Imported QtWebKit TP3 (git b57bc6801f1876c3220d5a4bfea33d620d477443)

Change-Id: I3b1d8a2808782c9f34d50240000e20cb38d3680f
Reviewed-by: Konstantin Tokarev <annulen@yandex.ru>

1 files changed, 322 insertions, 786 deletions

diff --git a/Source/JavaScriptCore/runtime/JSArray.cpp b/Source/JavaScriptCore/runtime/JSArray.cpp
index bc6f73672..afdbe0de7 100644
--- a/Source/JavaScriptCore/runtime/JSArray.cpp
+++ b/Source/JavaScriptCore/runtime/JSArray.cpp
@@ -1,6 +1,6 @@
 /*
  *  Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
- *  Copyright (C) 2003, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
+ *  Copyright (C) 2003, 2007, 2008, 2009, 2012, 2013, 2015 Apple Inc. All rights reserved.
  *  Copyright (C) 2003 Peter Kelly (pmk@post.com)
  *  Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
@@ -26,32 +26,31 @@
 #include "ArrayPrototype.h"
 #include "ButterflyInlines.h"
 #include "CachedCall.h"
+#include "CodeBlock.h"
 #include "CopiedSpace.h"
-#include "CopiedSpaceInlines.h"
 #include "Error.h"
 #include "Executable.h"
 #include "GetterSetter.h"
 #include "IndexingHeaderInlines.h"
+#include "JSCInlines.h"
 #include "PropertyNameArray.h"
 #include "Reject.h"
-#include <wtf/AVLTree.h>
 #include <wtf/Assertions.h>
-#include <wtf/OwnPtr.h>
-#include <Operations.h>
 
 using namespace std;
 using namespace WTF;
 
 namespace JSC {
 
-ASSERT_HAS_TRIVIAL_DESTRUCTOR(JSArray);
+STATIC_ASSERT_IS_TRIVIALLY_DESTRUCTIBLE(JSArray);
 
-const ClassInfo JSArray::s_info = {"Array", &JSNonFinalObject::s_info, 0, 0, CREATE_METHOD_TABLE(JSArray)};
+const ClassInfo JSArray::s_info = {"Array", &JSNonFinalObject::s_info, 0, CREATE_METHOD_TABLE(JSArray)};
 
-Butterfly* createArrayButterflyInDictionaryIndexingMode(VM& vm, unsigned initialLength)
+Butterfly* createArrayButterflyInDictionaryIndexingMode(
+    VM& vm, JSCell* intendedOwner, unsigned initialLength)
 {
     Butterfly* butterfly = Butterfly::create(
-        vm, 0, 0, true, IndexingHeader(), ArrayStorage::sizeFor(0));
+        vm, intendedOwner, 0, 0, true, IndexingHeader(), ArrayStorage::sizeFor(0));
     ArrayStorage* storage = butterfly->arrayStorage();
     storage->setLength(initialLength);
     storage->setVectorLength(0);
@@ -75,7 +74,7 @@ void JSArray::setLengthWritable(ExecState* exec, bool writable)
 }
 
 // Defined in ES5.1 15.4.5.1
-bool JSArray::defineOwnProperty(JSObject* object, ExecState* exec, PropertyName propertyName, PropertyDescriptor& descriptor, bool throwException)
+bool JSArray::defineOwnProperty(JSObject* object, ExecState* exec, PropertyName propertyName, const PropertyDescriptor& descriptor, bool throwException)
 {
     JSArray* array = jsCast<JSArray*>(object);
 
@@ -108,11 +107,12 @@ bool JSArray::defineOwnProperty(JSObject* object, ExecState* exec, PropertyName
         unsigned newLen = descriptor.value().toUInt32(exec);
         // d. If newLen is not equal to ToNumber( Desc.[[Value]]), throw a RangeError exception.
         if (newLen != descriptor.value().toNumber(exec)) {
-            throwError(exec, createRangeError(exec, "Invalid array length"));
+            exec->vm().throwException(exec, createRangeError(exec, ASCIILiteral("Invalid array length")));
             return false;
         }
 
         // Based on SameValue check in 8.12.9, this is always okay.
+        // FIXME: Nothing prevents this from being called on a RuntimeArray, and the length function will always return 0 in that case.
         if (newLen == array->length()) {
             if (descriptor.writablePresent())
                 array->setLengthWritable(exec, descriptor.writable());
@@ -159,9 +159,10 @@ bool JSArray::defineOwnProperty(JSObject* object, ExecState* exec, PropertyName
 
     // 4. Else if P is an array index (15.4), then
     // a. Let index be ToUint32(P).
-    unsigned index = propertyName.asIndex();
-    if (index != PropertyName::NotAnIndex) {
+    if (Optional<uint32_t> optionalIndex = parseIndex(propertyName)) {
         // b. Reject if index >= oldLen and oldLenDesc.[[Writable]] is false.
+        uint32_t index = optionalIndex.value();
+        // FIXME: Nothing prevents this from being called on a RuntimeArray, and the length function will always return 0 in that case.
         if (index >= array->length() && !array->isLengthWritable())
             return reject(exec, throwException, "Attempting to define numeric property on array with non-writable length property.");
         // c. Let succeeded be the result of calling the default [[DefineOwnProperty]] internal method (8.12.9) on A passing P, Desc, and false as arguments.
@@ -176,26 +177,16 @@ bool JSArray::defineOwnProperty(JSObject* object, ExecState* exec, PropertyName
     return array->JSObject::defineOwnNonIndexProperty(exec, propertyName, descriptor, throwException);
 }
 
-bool JSArray::getOwnPropertySlot(JSCell* cell, ExecState* exec, PropertyName propertyName, PropertySlot& slot)
-{
-    JSArray* thisObject = jsCast<JSArray*>(cell);
-    if (propertyName == exec->propertyNames().length) {
-        slot.setValue(jsNumber(thisObject->length()));
-        return true;
-    }
-
-    return JSObject::getOwnPropertySlot(thisObject, exec, propertyName, slot);
-}
-
-bool JSArray::getOwnPropertyDescriptor(JSObject* object, ExecState* exec, PropertyName propertyName, PropertyDescriptor& descriptor)
+bool JSArray::getOwnPropertySlot(JSObject* object, ExecState* exec, PropertyName propertyName, PropertySlot& slot)
 {
     JSArray* thisObject = jsCast<JSArray*>(object);
     if (propertyName == exec->propertyNames().length) {
-        descriptor.setDescriptor(jsNumber(thisObject->length()), thisObject->isLengthWritable() ? DontDelete | DontEnum : DontDelete | DontEnum | ReadOnly);
+        unsigned attributes = thisObject->isLengthWritable() ? DontDelete | DontEnum : DontDelete | DontEnum | ReadOnly;
+        slot.setValue(thisObject, attributes, jsNumber(thisObject->length()));
         return true;
     }
 
-    return JSObject::getOwnPropertyDescriptor(thisObject, exec, propertyName, descriptor);
+    return JSObject::getOwnPropertySlot(thisObject, exec, propertyName, slot);
 }
 
 // ECMA 15.4.5.1
@@ -206,7 +197,7 @@ void JSArray::put(JSCell* cell, ExecState* exec, PropertyName propertyName, JSVa
     if (propertyName == exec->propertyNames().length) {
         unsigned newLength = value.toUInt32(exec);
         if (value.toNumber(exec) != static_cast<double>(newLength)) {
-            throwError(exec, createRangeError(exec, ASCIILiteral("Invalid array length")));
+            exec->vm().throwException(exec, createRangeError(exec, ASCIILiteral("Invalid array length")));
             return;
         }
         thisObject->setLength(exec, newLength, slot.isStrictMode());
@@ -237,7 +228,7 @@ void JSArray::getOwnNonIndexPropertyNames(JSObject* object, ExecState* exec, Pro
 {
     JSArray* thisObject = jsCast<JSArray*>(object);
 
-    if (mode == IncludeDontEnumProperties)
+    if (mode.includeDontEnumProperties())
         propertyNames.add(exec->propertyNames().length);
 
     JSObject::getOwnNonIndexPropertyNames(thisObject, exec, propertyNames, mode);
@@ -248,8 +239,8 @@ bool JSArray::unshiftCountSlowCase(VM& vm, bool addToFront, unsigned count)
 {
     ArrayStorage* storage = ensureArrayStorage(vm);
     Butterfly* butterfly = storage->butterfly();
-    unsigned propertyCapacity = structure()->outOfLineCapacity();
-    unsigned propertySize = structure()->outOfLineSize();
+    unsigned propertyCapacity = structure(vm)->outOfLineCapacity();
+    unsigned propertySize = structure(vm)->outOfLineSize();
 
     // If not, we should have handled this on the fast path.
     ASSERT(!addToFront || count > storage->m_indexBias);
@@ -278,15 +269,16 @@ bool JSArray::unshiftCountSlowCase(VM& vm, bool addToFront, unsigned count)
     // Step 2:
     // We're either going to choose to allocate a new ArrayStorage, or we're going to reuse the existing one.
 
+    DeferGC deferGC(vm.heap);
     void* newAllocBase = 0;
     unsigned newStorageCapacity;
     // If the current storage array is sufficiently large (but not too large!) then just keep using it.
     if (currentCapacity > desiredCapacity && isDenseEnoughForVector(currentCapacity, requiredVectorLength)) {
-        newAllocBase = butterfly->base(structure());
+        newAllocBase = butterfly->base(structure(vm));
         newStorageCapacity = currentCapacity;
     } else {
         size_t newSize = Butterfly::totalSize(0, propertyCapacity, true, ArrayStorage::sizeFor(desiredCapacity));
-        if (!vm.heap.tryAllocateStorage(newSize, &newAllocBase))
+        if (!vm.heap.tryAllocateStorage(this, newSize, &newAllocBase))
             return false;
         newStorageCapacity = desiredCapacity;
     }
@@ -306,7 +298,7 @@ bool JSArray::unshiftCountSlowCase(VM& vm, bool addToFront, unsigned count)
         // Atomic decay, + the post-capacity cannot be greater than what is available.
         postCapacity = min((storage->vectorLength() - length) >> 1, newStorageCapacity - requiredVectorLength);
         // If we're moving contents within the same allocation, the post-capacity is being reduced.
-        ASSERT(newAllocBase != butterfly->base(structure()) || postCapacity < storage->vectorLength() - length);
+        ASSERT(newAllocBase != butterfly->base(structure(vm)) || postCapacity < storage->vectorLength() - length);
     }
 
     unsigned newVectorLength = requiredVectorLength + postCapacity;
@@ -318,7 +310,7 @@ bool JSArray::unshiftCountSlowCase(VM& vm, bool addToFront, unsigned count)
         ASSERT(count + usedVectorLength <= newVectorLength);
         memmove(newButterfly->arrayStorage()->m_vector + count, storage->m_vector, sizeof(JSValue) * usedVectorLength);
         memmove(newButterfly->propertyStorage() - propertySize, butterfly->propertyStorage() - propertySize, sizeof(JSValue) * propertySize + sizeof(IndexingHeader) + ArrayStorage::sizeFor(0));
-    } else if ((newAllocBase != butterfly->base(structure())) || (newIndexBias != storage->m_indexBias)) {
+    } else if ((newAllocBase != butterfly->base(structure(vm))) || (newIndexBias != storage->m_indexBias)) {
         memmove(newButterfly->propertyStorage() - propertySize, butterfly->propertyStorage() - propertySize, sizeof(JSValue) * propertySize + sizeof(IndexingHeader) + ArrayStorage::sizeFor(0));
         memmove(newButterfly->arrayStorage()->m_vector, storage->m_vector, sizeof(JSValue) * usedVectorLength);
 
@@ -329,8 +321,7 @@ bool JSArray::unshiftCountSlowCase(VM& vm, bool addToFront, unsigned count)
 
     newButterfly->arrayStorage()->setVectorLength(newVectorLength);
     newButterfly->arrayStorage()->m_indexBias = newIndexBias;
-
-    m_butterfly = newButterfly;
+    setButterflyWithoutChangingStructure(vm, newButterfly);
 
     return true;
 }
@@ -388,7 +379,7 @@ bool JSArray::setLengthWithArrayStorage(ExecState* exec, unsigned newLength, boo
         unsigned usedVectorLength = min(length, storage->vectorLength());
         for (unsigned i = newLength; i < usedVectorLength; ++i) {
             WriteBarrier<Unknown>& valueSlot = storage->m_vector[i];
-            bool hadValue = valueSlot;
+            bool hadValue = !!valueSlot;
             valueSlot.clear();
             storage->m_numValuesInVector -= hadValue;
         }
@@ -401,7 +392,8 @@ bool JSArray::setLengthWithArrayStorage(ExecState* exec, unsigned newLength, boo
 
 bool JSArray::setLength(ExecState* exec, unsigned newLength, bool throwException)
 {
-    switch (structure()->indexingType()) {
+    Butterfly* butterfly = m_butterfly.get(this);
+    switch (indexingType()) {
     case ArrayClass:
         if (!newLength)
             return true;
@@ -416,8 +408,8 @@ bool JSArray::setLength(ExecState* exec, unsigned newLength, bool throwException
     case ArrayWithUndecided:
     case ArrayWithInt32:
     case ArrayWithDouble:
-    case ArrayWithContiguous:
-        if (newLength == m_butterfly->publicLength())
+    case ArrayWithContiguous: {
+        if (newLength == butterfly->publicLength())
             return true;
         if (newLength >= MAX_ARRAY_INDEX // This case ensures that we can do fast push.
             || (newLength >= MIN_SPARSE_ARRAY_INDEX
@@ -426,19 +418,28 @@ bool JSArray::setLength(ExecState* exec, unsigned newLength, bool throwException
                 exec, newLength, throwException,
                 ensureArrayStorage(exec->vm()));
         }
-        if (newLength > m_butterfly->publicLength()) {
+        if (newLength > butterfly->publicLength()) {
             ensureLength(exec->vm(), newLength);
             return true;
         }
-        if (structure()->indexingType() == ArrayWithDouble) {
-            for (unsigned i = m_butterfly->publicLength(); i-- > newLength;)
-                m_butterfly->contiguousDouble()[i] = QNaN;
+
+        unsigned lengthToClear = butterfly->publicLength() - newLength;
+        unsigned costToAllocateNewButterfly = 64; // a heuristic.
+        if (lengthToClear > newLength && lengthToClear > costToAllocateNewButterfly) {
+            reallocateAndShrinkButterfly(exec->vm(), newLength);
+            return true;
+        }
+
+        if (indexingType() == ArrayWithDouble) {
+            for (unsigned i = butterfly->publicLength(); i-- > newLength;)
+                butterfly->contiguousDouble()[i] = PNaN;
         } else {
-            for (unsigned i = m_butterfly->publicLength(); i-- > newLength;)
-                m_butterfly->contiguous()[i].clear();
+            for (unsigned i = butterfly->publicLength(); i-- > newLength;)
+                butterfly->contiguous()[i].clear();
         }
-        m_butterfly->setPublicLength(newLength);
+        butterfly->setPublicLength(newLength);
         return true;
+    }
         
     case ArrayWithArrayStorage:
     case ArrayWithSlowPutArrayStorage:
@@ -452,51 +453,53 @@ bool JSArray::setLength(ExecState* exec, unsigned newLength, bool throwException
 
 JSValue JSArray::pop(ExecState* exec)
 {
-    switch (structure()->indexingType()) {
+    Butterfly* butterfly = m_butterfly.get(this);
+    
+    switch (indexingType()) {
     case ArrayClass:
         return jsUndefined();
         
     case ArrayWithUndecided:
-        if (!m_butterfly->publicLength())
+        if (!butterfly->publicLength())
             return jsUndefined();
         // We have nothing but holes. So, drop down to the slow version.
         break;
         
     case ArrayWithInt32:
     case ArrayWithContiguous: {
-        unsigned length = m_butterfly->publicLength();
+        unsigned length = butterfly->publicLength();
         
         if (!length--)
             return jsUndefined();
         
-        RELEASE_ASSERT(length < m_butterfly->vectorLength());
-        JSValue value = m_butterfly->contiguous()[length].get();
+        RELEASE_ASSERT(length < butterfly->vectorLength());
+        JSValue value = butterfly->contiguous()[length].get();
         if (value) {
-            m_butterfly->contiguous()[length].clear();
-            m_butterfly->setPublicLength(length);
+            butterfly->contiguous()[length].clear();
+            butterfly->setPublicLength(length);
             return value;
         }
         break;
     }
         
     case ArrayWithDouble: {
-        unsigned length = m_butterfly->publicLength();
+        unsigned length = butterfly->publicLength();
         
         if (!length--)
             return jsUndefined();
         
-        RELEASE_ASSERT(length < m_butterfly->vectorLength());
-        double value = m_butterfly->contiguousDouble()[length];
+        RELEASE_ASSERT(length < butterfly->vectorLength());
+        double value = butterfly->contiguousDouble()[length];
         if (value == value) {
-            m_butterfly->contiguousDouble()[length] = QNaN;
-            m_butterfly->setPublicLength(length);
+            butterfly->contiguousDouble()[length] = PNaN;
+            butterfly->setPublicLength(length);
             return JSValue(JSValue::EncodeAsDouble, value);
         }
         break;
     }
         
     case ARRAY_WITH_ARRAY_STORAGE_INDEXING_TYPES: {
-        ArrayStorage* storage = m_butterfly->arrayStorage();
+        ArrayStorage* storage = butterfly->arrayStorage();
     
         unsigned length = storage->length();
         if (!length) {
@@ -533,7 +536,7 @@ JSValue JSArray::pop(ExecState* exec)
         return jsUndefined();
     // Call the [[Delete]] internal method of O with arguments indx and true.
     if (!deletePropertyByIndex(this, exec, index)) {
-        throwTypeError(exec, "Unable to delete property.");
+        throwTypeError(exec, ASCIILiteral("Unable to delete property."));
         return jsUndefined();
     }
     // Call the [[Put]] internal method of O with arguments "length", indx, and true.
@@ -547,10 +550,12 @@ JSValue JSArray::pop(ExecState* exec)
 //  - pushing to an array of length 2^32-1 stores the property, but throws a range error.
 void JSArray::push(ExecState* exec, JSValue value)
 {
-    switch (structure()->indexingType()) {
+    Butterfly* butterfly = m_butterfly.get(this);
+    
+    switch (indexingType()) {
     case ArrayClass: {
         createInitialUndecided(exec->vm(), 0);
-        // Fall through.
+        FALLTHROUGH;
     }
         
     case ArrayWithUndecided: {
@@ -566,18 +571,18 @@ void JSArray::push(ExecState* exec, JSValue value)
             return;
         }
 
-        unsigned length = m_butterfly->publicLength();
-        ASSERT(length <= m_butterfly->vectorLength());
-        if (length < m_butterfly->vectorLength()) {
-            m_butterfly->contiguousInt32()[length].setWithoutWriteBarrier(value);
-            m_butterfly->setPublicLength(length + 1);
+        unsigned length = butterfly->publicLength();
+        ASSERT(length <= butterfly->vectorLength());
+        if (length < butterfly->vectorLength()) {
+            butterfly->contiguousInt32()[length].setWithoutWriteBarrier(value);
+            butterfly->setPublicLength(length + 1);
             return;
         }
         
         if (length > MAX_ARRAY_INDEX) {
-            methodTable()->putByIndex(this, exec, length, value, true);
+            methodTable(exec->vm())->putByIndex(this, exec, length, value, true);
             if (!exec->hadException())
-                throwError(exec, createRangeError(exec, "Invalid array length"));
+                exec->vm().throwException(exec, createRangeError(exec, ASCIILiteral("Invalid array length")));
             return;
         }
         
@@ -586,18 +591,18 @@ void JSArray::push(ExecState* exec, JSValue value)
     }
 
     case ArrayWithContiguous: {
-        unsigned length = m_butterfly->publicLength();
-        ASSERT(length <= m_butterfly->vectorLength());
-        if (length < m_butterfly->vectorLength()) {
-            m_butterfly->contiguous()[length].set(exec->vm(), this, value);
-            m_butterfly->setPublicLength(length + 1);
+        unsigned length = butterfly->publicLength();
+        ASSERT(length <= butterfly->vectorLength());
+        if (length < butterfly->vectorLength()) {
+            butterfly->contiguous()[length].set(exec->vm(), this, value);
+            butterfly->setPublicLength(length + 1);
             return;
         }
         
         if (length > MAX_ARRAY_INDEX) {
-            methodTable()->putByIndex(this, exec, length, value, true);
+            methodTable(exec->vm())->putByIndex(this, exec, length, value, true);
             if (!exec->hadException())
-                throwError(exec, createRangeError(exec, "Invalid array length"));
+                exec->vm().throwException(exec, createRangeError(exec, ASCIILiteral("Invalid array length")));
             return;
         }
         
@@ -618,18 +623,18 @@ void JSArray::push(ExecState* exec, JSValue value)
             return;
         }
 
-        unsigned length = m_butterfly->publicLength();
-        ASSERT(length <= m_butterfly->vectorLength());
-        if (length < m_butterfly->vectorLength()) {
-            m_butterfly->contiguousDouble()[length] = valueAsDouble;
-            m_butterfly->setPublicLength(length + 1);
+        unsigned length = butterfly->publicLength();
+        ASSERT(length <= butterfly->vectorLength());
+        if (length < butterfly->vectorLength()) {
+            butterfly->contiguousDouble()[length] = valueAsDouble;
+            butterfly->setPublicLength(length + 1);
             return;
         }
         
         if (length > MAX_ARRAY_INDEX) {
-            methodTable()->putByIndex(this, exec, length, value, true);
+            methodTable(exec->vm())->putByIndex(this, exec, length, value, true);
             if (!exec->hadException())
-                throwError(exec, createRangeError(exec, "Invalid array length"));
+                exec->vm().throwException(exec, createRangeError(exec, ASCIILiteral("Invalid array length")));
             return;
         }
         
@@ -644,11 +649,11 @@ void JSArray::push(ExecState* exec, JSValue value)
                 setLength(exec, oldLength + 1, true);
             return;
         }
-        // Fall through.
+        FALLTHROUGH;
     }
         
     case ArrayWithArrayStorage: {
-        ArrayStorage* storage = m_butterfly->arrayStorage();
+        ArrayStorage* storage = butterfly->arrayStorage();
 
         // Fast case - push within vector, always update m_length & m_numValuesInVector.
         unsigned length = storage->length();
@@ -661,10 +666,10 @@ void JSArray::push(ExecState* exec, JSValue value)
 
         // Pushing to an array of invalid length (2^31-1) stores the property, but throws a range error.
         if (storage->length() > MAX_ARRAY_INDEX) {
-            methodTable()->putByIndex(this, exec, storage->length(), value, true);
+            methodTable(exec->vm())->putByIndex(this, exec, storage->length(), value, true);
             // Per ES5.1 15.4.4.7 step 6 & 15.4.5.1 step 3.d.
             if (!exec->hadException())
-                throwError(exec, createRangeError(exec, "Invalid array length"));
+                exec->vm().throwException(exec, createRangeError(exec, ASCIILiteral("Invalid array length")));
             return;
         }
 
@@ -678,15 +683,80 @@ void JSArray::push(ExecState* exec, JSValue value)
     }
 }
 
-bool JSArray::shiftCountWithArrayStorage(unsigned startIndex, unsigned count, ArrayStorage* storage)
+JSArray* JSArray::fastSlice(ExecState& exec, unsigned startIndex, unsigned count)
+{
+    auto arrayType = indexingType();
+    switch (arrayType) {
+    case ArrayWithDouble:
+    case ArrayWithInt32:
+    case ArrayWithContiguous: {
+        VM& vm = exec.vm();
+        if (count >= MIN_SPARSE_ARRAY_INDEX || structure(vm)->holesMustForwardToPrototype(vm))
+            return nullptr;
+
+        Structure* resultStructure = exec.lexicalGlobalObject()->arrayStructureForIndexingTypeDuringAllocation(arrayType);
+        JSArray* resultArray = JSArray::tryCreateUninitialized(vm, resultStructure, count);
+        if (!resultArray)
+            return nullptr;
+
+        auto& resultButterfly = *resultArray->butterfly();
+        if (arrayType == ArrayWithDouble)
+            memcpy(resultButterfly.contiguousDouble().data(), m_butterfly.get(this)->contiguousDouble().data() + startIndex, sizeof(JSValue) * count);
+        else
+            memcpy(resultButterfly.contiguous().data(), m_butterfly.get(this)->contiguous().data() + startIndex, sizeof(JSValue) * count);
+        resultButterfly.setPublicLength(count);
+
+        return resultArray;
+    }
+    default:
+        return nullptr;
+    }
+}
+
+EncodedJSValue JSArray::fastConcatWith(ExecState& exec, JSArray& otherArray)
+{
+    auto newArrayType = indexingType();
+
+    VM& vm = exec.vm();
+    ASSERT(newArrayType == fastConcatType(vm, *this, otherArray));
+
+    unsigned thisArraySize = m_butterfly.get(this)->publicLength();
+    unsigned otherArraySize = otherArray.m_butterfly.get(this)->publicLength();
+    ASSERT(thisArraySize + otherArraySize < MIN_SPARSE_ARRAY_INDEX);
+
+    Structure* resultStructure = exec.lexicalGlobalObject()->arrayStructureForIndexingTypeDuringAllocation(newArrayType);
+    JSArray* resultArray = JSArray::tryCreateUninitialized(vm, resultStructure, thisArraySize + otherArraySize);
+    if (!resultArray)
+        return JSValue::encode(throwOutOfMemoryError(&exec));
+
+    auto& resultButterfly = *resultArray->butterfly();
+    auto& otherButterfly = *otherArray.butterfly();
+    if (newArrayType == ArrayWithDouble) {
+        auto buffer = resultButterfly.contiguousDouble().data();
+        memcpy(buffer, m_butterfly.get(this)->contiguousDouble().data(), sizeof(JSValue) * thisArraySize);
+        memcpy(buffer + thisArraySize, otherButterfly.contiguousDouble().data(), sizeof(JSValue) * otherArraySize);
+    } else {
+        auto buffer = resultButterfly.contiguous().data();
+        memcpy(buffer, m_butterfly.get(this)->contiguous().data(), sizeof(JSValue) * thisArraySize);
+        memcpy(buffer + thisArraySize, otherButterfly.contiguous().data(), sizeof(JSValue) * otherArraySize);
+    }
+
+    resultButterfly.setPublicLength(thisArraySize + otherArraySize);
+    return JSValue::encode(resultArray);
+}
+
+bool JSArray::shiftCountWithArrayStorage(VM& vm, unsigned startIndex, unsigned count, ArrayStorage* storage)
 {
     unsigned oldLength = storage->length();
     RELEASE_ASSERT(count <= oldLength);
     
     // If the array contains holes or is otherwise in an abnormal state,
     // use the generic algorithm in ArrayPrototype.
-    if (oldLength != storage->m_numValuesInVector || inSparseIndexingMode() || shouldUseSlowPut(structure()->indexingType()))
+    if ((storage->hasHoles() && this->structure(vm)->holesMustForwardToPrototype(vm)) 
+        || hasSparseMap() 
+        || shouldUseSlowPut(indexingType())) {
         return false;
+    }
 
     if (!oldLength)
         return true;
@@ -708,37 +778,86 @@ bool JSArray::shiftCountWithArrayStorage(unsigned startIndex, unsigned count, Ar
     
     unsigned usedVectorLength = min(vectorLength, oldLength);
     
-    vectorLength -= count;
-    storage->setVectorLength(vectorLength);
-    
-    if (vectorLength) {
-        if (startIndex < usedVectorLength - (startIndex + count)) {
-            if (startIndex) {
-                memmove(
-                    storage->m_vector + count,
+    unsigned numElementsBeforeShiftRegion = startIndex;
+    unsigned firstIndexAfterShiftRegion = startIndex + count;
+    unsigned numElementsAfterShiftRegion = usedVectorLength - firstIndexAfterShiftRegion;
+    ASSERT(numElementsBeforeShiftRegion + count + numElementsAfterShiftRegion == usedVectorLength);
+
+    // The point of this comparison seems to be to minimize the amount of elements that have to 
+    // be moved during a shift operation.
+    if (numElementsBeforeShiftRegion < numElementsAfterShiftRegion) {
+        // The number of elements before the shift region is less than the number of elements
+        // after the shift region, so we move the elements before to the right.
+        if (numElementsBeforeShiftRegion) {
+            RELEASE_ASSERT(count + startIndex <= vectorLength);
+            if (storage->hasHoles()) {
+                for (unsigned i = startIndex; i-- > 0;) {
+                    unsigned destinationIndex = count + i;
+                    JSValue source = storage->m_vector[i].get();
+                    JSValue dest = storage->m_vector[destinationIndex].get();
+                    // Any time we overwrite a hole we know we overcounted the number of values we removed 
+                    // when we subtracted count from m_numValuesInVector above.
+                    if (!dest && destinationIndex >= firstIndexAfterShiftRegion)
+                        storage->m_numValuesInVector++;
+                    storage->m_vector[count + i].setWithoutWriteBarrier(source);
+                }
+            } else {
+                memmove(storage->m_vector + count,
                     storage->m_vector,
                     sizeof(JSValue) * startIndex);
             }
-            m_butterfly = m_butterfly->shift(structure(), count);
-            storage = m_butterfly->arrayStorage();
-            storage->m_indexBias += count;
+        }
+        // Adjust the Butterfly and the index bias. We only need to do this here because we're changing
+        // the start of the Butterfly, which needs to point at the first indexed property in the used
+        // portion of the vector.
+        Butterfly* butterfly = m_butterfly.get(this)->shift(structure(), count);
+        m_butterfly.setWithoutBarrier(butterfly);
+        storage = butterfly->arrayStorage();
+        storage->m_indexBias += count;
+
+        // Since we're consuming part of the vector by moving its beginning to the left,
+        // we need to modify the vector length appropriately.
+        storage->setVectorLength(vectorLength - count);
+    } else {
+        // The number of elements before the shift region is greater than or equal to the number 
+        // of elements after the shift region, so we move the elements after the shift region to the left.
+        if (storage->hasHoles()) {
+            for (unsigned i = 0; i < numElementsAfterShiftRegion; ++i) {
+                unsigned destinationIndex = startIndex + i;
+                JSValue source = storage->m_vector[firstIndexAfterShiftRegion + i].get();
+                JSValue dest = storage->m_vector[destinationIndex].get();
+                // Any time we overwrite a hole we know we overcounted the number of values we removed 
+                // when we subtracted count from m_numValuesInVector above.
+                if (!dest && destinationIndex < firstIndexAfterShiftRegion)
+                    storage->m_numValuesInVector++;
+                storage->m_vector[startIndex + i].setWithoutWriteBarrier(source);
+            }
         } else {
-            memmove(
-                storage->m_vector + startIndex,
-                storage->m_vector + startIndex + count,
-                sizeof(JSValue) * (usedVectorLength - (startIndex + count)));
-            for (unsigned i = usedVectorLength - count; i < usedVectorLength; ++i)
-                storage->m_vector[i].clear();
+            memmove(storage->m_vector + startIndex,
+                storage->m_vector + firstIndexAfterShiftRegion,
+                sizeof(JSValue) * numElementsAfterShiftRegion);
         }
+        // Clear the slots of the elements we just moved.
+        unsigned startOfEmptyVectorTail = usedVectorLength - count;
+        for (unsigned i = startOfEmptyVectorTail; i < usedVectorLength; ++i)
+            storage->m_vector[i].clear();
+        // We don't modify the index bias or the Butterfly pointer in this case because we're not changing 
+        // the start of the Butterfly, which needs to point at the first indexed property in the used 
+        // portion of the vector. We also don't modify the vector length because we're not actually changing
+        // its length; we're just using less of it.
     }
+    
     return true;
 }
 
-bool JSArray::shiftCountWithAnyIndexingType(ExecState* exec, unsigned startIndex, unsigned count)
+bool JSArray::shiftCountWithAnyIndexingType(ExecState* exec, unsigned& startIndex, unsigned count)
 {
+    VM& vm = exec->vm();
     RELEASE_ASSERT(count > 0);
+
+    Butterfly* butterfly = m_butterfly.get(this);
     
-    switch (structure()->indexingType()) {
+    switch (indexingType()) {
     case ArrayClass:
         return true;
         
@@ -748,78 +867,79 @@ bool JSArray::shiftCountWithAnyIndexingType(ExecState* exec, unsigned startIndex
         
     case ArrayWithInt32:
     case ArrayWithContiguous: {
-        unsigned oldLength = m_butterfly->publicLength();
+        unsigned oldLength = butterfly->publicLength();
         RELEASE_ASSERT(count <= oldLength);
         
         // We may have to walk the entire array to do the shift. We're willing to do
         // so only if it's not horribly slow.
         if (oldLength - (startIndex + count) >= MIN_SPARSE_ARRAY_INDEX)
-            return shiftCountWithArrayStorage(startIndex, count, ensureArrayStorage(exec->vm()));
+            return shiftCountWithArrayStorage(vm, startIndex, count, ensureArrayStorage(vm));
 
-        // Storing to a hole is fine since we're still having a good time. But reading from a hole
+        // Storing to a hole is fine since we're still having a good time. But reading from a hole 
         // is totally not fine, since we might have to read from the proto chain.
-        // We have to check for holes before we start moving things around so that we don't get halfway
+        // We have to check for holes before we start moving things around so that we don't get halfway 
         // through shifting and then realize we should have been in ArrayStorage mode.
         unsigned end = oldLength - count;
-        for (unsigned i = startIndex; i < end; ++i) {
-            JSValue v = m_butterfly->contiguous()[i + count].get();
-            if (UNLIKELY(!v))
-                return shiftCountWithArrayStorage(startIndex, count, ensureArrayStorage(exec->vm()));
+        if (this->structure(vm)->holesMustForwardToPrototype(vm)) {
+            for (unsigned i = startIndex; i < end; ++i) {
+                JSValue v = butterfly->contiguous()[i + count].get();
+                if (UNLIKELY(!v)) {
+                    startIndex = i;
+                    return shiftCountWithArrayStorage(vm, startIndex, count, ensureArrayStorage(vm));
+                }
+                butterfly->contiguous()[i].setWithoutWriteBarrier(v);
+            }
+        } else {
+            memmove(butterfly->contiguous().data() + startIndex, 
+                butterfly->contiguous().data() + startIndex + count, 
+                sizeof(JSValue) * (end - startIndex));
         }
 
-        for (unsigned i = startIndex; i < end; ++i) {
-            JSValue v = m_butterfly->contiguous()[i + count].get();
-            ASSERT(v);
-            // No need for a barrier since we're just moving data around in the same vector.
-            // This is in line with our standing assumption that we won't have a deletion
-            // barrier.
-            m_butterfly->contiguous()[i].setWithoutWriteBarrier(v);
-        }
         for (unsigned i = end; i < oldLength; ++i)
-            m_butterfly->contiguous()[i].clear();
+            butterfly->contiguous()[i].clear();
         
-        m_butterfly->setPublicLength(oldLength - count);
+        butterfly->setPublicLength(oldLength - count);
         return true;
     }
         
     case ArrayWithDouble: {
-        unsigned oldLength = m_butterfly->publicLength();
+        unsigned oldLength = butterfly->publicLength();
         RELEASE_ASSERT(count <= oldLength);
         
         // We may have to walk the entire array to do the shift. We're willing to do
         // so only if it's not horribly slow.
         if (oldLength - (startIndex + count) >= MIN_SPARSE_ARRAY_INDEX)
-            return shiftCountWithArrayStorage(startIndex, count, ensureArrayStorage(exec->vm()));
+            return shiftCountWithArrayStorage(vm, startIndex, count, ensureArrayStorage(vm));
 
-        // Storing to a hole is fine since we're still having a good time. But reading from a hole
+        // Storing to a hole is fine since we're still having a good time. But reading from a hole 
         // is totally not fine, since we might have to read from the proto chain.
-        // We have to check for holes before we start moving things around so that we don't get halfway
+        // We have to check for holes before we start moving things around so that we don't get halfway 
         // through shifting and then realize we should have been in ArrayStorage mode.
         unsigned end = oldLength - count;
-        for (unsigned i = startIndex; i < end; ++i) {
-            double v = m_butterfly->contiguousDouble()[i + count];
-            if (UNLIKELY(v != v))
-                return shiftCountWithArrayStorage(startIndex, count, ensureArrayStorage(exec->vm()));
-        }
-
-        for (unsigned i = startIndex; i < end; ++i) {
-            double v = m_butterfly->contiguousDouble()[i + count];
-            ASSERT(v == v);
-            // No need for a barrier since we're just moving data around in the same vector.
-            // This is in line with our standing assumption that we won't have a deletion
-            // barrier.
-            m_butterfly->contiguousDouble()[i] = v;
+        if (this->structure(vm)->holesMustForwardToPrototype(vm)) {
+            for (unsigned i = startIndex; i < end; ++i) {
+                double v = butterfly->contiguousDouble()[i + count];
+                if (UNLIKELY(v != v)) {
+                    startIndex = i;
+                    return shiftCountWithArrayStorage(vm, startIndex, count, ensureArrayStorage(vm));
+                }
+                butterfly->contiguousDouble()[i] = v;
+            }
+        } else {
+            memmove(butterfly->contiguousDouble().data() + startIndex,
+                butterfly->contiguousDouble().data() + startIndex + count,
+                sizeof(JSValue) * (end - startIndex));
         }
         for (unsigned i = end; i < oldLength; ++i)
-            m_butterfly->contiguousDouble()[i] = QNaN;
+            butterfly->contiguousDouble()[i] = PNaN;
         
-        m_butterfly->setPublicLength(oldLength - count);
+        butterfly->setPublicLength(oldLength - count);
         return true;
     }
         
     case ArrayWithArrayStorage:
     case ArrayWithSlowPutArrayStorage:
-        return shiftCountWithArrayStorage(startIndex, count, arrayStorage());
+        return shiftCountWithArrayStorage(vm, startIndex, count, arrayStorage());
         
     default:
         CRASH();
@@ -836,7 +956,7 @@ bool JSArray::unshiftCountWithArrayStorage(ExecState* exec, unsigned startIndex,
 
     // If the array contains holes or is otherwise in an abnormal state,
     // use the generic algorithm in ArrayPrototype.
-    if (length != storage->m_numValuesInVector || storage->inSparseMode() || shouldUseSlowPut(structure()->indexingType()))
+    if (storage->hasHoles() || storage->inSparseMode() || shouldUseSlowPut(indexingType()))
         return false;
 
     bool moveFront = !startIndex || startIndex < length / 2;
@@ -844,10 +964,11 @@ bool JSArray::unshiftCountWithArrayStorage(ExecState* exec, unsigned startIndex,
     unsigned vectorLength = storage->vectorLength();
 
     if (moveFront && storage->m_indexBias >= count) {
-        m_butterfly = storage->butterfly()->unshift(structure(), count);
-        storage = m_butterfly->arrayStorage();
+        Butterfly* newButterfly = storage->butterfly()->unshift(structure(), count);
+        storage = newButterfly->arrayStorage();
         storage->m_indexBias -= count;
         storage->setVectorLength(vectorLength + count);
+        setButterflyWithoutChangingStructure(exec->vm(), newButterfly);
     } else if (!moveFront && vectorLength - length >= count)
         storage = storage->butterfly()->arrayStorage();
     else if (unshiftCountSlowCase(exec->vm(), moveFront, count))
@@ -873,7 +994,9 @@ bool JSArray::unshiftCountWithArrayStorage(ExecState* exec, unsigned startIndex,
 
 bool JSArray::unshiftCountWithAnyIndexingType(ExecState* exec, unsigned startIndex, unsigned count)
 {
-    switch (structure()->indexingType()) {
+    Butterfly* butterfly = m_butterfly.get(this);
+    
+    switch (indexingType()) {
     case ArrayClass:
     case ArrayWithUndecided:
         // We could handle this. But it shouldn't ever come up, so we won't.
@@ -881,7 +1004,7 @@ bool JSArray::unshiftCountWithAnyIndexingType(ExecState* exec, unsigned startInd
 
     case ArrayWithInt32:
     case ArrayWithContiguous: {
-        unsigned oldLength = m_butterfly->publicLength();
+        unsigned oldLength = butterfly->publicLength();
         
         // We may have to walk the entire array to do the unshift. We're willing to do so
         // only if it's not horribly slow.
@@ -889,19 +1012,20 @@ bool JSArray::unshiftCountWithAnyIndexingType(ExecState* exec, unsigned startInd
             return unshiftCountWithArrayStorage(exec, startIndex, count, ensureArrayStorage(exec->vm()));
         
         ensureLength(exec->vm(), oldLength + count);
+        butterfly = m_butterfly.get(this);
 
-        // We have to check for holes before we start moving things around so that we don't get halfway
+        // We have to check for holes before we start moving things around so that we don't get halfway 
         // through shifting and then realize we should have been in ArrayStorage mode.
         for (unsigned i = oldLength; i-- > startIndex;) {
-            JSValue v = m_butterfly->contiguous()[i].get();
+            JSValue v = butterfly->contiguous()[i].get();
             if (UNLIKELY(!v))
                 return unshiftCountWithArrayStorage(exec, startIndex, count, ensureArrayStorage(exec->vm()));
         }
 
         for (unsigned i = oldLength; i-- > startIndex;) {
-            JSValue v = m_butterfly->contiguous()[i].get();
+            JSValue v = butterfly->contiguous()[i].get();
             ASSERT(v);
-            m_butterfly->contiguous()[i + count].setWithoutWriteBarrier(v);
+            butterfly->contiguous()[i + count].setWithoutWriteBarrier(v);
         }
         
         // NOTE: we're leaving being garbage in the part of the array that we shifted out
@@ -913,7 +1037,7 @@ bool JSArray::unshiftCountWithAnyIndexingType(ExecState* exec, unsigned startInd
     }
         
     case ArrayWithDouble: {
-        unsigned oldLength = m_butterfly->publicLength();
+        unsigned oldLength = butterfly->publicLength();
         
         // We may have to walk the entire array to do the unshift. We're willing to do so
         // only if it's not horribly slow.
@@ -921,19 +1045,20 @@ bool JSArray::unshiftCountWithAnyIndexingType(ExecState* exec, unsigned startInd
             return unshiftCountWithArrayStorage(exec, startIndex, count, ensureArrayStorage(exec->vm()));
         
         ensureLength(exec->vm(), oldLength + count);
+        butterfly = m_butterfly.get(this);
         
-        // We have to check for holes before we start moving things around so that we don't get halfway
+        // We have to check for holes before we start moving things around so that we don't get halfway 
         // through shifting and then realize we should have been in ArrayStorage mode.
         for (unsigned i = oldLength; i-- > startIndex;) {
-            double v = m_butterfly->contiguousDouble()[i];
+            double v = butterfly->contiguousDouble()[i];
             if (UNLIKELY(v != v))
                 return unshiftCountWithArrayStorage(exec, startIndex, count, ensureArrayStorage(exec->vm()));
         }
 
         for (unsigned i = oldLength; i-- > startIndex;) {
-            double v = m_butterfly->contiguousDouble()[i];
+            double v = butterfly->contiguousDouble()[i];
             ASSERT(v == v);
-            m_butterfly->contiguousDouble()[i + count] = v;
+            butterfly->contiguousDouble()[i + count] = v;
         }
         
         // NOTE: we're leaving being garbage in the part of the array that we shifted out
@@ -954,526 +1079,15 @@ bool JSArray::unshiftCountWithAnyIndexingType(ExecState* exec, unsigned startInd
     }
 }
 
-static int compareNumbersForQSortWithInt32(const void* a, const void* b)
-{
-    int32_t ia = static_cast<const JSValue*>(a)->asInt32();
-    int32_t ib = static_cast<const JSValue*>(b)->asInt32();
-    return ia - ib;
-}
-
-static int compareNumbersForQSortWithDouble(const void* a, const void* b)
-{
-    double da = *static_cast<const double*>(a);
-    double db = *static_cast<const double*>(b);
-    return (da > db) - (da < db);
-}
-
-static int compareNumbersForQSort(const void* a, const void* b)
-{
-    double da = static_cast<const JSValue*>(a)->asNumber();
-    double db = static_cast<const JSValue*>(b)->asNumber();
-    return (da > db) - (da < db);
-}
-
-static int compareByStringPairForQSort(const void* a, const void* b)
-{
-    const ValueStringPair* va = static_cast<const ValueStringPair*>(a);
-    const ValueStringPair* vb = static_cast<const ValueStringPair*>(b);
-    return codePointCompare(va->second, vb->second);
-}
-
-template<IndexingType indexingType>
-void JSArray::sortNumericVector(ExecState* exec, JSValue compareFunction, CallType callType, const CallData& callData)
-{
-    ASSERT(indexingType == ArrayWithInt32 || indexingType == ArrayWithDouble || indexingType == ArrayWithContiguous || indexingType == ArrayWithArrayStorage);
-    
-    unsigned lengthNotIncludingUndefined;
-    unsigned newRelevantLength;
-    compactForSorting<indexingType>(
-        lengthNotIncludingUndefined,
-        newRelevantLength);
-    
-    ContiguousJSValues data = indexingData<indexingType>();
-    
-    if (indexingType == ArrayWithArrayStorage && arrayStorage()->m_sparseMap.get()) {
-        throwOutOfMemoryError(exec);
-        return;
-    }
-    
-    if (!lengthNotIncludingUndefined)
-        return;
-    
-    bool allValuesAreNumbers = true;
-    switch (indexingType) {
-    case ArrayWithInt32:
-    case ArrayWithDouble:
-        break;
-        
-    default:
-        for (size_t i = 0; i < newRelevantLength; ++i) {
-            if (!data[i].isNumber()) {
-                allValuesAreNumbers = false;
-                break;
-            }
-        }
-        break;
-    }
-    
-    if (!allValuesAreNumbers)
-        return sort(exec, compareFunction, callType, callData);
-    
-    // For numeric comparison, which is fast, qsort is faster than mergesort. We
-    // also don't require mergesort's stability, since there's no user visible
-    // side-effect from swapping the order of equal primitive values.
-    int (*compare)(const void*, const void*);
-    switch (indexingType) {
-    case ArrayWithInt32:
-        compare = compareNumbersForQSortWithInt32;
-        break;
-        
-    case ArrayWithDouble:
-        compare = compareNumbersForQSortWithDouble;
-        ASSERT(sizeof(WriteBarrier<Unknown>) == sizeof(double));
-        break;
-        
-    default:
-        compare = compareNumbersForQSort;
-        break;
-    }
-    ASSERT(data.length() >= newRelevantLength);
-    qsort(data.data(), newRelevantLength, sizeof(WriteBarrier<Unknown>), compare);
-    return;
-}
-
-void JSArray::sortNumeric(ExecState* exec, JSValue compareFunction, CallType callType, const CallData& callData)
-{
-    ASSERT(!inSparseIndexingMode());
-
-    switch (structure()->indexingType()) {
-    case ArrayClass:
-        return;
-        
-    case ArrayWithInt32:
-        sortNumericVector<ArrayWithInt32>(exec, compareFunction, callType, callData);
-        break;
-        
-    case ArrayWithDouble:
-        sortNumericVector<ArrayWithDouble>(exec, compareFunction, callType, callData);
-        break;
-        
-    case ArrayWithContiguous:
-        sortNumericVector<ArrayWithContiguous>(exec, compareFunction, callType, callData);
-        return;
-
-    case ArrayWithArrayStorage:
-        sortNumericVector<ArrayWithArrayStorage>(exec, compareFunction, callType, callData);
-        return;
-        
-    default:
-        CRASH();
-        return;
-    }
-}
-
-template <IndexingType> struct ContiguousTypeAccessor {
-    typedef WriteBarrier<Unknown> Type;
-    static JSValue getAsValue(ContiguousData<Type> data, size_t i) { return data[i].get(); }
-    static void setWithValue(VM& vm, JSArray* thisValue, ContiguousData<Type> data, size_t i, JSValue value)
-    {
-        data[i].set(vm, thisValue, value);
-    }
-    static void replaceDataReference(ContiguousData<Type>* outData, ContiguousJSValues inData)
-    {
-        *outData = inData;
-    }
-};
-
-template <> struct ContiguousTypeAccessor<ArrayWithDouble> {
-    typedef double Type;
-    static JSValue getAsValue(ContiguousData<Type> data, size_t i) { ASSERT(data[i] == data[i]); return JSValue(JSValue::EncodeAsDouble, data[i]); }
-    static void setWithValue(VM&, JSArray*, ContiguousData<Type> data, size_t i, JSValue value)
-    {
-        data[i] = value.asNumber();
-    }
-    static NO_RETURN_DUE_TO_CRASH void replaceDataReference(ContiguousData<Type>*, ContiguousJSValues)
-    {
-        RELEASE_ASSERT_WITH_MESSAGE(0, "Inconsistent indexing types during compact array sort.");
-    }
-};
-
-
-template<IndexingType indexingType, typename StorageType>
-void JSArray::sortCompactedVector(ExecState* exec, ContiguousData<StorageType> data, unsigned relevantLength)
-{
-    if (!relevantLength)
-        return;
-    
-    VM& vm = exec->vm();
-
-    // Converting JavaScript values to strings can be expensive, so we do it once up front and sort based on that.
-    // This is a considerable improvement over doing it twice per comparison, though it requires a large temporary
-    // buffer. Besides, this protects us from crashing if some objects have custom toString methods that return
-    // random or otherwise changing results, effectively making compare function inconsistent.
-        
-    Vector<ValueStringPair, 0, UnsafeVectorOverflow> values(relevantLength);
-    if (!values.begin()) {
-        throwOutOfMemoryError(exec);
-        return;
-    }
-        
-    Heap::heap(this)->pushTempSortVector(&values);
-        
-    bool isSortingPrimitiveValues = true;
-
-    for (size_t i = 0; i < relevantLength; i++) {
-        JSValue value = ContiguousTypeAccessor<indexingType>::getAsValue(data, i);
-        ASSERT(indexingType != ArrayWithInt32 || value.isInt32());
-        ASSERT(!value.isUndefined());
-        values[i].first = value;
-        if (indexingType != ArrayWithDouble && indexingType != ArrayWithInt32)
-            isSortingPrimitiveValues = isSortingPrimitiveValues && value.isPrimitive();
-    }
-        
-    // FIXME: The following loop continues to call toString on subsequent values even after
-    // a toString call raises an exception.
-        
-    for (size_t i = 0; i < relevantLength; i++)
-        values[i].second = values[i].first.toWTFStringInline(exec);
-        
-    if (exec->hadException()) {
-        Heap::heap(this)->popTempSortVector(&values);
-        return;
-    }
-        
-    // FIXME: Since we sort by string value, a fast algorithm might be to use a radix sort. That would be O(N) rather
-    // than O(N log N).
-        
-#if HAVE(MERGESORT)
-    if (isSortingPrimitiveValues)
-        qsort(values.begin(), values.size(), sizeof(ValueStringPair), compareByStringPairForQSort);
-    else
-        mergesort(values.begin(), values.size(), sizeof(ValueStringPair), compareByStringPairForQSort);
-#else
-    // FIXME: The qsort library function is likely to not be a stable sort.
-    // ECMAScript-262 does not specify a stable sort, but in practice, browsers perform a stable sort.
-    qsort(values.begin(), values.size(), sizeof(ValueStringPair), compareByStringPairForQSort);
-#endif
-    
-    // If the toString function changed the length of the array or vector storage,
-    // increase the length to handle the orignal number of actual values.
-    switch (indexingType) {
-    case ArrayWithInt32:
-    case ArrayWithDouble:
-    case ArrayWithContiguous:
-        ensureLength(vm, relevantLength);
-        break;
-        
-    case ArrayWithArrayStorage:
-        if (arrayStorage()->vectorLength() < relevantLength) {
-            increaseVectorLength(exec->vm(), relevantLength);
-            ContiguousTypeAccessor<indexingType>::replaceDataReference(&data, arrayStorage()->vector());
-        }
-        if (arrayStorage()->length() < relevantLength)
-            arrayStorage()->setLength(relevantLength);
-        break;
-        
-    default:
-        CRASH();
-    }
-
-    for (size_t i = 0; i < relevantLength; i++)
-        ContiguousTypeAccessor<indexingType>::setWithValue(vm, this, data, i, values[i].first);
-    
-    Heap::heap(this)->popTempSortVector(&values);
-}
-
-void JSArray::sort(ExecState* exec)
-{
-    ASSERT(!inSparseIndexingMode());
-    
-    switch (structure()->indexingType()) {
-    case ArrayClass:
-    case ArrayWithUndecided:
-        return;
-        
-    case ArrayWithInt32: {
-        unsigned lengthNotIncludingUndefined;
-        unsigned newRelevantLength;
-        compactForSorting<ArrayWithInt32>(
-            lengthNotIncludingUndefined, newRelevantLength);
-        
-        sortCompactedVector<ArrayWithInt32>(
-            exec, m_butterfly->contiguousInt32(), lengthNotIncludingUndefined);
-        return;
-    }
-        
-    case ArrayWithDouble: {
-        unsigned lengthNotIncludingUndefined;
-        unsigned newRelevantLength;
-        compactForSorting<ArrayWithDouble>(
-            lengthNotIncludingUndefined, newRelevantLength);
-        
-        sortCompactedVector<ArrayWithDouble>(
-            exec, m_butterfly->contiguousDouble(), lengthNotIncludingUndefined);
-        return;
-    }
-        
-    case ArrayWithContiguous: {
-        unsigned lengthNotIncludingUndefined;
-        unsigned newRelevantLength;
-        compactForSorting<ArrayWithContiguous>(
-            lengthNotIncludingUndefined, newRelevantLength);
-        
-        sortCompactedVector<ArrayWithContiguous>(
-            exec, m_butterfly->contiguous(), lengthNotIncludingUndefined);
-        return;
-    }
-        
-    case ArrayWithArrayStorage: {
-        unsigned lengthNotIncludingUndefined;
-        unsigned newRelevantLength;
-        compactForSorting<ArrayWithArrayStorage>(
-            lengthNotIncludingUndefined, newRelevantLength);
-        ArrayStorage* storage = m_butterfly->arrayStorage();
-        ASSERT(!storage->m_sparseMap);
-        
-        sortCompactedVector<ArrayWithArrayStorage>(exec, storage->vector(), lengthNotIncludingUndefined);
-        return;
-    }
-        
-    default:
-        RELEASE_ASSERT_NOT_REACHED();
-    }
-}
-
-struct AVLTreeNodeForArrayCompare {
-    JSValue value;
-
-    // Child pointers.  The high bit of gt is robbed and used as the
-    // balance factor sign.  The high bit of lt is robbed and used as
-    // the magnitude of the balance factor.
-    int32_t gt;
-    int32_t lt;
-};
-
-struct AVLTreeAbstractorForArrayCompare {
-    typedef int32_t handle; // Handle is an index into m_nodes vector.
-    typedef JSValue key;
-    typedef int32_t size;
-
-    Vector<AVLTreeNodeForArrayCompare, 0, UnsafeVectorOverflow> m_nodes;
-    ExecState* m_exec;
-    JSValue m_compareFunction;
-    CallType m_compareCallType;
-    const CallData* m_compareCallData;
-    OwnPtr<CachedCall> m_cachedCall;
-
-    handle get_less(handle h) { return m_nodes[h].lt & 0x7FFFFFFF; }
-    void set_less(handle h, handle lh) { m_nodes[h].lt &= 0x80000000; m_nodes[h].lt |= lh; }
-    handle get_greater(handle h) { return m_nodes[h].gt & 0x7FFFFFFF; }
-    void set_greater(handle h, handle gh) { m_nodes[h].gt &= 0x80000000; m_nodes[h].gt |= gh; }
-
-    int get_balance_factor(handle h)
-    {
-        if (m_nodes[h].gt & 0x80000000)
-            return -1;
-        return static_cast<unsigned>(m_nodes[h].lt) >> 31;
-    }
-
-    void set_balance_factor(handle h, int bf)
-    {
-        if (bf == 0) {
-            m_nodes[h].lt &= 0x7FFFFFFF;
-            m_nodes[h].gt &= 0x7FFFFFFF;
-        } else {
-            m_nodes[h].lt |= 0x80000000;
-            if (bf < 0)
-                m_nodes[h].gt |= 0x80000000;
-            else
-                m_nodes[h].gt &= 0x7FFFFFFF;
-        }
-    }
-
-    int compare_key_key(key va, key vb)
-    {
-        ASSERT(!va.isUndefined());
-        ASSERT(!vb.isUndefined());
-
-        if (m_exec->hadException())
-            return 1;
-
-        double compareResult;
-        if (m_cachedCall) {
-            m_cachedCall->setThis(jsUndefined());
-            m_cachedCall->setArgument(0, va);
-            m_cachedCall->setArgument(1, vb);
-            compareResult = m_cachedCall->call().toNumber(m_cachedCall->newCallFrame(m_exec));
-        } else {
-            MarkedArgumentBuffer arguments;
-            arguments.append(va);
-            arguments.append(vb);
-            compareResult = call(m_exec, m_compareFunction, m_compareCallType, *m_compareCallData, jsUndefined(), arguments).toNumber(m_exec);
-        }
-        return (compareResult < 0) ? -1 : 1; // Not passing equality through, because we need to store all values, even if equivalent.
-    }
-
-    int compare_key_node(key k, handle h) { return compare_key_key(k, m_nodes[h].value); }
-    int compare_node_node(handle h1, handle h2) { return compare_key_key(m_nodes[h1].value, m_nodes[h2].value); }
-
-    static handle null() { return 0x7FFFFFFF; }
-};
-
-template<IndexingType indexingType>
-void JSArray::sortVector(ExecState* exec, JSValue compareFunction, CallType callType, const CallData& callData)
-{
-    ASSERT(!inSparseIndexingMode());
-    ASSERT(indexingType == structure()->indexingType());
-    
-    // FIXME: This ignores exceptions raised in the compare function or in toNumber.
-        
-    // The maximum tree depth is compiled in - but the caller is clearly up to no good
-    // if a larger array is passed.
-    ASSERT(m_butterfly->publicLength() <= static_cast<unsigned>(std::numeric_limits<int>::max()));
-    if (m_butterfly->publicLength() > static_cast<unsigned>(std::numeric_limits<int>::max()))
-        return;
-        
-    unsigned usedVectorLength = relevantLength<indexingType>();
-    unsigned nodeCount = usedVectorLength;
-        
-    if (!nodeCount)
-        return;
-        
-    AVLTree<AVLTreeAbstractorForArrayCompare, 44> tree; // Depth 44 is enough for 2^31 items
-    tree.abstractor().m_exec = exec;
-    tree.abstractor().m_compareFunction = compareFunction;
-    tree.abstractor().m_compareCallType = callType;
-    tree.abstractor().m_compareCallData = &callData;
-    tree.abstractor().m_nodes.grow(nodeCount);
-        
-    if (callType == CallTypeJS)
-        tree.abstractor().m_cachedCall = adoptPtr(new CachedCall(exec, jsCast<JSFunction*>(compareFunction), 2));
-        
-    if (!tree.abstractor().m_nodes.begin()) {
-        throwOutOfMemoryError(exec);
-        return;
-    }
-        
-    // FIXME: If the compare function modifies the array, the vector, map, etc. could be modified
-    // right out from under us while we're building the tree here.
-        
-    unsigned numDefined = 0;
-    unsigned numUndefined = 0;
-    
-    // Iterate over the array, ignoring missing values, counting undefined ones, and inserting all other ones into the tree.
-    for (; numDefined < usedVectorLength; ++numDefined) {
-        if (numDefined >= m_butterfly->vectorLength())
-            break;
-        JSValue v = getHolyIndexQuickly(numDefined);
-        if (!v || v.isUndefined())
-            break;
-        tree.abstractor().m_nodes[numDefined].value = v;
-        tree.insert(numDefined);
-    }
-    for (unsigned i = numDefined; i < usedVectorLength; ++i) {
-        if (i >= m_butterfly->vectorLength())
-            break;
-        JSValue v = getHolyIndexQuickly(i);
-        if (v) {
-            if (v.isUndefined())
-                ++numUndefined;
-            else {
-                tree.abstractor().m_nodes[numDefined].value = v;
-                tree.insert(numDefined);
-                ++numDefined;
-            }
-        }
-    }
-    
-    unsigned newUsedVectorLength = numDefined + numUndefined;
-        
-    // The array size may have changed. Figure out the new bounds.
-    unsigned newestUsedVectorLength = currentRelevantLength();
-        
-    unsigned elementsToExtractThreshold = min(min(newestUsedVectorLength, numDefined), static_cast<unsigned>(tree.abstractor().m_nodes.size()));
-    unsigned undefinedElementsThreshold = min(newestUsedVectorLength, newUsedVectorLength);
-    unsigned clearElementsThreshold = min(newestUsedVectorLength, usedVectorLength);
-        
-    // Copy the values back into m_storage.
-    AVLTree<AVLTreeAbstractorForArrayCompare, 44>::Iterator iter;
-    iter.start_iter_least(tree);
-    VM& vm = exec->vm();
-    for (unsigned i = 0; i < elementsToExtractThreshold; ++i) {
-        ASSERT(i < butterfly()->vectorLength());
-        if (structure()->indexingType() == ArrayWithDouble)
-            butterfly()->contiguousDouble()[i] = tree.abstractor().m_nodes[*iter].value.asNumber();
-        else
-            currentIndexingData()[i].set(vm, this, tree.abstractor().m_nodes[*iter].value);
-        ++iter;
-    }
-    // Put undefined values back in.
-    switch (structure()->indexingType()) {
-    case ArrayWithInt32:
-    case ArrayWithDouble:
-        ASSERT(elementsToExtractThreshold == undefinedElementsThreshold);
-        break;
-        
-    default:
-        for (unsigned i = elementsToExtractThreshold; i < undefinedElementsThreshold; ++i) {
-            ASSERT(i < butterfly()->vectorLength());
-            currentIndexingData()[i].setUndefined();
-        }
-    }
-
-    // Ensure that unused values in the vector are zeroed out.
-    for (unsigned i = undefinedElementsThreshold; i < clearElementsThreshold; ++i) {
-        ASSERT(i < butterfly()->vectorLength());
-        if (structure()->indexingType() == ArrayWithDouble)
-            butterfly()->contiguousDouble()[i] = QNaN;
-        else
-            currentIndexingData()[i].clear();
-    }
-    
-    if (hasArrayStorage(structure()->indexingType()))
-        arrayStorage()->m_numValuesInVector = newUsedVectorLength;
-}
-
-void JSArray::sort(ExecState* exec, JSValue compareFunction, CallType callType, const CallData& callData)
-{
-    ASSERT(!inSparseIndexingMode());
-    
-    switch (structure()->indexingType()) {
-    case ArrayClass:
-    case ArrayWithUndecided:
-        return;
-        
-    case ArrayWithInt32:
-        sortVector<ArrayWithInt32>(exec, compareFunction, callType, callData);
-        return;
-
-    case ArrayWithDouble:
-        sortVector<ArrayWithDouble>(exec, compareFunction, callType, callData);
-        return;
-
-    case ArrayWithContiguous:
-        sortVector<ArrayWithContiguous>(exec, compareFunction, callType, callData);
-        return;
-
-    case ArrayWithArrayStorage:
-        sortVector<ArrayWithArrayStorage>(exec, compareFunction, callType, callData);
-        return;
-        
-    default:
-        RELEASE_ASSERT_NOT_REACHED();
-    }
-}
-
 void JSArray::fillArgList(ExecState* exec, MarkedArgumentBuffer& args)
 {
     unsigned i = 0;
     unsigned vectorEnd;
     WriteBarrier<Unknown>* vector;
+
+    Butterfly* butterfly = m_butterfly.get(this);
     
-    switch (structure()->indexingType()) {
+    switch (indexingType()) {
     case ArrayClass:
         return;
         
@@ -1485,16 +1099,16 @@ void JSArray::fillArgList(ExecState* exec, MarkedArgumentBuffer& args)
         
     case ArrayWithInt32:
     case ArrayWithContiguous: {
-        vectorEnd = m_butterfly->publicLength();
-        vector = m_butterfly->contiguous().data();
+        vectorEnd = butterfly->publicLength();
+        vector = butterfly->contiguous().data();
         break;
     }
         
     case ArrayWithDouble: {
         vector = 0;
         vectorEnd = 0;
-        for (; i < m_butterfly->publicLength(); ++i) {
-            double v = butterfly()->contiguousDouble()[i];
+        for (; i < butterfly->publicLength(); ++i) {
+            double v = butterfly->contiguousDouble()[i];
             if (v != v)
                 break;
             args.append(JSValue(JSValue::EncodeAsDouble, v));
@@ -1503,7 +1117,7 @@ void JSArray::fillArgList(ExecState* exec, MarkedArgumentBuffer& args)
     }
     
     case ARRAY_WITH_ARRAY_STORAGE_INDEXING_TYPES: {
-        ArrayStorage* storage = m_butterfly->arrayStorage();
+        ArrayStorage* storage = butterfly->arrayStorage();
         
         vector = storage->m_vector;
         vectorEnd = min(storage->length(), storage->vectorLength());
@@ -1512,9 +1126,11 @@ void JSArray::fillArgList(ExecState* exec, MarkedArgumentBuffer& args)
         
     default:
         CRASH();
+#if COMPILER_QUIRK(CONSIDERS_UNREACHABLE_CODE)
         vector = 0;
         vectorEnd = 0;
         break;
+#endif
     }
     
     for (; i < vectorEnd; ++i) {
@@ -1523,19 +1139,25 @@ void JSArray::fillArgList(ExecState* exec, MarkedArgumentBuffer& args)
             break;
         args.append(v.get());
     }
-    
+
+    // FIXME: What prevents this from being called with a RuntimeArray? The length function will always return 0 in that case.
     for (; i < length(); ++i)
         args.append(get(exec, i));
 }
 
-void JSArray::copyToArguments(ExecState* exec, CallFrame* callFrame, uint32_t length)
+void JSArray::copyToArguments(ExecState* exec, VirtualRegister firstElementDest, unsigned offset, unsigned length)
 {
-    unsigned i = 0;
+    unsigned i = offset;
     WriteBarrier<Unknown>* vector;
     unsigned vectorEnd;
-    
+    length += offset; // We like to think of the length as being our length, rather than the output length.
+
+    // FIXME: What prevents this from being called with a RuntimeArray? The length function will always return 0 in that case.
     ASSERT(length == this->length());
-    switch (structure()->indexingType()) {
+
+    Butterfly* butterfly = m_butterfly.get(this);
+    
+    switch (indexingType()) {
     case ArrayClass:
         return;
         
@@ -1547,26 +1169,26 @@ void JSArray::copyToArguments(ExecState* exec, CallFrame* callFrame, uint32_t le
         
     case ArrayWithInt32:
     case ArrayWithContiguous: {
-        vector = m_butterfly->contiguous().data();
-        vectorEnd = m_butterfly->publicLength();
+        vector = butterfly->contiguous().data();
+        vectorEnd = butterfly->publicLength();
         break;
     }
         
     case ArrayWithDouble: {
         vector = 0;
         vectorEnd = 0;
-        for (; i < m_butterfly->publicLength(); ++i) {
-            ASSERT(i < butterfly()->vectorLength());
-            double v = m_butterfly->contiguousDouble()[i];
+        for (; i < butterfly->publicLength(); ++i) {
+            ASSERT(i < butterfly->vectorLength());
+            double v = butterfly->contiguousDouble()[i];
             if (v != v)
                 break;
-            callFrame->setArgument(i, JSValue(JSValue::EncodeAsDouble, v));
+            exec->r(firstElementDest + i - offset) = JSValue(JSValue::EncodeAsDouble, v);
         }
         break;
     }
         
     case ARRAY_WITH_ARRAY_STORAGE_INDEXING_TYPES: {
-        ArrayStorage* storage = m_butterfly->arrayStorage();
+        ArrayStorage* storage = butterfly->arrayStorage();
         vector = storage->m_vector;
         vectorEnd = min(length, storage->vectorLength());
         break;
@@ -1574,111 +1196,25 @@ void JSArray::copyToArguments(ExecState* exec, CallFrame* callFrame, uint32_t le
         
     default:
         CRASH();
+#if COMPILER_QUIRK(CONSIDERS_UNREACHABLE_CODE)
         vector = 0;
         vectorEnd = 0;
         break;
+#endif
     }
     
     for (; i < vectorEnd; ++i) {
         WriteBarrier<Unknown>& v = vector[i];
         if (!v)
             break;
-        callFrame->setArgument(i, v.get());
-    }
-    
-    for (; i < length; ++i)
-        callFrame->setArgument(i, get(exec, i));
-}
-
-template<IndexingType indexingType>
-void JSArray::compactForSorting(unsigned& numDefined, unsigned& newRelevantLength)
-{
-    ASSERT(!inSparseIndexingMode());
-    ASSERT(indexingType == structure()->indexingType());
-
-    unsigned myRelevantLength = relevantLength<indexingType>();
-    
-    numDefined = 0;
-    unsigned numUndefined = 0;
-        
-    for (; numDefined < myRelevantLength; ++numDefined) {
-        ASSERT(numDefined < m_butterfly->vectorLength());
-        if (indexingType == ArrayWithInt32) {
-            JSValue v = m_butterfly->contiguousInt32()[numDefined].get();
-            if (!v)
-                break;
-            ASSERT(v.isInt32());
-            continue;
-        }
-        if (indexingType == ArrayWithDouble) {
-            double v = m_butterfly->contiguousDouble()[numDefined];
-            if (v != v)
-                break;
-            continue;
-        }
-        JSValue v = indexingData<indexingType>()[numDefined].get();
-        if (!v || v.isUndefined())
-            break;
+        exec->r(firstElementDest + i - offset) = v.get();
     }
-        
-    for (unsigned i = numDefined; i < myRelevantLength; ++i) {
-        ASSERT(i < m_butterfly->vectorLength());
-        if (indexingType == ArrayWithInt32) {
-            JSValue v = m_butterfly->contiguousInt32()[i].get();
-            if (!v)
-                continue;
-            ASSERT(v.isInt32());
-            ASSERT(numDefined < m_butterfly->vectorLength());
-            m_butterfly->contiguousInt32()[numDefined++].setWithoutWriteBarrier(v);
-            continue;
-        }
-        if (indexingType == ArrayWithDouble) {
-            double v = m_butterfly->contiguousDouble()[i];
-            if (v != v)
-                continue;
-            ASSERT(numDefined < m_butterfly->vectorLength());
-            m_butterfly->contiguousDouble()[numDefined++] = v;
-            continue;
-        }
-        JSValue v = indexingData<indexingType>()[i].get();
-        if (v) {
-            if (v.isUndefined())
-                ++numUndefined;
-            else {
-                ASSERT(numDefined < m_butterfly->vectorLength());
-                indexingData<indexingType>()[numDefined++].setWithoutWriteBarrier(v);
-            }
-        }
-    }
-        
-    newRelevantLength = numDefined + numUndefined;
     
-    if (hasArrayStorage(indexingType))
-        RELEASE_ASSERT(!arrayStorage()->m_sparseMap);
-    
-    switch (indexingType) {
-    case ArrayWithInt32:
-    case ArrayWithDouble:
-        RELEASE_ASSERT(numDefined == newRelevantLength);
-        break;
-        
-    default:
-        for (unsigned i = numDefined; i < newRelevantLength; ++i) {
-            ASSERT(i < m_butterfly->vectorLength());
-            indexingData<indexingType>()[i].setUndefined();
-        }
-        break;
-    }
-    for (unsigned i = newRelevantLength; i < myRelevantLength; ++i) {
-        ASSERT(i < m_butterfly->vectorLength());
-        if (indexingType == ArrayWithDouble)
-            m_butterfly->contiguousDouble()[i] = QNaN;
-        else
-            indexingData<indexingType>()[i].clear();
+    for (; i < length; ++i) {
+        exec->r(firstElementDest + i - offset) = get(exec, i);
+        if (UNLIKELY(exec->vm().exception()))
+            return;
     }
-
-    if (hasArrayStorage(indexingType))
-        arrayStorage()->m_numValuesInVector = newRelevantLength;
 }
 
 } // namespace JSC