]> git.saurik.com Git - apple/javascriptcore.git/blobdiff - runtime/JSObject.h
JavaScriptCore-7601.1.46.3.tar.gz
[apple/javascriptcore.git] / runtime / JSObject.h
index 7a78a46a6fd70040e53ee1c3c4c48fcba7aa1fd2..5c9622cc4de4adabe51136c239c5ea1732382f2f 100644 (file)
@@ -1,7 +1,7 @@
 /*
  *  Copyright (C) 1999-2001 Harri Porten (porten@kde.org)
  *  Copyright (C) 2001 Peter Kelly (pmk@post.com)
- *  Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
+ *  Copyright (C) 2003-2009, 2012-2015 Apple Inc. All rights reserved.
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Library General Public
 #include "ArrayConventions.h"
 #include "ArrayStorage.h"
 #include "Butterfly.h"
+#include "CallFrame.h"
 #include "ClassInfo.h"
 #include "CommonIdentifiers.h"
-#include "CallFrame.h"
+#include "CopyWriteBarrier.h"
+#include "CustomGetterSetter.h"
+#include "DeferGC.h"
+#include "Heap.h"
+#include "HeapInlines.h"
+#include "IndexingHeaderInlines.h"
 #include "JSCell.h"
 #include "PropertySlot.h"
 #include "PropertyStorage.h"
@@ -39,7 +45,6 @@
 #include "Structure.h"
 #include "VM.h"
 #include "JSString.h"
-#include "SlotVisitorInlines.h"
 #include "SparseArrayValueMap.h"
 #include <wtf/StdLibExtras.h>
 
@@ -47,44 +52,25 @@ namespace JSC {
 
 inline JSCell* getJSFunction(JSValue value)
 {
-    if (value.isCell() && (value.asCell()->structure()->typeInfo().type() == JSFunctionType))
+    if (value.isCell() && (value.asCell()->type() == JSFunctionType))
         return value.asCell();
     return 0;
 }
 
-JS_EXPORT_PRIVATE JSCell* getCallableObjectSlow(JSCell*);
-
-inline JSCell* getCallableObject(JSValue value)
-{
-    if (!value.isCell())
-        return 0;
-    return getCallableObjectSlow(value.asCell());
-}
-
 class GetterSetter;
-class HashEntry;
 class InternalFunction;
+class JSFunction;
 class LLIntOffsetsExtractor;
 class MarkedBlock;
 class PropertyDescriptor;
 class PropertyNameArray;
 class Structure;
 struct HashTable;
+struct HashTableValue;
 
 JS_EXPORT_PRIVATE JSObject* throwTypeError(ExecState*, const String&);
 extern JS_EXPORTDATA const char* StrictModeReadonlyPropertyWriteError;
 
-// ECMA 262-3 8.6.1
-// Property attributes
-enum Attribute {
-    None         = 0,
-    ReadOnly     = 1 << 1,  // property can be only read, not written
-    DontEnum     = 1 << 2,  // property doesn't appear in (for .. in ..)
-    DontDelete   = 1 << 3,  // property can't be deleted
-    Function     = 1 << 4,  // property is a function - only used by static hashtables
-    Accessor     = 1 << 5,  // property is a getter/setter
-};
-
 COMPILE_ASSERT(None < FirstInternalAttribute, None_is_below_FirstInternalAttribute);
 COMPILE_ASSERT(ReadOnly < FirstInternalAttribute, ReadOnly_is_below_FirstInternalAttribute);
 COMPILE_ASSERT(DontEnum < FirstInternalAttribute, DontEnum_is_below_FirstInternalAttribute);
@@ -100,7 +86,7 @@ class JSObject : public JSCell {
     friend class JSCell;
     friend class JSFinalObject;
     friend class MarkedBlock;
-    JS_EXPORT_PRIVATE friend bool setUpStaticFunctionSlot(ExecState*, const HashEntry*, JSObject*, PropertyName, PropertySlot&);
+    JS_EXPORT_PRIVATE friend bool setUpStaticFunctionSlot(ExecState*, const HashTableValue*, JSObject*, PropertyName, PropertySlot&);
 
     enum PutMode {
         PutModePut,
@@ -110,19 +96,15 @@ class JSObject : public JSCell {
 public:
     typedef JSCell Base;
         
-    static size_t allocationSize(size_t inlineCapacity)
-    {
-        return sizeof(JSObject) + inlineCapacity * sizeof(WriteBarrierBase<Unknown>);
-    }
-        
     JS_EXPORT_PRIVATE static void visitChildren(JSCell*, SlotVisitor&);
-    JS_EXPORT_PRIVATE static void copyBackingStore(JSCell*, CopyVisitor&);
+    JS_EXPORT_PRIVATE static void copyBackingStore(JSCell*, CopyVisitor&, CopyToken);
 
     JS_EXPORT_PRIVATE static String className(const JSObject*);
+    JS_EXPORT_PRIVATE static String calculatedClassName(JSObject*);
 
     JSValue prototype() const;
-    void setPrototype(VM&, JSValue prototype);
-    bool setPrototypeWithCycleCheck(VM&, JSValue prototype);
+    JS_EXPORT_PRIVATE void setPrototype(VM&, JSValue prototype);
+    JS_EXPORT_PRIVATE bool setPrototypeWithCycleCheck(ExecState*, JSValue prototype);
         
     bool mayInterceptIndexedAccesses()
     {
@@ -132,26 +114,30 @@ public:
     JSValue get(ExecState*, PropertyName) const;
     JSValue get(ExecState*, unsigned propertyName) const;
 
+    bool fastGetOwnPropertySlot(ExecState*, VM&, Structure&, PropertyName, PropertySlot&);
     bool getPropertySlot(ExecState*, PropertyName, PropertySlot&);
     bool getPropertySlot(ExecState*, unsigned propertyName, PropertySlot&);
-    JS_EXPORT_PRIVATE bool getPropertyDescriptor(ExecState*, PropertyName, PropertyDescriptor&);
 
-    static bool getOwnPropertySlot(JSCell*, ExecState*, PropertyName, PropertySlot&);
-    JS_EXPORT_PRIVATE static bool getOwnPropertySlotByIndex(JSCell*, ExecState*, unsigned propertyName, PropertySlot&);
-    JS_EXPORT_PRIVATE static bool getOwnPropertyDescriptor(JSObject*, ExecState*, PropertyName, PropertyDescriptor&);
+    static bool getOwnPropertySlot(JSObject*, ExecState*, PropertyName, PropertySlot&);
+    JS_EXPORT_PRIVATE static bool getOwnPropertySlotByIndex(JSObject*, ExecState*, unsigned propertyName, PropertySlot&);
+
+    // The key difference between this and getOwnPropertySlot is that getOwnPropertySlot
+    // currently returns incorrect results for the DOM window (with non-own properties)
+    // being returned. Once this is fixed we should migrate code & remove this method.
+    JS_EXPORT_PRIVATE bool getOwnPropertyDescriptor(ExecState*, PropertyName, PropertyDescriptor&);
 
-    bool allowsAccessFrom(ExecState*);
+    JS_EXPORT_PRIVATE bool allowsAccessFrom(ExecState*);
 
     unsigned getArrayLength() const
     {
-        if (!hasIndexedProperties(structure()->indexingType()))
+        if (!hasIndexedProperties(indexingType()))
             return 0;
         return m_butterfly->publicLength();
     }
         
     unsigned getVectorLength()
     {
-        if (!hasIndexedProperties(structure()->indexingType()))
+        if (!hasIndexedProperties(indexingType()))
             return 0;
         return m_butterfly->vectorLength();
     }
@@ -159,13 +145,13 @@ public:
     JS_EXPORT_PRIVATE static void put(JSCell*, ExecState*, PropertyName, JSValue, PutPropertySlot&);
     JS_EXPORT_PRIVATE static void putByIndex(JSCell*, ExecState*, unsigned propertyName, JSValue, bool shouldThrow);
         
-    void putByIndexInline(ExecState* exec, unsigned propertyName, JSValue value, bool shouldThrow)
+    ALWAYS_INLINE void putByIndexInline(ExecState* exec, unsigned propertyName, JSValue value, bool shouldThrow)
     {
         if (canSetIndexQuickly(propertyName)) {
             setIndexQuickly(exec->vm(), propertyName, value);
             return;
         }
-        methodTable()->putByIndex(this, exec, propertyName, value, shouldThrow);
+        methodTable(exec->vm())->putByIndex(this, exec, propertyName, value, shouldThrow);
     }
         
     // This is similar to the putDirect* methods:
@@ -189,9 +175,14 @@ public:
     // A non-throwing version of putDirect and putDirectIndex.
     JS_EXPORT_PRIVATE void putDirectMayBeIndex(ExecState*, PropertyName, JSValue);
         
+    bool hasIndexingHeader() const
+    {
+        return structure()->hasIndexingHeader(this);
+    }
+    
     bool canGetIndexQuickly(unsigned i)
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_BLANK_INDEXING_TYPES:
         case ALL_UNDECIDED_INDEXING_TYPES:
             return false;
@@ -216,8 +207,9 @@ public:
         
     JSValue getIndexQuickly(unsigned i)
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_INT32_INDEXING_TYPES:
+            return jsNumber(m_butterfly->contiguous()[i].get().asInt32());
         case ALL_CONTIGUOUS_INDEXING_TYPES:
             return m_butterfly->contiguous()[i].get();
         case ALL_DOUBLE_INDEXING_TYPES:
@@ -232,11 +224,17 @@ public:
         
     JSValue tryGetIndexQuickly(unsigned i)
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_BLANK_INDEXING_TYPES:
         case ALL_UNDECIDED_INDEXING_TYPES:
             break;
         case ALL_INT32_INDEXING_TYPES:
+            if (i < m_butterfly->publicLength()) {
+                JSValue result = m_butterfly->contiguous()[i].get();
+                ASSERT(result.isInt32() || !result);
+                return result;
+            }
+            break;
         case ALL_CONTIGUOUS_INDEXING_TYPES:
             if (i < m_butterfly->publicLength())
                 return m_butterfly->contiguous()[i].get();
@@ -265,7 +263,7 @@ public:
         if (JSValue result = tryGetIndexQuickly(i))
             return result;
         PropertySlot slot(this);
-        if (methodTable()->getOwnPropertySlotByIndex(this, exec, i, slot))
+        if (methodTable(exec->vm())->getOwnPropertySlotByIndex(this, exec, i, slot))
             return slot.getValue(exec, i);
         return JSValue();
     }
@@ -279,7 +277,7 @@ public:
         
     bool canSetIndexQuickly(unsigned i)
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_BLANK_INDEXING_TYPES:
         case ALL_UNDECIDED_INDEXING_TYPES:
             return false;
@@ -301,7 +299,7 @@ public:
         
     bool canSetIndexQuicklyForPutDirect(unsigned i)
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_BLANK_INDEXING_TYPES:
         case ALL_UNDECIDED_INDEXING_TYPES:
             return false;
@@ -318,14 +316,14 @@ public:
         
     void setIndexQuickly(VM& vm, unsigned i, JSValue v)
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_INT32_INDEXING_TYPES: {
             ASSERT(i < m_butterfly->vectorLength());
             if (!v.isInt32()) {
                 convertInt32ToDoubleOrContiguousWhilePerformingSetIndex(vm, i, v);
                 return;
             }
-            // Fall through to contiguous case.
+            FALLTHROUGH;
         }
         case ALL_CONTIGUOUS_INDEXING_TYPES: {
             ASSERT(i < m_butterfly->vectorLength());
@@ -366,10 +364,15 @@ public:
             RELEASE_ASSERT_NOT_REACHED();
         }
     }
-        
+
     void initializeIndex(VM& vm, unsigned i, JSValue v)
     {
-        switch (structure()->indexingType()) {
+        initializeIndex(vm, i, v, indexingType());
+    }
+
+    void initializeIndex(VM& vm, unsigned i, JSValue v, IndexingType indexingType)
+    {
+        switch (indexingType) {
         case ALL_UNDECIDED_INDEXING_TYPES: {
             setIndexQuicklyToUndecided(vm, i, v);
             break;
@@ -381,7 +384,7 @@ public:
                 convertInt32ToDoubleOrContiguousWhilePerformingSetIndex(vm, i, v);
                 break;
             }
-            // Fall through.
+            FALLTHROUGH;
         }
         case ALL_CONTIGUOUS_INDEXING_TYPES: {
             ASSERT(i < m_butterfly->publicLength());
@@ -418,7 +421,7 @@ public:
         
     bool hasSparseMap()
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_BLANK_INDEXING_TYPES:
         case ALL_UNDECIDED_INDEXING_TYPES:
         case ALL_INT32_INDEXING_TYPES:
@@ -426,7 +429,7 @@ public:
         case ALL_CONTIGUOUS_INDEXING_TYPES:
             return false;
         case ALL_ARRAY_STORAGE_INDEXING_TYPES:
-            return m_butterfly->arrayStorage()->m_sparseMap;
+            return !!m_butterfly->arrayStorage()->m_sparseMap;
         default:
             RELEASE_ASSERT_NOT_REACHED();
             return false;
@@ -435,7 +438,7 @@ public:
         
     bool inSparseIndexingMode()
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_BLANK_INDEXING_TYPES:
         case ALL_UNDECIDED_INDEXING_TYPES:
         case ALL_INT32_INDEXING_TYPES:
@@ -457,17 +460,20 @@ public:
     //  - accessors are not called.
     //  - attributes will be respected (after the call the property will exist with the given attributes)
     //  - the property name is assumed to not be an index.
-    JS_EXPORT_PRIVATE static void putDirectVirtual(JSObject*, ExecState*, PropertyName, JSValue, unsigned attributes);
     void putDirect(VM&, PropertyName, JSValue, unsigned attributes = 0);
     void putDirect(VM&, PropertyName, JSValue, PutPropertySlot&);
     void putDirectWithoutTransition(VM&, PropertyName, JSValue, unsigned attributes = 0);
+    void putDirectNonIndexAccessor(VM&, PropertyName, JSValue, unsigned attributes);
     void putDirectAccessor(ExecState*, PropertyName, JSValue, unsigned attributes);
+    JS_EXPORT_PRIVATE void putDirectCustomAccessor(VM&, PropertyName, JSValue, unsigned attributes);
 
-    bool propertyIsEnumerable(ExecState*, const Identifier& propertyName) const;
+    void putGetter(ExecState*, PropertyName, JSValue);
+    void putSetter(ExecState*, PropertyName, JSValue);
 
     JS_EXPORT_PRIVATE bool hasProperty(ExecState*, PropertyName) const;
     JS_EXPORT_PRIVATE bool hasProperty(ExecState*, unsigned propertyName) const;
     bool hasOwnProperty(ExecState*, PropertyName) const;
+    bool hasOwnProperty(ExecState*, unsigned) const;
 
     JS_EXPORT_PRIVATE static bool deleteProperty(JSCell*, ExecState*, PropertyName);
     JS_EXPORT_PRIVATE static bool deletePropertyByIndex(JSCell*, ExecState*, unsigned propertyName);
@@ -481,29 +487,47 @@ public:
     JS_EXPORT_PRIVATE static void getOwnNonIndexPropertyNames(JSObject*, ExecState*, PropertyNameArray&, EnumerationMode);
     JS_EXPORT_PRIVATE static void getPropertyNames(JSObject*, ExecState*, PropertyNameArray&, EnumerationMode);
 
+    JS_EXPORT_PRIVATE static uint32_t getEnumerableLength(ExecState*, JSObject*);
+    JS_EXPORT_PRIVATE static void getStructurePropertyNames(JSObject*, ExecState*, PropertyNameArray&, EnumerationMode);
+    JS_EXPORT_PRIVATE static void getGenericPropertyNames(JSObject*, ExecState*, PropertyNameArray&, EnumerationMode);
+
     JSValue toPrimitive(ExecState*, PreferredPrimitiveType = NoPreference) const;
     bool getPrimitiveNumber(ExecState*, double& number, JSValue&) const;
     JS_EXPORT_PRIVATE double toNumber(ExecState*) const;
     JS_EXPORT_PRIVATE JSString* toString(ExecState*) const;
 
-    // NOTE: JSObject and its subclasses must be able to gracefully handle ExecState* = 0,
-    // because this call may come from inside the compiler.
-    JS_EXPORT_PRIVATE static JSObject* toThisObject(JSCell*, ExecState*);
-
-    bool getPropertySpecificValue(ExecState*, PropertyName, JSCell*& specificFunction) const;
+    JS_EXPORT_PRIVATE static JSValue toThis(JSCell*, ExecState*, ECMAMode);
 
     // This get function only looks at the property map.
     JSValue getDirect(VM& vm, PropertyName propertyName) const
     {
-        PropertyOffset offset = structure()->get(vm, propertyName);
-        checkOffset(offset, structure()->inlineCapacity());
+        Structure* structure = this->structure(vm);
+        PropertyOffset offset = structure->get(vm, propertyName);
+        checkOffset(offset, structure->inlineCapacity());
+        return offset != invalidOffset ? getDirect(offset) : JSValue();
+    }
+    
+    JSValue getDirect(VM& vm, PropertyName propertyName, unsigned& attributes) const
+    {
+        Structure* structure = this->structure(vm);
+        PropertyOffset offset = structure->get(vm, propertyName, attributes);
+        checkOffset(offset, structure->inlineCapacity());
         return offset != invalidOffset ? getDirect(offset) : JSValue();
     }
 
     PropertyOffset getDirectOffset(VM& vm, PropertyName propertyName)
     {
-        PropertyOffset offset = structure()->get(vm, propertyName);
-        checkOffset(offset, structure()->inlineCapacity());
+        Structure* structure = this->structure(vm);
+        PropertyOffset offset = structure->get(vm, propertyName);
+        checkOffset(offset, structure->inlineCapacity());
+        return offset;
+    }
+
+    PropertyOffset getDirectOffset(VM& vm, PropertyName propertyName, unsigned& attributes)
+    {
+        Structure* structure = this->structure(vm);
+        PropertyOffset offset = structure->get(vm, propertyName, attributes);
+        checkOffset(offset, structure->inlineCapacity());
         return offset;
     }
 
@@ -527,8 +551,8 @@ public:
         return inlineStorageUnsafe();
     }
         
-    const Butterfly* butterfly() const { return m_butterfly; }
-    Butterfly* butterfly() { return m_butterfly; }
+    const Butterfly* butterfly() const { return m_butterfly.get(); }
+    Butterfly* butterfly() { return m_butterfly.get(); }
         
     ConstPropertyStorage outOfLineStorage() const { return m_butterfly->propertyStorage(); }
     PropertyStorage outOfLineStorage() { return m_butterfly->propertyStorage(); }
@@ -549,15 +573,16 @@ public:
 
     void transitionTo(VM&, Structure*);
 
-    bool removeDirect(VM&, PropertyName); // Return true if anything is removed.
+    JS_EXPORT_PRIVATE bool removeDirect(VM&, PropertyName); // Return true if anything is removed.
     bool hasCustomProperties() { return structure()->didTransition(); }
     bool hasGetterSetterProperties() { return structure()->hasGetterSetterProperties(); }
+    bool hasCustomGetterSetterProperties() { return structure()->hasCustomGetterSetterProperties(); }
 
     // putOwnDataProperty has 'put' like semantics, however this method:
     //  - assumes the object contains no own getter/setter properties.
     //  - provides no special handling for __proto__
     //  - does not walk the prototype chain (to check for accessors or non-writable properties).
-    // This is used by JSActivation.
+    // This is used by JSLexicalEnvironment.
     bool putOwnDataProperty(VM&, PropertyName, JSValue, PutPropertySlot&);
 
     // Fast access to known property offsets.
@@ -565,22 +590,28 @@ public:
     void putDirect(VM& vm, PropertyOffset offset, JSValue value) { locationForOffset(offset)->set(vm, this, value); }
     void putDirectUndefined(PropertyOffset offset) { locationForOffset(offset)->setUndefined(); }
 
-    void putDirectNativeFunction(ExecState*, JSGlobalObject*, const PropertyName&, unsigned functionLength, NativeFunction, Intrinsic, unsigned attributes);
+    JS_EXPORT_PRIVATE void putDirectNativeFunction(VM&, JSGlobalObject*, const PropertyName&, unsigned functionLength, NativeFunction, Intrinsic, unsigned attributes);
+    JS_EXPORT_PRIVATE JSFunction* putDirectBuiltinFunction(VM&, JSGlobalObject*, const PropertyName&, FunctionExecutable*, unsigned attributes);
+    JSFunction* putDirectBuiltinFunctionWithoutTransition(VM&, JSGlobalObject*, const PropertyName&, FunctionExecutable*, unsigned attributes);
+    JS_EXPORT_PRIVATE void putDirectNativeFunctionWithoutTransition(VM&, JSGlobalObject*, const PropertyName&, unsigned functionLength, NativeFunction, Intrinsic, unsigned attributes);
 
-    JS_EXPORT_PRIVATE static bool defineOwnProperty(JSObject*, ExecState*, PropertyName, PropertyDescriptor&, bool shouldThrow);
+    JS_EXPORT_PRIVATE static bool defineOwnProperty(JSObject*, ExecState*, PropertyName, const PropertyDescriptor&, bool shouldThrow);
 
     bool isGlobalObject() const;
     bool isVariableObject() const;
     bool isStaticScopeObject() const;
     bool isNameScopeObject() const;
+    bool isCatchScopeObject() const;
+    bool isFunctionNameScopeObject() const;
     bool isActivationObject() const;
     bool isErrorInstance() const;
+    bool isWithScope() const;
 
-    void seal(VM&);
-    void freeze(VM&);
+    JS_EXPORT_PRIVATE void seal(VM&);
+    JS_EXPORT_PRIVATE void freeze(VM&);
     JS_EXPORT_PRIVATE void preventExtensions(VM&);
-    bool isSealed(VM& vm) { return structure()->isSealed(vm); }
-    bool isFrozen(VM& vm) { return structure()->isFrozen(vm); }
+    bool isSealed(VM& vm) { return structure(vm)->isSealed(vm); }
+    bool isFrozen(VM& vm) { return structure(vm)->isFrozen(vm); }
     bool isExtensible() { return structure()->isExtensible(); }
     bool indexingShouldBeSparse()
     {
@@ -592,17 +623,23 @@ public:
     void reifyStaticFunctionsForDelete(ExecState* exec);
 
     JS_EXPORT_PRIVATE Butterfly* growOutOfLineStorage(VM&, size_t oldSize, size_t newSize);
-    void setButterfly(VM&, Butterfly*, Structure*);
-    void setButterflyWithoutChangingStructure(Butterfly*); // You probably don't want to call this.
+    void setButterflyWithoutChangingStructure(VM&, Butterfly*);
         
-    void setStructure(VM&, Structure*, Butterfly* = 0);
+    void setStructure(VM&, Structure*);
+    void setStructureAndButterfly(VM&, Structure*, Butterfly*);
     void setStructureAndReallocateStorageIfNecessary(VM&, unsigned oldCapacity, Structure*);
     void setStructureAndReallocateStorageIfNecessary(VM&, Structure*);
 
+    void convertToDictionary(VM& vm)
+    {
+        setStructure(vm, Structure::toCacheableDictionaryTransition(vm, structure(vm)));
+    }
+
     void flattenDictionaryObject(VM& vm)
     {
-        structure()->flattenDictionaryStructure(vm, this);
+        structure(vm)->flattenDictionaryStructure(vm, this);
     }
+    void shiftButterflyAfterFlattening(VM&, size_t outOfLineCapacityBefore, size_t outOfLineCapacityAfter);
 
     JSGlobalObject* globalObject() const
     {
@@ -628,7 +665,7 @@ public:
     // contiguous, array storage).
     ContiguousJSValues ensureInt32(VM& vm)
     {
-        if (LIKELY(hasInt32(structure()->indexingType())))
+        if (LIKELY(hasInt32(indexingType())))
             return m_butterfly->contiguousInt32();
             
         return ensureInt32Slow(vm);
@@ -640,7 +677,7 @@ public:
     // or array storage).
     ContiguousDoubles ensureDouble(VM& vm)
     {
-        if (LIKELY(hasDouble(structure()->indexingType())))
+        if (LIKELY(hasDouble(indexingType())))
             return m_butterfly->contiguousDouble();
             
         return ensureDoubleSlow(vm);
@@ -650,32 +687,21 @@ public:
     // indexing should be sparse or because we're having a bad time.
     ContiguousJSValues ensureContiguous(VM& vm)
     {
-        if (LIKELY(hasContiguous(structure()->indexingType())))
+        if (LIKELY(hasContiguous(indexingType())))
             return m_butterfly->contiguous();
             
         return ensureContiguousSlow(vm);
     }
-        
-    // Same as ensureContiguous(), except that if the indexed storage is in
-    // double mode, then it does a rage conversion to contiguous: it
-    // attempts to convert each double to an int32.
-    ContiguousJSValues rageEnsureContiguous(VM& vm)
-    {
-        if (LIKELY(hasContiguous(structure()->indexingType())))
-            return m_butterfly->contiguous();
-            
-        return rageEnsureContiguousSlow(vm);
-    }
-        
+
     // Ensure that the object is in a mode where it has array storage. Use
     // this if you're about to perform actions that would have required the
     // object to be converted to have array storage, if it didn't have it
     // already.
     ArrayStorage* ensureArrayStorage(VM& vm)
     {
-        if (LIKELY(hasArrayStorage(structure()->indexingType())))
+        if (LIKELY(hasAnyArrayStorage(indexingType())))
             return m_butterfly->arrayStorage();
-            
+
         return ensureArrayStorageSlow(vm);
     }
         
@@ -691,15 +717,13 @@ public:
         return &m_butterfly;
     }
 
-    static JS_EXPORTDATA const ClassInfo s_info;
+    DECLARE_EXPORT_INFO;
 
 protected:
     void finishCreation(VM& vm)
     {
         Base::finishCreation(vm);
-        ASSERT(inherits(&s_info));
-        ASSERT(!structure()->outOfLineCapacity());
-        ASSERT(structure()->isEmpty());
+        ASSERT(inherits(info()));
         ASSERT(prototype().isNull() || Heap::heap(this) == Heap::heap(prototype()));
         ASSERT(structure()->isObject());
         ASSERT(classInfo());
@@ -707,7 +731,7 @@ protected:
 
     static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
     {
-        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), &s_info);
+        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), info());
     }
 
     // To instantiate objects you likely want JSFinalObject, below.
@@ -721,7 +745,7 @@ protected:
     // storage. This will assert otherwise.
     ArrayStorage* arrayStorage()
     {
-        ASSERT(hasArrayStorage(structure()->indexingType()));
+        ASSERT(hasAnyArrayStorage(indexingType()));
         return m_butterfly->arrayStorage();
     }
         
@@ -729,7 +753,7 @@ protected:
     // object is in a mode where it has array storage.
     ArrayStorage* arrayStorageOrNull()
     {
-        switch (structure()->indexingType()) {
+        switch (indexingType()) {
         case ALL_ARRAY_STORAGE_INDEXING_TYPES:
             return m_butterfly->arrayStorage();
                 
@@ -738,12 +762,16 @@ protected:
         }
     }
         
+    size_t butterflyTotalSize();
+    size_t butterflyPreCapacity();
+
     Butterfly* createInitialUndecided(VM&, unsigned length);
     ContiguousJSValues createInitialInt32(VM&, unsigned length);
     ContiguousDoubles createInitialDouble(VM&, unsigned length);
     ContiguousJSValues createInitialContiguous(VM&, unsigned length);
         
     void convertUndecidedForValue(VM&, JSValue);
+    void createInitialForValueAndSet(VM&, unsigned index, JSValue);
     void convertInt32ForValue(VM&, JSValue);
         
     ArrayStorage* createArrayStorage(VM&, unsigned length, unsigned vectorLength);
@@ -752,30 +780,25 @@ protected:
     ContiguousJSValues convertUndecidedToInt32(VM&);
     ContiguousDoubles convertUndecidedToDouble(VM&);
     ContiguousJSValues convertUndecidedToContiguous(VM&);
-    ArrayStorage* convertUndecidedToArrayStorage(VM&, NonPropertyTransition, unsigned neededLength);
     ArrayStorage* convertUndecidedToArrayStorage(VM&, NonPropertyTransition);
     ArrayStorage* convertUndecidedToArrayStorage(VM&);
         
     ContiguousDoubles convertInt32ToDouble(VM&);
     ContiguousJSValues convertInt32ToContiguous(VM&);
-    ArrayStorage* convertInt32ToArrayStorage(VM&, NonPropertyTransition, unsigned neededLength);
     ArrayStorage* convertInt32ToArrayStorage(VM&, NonPropertyTransition);
     ArrayStorage* convertInt32ToArrayStorage(VM&);
     
     ContiguousJSValues convertDoubleToContiguous(VM&);
-    ContiguousJSValues rageConvertDoubleToContiguous(VM&);
-    ArrayStorage* convertDoubleToArrayStorage(VM&, NonPropertyTransition, unsigned neededLength);
     ArrayStorage* convertDoubleToArrayStorage(VM&, NonPropertyTransition);
     ArrayStorage* convertDoubleToArrayStorage(VM&);
         
-    ArrayStorage* convertContiguousToArrayStorage(VM&, NonPropertyTransition, unsigned neededLength);
     ArrayStorage* convertContiguousToArrayStorage(VM&, NonPropertyTransition);
     ArrayStorage* convertContiguousToArrayStorage(VM&);
 
         
     ArrayStorage* ensureArrayStorageExistsAndEnterDictionaryIndexingMode(VM&);
         
-    bool defineOwnNonIndexProperty(ExecState*, PropertyName, PropertyDescriptor&, bool throwException);
+    bool defineOwnNonIndexProperty(ExecState*, PropertyName, const PropertyDescriptor&, bool throwException);
 
     template<IndexingType indexingShape>
     void putByIndexBeyondVectorLengthWithoutAttributes(ExecState*, unsigned propertyName, JSValue);
@@ -783,7 +806,7 @@ protected:
 
     bool increaseVectorLength(VM&, unsigned newLength);
     void deallocateSparseIndexMap();
-    bool defineOwnIndexedProperty(ExecState*, unsigned, PropertyDescriptor&, bool throwException);
+    bool defineOwnIndexedProperty(ExecState*, unsigned, const PropertyDescriptor&, bool throwException);
     SparseArrayValueMap* allocateSparseIndexMap(VM&);
         
     void notifyPresenceOfIndexedAccessors(VM&);
@@ -795,7 +818,7 @@ protected:
     void ensureLength(VM& vm, unsigned length)
     {
         ASSERT(length < MAX_ARRAY_INDEX);
-        ASSERT(hasContiguous(structure()->indexingType()) || hasInt32(structure()->indexingType()) || hasDouble(structure()->indexingType()) || hasUndecided(structure()->indexingType()));
+        ASSERT(hasContiguous(indexingType()) || hasInt32(indexingType()) || hasDouble(indexingType()) || hasUndecided(indexingType()));
             
         if (m_butterfly->vectorLength() < length)
             ensureLengthSlow(vm, length);
@@ -804,109 +827,16 @@ protected:
             m_butterfly->setPublicLength(length);
     }
         
+    // Call this if you want to shrink the butterfly backing store, and you're
+    // sure that the array is contiguous.
+    void reallocateAndShrinkButterfly(VM&, unsigned length);
+    
     template<IndexingType indexingShape>
     unsigned countElements(Butterfly*);
         
     // This is relevant to undecided, int32, double, and contiguous.
     unsigned countElements();
         
-    // This strange method returns a pointer to the start of the indexed data
-    // as if it contained JSValues. But it won't always contain JSValues.
-    // Make sure you cast this to the appropriate type before using.
-    template<IndexingType indexingType>
-    ContiguousJSValues indexingData()
-    {
-        switch (indexingType) {
-        case ALL_INT32_INDEXING_TYPES:
-        case ALL_DOUBLE_INDEXING_TYPES:
-        case ALL_CONTIGUOUS_INDEXING_TYPES:
-            return m_butterfly->contiguous();
-                
-        case ALL_ARRAY_STORAGE_INDEXING_TYPES:
-            return m_butterfly->arrayStorage()->vector();
-
-        default:
-            CRASH();
-            return ContiguousJSValues();
-        }
-    }
-
-    ContiguousJSValues currentIndexingData()
-    {
-        switch (structure()->indexingType()) {
-        case ALL_INT32_INDEXING_TYPES:
-        case ALL_CONTIGUOUS_INDEXING_TYPES:
-            return m_butterfly->contiguous();
-
-        case ALL_ARRAY_STORAGE_INDEXING_TYPES:
-            return m_butterfly->arrayStorage()->vector();
-
-        default:
-            CRASH();
-            return ContiguousJSValues();
-        }
-    }
-        
-    JSValue getHolyIndexQuickly(unsigned i)
-    {
-        ASSERT(i < m_butterfly->vectorLength());
-        switch (structure()->indexingType()) {
-        case ALL_INT32_INDEXING_TYPES:
-        case ALL_CONTIGUOUS_INDEXING_TYPES:
-            return m_butterfly->contiguous()[i].get();
-        case ALL_DOUBLE_INDEXING_TYPES: {
-            double value = m_butterfly->contiguousDouble()[i];
-            if (value == value)
-                return JSValue(JSValue::EncodeAsDouble, value);
-            return JSValue();
-        }
-        case ALL_ARRAY_STORAGE_INDEXING_TYPES:
-            return m_butterfly->arrayStorage()->m_vector[i].get();
-        default:
-            CRASH();
-            return JSValue();
-        }
-    }
-        
-    template<IndexingType indexingType>
-    unsigned relevantLength()
-    {
-        switch (indexingType) {
-        case ALL_INT32_INDEXING_TYPES:
-        case ALL_DOUBLE_INDEXING_TYPES:
-        case ALL_CONTIGUOUS_INDEXING_TYPES:
-            return m_butterfly->publicLength();
-                
-        case ALL_ARRAY_STORAGE_INDEXING_TYPES:
-            return std::min(
-                m_butterfly->arrayStorage()->length(),
-                m_butterfly->arrayStorage()->vectorLength());
-                
-        default:
-            CRASH();
-            return 0;
-        }
-    }
-
-    unsigned currentRelevantLength()
-    {
-        switch (structure()->indexingType()) {
-        case ALL_INT32_INDEXING_TYPES:
-        case ALL_DOUBLE_INDEXING_TYPES:
-        case ALL_CONTIGUOUS_INDEXING_TYPES:
-            return m_butterfly->publicLength();
-
-        case ALL_ARRAY_STORAGE_INDEXING_TYPES:
-            return std::min(
-                m_butterfly->arrayStorage()->length(),
-                m_butterfly->arrayStorage()->vectorLength());
-
-        default:
-            CRASH();
-            return 0;
-        }
-    }
-
 private:
     friend class LLIntOffsetsExtractor;
         
@@ -923,14 +853,15 @@ private:
     ArrayStorage* enterDictionaryIndexingModeWhenArrayStorageAlreadyExists(VM&, ArrayStorage*);
         
     template<PutMode>
-    bool putDirectInternal(VM&, PropertyName, JSValue, unsigned attr, PutPropertySlot&, JSCell*);
+    bool putDirectInternal(VM&, PropertyName, JSValue, unsigned attr, PutPropertySlot&);
 
-    bool inlineGetOwnPropertySlot(ExecState*, PropertyName, PropertySlot&);
-    JS_EXPORT_PRIVATE void fillGetterPropertySlot(PropertySlot&, PropertyOffset);
+    bool inlineGetOwnPropertySlot(VM&, Structure&, PropertyName, PropertySlot&);
+    JS_EXPORT_PRIVATE void fillGetterPropertySlot(PropertySlot&, JSValue, unsigned, PropertyOffset);
+    void fillCustomGetterPropertySlot(PropertySlot&, JSValue, unsigned, Structure&);
 
-    const HashEntry* findPropertyHashEntry(ExecState*, PropertyName) const;
+    const HashTableValue* findPropertyHashEntry(PropertyName) const;
         
-    void putIndexedDescriptor(ExecState*, SparseArrayEntry*, PropertyDescriptor&, PropertyDescriptor& old);
+    void putIndexedDescriptor(ExecState*, SparseArrayEntry*, const PropertyDescriptor&, PropertyDescriptor& old);
         
     void putByIndexBeyondVectorLength(ExecState*, unsigned propertyName, JSValue, bool shouldThrow);
     bool putDirectIndexBeyondVectorLengthWithArrayStorage(ExecState*, unsigned propertyName, JSValue, unsigned attributes, PutDirectIndexMode, ArrayStorage*);
@@ -939,8 +870,6 @@ private:
     unsigned getNewVectorLength(unsigned currentVectorLength, unsigned currentLength, unsigned desiredLength);
     unsigned getNewVectorLength(unsigned desiredLength);
 
-    JS_EXPORT_PRIVATE bool getOwnPropertySlotSlow(ExecState*, PropertyName, PropertySlot&);
-        
     ArrayStorage* constructConvertedArrayStorageWithoutCopyingElements(VM&, unsigned neededLength);
         
     JS_EXPORT_PRIVATE void setIndexQuicklyToUndecided(VM&, unsigned index, JSValue);
@@ -952,16 +881,14 @@ private:
     ContiguousJSValues ensureInt32Slow(VM&);
     ContiguousDoubles ensureDoubleSlow(VM&);
     ContiguousJSValues ensureContiguousSlow(VM&);
-    ContiguousJSValues rageEnsureContiguousSlow(VM&);
-    ArrayStorage* ensureArrayStorageSlow(VM&);
-    
-    enum DoubleToContiguousMode { EncodeValueAsDouble, RageConvertDoubleToValue };
-    template<DoubleToContiguousMode mode>
-    ContiguousJSValues genericConvertDoubleToContiguous(VM&);
-    ContiguousJSValues ensureContiguousSlow(VM&, DoubleToContiguousMode);
-    
+    JS_EXPORT_PRIVATE ArrayStorage* ensureArrayStorageSlow(VM&);
+
 protected:
-    Butterfly* m_butterfly;
+    CopyWriteBarrier<Butterfly> m_butterfly;
+#if USE(JSVALUE32_64)
+private:
+    uint32_t m_padding;
+#endif
 };
 
 // JSNonFinalObject is a type of JSObject that has some internal storage,
@@ -975,7 +902,7 @@ public:
 
     static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype)
     {
-        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), &s_info);
+        return Structure::create(vm, globalObject, prototype, TypeInfo(ObjectType, StructureFlags), info());
     }
 
 protected:
@@ -987,7 +914,7 @@ protected:
     void finishCreation(VM& vm)
     {
         Base::finishCreation(vm);
-        ASSERT(!this->structure()->totalStorageCapacity());
+        ASSERT(!this->structure()->hasInlineStorage());
         ASSERT(classInfo());
     }
 };
@@ -1001,7 +928,13 @@ class JSFinalObject : public JSObject {
 
 public:
     typedef JSObject Base;
+    static const unsigned StructureFlags = Base::StructureFlags;
 
+    static size_t allocationSize(size_t inlineCapacity)
+    {
+        return sizeof(JSObject) + inlineCapacity * sizeof(WriteBarrierBase<Unknown>);
+    }
+        
     static const unsigned defaultSize = 64;
     static inline unsigned defaultInlineCapacity()
     {
@@ -1014,15 +947,16 @@ public:
         return (maxSize - allocationSize(0)) / sizeof(WriteBarrier<Unknown>);
     }
 
-    static JSFinalObject* create(ExecState*, Structure*);
+    static JSFinalObject* create(ExecState*, Structure*, Butterfly* = nullptr);
+    static JSFinalObject* create(VM&, Structure*);
     static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue prototype, unsigned inlineCapacity)
     {
-        return Structure::create(vm, globalObject, prototype, TypeInfo(FinalObjectType, StructureFlags), &s_info, NonArray, inlineCapacity);
+        return Structure::create(vm, globalObject, prototype, TypeInfo(FinalObjectType, StructureFlags), info(), NonArray, inlineCapacity);
     }
 
     JS_EXPORT_PRIVATE static void visitChildren(JSCell*, SlotVisitor&);
 
-    static JS_EXPORTDATA const ClassInfo s_info;
+    DECLARE_EXPORT_INFO;
 
 protected:
     void visitChildrenCommon(SlotVisitor&);
@@ -1037,15 +971,14 @@ protected:
 private:
     friend class LLIntOffsetsExtractor;
 
-    explicit JSFinalObject(VM& vm, Structure* structure)
-        : JSObject(vm, structure)
+    explicit JSFinalObject(VM& vm, Structure* structure, Butterfly* butterfly = nullptr)
+        : JSObject(vm, structure, butterfly)
     {
     }
-
-    static const unsigned StructureFlags = JSObject::StructureFlags;
 };
 
-inline JSFinalObject* JSFinalObject::create(ExecState* exec, Structure* structure)
+inline JSFinalObject* JSFinalObject::create(
+    ExecState* exec, Structure* structure, Butterfly* butterfly)
 {
     JSFinalObject* finalObject = new (
         NotNull, 
@@ -1053,14 +986,21 @@ inline JSFinalObject* JSFinalObject::create(ExecState* exec, Structure* structur
             *exec->heap(),
             allocationSize(structure->inlineCapacity())
         )
-    ) JSFinalObject(exec->vm(), structure);
+    ) JSFinalObject(exec->vm(), structure, butterfly);
     finalObject->finishCreation(exec->vm());
     return finalObject;
 }
 
+inline JSFinalObject* JSFinalObject::create(VM& vm, Structure* structure)
+{
+    JSFinalObject* finalObject = new (NotNull, allocateCell<JSFinalObject>(vm.heap, allocationSize(structure->inlineCapacity()))) JSFinalObject(vm, structure);
+    finalObject->finishCreation(vm);
+    return finalObject;
+}
+
 inline bool isJSFinalObject(JSCell* cell)
 {
-    return cell->classInfo() == &JSFinalObject::s_info;
+    return cell->classInfo() == JSFinalObject::info();
 }
 
 inline bool isJSFinalObject(JSValue value)
@@ -1075,48 +1015,58 @@ inline size_t JSObject::offsetOfInlineStorage()
 
 inline bool JSObject::isGlobalObject() const
 {
-    return structure()->typeInfo().type() == GlobalObjectType;
+    return type() == GlobalObjectType;
 }
 
 inline bool JSObject::isVariableObject() const
 {
-    return structure()->typeInfo().type() >= VariableObjectType;
+    return type() == GlobalObjectType || type() == ActivationObjectType;
 }
 
-
 inline bool JSObject::isStaticScopeObject() const
 {
-    JSType type = structure()->typeInfo().type();
+    JSType type = this->type();
     return type == NameScopeObjectType || type == ActivationObjectType;
 }
 
-
 inline bool JSObject::isNameScopeObject() const
 {
-    return structure()->typeInfo().type() == NameScopeObjectType;
+    return type() == NameScopeObjectType;
 }
 
 inline bool JSObject::isActivationObject() const
 {
-    return structure()->typeInfo().type() == ActivationObjectType;
+    return type() == ActivationObjectType;
 }
 
 inline bool JSObject::isErrorInstance() const
 {
-    return structure()->typeInfo().type() == ErrorInstanceType;
+    return type() == ErrorInstanceType;
+}
+
+inline bool JSObject::isWithScope() const
+{
+    return type() == WithScopeType;
+}
+
+inline void JSObject::setStructureAndButterfly(VM& vm, Structure* structure, Butterfly* butterfly)
+{
+    ASSERT(structure);
+    ASSERT(!butterfly == (!structure->outOfLineCapacity() && !structure->hasIndexingHeader(this)));
+    m_butterfly.set(vm, this, butterfly);
+    setStructure(vm, structure);
 }
 
-inline void JSObject::setButterfly(VM& vm, Butterfly* butterfly, Structure* structure)
+inline void JSObject::setStructure(VM& vm, Structure* structure)
 {
     ASSERT(structure);
-    ASSERT(!butterfly == (!structure->outOfLineCapacity() && !hasIndexingHeader(structure->indexingType())));
-    setStructure(vm, structure, butterfly);
-    m_butterfly = butterfly;
+    ASSERT(!m_butterfly == !(structure->outOfLineCapacity() || structure->hasIndexingHeader(this)));
+    JSCell::setStructure(vm, structure);
 }
 
-inline void JSObject::setButterflyWithoutChangingStructure(Butterfly* butterfly)
+inline void JSObject::setButterflyWithoutChangingStructure(VM& vm, Butterfly* butterfly)
 {
-    m_butterfly = butterfly;
+    m_butterfly.set(vm, this, butterfly);
 }
 
 inline CallType getCallData(JSValue value, CallData& callData)
@@ -1146,8 +1096,9 @@ inline JSObject* asObject(JSValue value)
 
 inline JSObject::JSObject(VM& vm, Structure* structure, Butterfly* butterfly)
     : JSCell(vm, structure)
-    , m_butterfly(butterfly)
+    , m_butterfly(vm, this, butterfly)
 {
+    vm.heap.ascribeOwner(this, butterfly);
 }
 
 inline JSValue JSObject::prototype() const
@@ -1155,51 +1106,86 @@ inline JSValue JSObject::prototype() const
     return structure()->storedPrototype();
 }
 
-ALWAYS_INLINE bool JSObject::inlineGetOwnPropertySlot(ExecState* exec, PropertyName propertyName, PropertySlot& slot)
+ALWAYS_INLINE bool JSObject::inlineGetOwnPropertySlot(VM& vm, Structure& structure, PropertyName propertyName, PropertySlot& slot)
 {
-    PropertyOffset offset = structure()->get(exec->vm(), propertyName);
-    if (LIKELY(isValidOffset(offset))) {
-        JSValue value = getDirect(offset);
-        if (structure()->hasGetterSetterProperties() && value.isGetterSetter())
-            fillGetterPropertySlot(slot, offset);
-        else
-            slot.setValue(this, value, offset);
-        return true;
-    }
+    unsigned attributes;
+    PropertyOffset offset = structure.get(vm, propertyName, attributes);
+    if (!isValidOffset(offset))
+        return false;
+
+    JSValue value = getDirect(offset);
+    if (structure.hasGetterSetterProperties() && value.isGetterSetter())
+        fillGetterPropertySlot(slot, value, attributes, offset);
+    else if (structure.hasCustomGetterSetterProperties() && value.isCustomGetterSetter())
+        fillCustomGetterPropertySlot(slot, value, attributes, structure);
+    else
+        slot.setValue(this, attributes, value, offset);
 
-    return getOwnPropertySlotSlow(exec, propertyName, slot);
+    return true;
+}
+
+ALWAYS_INLINE void JSObject::fillCustomGetterPropertySlot(PropertySlot& slot, JSValue customGetterSetter, unsigned attributes, Structure& structure)
+{
+    if (structure.isDictionary()) {
+        slot.setCustom(this, attributes, jsCast<CustomGetterSetter*>(customGetterSetter)->getter());
+        return;
+    }
+    slot.setCacheableCustom(this, attributes, jsCast<CustomGetterSetter*>(customGetterSetter)->getter());
 }
 
 // It may seem crazy to inline a function this large, especially a virtual function,
 // but it makes a big difference to property lookup that derived classes can inline their
 // base class call to this.
-ALWAYS_INLINE bool JSObject::getOwnPropertySlot(JSCell* cell, ExecState* exec, PropertyName propertyName, PropertySlot& slot)
+ALWAYS_INLINE bool JSObject::getOwnPropertySlot(JSObject* object, ExecState* exec, PropertyName propertyName, PropertySlot& slot)
 {
-    return jsCast<JSObject*>(cell)->inlineGetOwnPropertySlot(exec, propertyName, slot);
+    VM& vm = exec->vm();
+    Structure& structure = *object->structure(vm);
+    if (object->inlineGetOwnPropertySlot(vm, structure, propertyName, slot))
+        return true;
+    if (Optional<uint32_t> index = parseIndex(propertyName))
+        return getOwnPropertySlotByIndex(object, exec, index.value(), slot);
+    return false;
+}
+
+ALWAYS_INLINE bool JSObject::fastGetOwnPropertySlot(ExecState* exec, VM& vm, Structure& structure, PropertyName propertyName, PropertySlot& slot)
+{
+    if (LIKELY(!TypeInfo::overridesGetOwnPropertySlot(inlineTypeFlags())))
+        return inlineGetOwnPropertySlot(vm, structure, propertyName, slot);
+    return structure.classInfo()->methodTable.getOwnPropertySlot(this, exec, propertyName, slot);
 }
 
 // It may seem crazy to inline a function this large but it makes a big difference
 // since this is function very hot in variable lookup
 ALWAYS_INLINE bool JSObject::getPropertySlot(ExecState* exec, PropertyName propertyName, PropertySlot& slot)
 {
+    VM& vm = exec->vm();
+    auto& structureIDTable = vm.heap.structureIDTable();
     JSObject* object = this;
     while (true) {
-        if (object->fastGetOwnPropertySlot(exec, propertyName, slot))
+        Structure& structure = *structureIDTable.get(object->structureID());
+        if (object->fastGetOwnPropertySlot(exec, vm, structure, propertyName, slot))
             return true;
-        JSValue prototype = object->prototype();
+        JSValue prototype = structure.storedPrototype();
         if (!prototype.isObject())
-            return false;
+            break;
         object = asObject(prototype);
     }
+
+    if (Optional<uint32_t> index = parseIndex(propertyName))
+        return getPropertySlot(exec, index.value(), slot);
+    return false;
 }
 
 ALWAYS_INLINE bool JSObject::getPropertySlot(ExecState* exec, unsigned propertyName, PropertySlot& slot)
 {
+    VM& vm = exec->vm();
+    auto& structureIDTable = vm.heap.structureIDTable();
     JSObject* object = this;
     while (true) {
-        if (object->methodTable()->getOwnPropertySlotByIndex(object, exec, propertyName, slot))
+        Structure& structure = *structureIDTable.get(object->structureID());
+        if (structure.classInfo()->methodTable.getOwnPropertySlotByIndex(object, exec, propertyName, slot))
             return true;
-        JSValue prototype = object->prototype();
+        JSValue prototype = structure.storedPrototype();
         if (!prototype.isObject())
             return false;
         object = asObject(prototype);
@@ -1225,150 +1211,121 @@ inline JSValue JSObject::get(ExecState* exec, unsigned propertyName) const
 }
 
 template<JSObject::PutMode mode>
-inline bool JSObject::putDirectInternal(VM& vm, PropertyName propertyName, JSValue value, unsigned attributes, PutPropertySlot& slot, JSCell* specificFunction)
+inline bool JSObject::putDirectInternal(VM& vm, PropertyName propertyName, JSValue value, unsigned attributes, PutPropertySlot& slot)
 {
     ASSERT(value);
     ASSERT(value.isGetterSetter() == !!(attributes & Accessor));
     ASSERT(!Heap::heap(value) || Heap::heap(value) == Heap::heap(this));
-    ASSERT(propertyName.asIndex() == PropertyName::NotAnIndex);
+    ASSERT(!parseIndex(propertyName));
 
-    if (structure()->isDictionary()) {
+    Structure* structure = this->structure(vm);
+    if (structure->isDictionary()) {
         unsigned currentAttributes;
-        JSCell* currentSpecificFunction;
-        PropertyOffset offset = structure()->get(vm, propertyName, currentAttributes, currentSpecificFunction);
+        PropertyOffset offset = structure->get(vm, propertyName, currentAttributes);
         if (offset != invalidOffset) {
-            // If there is currently a specific function, and there now either isn't,
-            // or the new value is different, then despecify.
-            if (currentSpecificFunction && (specificFunction != currentSpecificFunction))
-                structure()->despecifyDictionaryFunction(vm, propertyName);
             if ((mode == PutModePut) && currentAttributes & ReadOnly)
                 return false;
 
             putDirect(vm, offset, value);
-            // At this point, the objects structure only has a specific value set if previously there
-            // had been one set, and if the new value being specified is the same (otherwise we would
-            // have despecified, above).  So, if currentSpecificFunction is not set, or if the new
-            // value is different (or there is no new value), then the slot now has no value - and
-            // as such it is cachable.
-            // If there was previously a value, and the new value is the same, then we cannot cache.
-            if (!currentSpecificFunction || (specificFunction != currentSpecificFunction))
-                slot.setExistingProperty(this, offset);
+            structure->didReplaceProperty(offset);
+            slot.setExistingProperty(this, offset);
+
+            if ((attributes & Accessor) != (currentAttributes & Accessor)) {
+                ASSERT(!(attributes & ReadOnly));
+                setStructure(vm, Structure::attributeChangeTransition(vm, structure, propertyName, attributes));
+            }
             return true;
         }
 
         if ((mode == PutModePut) && !isExtensible())
             return false;
 
-        Butterfly* newButterfly = m_butterfly;
-        if (structure()->putWillGrowOutOfLineStorage())
-            newButterfly = growOutOfLineStorage(vm, structure()->outOfLineCapacity(), structure()->suggestedNewOutOfLineStorageCapacity());
-        offset = structure()->addPropertyWithoutTransition(vm, propertyName, attributes, specificFunction);
-        setButterfly(vm, newButterfly, structure());
+        DeferGC deferGC(vm.heap);
+        Butterfly* newButterfly = butterfly();
+        if (this->structure()->putWillGrowOutOfLineStorage())
+            newButterfly = growOutOfLineStorage(vm, this->structure()->outOfLineCapacity(), this->structure()->suggestedNewOutOfLineStorageCapacity());
+        offset = this->structure()->addPropertyWithoutTransition(vm, propertyName, attributes);
+        setStructureAndButterfly(vm, this->structure(), newButterfly);
 
         validateOffset(offset);
-        ASSERT(structure()->isValidOffset(offset));
+        ASSERT(this->structure()->isValidOffset(offset));
         putDirect(vm, offset, value);
-        // See comment on setNewProperty call below.
-        if (!specificFunction)
-            slot.setNewProperty(this, offset);
+        slot.setNewProperty(this, offset);
         if (attributes & ReadOnly)
-            structure()->setContainsReadOnlyProperties();
+            this->structure()->setContainsReadOnlyProperties();
         return true;
     }
 
     PropertyOffset offset;
-    size_t currentCapacity = structure()->outOfLineCapacity();
-    if (Structure* structure = Structure::addPropertyTransitionToExistingStructure(this->structure(), propertyName, attributes, specificFunction, offset)) {
-        Butterfly* newButterfly = m_butterfly;
-        if (currentCapacity != structure->outOfLineCapacity())
+    size_t currentCapacity = this->structure()->outOfLineCapacity();
+    if (Structure* structure = Structure::addPropertyTransitionToExistingStructure(this->structure(), propertyName, attributes, offset)) {
+        DeferGC deferGC(vm.heap);
+        Butterfly* newButterfly = butterfly();
+        if (currentCapacity != structure->outOfLineCapacity()) {
+            ASSERT(structure != this->structure());
             newButterfly = growOutOfLineStorage(vm, currentCapacity, structure->outOfLineCapacity());
+        }
 
         validateOffset(offset);
         ASSERT(structure->isValidOffset(offset));
-        setButterfly(vm, newButterfly, structure);
+        setStructureAndButterfly(vm, structure, newButterfly);
         putDirect(vm, offset, value);
-        // This is a new property; transitions with specific values are not currently cachable,
-        // so leave the slot in an uncachable state.
-        if (!specificFunction)
-            slot.setNewProperty(this, offset);
+        slot.setNewProperty(this, offset);
         return true;
     }
 
     unsigned currentAttributes;
-    JSCell* currentSpecificFunction;
-    offset = structure()->get(vm, propertyName, currentAttributes, currentSpecificFunction);
+    offset = structure->get(vm, propertyName, currentAttributes);
     if (offset != invalidOffset) {
         if ((mode == PutModePut) && currentAttributes & ReadOnly)
             return false;
 
-        // There are three possibilities here:
-        //  (1) There is an existing specific value set, and we're overwriting with *the same value*.
-        //       * Do nothing - no need to despecify, but that means we can't cache (a cached
-        //         put could write a different value). Leave the slot in an uncachable state.
-        //  (2) There is a specific value currently set, but we're writing a different value.
-        //       * First, we have to despecify.  Having done so, this is now a regular slot
-        //         with no specific value, so go ahead & cache like normal.
-        //  (3) Normal case, there is no specific value set.
-        //       * Go ahead & cache like normal.
-        if (currentSpecificFunction) {
-            // case (1) Do the put, then return leaving the slot uncachable.
-            if (specificFunction == currentSpecificFunction) {
-                putDirect(vm, offset, value);
-                return true;
-            }
-            // case (2) Despecify, fall through to (3).
-            setStructure(vm, Structure::despecifyFunctionTransition(vm, structure(), propertyName), m_butterfly);
-        }
-
-        // case (3) set the slot, do the put, return.
+        structure->didReplaceProperty(offset);
         slot.setExistingProperty(this, offset);
         putDirect(vm, offset, value);
+
+        if ((attributes & Accessor) != (currentAttributes & Accessor)) {
+            ASSERT(!(attributes & ReadOnly));
+            setStructure(vm, Structure::attributeChangeTransition(vm, structure, propertyName, attributes));
+        }
         return true;
     }
 
     if ((mode == PutModePut) && !isExtensible())
         return false;
 
-    Structure* structure = Structure::addPropertyTransition(vm, this->structure(), propertyName, attributes, specificFunction, offset);
+    structure = Structure::addPropertyTransition(vm, structure, propertyName, attributes, offset, slot.context());
     
     validateOffset(offset);
     ASSERT(structure->isValidOffset(offset));
     setStructureAndReallocateStorageIfNecessary(vm, structure);
 
     putDirect(vm, offset, value);
-    // This is a new property; transitions with specific values are not currently cachable,
-    // so leave the slot in an uncachable state.
-    if (!specificFunction)
-        slot.setNewProperty(this, offset);
+    slot.setNewProperty(this, offset);
     if (attributes & ReadOnly)
         structure->setContainsReadOnlyProperties();
     return true;
 }
 
-inline void JSObject::setStructure(VM& vm, Structure* structure, Butterfly* butterfly)
-{
-    JSCell::setStructure(vm, structure);
-    ASSERT_UNUSED(butterfly, !butterfly == !(structure->outOfLineCapacity() || hasIndexingHeader(structure->indexingType())));
-}
-
 inline void JSObject::setStructureAndReallocateStorageIfNecessary(VM& vm, unsigned oldCapacity, Structure* newStructure)
 {
     ASSERT(oldCapacity <= newStructure->outOfLineCapacity());
     
     if (oldCapacity == newStructure->outOfLineCapacity()) {
-        setStructure(vm, newStructure, m_butterfly);
+        setStructure(vm, newStructure);
         return;
     }
-    
+
+    DeferGC deferGC(vm.heap); 
     Butterfly* newButterfly = growOutOfLineStorage(
         vm, oldCapacity, newStructure->outOfLineCapacity());
-    setButterfly(vm, newButterfly, newStructure);
+    setStructureAndButterfly(vm, newStructure, newButterfly);
 }
 
 inline void JSObject::setStructureAndReallocateStorageIfNecessary(VM& vm, Structure* newStructure)
 {
     setStructureAndReallocateStorageIfNecessary(
-        vm, structure()->outOfLineCapacity(), newStructure);
+        vm, structure(vm)->outOfLineCapacity(), newStructure);
 }
 
 inline bool JSObject::putOwnDataProperty(VM& vm, PropertyName propertyName, JSValue value, PutPropertySlot& slot)
@@ -1376,31 +1333,36 @@ inline bool JSObject::putOwnDataProperty(VM& vm, PropertyName propertyName, JSVa
     ASSERT(value);
     ASSERT(!Heap::heap(value) || Heap::heap(value) == Heap::heap(this));
     ASSERT(!structure()->hasGetterSetterProperties());
+    ASSERT(!structure()->hasCustomGetterSetterProperties());
 
-    return putDirectInternal<PutModePut>(vm, propertyName, value, 0, slot, getCallableObject(value));
+    return putDirectInternal<PutModePut>(vm, propertyName, value, 0, slot);
 }
 
 inline void JSObject::putDirect(VM& vm, PropertyName propertyName, JSValue value, unsigned attributes)
 {
     ASSERT(!value.isGetterSetter() && !(attributes & Accessor));
-    PutPropertySlot slot;
-    putDirectInternal<PutModeDefineOwnProperty>(vm, propertyName, value, attributes, slot, getCallableObject(value));
+    ASSERT(!value.isCustomGetterSetter());
+    PutPropertySlot slot(this);
+    putDirectInternal<PutModeDefineOwnProperty>(vm, propertyName, value, attributes, slot);
 }
 
 inline void JSObject::putDirect(VM& vm, PropertyName propertyName, JSValue value, PutPropertySlot& slot)
 {
     ASSERT(!value.isGetterSetter());
-    putDirectInternal<PutModeDefineOwnProperty>(vm, propertyName, value, 0, slot, getCallableObject(value));
+    ASSERT(!value.isCustomGetterSetter());
+    putDirectInternal<PutModeDefineOwnProperty>(vm, propertyName, value, 0, slot);
 }
 
 inline void JSObject::putDirectWithoutTransition(VM& vm, PropertyName propertyName, JSValue value, unsigned attributes)
 {
+    DeferGC deferGC(vm.heap);
     ASSERT(!value.isGetterSetter() && !(attributes & Accessor));
-    Butterfly* newButterfly = m_butterfly;
+    ASSERT(!value.isCustomGetterSetter());
+    Butterfly* newButterfly = m_butterfly.get();
     if (structure()->putWillGrowOutOfLineStorage())
         newButterfly = growOutOfLineStorage(vm, structure()->outOfLineCapacity(), structure()->suggestedNewOutOfLineStorageCapacity());
-    PropertyOffset offset = structure()->addPropertyWithoutTransition(vm, propertyName, attributes, getCallableObject(value));
-    setButterfly(vm, newButterfly, structure());
+    PropertyOffset offset = structure()->addPropertyWithoutTransition(vm, propertyName, attributes);
+    setStructureAndButterfly(vm, structure(), newButterfly);
     putDirect(vm, offset, value);
 }
 
@@ -1409,18 +1371,15 @@ inline JSValue JSObject::toPrimitive(ExecState* exec, PreferredPrimitiveType pre
     return methodTable()->defaultValue(this, exec, preferredType);
 }
 
-ALWAYS_INLINE JSObject* Register::function() const
+ALWAYS_INLINE JSObject* Register::object() const
 {
-    if (!jsValue())
-        return 0;
     return asObject(jsValue());
 }
 
-ALWAYS_INLINE Register Register::withCallee(JSObject* callee)
+ALWAYS_INLINE Register& Register::operator=(JSObject* object)
 {
-    Register r;
-    r = JSValue(callee);
-    return r;
+    u.value = JSValue::encode(JSValue(object));
+    return *this;
 }
 
 inline size_t offsetInButterfly(PropertyOffset offset)
@@ -1428,6 +1387,32 @@ inline size_t offsetInButterfly(PropertyOffset offset)
     return offsetInOutOfLineStorage(offset) + Butterfly::indexOfPropertyStorage();
 }
 
+inline size_t JSObject::butterflyPreCapacity()
+{
+    if (UNLIKELY(hasIndexingHeader()))
+        return butterfly()->indexingHeader()->preCapacity(structure());
+    return 0;
+}
+
+inline size_t JSObject::butterflyTotalSize()
+{
+    Structure* structure = this->structure();
+    Butterfly* butterfly = this->butterfly();
+    size_t preCapacity;
+    size_t indexingPayloadSizeInBytes;
+    bool hasIndexingHeader = this->hasIndexingHeader();
+
+    if (UNLIKELY(hasIndexingHeader)) {
+        preCapacity = butterfly->indexingHeader()->preCapacity(structure);
+        indexingPayloadSizeInBytes = butterfly->indexingHeader()->indexingPayloadSizeInBytes(structure);
+    } else {
+        preCapacity = 0;
+        indexingPayloadSizeInBytes = 0;
+    }
+
+    return Butterfly::totalSize(preCapacity, structure->outOfLineCapacity(), hasIndexingHeader, indexingPayloadSizeInBytes);
+}
+
 // Helpers for patching code where you want to emit a load or store and
 // the base is:
 // For inline offsets: a pointer to the out-of-line storage pointer.
@@ -1467,12 +1452,12 @@ inline int offsetRelativeToBase(PropertyOffset offset)
 
 COMPILE_ASSERT(!(sizeof(JSObject) % sizeof(WriteBarrierBase<Unknown>)), JSObject_inline_storage_has_correct_alignment);
 
-ALWAYS_INLINE Identifier makeIdentifier(ExecState* exec, const char* name)
+ALWAYS_INLINE Identifier makeIdentifier(VM& vm, const char* name)
 {
-    return Identifier(exec, name);
+    return Identifier::fromString(&vm, name);
 }
 
-ALWAYS_INLINE Identifier makeIdentifier(ExecState*, const Identifier& name)
+ALWAYS_INLINE Identifier makeIdentifier(VM&, const Identifier& name)
 {
     return name;
 }
@@ -1483,7 +1468,7 @@ ALWAYS_INLINE Identifier makeIdentifier(ExecState*, const Identifier& name)
 // have the expected meanings.
 #define JSC_NATIVE_INTRINSIC_FUNCTION(jsName, cppName, attributes, length, intrinsic) \
     putDirectNativeFunction(\
-        exec, globalObject, makeIdentifier(exec, (jsName)), (length), cppName, \
+        vm, globalObject, makeIdentifier(vm, (jsName)), (length), cppName, \
         (intrinsic), (attributes))
 
 // As above, but this assumes that the function you're defining doesn't have an
@@ -1491,6 +1476,12 @@ ALWAYS_INLINE Identifier makeIdentifier(ExecState*, const Identifier& name)
 #define JSC_NATIVE_FUNCTION(jsName, cppName, attributes, length) \
     JSC_NATIVE_INTRINSIC_FUNCTION(jsName, cppName, (attributes), (length), NoIntrinsic)
 
+// Identical helpers but for builtins. Note that currently, we don't support builtins that are
+// also intrinsics, but we probably will do that eventually.
+#define JSC_BUILTIN_FUNCTION(jsName, generatorName, attributes) \
+    putDirectBuiltinFunction(\
+        vm, globalObject, makeIdentifier(vm, (jsName)), (generatorName)(vm), (attributes))
+
 } // namespace JSC
 
 #endif // JSObject_h