Remove "virtual" from all lines that have both "virtual" and "override".
[WebKit-https.git] / Source / JavaScriptCore / runtime / Structure.h
index d37ad5c..ad559a4 100644 (file)
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008, 2009, 2012 Apple Inc. All rights reserved.
+ * Copyright (C) 2008, 2009, 2012-2016 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  *    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 COMPUTER, INC. ``AS IS'' AND ANY
+ * 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 COMPUTER, INC. OR
+ * 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
 #define Structure_h
 
 #include "ClassInfo.h"
+#include "ConcurrentJITLock.h"
 #include "IndexingType.h"
+#include "InferredTypeTable.h"
 #include "JSCJSValue.h"
 #include "JSCell.h"
 #include "JSType.h"
-#include "PropertyMapHashTable.h"
 #include "PropertyName.h"
 #include "PropertyNameArray.h"
+#include "PropertyOffset.h"
 #include "Protect.h"
+#include "PutPropertySlot.h"
+#include "StructureIDBlob.h"
 #include "StructureRareData.h"
+#include "StructureRareDataInlines.h"
 #include "StructureTransitionTable.h"
 #include "JSTypeInfo.h"
 #include "Watchpoint.h"
 #include "Weak.h"
-#include <wtf/PassOwnPtr.h>
+#include "WriteBarrierInlines.h"
+#include <wtf/CompilationThread.h>
 #include <wtf/PassRefPtr.h>
+#include <wtf/PrintStream.h>
 #include <wtf/RefCounted.h>
-#include <wtf/text/StringImpl.h>
 
+namespace WTF {
+
+class UniquedStringImpl;
+
+} // namespace WTF
 
 namespace JSC {
 
-    class LLIntOffsetsExtractor;
-    class PropertyNameArray;
-    class PropertyNameArrayData;
-    class StructureChain;
-    class SlotVisitor;
-    class JSString;
+class DeferGC;
+class LLIntOffsetsExtractor;
+class PropertyNameArray;
+class PropertyNameArrayData;
+class PropertyTable;
+class StructureChain;
+class StructureShape;
+class SlotVisitor;
+class JSString;
+struct DumpContext;
+
+// The out-of-line property storage capacity to use when first allocating out-of-line
+// storage. Note that all objects start out without having any out-of-line storage;
+// this comes into play only on the first property store that exhausts inline storage.
+static const unsigned initialOutOfLineCapacity = 4;
+
+// The factor by which to grow out-of-line storage when it is exhausted, after the
+// initial allocation.
+static const unsigned outOfLineGrowthFactor = 2;
+
+struct PropertyMapEntry {
+    UniquedStringImpl* key;
+    PropertyOffset offset;
+    uint8_t attributes;
+    bool hasInferredType; // This caches whether or not a property has an inferred type in the inferred type table, and is used for a fast check in JSObject::putDirectInternal().
+
+    PropertyMapEntry()
+        : key(nullptr)
+        , offset(invalidOffset)
+        , attributes(0)
+        , hasInferredType(false)
+    {
+    }
+    
+    PropertyMapEntry(UniquedStringImpl* key, PropertyOffset offset, unsigned attributes)
+        : key(key)
+        , offset(offset)
+        , attributes(attributes)
+        , hasInferredType(false)
+    {
+        ASSERT(this->attributes == attributes);
+    }
+};
 
-    // The out-of-line property storage capacity to use when first allocating out-of-line
-    // storage. Note that all objects start out without having any out-of-line storage;
-    // this comes into play only on the first property store that exhausts inline storage.
-    static const unsigned initialOutOfLineCapacity = 4;
+class StructureFireDetail : public FireDetail {
+public:
+    StructureFireDetail(const Structure* structure)
+        : m_structure(structure)
+    {
+    }
+    
+    void dump(PrintStream& out) const override;
 
-    // The factor by which to grow out-of-line storage when it is exhausted, after the
-    // initial allocation.
-    static const unsigned outOfLineGrowthFactor = 2;
+private:
+    const Structure* m_structure;
+};
 
-    class Structure : public JSCell {
-    public:
-        friend class StructureTransitionTable;
+class DeferredStructureTransitionWatchpointFire {
+    WTF_MAKE_NONCOPYABLE(DeferredStructureTransitionWatchpointFire);
+public:
+    JS_EXPORT_PRIVATE DeferredStructureTransitionWatchpointFire();
+    JS_EXPORT_PRIVATE ~DeferredStructureTransitionWatchpointFire();
+    
+    void add(const Structure*);
+    
+private:
+    const Structure* m_structure;
+};
 
-        typedef JSCell Base;
+class Structure final : public JSCell {
+public:
+    friend class StructureTransitionTable;
 
-        static Structure* create(JSGlobalData&, JSGlobalObject*, JSValue prototype, const TypeInfo&, const ClassInfo*, IndexingType = NonArray, unsigned inlineCapacity = 0);
+    typedef JSCell Base;
+    static const unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;
+    
+    static Structure* create(VM&, JSGlobalObject*, JSValue prototype, const TypeInfo&, const ClassInfo*, IndexingType = NonArray, unsigned inlineCapacity = 0);
 
-    protected:
-        void finishCreation(JSGlobalData& globalData)
-        {
-            Base::finishCreation(globalData);
-            ASSERT(m_prototype);
-            ASSERT(m_prototype.isObject() || m_prototype.isNull());
-        }
+    ~Structure();
 
-        void finishCreation(JSGlobalData& globalData, CreatingEarlyCellTag)
-        {
-            Base::finishCreation(globalData, this, CreatingEarlyCell);
-            ASSERT(m_prototype);
-            ASSERT(m_prototype.isNull());
-            ASSERT(!globalData.structureStructure);
-        }
+protected:
+    void finishCreation(VM& vm)
+    {
+        Base::finishCreation(vm);
+        ASSERT(m_prototype);
+        ASSERT(m_prototype.isObject() || m_prototype.isNull());
+    }
 
-    public:
-        static void dumpStatistics();
-
-        JS_EXPORT_PRIVATE static Structure* addPropertyTransition(JSGlobalData&, Structure*, PropertyName, unsigned attributes, JSCell* specificValue, PropertyOffset&);
-        JS_EXPORT_PRIVATE static Structure* addPropertyTransitionToExistingStructure(Structure*, PropertyName, unsigned attributes, JSCell* specificValue, PropertyOffset&);
-        static Structure* removePropertyTransition(JSGlobalData&, Structure*, PropertyName, PropertyOffset&);
-        JS_EXPORT_PRIVATE static Structure* changePrototypeTransition(JSGlobalData&, Structure*, JSValue prototype);
-        JS_EXPORT_PRIVATE static Structure* despecifyFunctionTransition(JSGlobalData&, Structure*, PropertyName);
-        static Structure* attributeChangeTransition(JSGlobalData&, Structure*, PropertyName, unsigned attributes);
-        static Structure* toCacheableDictionaryTransition(JSGlobalData&, Structure*);
-        static Structure* toUncacheableDictionaryTransition(JSGlobalData&, Structure*);
-        static Structure* sealTransition(JSGlobalData&, Structure*);
-        static Structure* freezeTransition(JSGlobalData&, Structure*);
-        static Structure* preventExtensionsTransition(JSGlobalData&, Structure*);
-        static Structure* nonPropertyTransition(JSGlobalData&, Structure*, NonPropertyTransition);
-
-        bool isSealed(JSGlobalData&);
-        bool isFrozen(JSGlobalData&);
-        bool isExtensible() const { return !m_preventExtensions; }
-        bool didTransition() const { return m_didTransition; }
-        bool putWillGrowOutOfLineStorage()
-        {
-            ASSERT(outOfLineCapacity() >= outOfLineSize());
-            
-            if (!m_propertyTable) {
-                unsigned currentSize = numberOfOutOfLineSlotsForLastOffset(m_offset);
-                ASSERT(outOfLineCapacity() >= currentSize);
-                return currentSize == outOfLineCapacity();
-            }
-            
-            ASSERT(totalStorageCapacity() >= m_propertyTable->propertyStorageSize());
-            if (m_propertyTable->hasDeletedOffset())
-                return false;
-            
-            ASSERT(totalStorageCapacity() >= m_propertyTable->size());
-            return m_propertyTable->size() == totalStorageCapacity();
-        }
-        JS_EXPORT_PRIVATE size_t suggestedNewOutOfLineStorageCapacity(); 
+    void finishCreation(VM& vm, CreatingEarlyCellTag)
+    {
+        Base::finishCreation(vm, this, CreatingEarlyCell);
+        ASSERT(m_prototype);
+        ASSERT(m_prototype.isNull());
+        ASSERT(!vm.structureStructure);
+    }
 
-        Structure* flattenDictionaryStructure(JSGlobalData&, JSObject*);
+public:
+    StructureID id() const { return m_blob.structureID(); }
+    int32_t objectInitializationBlob() const { return m_blob.blobExcludingStructureID(); }
+    int64_t idBlob() const { return m_blob.blob(); }
 
-        static const bool needsDestruction = true;
-        static const bool hasImmortalStructure = true;
-        static void destroy(JSCell*);
+    bool isProxy() const
+    {
+        JSType type = m_blob.type();
+        return type == ImpureProxyType || type == PureForwardingProxyType;
+    }
 
-        // These should be used with caution.  
-        JS_EXPORT_PRIVATE PropertyOffset addPropertyWithoutTransition(JSGlobalData&, PropertyName, unsigned attributes, JSCell* specificValue);
-        PropertyOffset removePropertyWithoutTransition(JSGlobalData&, PropertyName);
-        void setPrototypeWithoutTransition(JSGlobalData& globalData, JSValue prototype) { m_prototype.set(globalData, this, prototype); }
+    static void dumpStatistics();
+
+    JS_EXPORT_PRIVATE static Structure* addPropertyTransition(VM&, Structure*, PropertyName, unsigned attributes, PropertyOffset&, PutPropertySlot::Context = PutPropertySlot::UnknownContext, DeferredStructureTransitionWatchpointFire* = nullptr);
+    static Structure* addPropertyTransitionToExistingStructureConcurrently(Structure*, UniquedStringImpl* uid, unsigned attributes, PropertyOffset&);
+    JS_EXPORT_PRIVATE static Structure* addPropertyTransitionToExistingStructure(Structure*, PropertyName, unsigned attributes, PropertyOffset&);
+    static Structure* removePropertyTransition(VM&, Structure*, PropertyName, PropertyOffset&);
+    JS_EXPORT_PRIVATE static Structure* changePrototypeTransition(VM&, Structure*, JSValue prototype);
+    JS_EXPORT_PRIVATE static Structure* attributeChangeTransition(VM&, Structure*, PropertyName, unsigned attributes);
+    JS_EXPORT_PRIVATE static Structure* toCacheableDictionaryTransition(VM&, Structure*, DeferredStructureTransitionWatchpointFire* = nullptr);
+    static Structure* toUncacheableDictionaryTransition(VM&, Structure*);
+    JS_EXPORT_PRIVATE static Structure* sealTransition(VM&, Structure*);
+    JS_EXPORT_PRIVATE static Structure* freezeTransition(VM&, Structure*);
+    static Structure* preventExtensionsTransition(VM&, Structure*);
+    JS_EXPORT_PRIVATE static Structure* nonPropertyTransition(VM&, Structure*, NonPropertyTransition);
+
+    JS_EXPORT_PRIVATE bool isSealed(VM&);
+    JS_EXPORT_PRIVATE bool isFrozen(VM&);
+    bool isStructureExtensible() const { return !didPreventExtensions(); }
+    bool putWillGrowOutOfLineStorage();
+    size_t suggestedNewOutOfLineStorageCapacity(); 
+
+    JS_EXPORT_PRIVATE Structure* flattenDictionaryStructure(VM&, JSObject*);
+
+    static const bool needsDestruction = true;
+    static void destroy(JSCell*);
+
+    // These should be used with caution.  
+    JS_EXPORT_PRIVATE PropertyOffset addPropertyWithoutTransition(VM&, PropertyName, unsigned attributes);
+    PropertyOffset removePropertyWithoutTransition(VM&, PropertyName);
+    void setPrototypeWithoutTransition(VM& vm, JSValue prototype) { m_prototype.set(vm, this, prototype); }
         
-        bool isDictionary() const { return m_dictionaryKind != NoneDictionaryKind; }
-        bool isUncacheableDictionary() const { return m_dictionaryKind == UncachedDictionaryKind; }
+    bool isDictionary() const { return dictionaryKind() != NoneDictionaryKind; }
+    bool isUncacheableDictionary() const { return dictionaryKind() == UncachedDictionaryKind; }
+  
+    bool propertyAccessesAreCacheable()
+    {
+        return dictionaryKind() != UncachedDictionaryKind
+            && !typeInfo().prohibitsPropertyCaching()
+            && !(typeInfo().getOwnPropertySlotIsImpure() && !typeInfo().newImpurePropertyFiresWatchpoints());
+    }
 
-        bool propertyAccessesAreCacheable() { return m_dictionaryKind != UncachedDictionaryKind && !typeInfo().prohibitsPropertyCaching(); }
+    bool propertyAccessesAreCacheableForAbsence()
+    {
+        return !typeInfo().getOwnPropertySlotIsImpureForPropertyAbsence();
+    }
+    
+    bool needImpurePropertyWatchpoint()
+    {
+        return propertyAccessesAreCacheable()
+            && typeInfo().getOwnPropertySlotIsImpure()
+            && typeInfo().newImpurePropertyFiresWatchpoints();
+    }
 
-        // Type accessors.
-        const TypeInfo& typeInfo() const { ASSERT(structure()->classInfo() == &s_info); return m_typeInfo; }
-        bool isObject() const { return typeInfo().isObject(); }
+    // We use SlowPath in GetByIdStatus for structures that may get new impure properties later to prevent
+    // DFG from inlining property accesses since structures don't transition when a new impure property appears.
+    bool takesSlowPathInDFGForImpureProperty()
+    {
+        return typeInfo().getOwnPropertySlotIsImpure();
+    }
+    
+    // Type accessors.
+    TypeInfo typeInfo() const { ASSERT(structure()->classInfo() == info()); return m_blob.typeInfo(m_outOfLineTypeFlags); }
+    bool isObject() const { return typeInfo().isObject(); }
 
-        IndexingType indexingType() const { return m_indexingType & AllArrayTypes; }
-        IndexingType indexingTypeIncludingHistory() const { return m_indexingType; }
-        
-        bool mayInterceptIndexedAccesses() const
-        {
-            return !!(indexingTypeIncludingHistory() & MayHaveIndexedAccessors);
-        }
+    IndexingType indexingType() const { return m_blob.indexingType() & AllArrayTypes; }
+    IndexingType indexingTypeIncludingHistory() const { return m_blob.indexingType(); }
         
-        bool anyObjectInChainMayInterceptIndexedAccesses() const;
+    bool mayInterceptIndexedAccesses() const
+    {
+        return !!(indexingTypeIncludingHistory() & MayHaveIndexedAccessors);
+    }
         
-        bool needsSlowPutIndexing() const;
-        NonPropertyTransition suggestedArrayStorageTransition() const;
+    JS_EXPORT_PRIVATE bool anyObjectInChainMayInterceptIndexedAccesses() const;
+    bool holesMustForwardToPrototype(VM&) const;
         
-        JSGlobalObject* globalObject() const { return m_globalObject.get(); }
-        void setGlobalObject(JSGlobalData& globalData, JSGlobalObject* globalObject) { m_globalObject.set(globalData, this, globalObject); }
+    bool needsSlowPutIndexing() const;
+    NonPropertyTransition suggestedArrayStorageTransition() const;
         
-        JSValue storedPrototype() const { return m_prototype.get(); }
-        JSValue prototypeForLookup(ExecState*) const;
-        JSValue prototypeForLookup(JSGlobalObject*) const;
-        JSValue prototypeForLookup(CodeBlock*) const;
-        StructureChain* prototypeChain(JSGlobalData&, JSGlobalObject*) const;
-        StructureChain* prototypeChain(ExecState*) const;
-        static void visitChildren(JSCell*, SlotVisitor&);
+    JSGlobalObject* globalObject() const { return m_globalObject.get(); }
+    void setGlobalObject(VM& vm, JSGlobalObject* globalObject) { m_globalObject.set(vm, this, globalObject); }
         
-        // Will just the prototype chain intercept this property access?
-        bool prototypeChainMayInterceptStoreTo(JSGlobalData&, PropertyName);
+    JSValue storedPrototype() const { return m_prototype.get(); }
+    JSObject* storedPrototypeObject() const;
+    Structure* storedPrototypeStructure() const;
+    JSValue prototypeForLookup(ExecState*) const;
+    JSValue prototypeForLookup(JSGlobalObject*) const;
+    JSValue prototypeForLookup(CodeBlock*) const;
+    StructureChain* prototypeChain(VM&, JSGlobalObject*) const;
+    StructureChain* prototypeChain(ExecState*) const;
+    static void visitChildren(JSCell*, SlotVisitor&);
         
-        bool transitionDidInvolveSpecificValue() const { return !!m_specificValueInPrevious; }
+    // Will just the prototype chain intercept this property access?
+    JS_EXPORT_PRIVATE bool prototypeChainMayInterceptStoreTo(VM&, PropertyName);
         
-        Structure* previousID() const
-        {
-            ASSERT(structure()->classInfo() == &s_info);
-            if (typeInfo().structureHasRareData())
-                return rareData()->previousID();
-            return previous();
-        }
-        bool transitivelyTransitionedFrom(Structure* structureToFind);
-
-        unsigned outOfLineCapacity() const
-        {
-            unsigned outOfLineSize = this->outOfLineSize();
-
-            if (!outOfLineSize)
-                return 0;
-
-            if (outOfLineSize <= initialOutOfLineCapacity)
-                return initialOutOfLineCapacity;
-
-            ASSERT(outOfLineSize > initialOutOfLineCapacity);
-            return WTF::roundUpToPowerOf<outOfLineGrowthFactor>(outOfLineSize);
-        }
-        unsigned outOfLineSize() const
-        {
-            ASSERT(structure()->classInfo() == &s_info);
-            if (m_propertyTable) {
-                unsigned totalSize = m_propertyTable->propertyStorageSize();
-                unsigned inlineCapacity = this->inlineCapacity();
-                if (totalSize < inlineCapacity)
-                    return 0;
-                return totalSize - inlineCapacity;
-            }
-            return numberOfOutOfLineSlotsForLastOffset(m_offset);
-        }
-        bool hasInlineStorage() const
-        {
-            return !!m_inlineCapacity;
-        }
-        unsigned inlineCapacity() const
-        {
-            return m_inlineCapacity;
-        }
-        unsigned inlineSize() const
-        {
-            unsigned result;
-            if (m_propertyTable)
-                result = m_propertyTable->propertyStorageSize();
-            else
-                result = m_offset + 1;
-            return std::min<unsigned>(result, m_inlineCapacity);
-        }
-        unsigned totalStorageSize() const
-        {
-            if (m_propertyTable)
-                return m_propertyTable->propertyStorageSize();
-            return numberOfSlotsForLastOffset(m_offset, m_inlineCapacity);
-        }
-        unsigned totalStorageCapacity() const
-        {
-            ASSERT(structure()->classInfo() == &s_info);
-            return outOfLineCapacity() + inlineCapacity();
-        }
-
-        PropertyOffset firstValidOffset() const
-        {
-            if (hasInlineStorage())
-                return 0;
-            return firstOutOfLineOffset;
-        }
-        PropertyOffset lastValidOffset() const
-        {
-            if (m_propertyTable)
-                return offsetForPropertyNumber(m_propertyTable->propertyStorageSize() - 1, m_inlineCapacity);
-            return m_offset;
-        }
-        bool isValidOffset(PropertyOffset offset) const
-        {
-            return offset >= firstValidOffset()
-                && offset <= lastValidOffset();
-        }
+    Structure* previousID() const
+    {
+        ASSERT(structure()->classInfo() == info());
+        if (hasRareData())
+            return rareData()->previousID();
+        return previous();
+    }
+    bool transitivelyTransitionedFrom(Structure* structureToFind);
 
-        bool masqueradesAsUndefined(JSGlobalObject* lexicalGlobalObject);
+    unsigned outOfLineCapacity() const
+    {
+        ASSERT(checkOffsetConsistency());
+            
+        unsigned outOfLineSize = this->outOfLineSize();
 
-        PropertyOffset get(JSGlobalData&, PropertyName);
-        PropertyOffset get(JSGlobalData&, const WTF::String& name);
-        JS_EXPORT_PRIVATE PropertyOffset get(JSGlobalData&, PropertyName, unsigned& attributes, JSCell*& specificValue);
+        if (!outOfLineSize)
+            return 0;
 
-        bool hasGetterSetterProperties() const { return m_hasGetterSetterProperties; }
-        bool hasReadOnlyOrGetterSetterPropertiesExcludingProto() const { return m_hasReadOnlyOrGetterSetterPropertiesExcludingProto; }
-        void setHasGetterSetterProperties(bool is__proto__)
-        {
-            m_hasGetterSetterProperties = true;
-            if (!is__proto__)
-                m_hasReadOnlyOrGetterSetterPropertiesExcludingProto = true;
-        }
-        void setContainsReadOnlyProperties()
-        {
-            m_hasReadOnlyOrGetterSetterPropertiesExcludingProto = true;
-        }
+        if (outOfLineSize <= initialOutOfLineCapacity)
+            return initialOutOfLineCapacity;
 
-        bool hasNonEnumerableProperties() const { return m_hasNonEnumerableProperties; }
-        
-        bool isEmpty() const
-        {
-            if (m_propertyTable)
-                return m_propertyTable->isEmpty();
-            return !JSC::isValidOffset(m_offset);
-        }
+        ASSERT(outOfLineSize > initialOutOfLineCapacity);
+        COMPILE_ASSERT(outOfLineGrowthFactor == 2, outOfLineGrowthFactor_is_two);
+        return WTF::roundUpToPowerOfTwo(outOfLineSize);
+    }
+    unsigned outOfLineSize() const
+    {
+        ASSERT(checkOffsetConsistency());
+        ASSERT(structure()->classInfo() == info());
+            
+        return numberOfOutOfLineSlotsForLastOffset(m_offset);
+    }
+    bool hasInlineStorage() const
+    {
+        return !!m_inlineCapacity;
+    }
+    unsigned inlineCapacity() const
+    {
+        return m_inlineCapacity;
+    }
+    unsigned inlineSize() const
+    {
+        return std::min<unsigned>(m_offset + 1, m_inlineCapacity);
+    }
+    unsigned totalStorageSize() const
+    {
+        return numberOfSlotsForLastOffset(m_offset, m_inlineCapacity);
+    }
+    unsigned totalStorageCapacity() const
+    {
+        ASSERT(structure()->classInfo() == info());
+        return outOfLineCapacity() + inlineCapacity();
+    }
 
-        JS_EXPORT_PRIVATE void despecifyDictionaryFunction(JSGlobalData&, PropertyName);
-        void disableSpecificFunctionTracking() { m_specificFunctionThrashCount = maxSpecificFunctionThrashCount; }
+    bool isValidOffset(PropertyOffset offset) const
+    {
+        return JSC::isValidOffset(offset)
+            && offset <= m_offset
+            && (offset < m_inlineCapacity || offset >= firstOutOfLineOffset);
+    }
 
-        void setEnumerationCache(JSGlobalData&, JSPropertyNameIterator* enumerationCache); // Defined in JSPropertyNameIterator.h.
-        JSPropertyNameIterator* enumerationCache(); // Defined in JSPropertyNameIterator.h.
-        void getPropertyNamesFromStructure(JSGlobalData&, PropertyNameArray&, EnumerationMode);
+    bool hijacksIndexingHeader() const
+    {
+        return isTypedView(m_classInfo->typedArrayStorageType);
+    }
+    
+    bool couldHaveIndexingHeader() const
+    {
+        return hasIndexedProperties(indexingType())
+            || hijacksIndexingHeader();
+    }
+    
+    bool hasIndexingHeader(const JSCell*) const;
+    
+    bool masqueradesAsUndefined(JSGlobalObject* lexicalGlobalObject);
+
+    PropertyOffset get(VM&, PropertyName);
+    PropertyOffset get(VM&, PropertyName, unsigned& attributes);
+    PropertyOffset get(VM&, PropertyName, unsigned& attributes, bool& hasInferredType);
+
+    // This is a somewhat internalish method. It will call your functor while possibly holding the
+    // Structure's lock. There is no guarantee whether the lock is held or not in any particular
+    // call. So, you have to assume the worst. Also, the functor returns true if it wishes for you
+    // to continue or false if it's done.
+    template<typename Functor>
+    void forEachPropertyConcurrently(const Functor&);
+    
+    PropertyOffset getConcurrently(UniquedStringImpl* uid);
+    PropertyOffset getConcurrently(UniquedStringImpl* uid, unsigned& attributes);
+    
+    Vector<PropertyMapEntry> getPropertiesConcurrently();
+    
+    void setHasGetterSetterPropertiesWithProtoCheck(bool is__proto__)
+    {
+        setHasGetterSetterProperties(true);
+        if (!is__proto__)
+            setHasReadOnlyOrGetterSetterPropertiesExcludingProto(true);
+    }
+    
+    void setContainsReadOnlyProperties() { setHasReadOnlyOrGetterSetterPropertiesExcludingProto(true); }
+    
+    void setHasCustomGetterSetterPropertiesWithProtoCheck(bool is__proto__)
+    {
+        setHasCustomGetterSetterProperties(true);
+        if (!is__proto__)
+            setHasReadOnlyOrGetterSetterPropertiesExcludingProto(true);
+    }
+    
+    bool isEmpty() const
+    {
+        ASSERT(checkOffsetConsistency());
+        return !JSC::isValidOffset(m_offset);
+    }
 
-        JSString* objectToStringValue()
-        {
-            if (!typeInfo().structureHasRareData())
-                return 0;
-            return rareData()->objectToStringValue();
-        }
+    void setCachedPropertyNameEnumerator(VM&, JSPropertyNameEnumerator*);
+    JSPropertyNameEnumerator* cachedPropertyNameEnumerator() const;
+    bool canCachePropertyNameEnumerator() const;
+    bool canAccessPropertiesQuicklyForEnumeration() const;
 
-        void setObjectToStringValue(JSGlobalData& globalData, const JSCell* owner, JSString* value)
-        {
-            if (!typeInfo().structureHasRareData())
-                allocateRareData(globalData);
-            rareData()->setObjectToStringValue(globalData, owner, value);
-        }
+    void getPropertyNamesFromStructure(VM&, PropertyNameArray&, EnumerationMode);
 
-        bool staticFunctionsReified()
-        {
-            return m_staticFunctionReified;
-        }
+    JSString* objectToStringValue()
+    {
+        if (!hasRareData())
+            return 0;
+        return rareData()->objectToStringValue();
+    }
 
-        void setStaticFunctionsReified()
-        {
-            m_staticFunctionReified = true;
-        }
+    void setObjectToStringValue(ExecState*, VM&, JSString* value, PropertySlot toStringTagSymbolSlot);
 
-        const ClassInfo* classInfo() const { return m_classInfo; }
+    const ClassInfo* classInfo() const { return m_classInfo; }
 
-        static ptrdiff_t prototypeOffset()
-        {
-            return OBJECT_OFFSETOF(Structure, m_prototype);
-        }
+    static ptrdiff_t structureIDOffset()
+    {
+        return OBJECT_OFFSETOF(Structure, m_blob) + StructureIDBlob::structureIDOffset();
+    }
 
-        static ptrdiff_t globalObjectOffset()
-        {
-            return OBJECT_OFFSETOF(Structure, m_globalObject);
-        }
+    static ptrdiff_t prototypeOffset()
+    {
+        return OBJECT_OFFSETOF(Structure, m_prototype);
+    }
 
-        static ptrdiff_t typeInfoFlagsOffset()
-        {
-            return OBJECT_OFFSETOF(Structure, m_typeInfo) + TypeInfo::flagsOffset();
-        }
+    static ptrdiff_t globalObjectOffset()
+    {
+        return OBJECT_OFFSETOF(Structure, m_globalObject);
+    }
 
-        static ptrdiff_t typeInfoTypeOffset()
-        {
-            return OBJECT_OFFSETOF(Structure, m_typeInfo) + TypeInfo::typeOffset();
-        }
-        
-        static ptrdiff_t classInfoOffset()
-        {
-            return OBJECT_OFFSETOF(Structure, m_classInfo);
-        }
+    static ptrdiff_t classInfoOffset()
+    {
+        return OBJECT_OFFSETOF(Structure, m_classInfo);
+    }
         
-        static ptrdiff_t indexingTypeOffset()
-        {
-            return OBJECT_OFFSETOF(Structure, m_indexingType);
-        }
+    static ptrdiff_t indexingTypeOffset()
+    {
+        return OBJECT_OFFSETOF(Structure, m_blob) + StructureIDBlob::indexingTypeOffset();
+    }
 
-        static Structure* createStructure(JSGlobalData&);
-        
-        bool transitionWatchpointSetHasBeenInvalidated() const
-        {
-            return m_transitionWatchpointSet.hasBeenInvalidated();
-        }
+    static Structure* createStructure(VM&);
         
-        bool transitionWatchpointSetIsStillValid() const
-        {
-            return m_transitionWatchpointSet.isStillValid();
-        }
-        
-        void addTransitionWatchpoint(Watchpoint* watchpoint) const
-        {
-            ASSERT(transitionWatchpointSetIsStillValid());
-            m_transitionWatchpointSet.add(watchpoint);
-        }
+    bool transitionWatchpointSetHasBeenInvalidated() const
+    {
+        return m_transitionWatchpointSet.hasBeenInvalidated();
+    }
         
-        void notifyTransitionFromThisStructure() const
-        {
-            m_transitionWatchpointSet.notifyWrite();
-        }
+    bool transitionWatchpointSetIsStillValid() const
+    {
+        return m_transitionWatchpointSet.isStillValid();
+    }
+    
+    bool dfgShouldWatchIfPossible() const
+    {
+        // FIXME: We would like to not watch things that are unprofitable to watch, like
+        // dictionaries. Unfortunately, we can't do such things: a dictionary could get flattened,
+        // in which case it will start to appear watchable and so the DFG will think that it is
+        // watching it. We should come up with a comprehensive story for not watching things that
+        // aren't profitable to watch.
+        // https://bugs.webkit.org/show_bug.cgi?id=133625
         
-        static JS_EXPORTDATA const ClassInfo s_info;
-
-    private:
-        friend class LLIntOffsetsExtractor;
-
-        JS_EXPORT_PRIVATE Structure(JSGlobalData&, JSGlobalObject*, JSValue prototype, const TypeInfo&, const ClassInfo*, IndexingType, unsigned inlineCapacity);
-        Structure(JSGlobalData&);
-        Structure(JSGlobalData&, const Structure*);
-
-        static Structure* create(JSGlobalData&, const Structure*);
+        // - We don't watch Structures that either decided not to be watched, or whose predecessors
+        //   decided not to be watched. This happens either when a transition is fired while being
+        //   watched.
+        if (transitionWatchpointIsLikelyToBeFired())
+            return false;
+
+        // - Don't watch Structures that had been dictionaries.
+        if (hasBeenDictionary())
+            return false;
         
-        typedef enum { 
-            NoneDictionaryKind = 0,
-            CachedDictionaryKind = 1,
-            UncachedDictionaryKind = 2
-        } DictionaryKind;
-        static Structure* toDictionaryTransition(JSGlobalData&, Structure*, DictionaryKind);
-
-        PropertyOffset putSpecificValue(JSGlobalData&, PropertyName, unsigned attributes, JSCell* specificValue);
-        PropertyOffset remove(PropertyName);
-
-        void createPropertyMap(unsigned keyCount = 0);
-        void checkConsistency();
-
-        bool despecifyFunction(JSGlobalData&, PropertyName);
-        void despecifyAllFunctions(JSGlobalData&);
-
-        PassOwnPtr<PropertyTable> copyPropertyTable(JSGlobalData&, Structure* owner);
-        PassOwnPtr<PropertyTable> copyPropertyTableForPinning(JSGlobalData&, Structure* owner);
-        JS_EXPORT_PRIVATE void materializePropertyMap(JSGlobalData&);
-        void materializePropertyMapIfNecessary(JSGlobalData& globalData)
-        {
-            ASSERT(structure()->classInfo() == &s_info);
-            if (!m_propertyTable && previousID())
-                materializePropertyMap(globalData);
-        }
-        void materializePropertyMapIfNecessaryForPinning(JSGlobalData& globalData)
-        {
-            ASSERT(structure()->classInfo() == &s_info);
-            if (!m_propertyTable)
-                materializePropertyMap(globalData);
-        }
-
-        void setPreviousID(JSGlobalData& globalData, Structure* transition, Structure* structure)
-        {
-            if (typeInfo().structureHasRareData())
-                rareData()->setPreviousID(globalData, transition, structure);
-            else
-                m_previousOrRareData.set(globalData, transition, structure);
-        }
-
-        void clearPreviousID()
-        {
-            if (typeInfo().structureHasRareData())
-                rareData()->clearPreviousID();
-            else
-                m_previousOrRareData.clear();
-        }
-
-        int transitionCount() const
-        {
-            // Since the number of transitions is always the same as m_offset, we keep the size of Structure down by not storing both.
-            return numberOfSlotsForLastOffset(m_offset, m_inlineCapacity);
-        }
-
-        bool isValid(JSGlobalObject*, StructureChain* cachedPrototypeChain) const;
-        bool isValid(ExecState*, StructureChain* cachedPrototypeChain) const;
+        return true;
+    }
+    
+    bool dfgShouldWatch() const
+    {
+        return dfgShouldWatchIfPossible() && transitionWatchpointSetIsStillValid();
+    }
         
-        void pin();
-
-        Structure* previous() const
-        {
-            ASSERT(!typeInfo().structureHasRareData());
-            return static_cast<Structure*>(m_previousOrRareData.get());
-        }
-
-        StructureRareData* rareData() const
-        {
-            ASSERT(typeInfo().structureHasRareData());
-            return static_cast<StructureRareData*>(m_previousOrRareData.get());
-        }
-
-        void allocateRareData(JSGlobalData&);
-        void cloneRareDataFrom(JSGlobalData&, const Structure*);
-
-        static const int s_maxTransitionLength = 64;
+    void addTransitionWatchpoint(Watchpoint* watchpoint) const
+    {
+        ASSERT(transitionWatchpointSetIsStillValid());
+        m_transitionWatchpointSet.add(watchpoint);
+    }
+    
+    void didTransitionFromThisStructure(DeferredStructureTransitionWatchpointFire* = nullptr) const;
+    
+    InlineWatchpointSet& transitionWatchpointSet() const
+    {
+        return m_transitionWatchpointSet;
+    }
+    
+    WatchpointSet* ensurePropertyReplacementWatchpointSet(VM&, PropertyOffset);
+    void startWatchingPropertyForReplacements(VM& vm, PropertyOffset offset)
+    {
+        ensurePropertyReplacementWatchpointSet(vm, offset);
+    }
+    void startWatchingPropertyForReplacements(VM&, PropertyName);
+    WatchpointSet* propertyReplacementWatchpointSet(PropertyOffset);
+    void didReplaceProperty(PropertyOffset);
+    void didCachePropertyReplacement(VM&, PropertyOffset);
+    
+    void startWatchingInternalPropertiesIfNecessary(VM& vm)
+    {
+        if (LIKELY(didWatchInternalProperties()))
+            return;
+        startWatchingInternalProperties(vm);
+    }
+    
+    void startWatchingInternalPropertiesIfNecessaryForEntireChain(VM& vm)
+    {
+        for (Structure* structure = this; structure; structure = structure->storedPrototypeStructure())
+            structure->startWatchingInternalPropertiesIfNecessary(vm);
+    }
 
-        static const unsigned maxSpecificFunctionThrashCount = 3;
+    bool hasInferredTypes() const
+    {
+        return !!m_inferredTypeTable;
+    }
 
-        TypeInfo m_typeInfo;
-        IndexingType m_indexingType;
-        
-        WriteBarrier<JSGlobalObject> m_globalObject;
-        WriteBarrier<Unknown> m_prototype;
-        mutable WriteBarrier<StructureChain> m_cachedPrototypeChain;
+    InferredType* inferredTypeFor(UniquedStringImpl* uid)
+    {
+        if (InferredTypeTable* table = m_inferredTypeTable.get())
+            return table->get(uid);
+        return nullptr;
+    }
 
-        WriteBarrier<JSCell> m_previousOrRareData;
+    InferredType::Descriptor inferredTypeDescriptorFor(UniquedStringImpl* uid)
+    {
+        if (InferredType* result = inferredTypeFor(uid))
+            return result->descriptor();
+        return InferredType::Top;
+    }
 
-        RefPtr<StringImpl> m_nameInPrevious;
-        WriteBarrier<JSCell> m_specificValueInPrevious;
+    // Call this when we know that this is a brand new property. Note that it's not enough for the
+    // property to be brand new to some object. It has to be brand new to the Structure.
+    ALWAYS_INLINE void willStoreValueForNewTransition(
+        VM& vm, PropertyName propertyName, JSValue value, bool shouldOptimize)
+    {
+        if (hasBeenDictionary() || (!shouldOptimize && !m_inferredTypeTable))
+            return;
+        willStoreValueSlow(vm, propertyName, value, shouldOptimize, InferredTypeTable::NewProperty);
+    }
 
-        const ClassInfo* m_classInfo;
+    // Call this when we know that this is a new property for the object, but not new for the
+    // structure. Therefore, under the InferredTypeTable's rules, absence of the property from the
+    // table means Top rather than Bottom.
+    ALWAYS_INLINE void willStoreValueForExistingTransition(
+        VM& vm, PropertyName propertyName, JSValue value, bool shouldOptimize)
+    {
+        if (hasBeenDictionary() || !m_inferredTypeTable)
+            return;
+        willStoreValueSlow(vm, propertyName, value, shouldOptimize, InferredTypeTable::NewProperty);
+    }
 
-        StructureTransitionTable m_transitionTable;
+    // Call this when we know that the inferred type table exists and has an entry for this property.
+    ALWAYS_INLINE void willStoreValueForReplace(
+        VM& vm, PropertyName propertyName, JSValue value, bool shouldOptimize)
+    {
+        if (hasBeenDictionary())
+            return;
+        willStoreValueSlow(vm, propertyName, value, shouldOptimize, InferredTypeTable::OldProperty);
+    }
 
-        OwnPtr<PropertyTable> m_propertyTable;
+    PassRefPtr<StructureShape> toStructureShape(JSValue);
+    
+    // Determines if the two structures match enough that this one could be used for allocations
+    // of the other one.
+    bool canUseForAllocationsOf(Structure*);
+    
+    void dump(PrintStream&) const;
+    void dumpInContext(PrintStream&, DumpContext*) const;
+    void dumpBrief(PrintStream&, const CString&) const;
+    
+    static void dumpContextHeader(PrintStream&);
+    
+    DECLARE_EXPORT_INFO;
+
+private:
+    typedef enum { 
+        NoneDictionaryKind = 0,
+        CachedDictionaryKind = 1,
+        UncachedDictionaryKind = 2
+    } DictionaryKind;
+
+public:
+#define DEFINE_BITFIELD(type, lowerName, upperName, width, offset) \
+    static const uint32_t s_##lowerName##Shift = offset;\
+    static const uint32_t s_##lowerName##Mask = ((1 << (width - 1)) | ((1 << (width - 1)) - 1));\
+    type lowerName() const { return static_cast<type>((m_bitField >> offset) & s_##lowerName##Mask); }\
+    void set##upperName(type newValue) \
+    {\
+        m_bitField &= ~(s_##lowerName##Mask << offset);\
+        m_bitField |= (newValue & s_##lowerName##Mask) << offset;\
+    }
 
-        mutable InlineWatchpointSet m_transitionWatchpointSet;
+    DEFINE_BITFIELD(DictionaryKind, dictionaryKind, DictionaryKind, 2, 0);
+    DEFINE_BITFIELD(bool, isPinnedPropertyTable, IsPinnedPropertyTable, 1, 2);
+    DEFINE_BITFIELD(bool, hasGetterSetterProperties, HasGetterSetterProperties, 1, 3);
+    DEFINE_BITFIELD(bool, hasReadOnlyOrGetterSetterPropertiesExcludingProto, HasReadOnlyOrGetterSetterPropertiesExcludingProto, 1, 4);
+    DEFINE_BITFIELD(bool, isQuickPropertyAccessAllowedForEnumeration, IsQuickPropertyAccessAllowedForEnumeration, 1, 5);
+    DEFINE_BITFIELD(unsigned, attributesInPrevious, AttributesInPrevious, 14, 6);
+    DEFINE_BITFIELD(bool, didPreventExtensions, DidPreventExtensions, 1, 20);
+    DEFINE_BITFIELD(bool, didTransition, DidTransition, 1, 21);
+    DEFINE_BITFIELD(bool, staticFunctionsReified, StaticFunctionsReified, 1, 22);
+    DEFINE_BITFIELD(bool, hasRareData, HasRareData, 1, 23);
+    DEFINE_BITFIELD(bool, hasBeenFlattenedBefore, HasBeenFlattenedBefore, 1, 24);
+    DEFINE_BITFIELD(bool, hasCustomGetterSetterProperties, HasCustomGetterSetterProperties, 1, 25);
+    DEFINE_BITFIELD(bool, didWatchInternalProperties, DidWatchInternalProperties, 1, 26);
+    DEFINE_BITFIELD(bool, transitionWatchpointIsLikelyToBeFired, TransitionWatchpointIsLikelyToBeFired, 1, 27);
+    DEFINE_BITFIELD(bool, hasBeenDictionary, HasBeenDictionary, 1, 28);
+
+private:
+    friend class LLIntOffsetsExtractor;
+
+    JS_EXPORT_PRIVATE Structure(VM&, JSGlobalObject*, JSValue prototype, const TypeInfo&, const ClassInfo*, IndexingType, unsigned inlineCapacity);
+    Structure(VM&);
+    Structure(VM&, Structure*, DeferredStructureTransitionWatchpointFire*);
+
+    static Structure* create(VM&, Structure*, DeferredStructureTransitionWatchpointFire* = nullptr);
+    
+    static Structure* addPropertyTransitionToExistingStructureImpl(Structure*, UniquedStringImpl* uid, unsigned attributes, PropertyOffset&);
 
-        uint8_t m_inlineCapacity;
-        COMPILE_ASSERT(firstOutOfLineOffset < 256, firstOutOfLineOffset_fits);
+    // This will return the structure that has a usable property table, that property table,
+    // and the list of structures that we visited before we got to it. If it returns a
+    // non-null structure, it will also lock the structure that it returns; it is your job
+    // to unlock it.
+    void findStructuresAndMapForMaterialization(Vector<Structure*, 8>& structures, Structure*&, PropertyTable*&);
+    
+    static Structure* toDictionaryTransition(VM&, Structure*, DictionaryKind, DeferredStructureTransitionWatchpointFire* = nullptr);
 
-        // m_offset does not account for anonymous slots
-        PropertyOffset m_offset;
+    PropertyOffset add(VM&, PropertyName, unsigned attributes);
+    PropertyOffset remove(PropertyName);
 
-        unsigned m_dictionaryKind : 2;
-        bool m_isPinnedPropertyTable : 1;
-        bool m_hasGetterSetterProperties : 1;
-        bool m_hasReadOnlyOrGetterSetterPropertiesExcludingProto : 1;
-        bool m_hasNonEnumerableProperties : 1;
-        unsigned m_attributesInPrevious : 22;
-        unsigned m_specificFunctionThrashCount : 2;
-        unsigned m_preventExtensions : 1;
-        unsigned m_didTransition : 1;
-        unsigned m_staticFunctionReified;
-    };
+    void createPropertyMap(const GCSafeConcurrentJITLocker&, VM&, unsigned keyCount = 0);
+    void checkConsistency();
 
-    inline Structure* Structure::create(JSGlobalData& globalData, JSGlobalObject* globalObject, JSValue prototype, const TypeInfo& typeInfo, const ClassInfo* classInfo, IndexingType indexingType, unsigned inlineCapacity)
-    {
-        ASSERT(globalData.structureStructure);
-        ASSERT(classInfo);
-        Structure* structure = new (NotNull, allocateCell<Structure>(globalData.heap)) Structure(globalData, globalObject, prototype, typeInfo, classInfo, indexingType, inlineCapacity);
-        structure->finishCreation(globalData);
-        return structure;
-    }
-        
-    inline Structure* Structure::createStructure(JSGlobalData& globalData)
+    WriteBarrier<PropertyTable>& propertyTable();
+    PropertyTable* takePropertyTableOrCloneIfPinned(VM&);
+    PropertyTable* copyPropertyTable(VM&);
+    PropertyTable* copyPropertyTableForPinning(VM&);
+    JS_EXPORT_PRIVATE void materializePropertyMap(VM&);
+    ALWAYS_INLINE void materializePropertyMapIfNecessary(VM& vm, DeferGC&)
     {
-        ASSERT(!globalData.structureStructure);
-        Structure* structure = new (NotNull, allocateCell<Structure>(globalData.heap)) Structure(globalData);
-        structure->finishCreation(globalData, CreatingEarlyCell);
-        return structure;
+        ASSERT(!isCompilationThread());
+        ASSERT(structure()->classInfo() == info());
+        ASSERT(checkOffsetConsistency());
+        if (!propertyTable() && previousID())
+            materializePropertyMap(vm);
     }
-
-    inline Structure* Structure::create(JSGlobalData& globalData, const Structure* structure)
+    ALWAYS_INLINE void materializePropertyMapIfNecessary(VM& vm, PropertyTable*& table)
     {
-        ASSERT(globalData.structureStructure);
-        Structure* newStructure = new (NotNull, allocateCell<Structure>(globalData.heap)) Structure(globalData, structure);
-        newStructure->finishCreation(globalData);
-        if (structure->typeInfo().structureHasRareData())
-            newStructure->cloneRareDataFrom(globalData, structure);
-        return newStructure;
+        ASSERT(!isCompilationThread());
+        ASSERT(structure()->classInfo() == info());
+        ASSERT(checkOffsetConsistency());
+        table = propertyTable().get();
+        if (!table && previousID()) {
+            DeferGC deferGC(vm.heap);
+            materializePropertyMap(vm);
+            table = propertyTable().get();
+        }
     }
-        
-    inline PropertyOffset Structure::get(JSGlobalData& globalData, PropertyName propertyName)
+    void materializePropertyMapIfNecessaryForPinning(VM& vm, DeferGC&)
     {
-        ASSERT(structure()->classInfo() == &s_info);
-        materializePropertyMapIfNecessary(globalData);
-        if (!m_propertyTable)
-            return invalidOffset;
-
-        PropertyMapEntry* entry = m_propertyTable->find(propertyName.uid()).first;
-        return entry ? entry->offset : invalidOffset;
+        ASSERT(structure()->classInfo() == info());
+        checkOffsetConsistency();
+        if (!propertyTable())
+            materializePropertyMap(vm);
     }
 
-    inline PropertyOffset Structure::get(JSGlobalData& globalData, const WTF::String& name)
+    void setPreviousID(VM& vm, Structure* structure)
     {
-        ASSERT(structure()->classInfo() == &s_info);
-        materializePropertyMapIfNecessary(globalData);
-        if (!m_propertyTable)
-            return invalidOffset;
-
-        PropertyMapEntry* entry = m_propertyTable->findWithString(name.impl()).first;
-        return entry ? entry->offset : invalidOffset;
+        if (hasRareData())
+            rareData()->setPreviousID(vm, structure);
+        else
+            m_previousOrRareData.set(vm, this, structure);
     }
-    
-    inline bool Structure::masqueradesAsUndefined(JSGlobalObject* lexicalGlobalObject)
+
+    void clearPreviousID()
     {
-        return typeInfo().masqueradesAsUndefined() && globalObject() == lexicalGlobalObject;
+        if (hasRareData())
+            rareData()->clearPreviousID();
+        else
+            m_previousOrRareData.clear();
     }
 
-    ALWAYS_INLINE void SlotVisitor::internalAppend(JSCell* cell)
+    int transitionCount() const
     {
-        ASSERT(!m_isCheckingForDefaultMarkViolation);
-        if (!cell)
-            return;
-#if ENABLE(GC_VALIDATION)
-        validate(cell);
-#endif
-        if (Heap::testAndSetMarked(cell) || !cell->structure())
-            return;
-
-        m_visitCount++;
-        
-        MARK_LOG_CHILD(*this, cell);
+        // Since the number of transitions is always the same as m_offset, we keep the size of Structure down by not storing both.
+        return numberOfSlotsForLastOffset(m_offset, m_inlineCapacity);
+    }
 
-        // Should never attempt to mark something that is zapped.
-        ASSERT(!cell->isZapped());
+    bool isValid(JSGlobalObject*, StructureChain* cachedPrototypeChain) const;
+    bool isValid(ExecState*, StructureChain* cachedPrototypeChain) const;
         
-        m_stack.append(cell);
-    }
+    void pin();
 
-    inline bool Structure::transitivelyTransitionedFrom(Structure* structureToFind)
+    Structure* previous() const
     {
-        for (Structure* current = this; current; current = current->previousID()) {
-            if (current == structureToFind)
-                return true;
-        }
-        return false;
+        ASSERT(!hasRareData());
+        return static_cast<Structure*>(m_previousOrRareData.get());
     }
 
-    inline void Structure::setEnumerationCache(JSGlobalData& globalData, JSPropertyNameIterator* enumerationCache)
+    StructureRareData* rareData() const
     {
-        ASSERT(!isDictionary());
-        if (!typeInfo().structureHasRareData())
-            allocateRareData(globalData);
-        rareData()->setEnumerationCache(globalData, this, enumerationCache);
+        ASSERT(hasRareData());
+        return static_cast<StructureRareData*>(m_previousOrRareData.get());
     }
+        
+    bool checkOffsetConsistency() const;
 
-    inline JSPropertyNameIterator* Structure::enumerationCache()
-    {
-        if (!typeInfo().structureHasRareData())
-            return 0;
-        return rareData()->enumerationCache();
-    }
+    JS_EXPORT_PRIVATE void allocateRareData(VM&);
+    
+    void startWatchingInternalProperties(VM&);
+
+    JS_EXPORT_PRIVATE void willStoreValueSlow(
+        VM&, PropertyName, JSValue, bool, InferredTypeTable::StoredPropertyAge);
+
+    static const int s_maxTransitionLength = 64;
+    static const int s_maxTransitionLengthForNonEvalPutById = 512;
+
+    // These need to be properly aligned at the beginning of the 'Structure'
+    // part of the object.
+    StructureIDBlob m_blob;
+    TypeInfo::OutOfLineTypeFlags m_outOfLineTypeFlags;
+
+    WriteBarrier<JSGlobalObject> m_globalObject;
+    WriteBarrier<Unknown> m_prototype;
+    mutable WriteBarrier<StructureChain> m_cachedPrototypeChain;
+
+    WriteBarrier<JSCell> m_previousOrRareData;
+
+    RefPtr<UniquedStringImpl> m_nameInPrevious;
+
+    const ClassInfo* m_classInfo;
+
+    StructureTransitionTable m_transitionTable;
+
+    // Should be accessed through propertyTable(). During GC, it may be set to 0 by another thread.
+    WriteBarrier<PropertyTable> m_propertyTableUnsafe;
+
+    WriteBarrier<InferredTypeTable> m_inferredTypeTable;
+
+    mutable InlineWatchpointSet m_transitionWatchpointSet;
+
+    COMPILE_ASSERT(firstOutOfLineOffset < 256, firstOutOfLineOffset_fits);
+
+    // m_offset does not account for anonymous slots
+    PropertyOffset m_offset;
+
+    uint8_t m_inlineCapacity;
+    
+    ConcurrentJITLock m_lock;
+    
+    uint32_t m_bitField;
+};
 
 } // namespace JSC