuationStates* aContinuationStates, WritingMode aContainerWM,
     bool aContainerReverseDir, const nsSize& aContainerSize) {
   nscoord lineSize =
       aContainerWM.IsVertical() ? aContainerSize.height : aContainerSize.width;
@@ -1671,7 +1671,7 @@ nscoord nsBidiPresUtils::RepositionFrame(
 
 void nsBidiPresUtils::InitContinuationStates(
     nsIFrame* aFrame, nsContinuationStates* aContinuationStates) {
-  aContinuationStates->PutEntry(aFrame);
+  aContinuationStates->Insert(aFrame);
   if (!IsBidiLeaf(aFrame) || RubyUtils::IsRubyBox(aFrame->Type())) {
     // Continue for child frames
     for (nsIFrame* frame : aFrame->PrincipalChildList()) {

layout/base/nsBidiPresUtils.h

@@ -12,6 +12,7 @@
 #include "nsBidiUtils.h"
 #include "nsHashKeys.h"
 #include "nsCoord.h"
+#include "nsTArray.h"
 
 #ifdef DrawText
 #  undef DrawText
@@ -68,10 +69,50 @@ struct nsFrameContinuationState : public nsVoidPtrHashKey {
   bool mHasContOnNextLines{false};
 };
 
-/*
- * Following type is used to pass needed hashtable to reordering methods
- */
-typedef nsTHashtable<nsFrameContinuationState> nsContinuationStates;
+// A table of nsFrameContinuationState objects.
+//
+// This state is used between calls to nsBidiPresUtils::IsFirstOrLast.
+struct nsContinuationStates {
+  static constexpr size_t kArrayMax = 32;
+
+  // We use the array to gather up all the continuation state objects.  If in
+  // the end there are more than kArrayMax of them, we convert it to a hash
+  // table for faster lookup.
+  bool mUseTable = false;
+  AutoTArray<nsFrameContinuationState, kArrayMax> mValues;
+  nsTHashtable<nsFrameContinuationState> mTable;
+
+  void Insert(nsIFrame* aFrame) {
+    if (MOZ_UNLIKELY(mUseTable)) {
+      mTable.PutEntry(aFrame);
+      return;
+    }
+    if (MOZ_LIKELY(mValues.Length() < kArrayMax)) {
+      mValues.AppendElement(aFrame);
+      return;
+    }
+    for (const auto& entry : mValues) {
+      mTable.PutEntry(entry.GetKey());
+    }
+    mTable.PutEntry(aFrame);
+    mValues.Clear();
+    mUseTable = true;
+  }
+
+  nsFrameContinuationState* Get(nsIFrame* aFrame) {
+    MOZ_ASSERT(mValues.IsEmpty() != mTable.IsEmpty(),
+               "expect entries to either be in mValues or in mTable");
+    if (mUseTable) {
+      return mTable.GetEntry(aFrame);
+    }
+    for (size_t i = 0, len = mValues.Length(); i != len; ++i) {
+      if (mValues[i].GetKey() == aFrame) {
+        return &mValues[i];
+      }
+    }
+    return nullptr;
+  }
+};
 
 /**
  * A structure representing a logical position which should be resolved
@@ -409,7 +450,7 @@ class nsBidiPresUtils {
    * Position ruby frames. Called from RepositionFrame.
    */
   static nscoord RepositionRubyFrame(
-      nsIFrame* aFrame, const nsContinuationStates* aContinuationStates,
+      nsIFrame* aFrame, nsContinuationStates* aContinuationStates,
       const mozilla::WritingMode aContainerWM,
       const mozilla::LogicalMargin& aBorderPadding);
 
@@ -430,11 +471,12 @@ class nsBidiPresUtils {
    *                             nsFrameContinuationState
    * @return                     The isize aFrame takes, including margins.
    */
-  static nscoord RepositionFrame(
-      nsIFrame* aFrame, bool aIsEvenLevel, nscoord aStartOrEnd,
-      const nsContinuationStates* aContinuationStates,
-      mozilla::WritingMode aContainerWM, bool aContainerReverseOrder,
-      const nsSize& aContainerSize);
+  static nscoord RepositionFrame(nsIFrame* aFrame, bool aIsEvenLevel,
+                                 nscoord aStartOrEnd,
+                                 nsContinuationStates* aContinuationStates,
+                                 mozilla::WritingMode aContainerWM,
+                                 bool aContainerReverseOrder,
+                                 const nsSize& aContainerSize);
 
   /*
    * Initialize the continuation state(nsFrameContinuationState) to
@@ -473,7 +515,7 @@ class nsBidiPresUtils {
    *                                    or continuation
    */
   static void IsFirstOrLast(nsIFrame* aFrame,
-                            const nsContinuationStates* aContinuationStates,
+                            nsContinuationStates* aContinuationStates,
                             bool aSpanInLineOrder /* in */,
                             bool& aIsFirst /* out */, bool& aIsLast /* out */);