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diff --git a/Source/JavaScriptCore/heap/HeapVerifier.cpp b/Source/JavaScriptCore/heap/HeapVerifier.cpp
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+++ b/Source/JavaScriptCore/heap/HeapVerifier.cpp
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+/*
+ * Copyright (C) 2014 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#include "config.h"
+#include "HeapVerifier.h"
+
+#include "ButterflyInlines.h"
+#include "CopiedSpaceInlines.h"
+#include "HeapIterationScope.h"
+#include "JSCInlines.h"
+#include "JSObject.h"
+
+namespace JSC {
+
+HeapVerifier::HeapVerifier(Heap* heap, unsigned numberOfGCCyclesToRecord)
+    : m_heap(heap)
+    , m_currentCycle(0)
+    , m_numberOfCycles(numberOfGCCyclesToRecord)
+{
+    RELEASE_ASSERT(m_numberOfCycles > 0);
+    m_cycles = std::make_unique<GCCycle[]>(m_numberOfCycles);
+}
+
+const char* HeapVerifier::collectionTypeName(HeapOperation type)
+{
+    switch (type) {
+    case NoOperation:
+        return "NoOperation";
+    case AnyCollection:
+        return "AnyCollection";
+    case Allocation:
+        return "Allocation";
+    case EdenCollection:
+        return "EdenCollection";
+    case FullCollection:
+        return "FullCollection";
+    }
+    RELEASE_ASSERT_NOT_REACHED();
+    return nullptr; // Silencing a compiler warning.
+}
+
+const char* HeapVerifier::phaseName(HeapVerifier::Phase phase)
+{
+    switch (phase) {
+    case Phase::BeforeGC:
+        return "BeforeGC";
+    case Phase::BeforeMarking:
+        return "BeforeMarking";
+    case Phase::AfterMarking:
+        return "AfterMarking";
+    case Phase::AfterGC:
+        return "AfterGC";
+    }
+    RELEASE_ASSERT_NOT_REACHED();
+    return nullptr; // Silencing a compiler warning.
+}
+
+static void getButterflyDetails(JSObject* obj, void*& butterflyBase, size_t& butterflyCapacityInBytes, CopiedBlock*& butterflyBlock)
+{
+    Structure* structure = obj->structure();
+    Butterfly* butterfly = obj->butterfly();
+    butterflyBase = butterfly->base(structure);
+    butterflyBlock = CopiedSpace::blockFor(butterflyBase);
+
+    size_t propertyCapacity = structure->outOfLineCapacity();
+    size_t preCapacity;
+    size_t indexingPayloadSizeInBytes;
+    bool hasIndexingHeader = obj->hasIndexingHeader();
+    if (UNLIKELY(hasIndexingHeader)) {
+        preCapacity = butterfly->indexingHeader()->preCapacity(structure);
+        indexingPayloadSizeInBytes = butterfly->indexingHeader()->indexingPayloadSizeInBytes(structure);
+    } else {
+        preCapacity = 0;
+        indexingPayloadSizeInBytes = 0;
+    }
+    butterflyCapacityInBytes = Butterfly::totalSize(preCapacity, propertyCapacity, hasIndexingHeader, indexingPayloadSizeInBytes);
+}
+
+void HeapVerifier::initializeGCCycle()
+{
+    Heap* heap = m_heap;
+    incrementCycle();
+    currentCycle().collectionType = heap->operationInProgress();
+}
+
+struct GatherLiveObjFunctor : MarkedBlock::CountFunctor {
+    GatherLiveObjFunctor(LiveObjectList& list)
+        : m_list(list)
+    {
+        ASSERT(!list.liveObjects.size());
+    }
+
+    inline void visit(JSCell* cell)
+    {
+        if (!cell->isObject())
+            return;        
+        LiveObjectData data(asObject(cell));
+        m_list.liveObjects.append(data);
+    }
+
+    IterationStatus operator()(JSCell* cell)
+    {
+        visit(cell);
+        return IterationStatus::Continue;
+    }
+
+    LiveObjectList& m_list;
+};
+
+void HeapVerifier::gatherLiveObjects(HeapVerifier::Phase phase)
+{
+    Heap* heap = m_heap;
+    LiveObjectList& list = *liveObjectListForGathering(phase);
+
+    HeapIterationScope iterationScope(*heap);
+    list.reset();
+    GatherLiveObjFunctor functor(list);
+    heap->m_objectSpace.forEachLiveCell(iterationScope, functor);
+}
+
+LiveObjectList* HeapVerifier::liveObjectListForGathering(HeapVerifier::Phase phase)
+{
+    switch (phase) {
+    case Phase::BeforeMarking:
+        return &currentCycle().before;
+    case Phase::AfterMarking:
+        return &currentCycle().after;
+    case Phase::BeforeGC:
+    case Phase::AfterGC:
+        // We should not be gathering live objects during these phases.
+        break;
+    }
+    RELEASE_ASSERT_NOT_REACHED();
+    return nullptr; // Silencing a compiler warning.
+}
+
+static void trimDeadObjectsFromList(HashSet<JSObject*>& knownLiveSet, LiveObjectList& list)
+{
+    if (!list.hasLiveObjects)
+        return;
+
+    size_t liveObjectsFound = 0;
+    for (size_t i = 0; i < list.liveObjects.size(); i++) {
+        LiveObjectData& objData = list.liveObjects[i];
+        if (objData.isConfirmedDead)
+            continue; // Don't "resurrect" known dead objects.
+        if (!knownLiveSet.contains(objData.obj)) {
+            objData.isConfirmedDead = true;
+            continue;
+        }
+        liveObjectsFound++;
+    }
+    list.hasLiveObjects = !!liveObjectsFound;
+}
+
+void HeapVerifier::trimDeadObjects()
+{
+    HashSet<JSObject*> knownLiveSet;
+
+    LiveObjectList& after = currentCycle().after;
+    for (size_t i = 0; i < after.liveObjects.size(); i++) {
+        LiveObjectData& objData = after.liveObjects[i];
+        knownLiveSet.add(objData.obj);
+    }
+
+    trimDeadObjectsFromList(knownLiveSet, currentCycle().before);
+
+    for (int i = -1; i > -m_numberOfCycles; i--) {
+        trimDeadObjectsFromList(knownLiveSet, cycleForIndex(i).before);
+        trimDeadObjectsFromList(knownLiveSet, cycleForIndex(i).after);
+    }
+}
+
+bool HeapVerifier::verifyButterflyIsInStorageSpace(Phase phase, LiveObjectList& list)
+{
+    auto& liveObjects = list.liveObjects;
+
+    CopiedSpace& storageSpace = m_heap->m_storageSpace;
+    bool listNamePrinted = false;
+    bool success = true;
+    for (size_t i = 0; i < liveObjects.size(); i++) {
+        LiveObjectData& objectData = liveObjects[i];
+        if (objectData.isConfirmedDead)
+            continue;
+
+        JSObject* obj = objectData.obj;
+        Butterfly* butterfly = obj->butterfly();
+        if (butterfly) {
+            void* butterflyBase;
+            size_t butterflyCapacityInBytes;
+            CopiedBlock* butterflyBlock;
+            getButterflyDetails(obj, butterflyBase, butterflyCapacityInBytes, butterflyBlock);
+
+            if (!storageSpace.contains(butterflyBlock)) {
+                if (!listNamePrinted) {
+                    dataLogF("Verification @ phase %s FAILED in object list '%s' (size %zu)\n",
+                        phaseName(phase), list.name, liveObjects.size());
+                    listNamePrinted = true;
+                }
+
+                Structure* structure = obj->structure();
+                const char* structureClassName = structure->classInfo()->className;
+                dataLogF("    butterfly %p (base %p size %zu block %p) NOT in StorageSpace | obj %p type '%s'\n",
+                    butterfly, butterflyBase, butterflyCapacityInBytes, butterflyBlock, obj, structureClassName);
+                success = false;
+            }
+        }
+    }
+    return success;
+}
+
+void HeapVerifier::verify(HeapVerifier::Phase phase)
+{
+    bool beforeVerified = verifyButterflyIsInStorageSpace(phase, currentCycle().before);
+    bool afterVerified = verifyButterflyIsInStorageSpace(phase, currentCycle().after);
+    RELEASE_ASSERT(beforeVerified && afterVerified);
+}
+
+void HeapVerifier::reportObject(LiveObjectData& objData, int cycleIndex, HeapVerifier::GCCycle& cycle, LiveObjectList& list)
+{
+    JSObject* obj = objData.obj;
+
+    if (objData.isConfirmedDead) {
+        dataLogF("FOUND dead obj %p in GC[%d] %s list '%s'\n",
+            obj, cycleIndex, cycle.collectionTypeName(), list.name);
+        return;
+    }
+
+    Structure* structure = obj->structure();
+    Butterfly* butterfly = obj->butterfly();
+    void* butterflyBase;
+    size_t butterflyCapacityInBytes;
+    CopiedBlock* butterflyBlock;
+    getButterflyDetails(obj, butterflyBase, butterflyCapacityInBytes, butterflyBlock);
+
+    dataLogF("FOUND obj %p type '%s' butterfly %p (base %p size %zu block %p) in GC[%d] %s list '%s'\n",
+        obj, structure->classInfo()->className,
+        butterfly, butterflyBase, butterflyCapacityInBytes, butterflyBlock,
+        cycleIndex, cycle.collectionTypeName(), list.name);
+}
+
+void HeapVerifier::checkIfRecorded(JSObject* obj)
+{
+    bool found = false;
+
+    for (int cycleIndex = 0; cycleIndex > -m_numberOfCycles; cycleIndex--) {
+        GCCycle& cycle = cycleForIndex(cycleIndex);
+        LiveObjectList& beforeList = cycle.before; 
+        LiveObjectList& afterList = cycle.after; 
+
+        LiveObjectData* objData;
+        objData = beforeList.findObject(obj);
+        if (objData) {
+            reportObject(*objData, cycleIndex, cycle, beforeList);
+            found = true;
+        }
+        objData = afterList.findObject(obj);
+        if (objData) {
+            reportObject(*objData, cycleIndex, cycle, afterList);
+            found = true;
+        }
+    }
+
+    if (!found)
+        dataLogF("obj %p NOT FOUND\n", obj);
+}
+
+} // namespace JSC