[SCM] WebKit Debian packaging branch, webkit-1.2, updated. upstream/1.1.90-6072-g9a69373

barraclough at apple.com barraclough at apple.com
Thu Apr 8 00:16:51 UTC 2010


The following commit has been merged in the webkit-1.2 branch:
commit 35d680c79e86fb949001ea0379493b7f2473da66
Author: barraclough at apple.com <barraclough at apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc>
Date:   Fri Dec 4 02:15:18 2009 +0000

    https://bugs.webkit.org/show_bug.cgi?id=32136
    Add a rope representation to JSString.  Presently JSString always holds its data in UString form.
    Instead, allow the result of a string concatenation to be represented in a tree form - with a
    variable sized, reference-counted rope node retaining a set of UString::Reps (or other rope nopes).
    
    Reviewed by Oliver "Brraaaaiiiinnnnnzzzzzzzz" Hunt.
    
    Strings must still currently be resolved down to a flat UString representation before being used,
    but by holding the string in a rope representation during construction we can avoid copying data
    until we know the final size of the string.
    
    ~2% progression on SunSpider (~25% on date-format-xparb, ~20% on string-validate-input).
    
    * JavaScriptCore.exp:
    
        - Update exports.
    
    * interpreter/Interpreter.cpp:
    (JSC::Interpreter::privateExecute):
    
        - Make use of new JSString::length() method to avoid prematurely resolving ropes.
    
    * jit/JITOpcodes.cpp:
    (JSC::JIT::privateCompileCTIMachineTrampolines):
    
        - Switch the string length trampoline to read the length directly from JSString::m_length,
          rather than from the JSString's UString::Rep's 'len' property.
    
    * jit/JITStubs.cpp:
    (JSC::DEFINE_STUB_FUNCTION):
    
        - Modify op_add such that addition of two strings, where either or both strings are already
          in rope representation, produces a rope as a result.
    
    * runtime/JSString.cpp:
    (JSC::JSString::Rope::~Rope):
    (JSC::copyChars):
    (JSC::JSString::resolveRope):
    (JSC::JSString::getPrimitiveNumber):
    (JSC::JSString::toBoolean):
    (JSC::JSString::toNumber):
    (JSC::JSString::toString):
    (JSC::JSString::toThisString):
    (JSC::JSString::getStringPropertyDescriptor):
    * runtime/JSString.h:
    (JSC::JSString::Rope::Fiber::Fiber):
    (JSC::JSString::Rope::Fiber::destroy):
    (JSC::JSString::Rope::Fiber::isRope):
    (JSC::JSString::Rope::Fiber::rope):
    (JSC::JSString::Rope::Fiber::string):
    (JSC::JSString::Rope::create):
    (JSC::JSString::Rope::initializeFiber):
    (JSC::JSString::Rope::ropeLength):
    (JSC::JSString::Rope::stringLength):
    (JSC::JSString::Rope::fibers):
    (JSC::JSString::Rope::Rope):
    (JSC::JSString::Rope::operator new):
    (JSC::JSString::JSString):
    (JSC::JSString::value):
    (JSC::JSString::length):
    (JSC::JSString::isRope):
    (JSC::JSString::rope):
    (JSC::JSString::string):
    (JSC::JSString::canGetIndex):
    (JSC::jsSingleCharacterSubstring):
    (JSC::JSString::getIndex):
    (JSC::jsSubstring):
    (JSC::JSString::getStringPropertySlot):
    
        - Add rope form.
    
    * runtime/Operations.h:
    (JSC::jsAdd):
    (JSC::concatenateStrings):
    
        - Update string concatenation, and addition of ropes, to produce ropes.
    
    * runtime/StringObject.cpp:
    (JSC::StringObject::getOwnPropertyNames):
    
        - Make use of new JSString::length() method to avoid prematurely resolving ropes.
    
    
    
    git-svn-id: http://svn.webkit.org/repository/webkit/trunk@51671 268f45cc-cd09-0410-ab3c-d52691b4dbfc

diff --git a/JavaScriptCore/ChangeLog b/JavaScriptCore/ChangeLog
index e247c17..9b5584f 100644
--- a/JavaScriptCore/ChangeLog
+++ b/JavaScriptCore/ChangeLog
@@ -1,3 +1,87 @@
+2009-12-03  Gavin Barraclough  <barraclough at apple.com>
+
+        Reviewed by Oliver "Brraaaaiiiinnnnnzzzzzzzz" Hunt.
+
+        https://bugs.webkit.org/show_bug.cgi?id=32136
+        Add a rope representation to JSString.  Presently JSString always holds its data in UString form.
+        Instead, allow the result of a string concatenation to be represented in a tree form - with a
+        variable sized, reference-counted rope node retaining a set of UString::Reps (or other rope nopes).
+
+        Strings must still currently be resolved down to a flat UString representation before being used,
+        but by holding the string in a rope representation during construction we can avoid copying data
+        until we know the final size of the string.
+
+        ~2% progression on SunSpider (~25% on date-format-xparb, ~20% on string-validate-input).
+
+        * JavaScriptCore.exp:
+
+            - Update exports.
+
+        * interpreter/Interpreter.cpp:
+        (JSC::Interpreter::privateExecute):
+
+            - Make use of new JSString::length() method to avoid prematurely resolving ropes.
+
+        * jit/JITOpcodes.cpp:
+        (JSC::JIT::privateCompileCTIMachineTrampolines):
+
+            - Switch the string length trampoline to read the length directly from JSString::m_length,
+              rather than from the JSString's UString::Rep's 'len' property.
+
+        * jit/JITStubs.cpp:
+        (JSC::DEFINE_STUB_FUNCTION):
+
+            - Modify op_add such that addition of two strings, where either or both strings are already
+              in rope representation, produces a rope as a result.
+
+        * runtime/JSString.cpp:
+        (JSC::JSString::Rope::~Rope):
+        (JSC::copyChars):
+        (JSC::JSString::resolveRope):
+        (JSC::JSString::getPrimitiveNumber):
+        (JSC::JSString::toBoolean):
+        (JSC::JSString::toNumber):
+        (JSC::JSString::toString):
+        (JSC::JSString::toThisString):
+        (JSC::JSString::getStringPropertyDescriptor):
+        * runtime/JSString.h:
+        (JSC::JSString::Rope::Fiber::Fiber):
+        (JSC::JSString::Rope::Fiber::destroy):
+        (JSC::JSString::Rope::Fiber::isRope):
+        (JSC::JSString::Rope::Fiber::rope):
+        (JSC::JSString::Rope::Fiber::string):
+        (JSC::JSString::Rope::create):
+        (JSC::JSString::Rope::initializeFiber):
+        (JSC::JSString::Rope::ropeLength):
+        (JSC::JSString::Rope::stringLength):
+        (JSC::JSString::Rope::fibers):
+        (JSC::JSString::Rope::Rope):
+        (JSC::JSString::Rope::operator new):
+        (JSC::JSString::JSString):
+        (JSC::JSString::value):
+        (JSC::JSString::length):
+        (JSC::JSString::isRope):
+        (JSC::JSString::rope):
+        (JSC::JSString::string):
+        (JSC::JSString::canGetIndex):
+        (JSC::jsSingleCharacterSubstring):
+        (JSC::JSString::getIndex):
+        (JSC::jsSubstring):
+        (JSC::JSString::getStringPropertySlot):
+
+            - Add rope form.
+
+        * runtime/Operations.h:
+        (JSC::jsAdd):
+        (JSC::concatenateStrings):
+
+            - Update string concatenation, and addition of ropes, to produce ropes.
+
+        * runtime/StringObject.cpp:
+        (JSC::StringObject::getOwnPropertyNames):
+
+            - Make use of new JSString::length() method to avoid prematurely resolving ropes.
+
 2009-11-23  Jeremy Moskovich  <jeremy at chromium.org>
 
         Reviewed by Eric Seidel.
diff --git a/JavaScriptCore/JavaScriptCore.exp b/JavaScriptCore/JavaScriptCore.exp
index d2f6035..c021c0b 100644
--- a/JavaScriptCore/JavaScriptCore.exp
+++ b/JavaScriptCore/JavaScriptCore.exp
@@ -402,6 +402,7 @@ __ZNK3JSC8JSObject8toObjectEPNS_9ExecStateE
 __ZNK3JSC8JSObject8toStringEPNS_9ExecStateE
 __ZNK3JSC8JSObject9classNameEv
 __ZNK3JSC8JSObject9toBooleanEPNS_9ExecStateE
+__ZNK3JSC8JSString11resolveRopeEv
 __ZNK3JSC9HashTable11createTableEPNS_12JSGlobalDataE
 __ZNK3JSC9HashTable11deleteTableEv
 __ZNK3WTF8Collator7collateEPKtmS2_m
diff --git a/JavaScriptCore/interpreter/Interpreter.cpp b/JavaScriptCore/interpreter/Interpreter.cpp
index 8124808..ba3a7d9 100644
--- a/JavaScriptCore/interpreter/Interpreter.cpp
+++ b/JavaScriptCore/interpreter/Interpreter.cpp
@@ -2265,7 +2265,7 @@ JSValue Interpreter::privateExecute(ExecutionFlag flag, RegisterFile* registerFi
         JSValue baseValue = callFrame->r(base).jsValue();
         if (LIKELY(isJSString(globalData, baseValue))) {
             int dst = vPC[1].u.operand;
-            callFrame->r(dst) = jsNumber(callFrame, asString(baseValue)->value().size());
+            callFrame->r(dst) = jsNumber(callFrame, asString(baseValue)->length());
             vPC += OPCODE_LENGTH(op_get_string_length);
             NEXT_INSTRUCTION();
         }
diff --git a/JavaScriptCore/jit/JITOpcodes.cpp b/JavaScriptCore/jit/JITOpcodes.cpp
index 87e845e..991d4ca 100644
--- a/JavaScriptCore/jit/JITOpcodes.cpp
+++ b/JavaScriptCore/jit/JITOpcodes.cpp
@@ -52,8 +52,7 @@ void JIT::privateCompileCTIMachineTrampolines(RefPtr<ExecutablePool>* executable
     Jump string_failureCases2 = branchPtr(NotEqual, Address(regT0), ImmPtr(m_globalData->jsStringVPtr));
 
     // Checks out okay! - get the length from the Ustring.
-    loadPtr(Address(regT0, OBJECT_OFFSETOF(JSString, m_value) + OBJECT_OFFSETOF(UString, m_rep)), regT2);
-    load32(Address(regT2, OBJECT_OFFSETOF(UString::Rep, len)), regT2);
+    load32(Address(regT0, OBJECT_OFFSETOF(JSString, m_length)), regT2);
 
     Jump string_failureCases3 = branch32(Above, regT2, Imm32(INT_MAX));
     move(regT2, regT0);
@@ -1593,8 +1592,7 @@ void JIT::privateCompileCTIMachineTrampolines(RefPtr<ExecutablePool>* executable
     Jump string_failureCases2 = branchPtr(NotEqual, Address(regT0), ImmPtr(m_globalData->jsStringVPtr));
 
     // Checks out okay! - get the length from the Ustring.
-    loadPtr(Address(regT0, OBJECT_OFFSETOF(JSString, m_value) + OBJECT_OFFSETOF(UString, m_rep)), regT0);
-    load32(Address(regT0, OBJECT_OFFSETOF(UString::Rep, len)), regT0);
+    load32(Address(regT0, OBJECT_OFFSETOF(JSString, m_length)), regT0);
 
     Jump string_failureCases3 = branch32(Above, regT0, Imm32(JSImmediate::maxImmediateInt));
 
diff --git a/JavaScriptCore/jit/JITStubs.cpp b/JavaScriptCore/jit/JITStubs.cpp
index 68f0a3c..0316a86 100644
--- a/JavaScriptCore/jit/JITStubs.cpp
+++ b/JavaScriptCore/jit/JITStubs.cpp
@@ -1043,6 +1043,14 @@ DEFINE_STUB_FUNCTION(EncodedJSValue, op_add)
 
     bool leftIsString = v1.isString();
     if (leftIsString && v2.isString()) {
+        if (asString(v1)->isRope() || asString(v2)->isRope()) {
+            RefPtr<JSString::Rope> rope = JSString::Rope::create(2);
+            rope->initializeFiber(0, asString(v1));
+            rope->initializeFiber(1, asString(v2));
+            JSGlobalData* globalData = &callFrame->globalData();
+            return JSValue::encode(new (globalData) JSString(globalData, rope.release()));
+        }
+
         RefPtr<UString::Rep> value = concatenate(asString(v1)->value().rep(), asString(v2)->value().rep());
         if (UNLIKELY(!value)) {
             throwOutOfMemoryError(callFrame);
diff --git a/JavaScriptCore/runtime/JSString.cpp b/JavaScriptCore/runtime/JSString.cpp
index 20ba868..c232c45 100644
--- a/JavaScriptCore/runtime/JSString.cpp
+++ b/JavaScriptCore/runtime/JSString.cpp
@@ -30,36 +30,121 @@
 
 namespace JSC {
 
+JSString::Rope::~Rope()
+{
+    for (unsigned i = 0; i < m_ropeLength; ++i) {
+        Fiber& fiber = m_fibers[i];
+        if (fiber.isRope())
+            fiber.rope()->deref();
+        else
+            fiber.string()->deref();
+    }
+}
+
+#define ROPE_COPY_CHARS_INLINE_CUTOFF 20
+
+static inline void copyChars(UChar* destination, const UChar* source, unsigned numCharacters)
+{
+#ifdef ROPE_COPY_CHARS_INLINE_CUTOFF
+    if (numCharacters <= ROPE_COPY_CHARS_INLINE_CUTOFF) {
+        for (unsigned i = 0; i < numCharacters; ++i)
+            destination[i] = source[i];
+        return;
+    }
+#endif
+    memcpy(destination, source, numCharacters * sizeof(UChar));
+}
+
+// Overview: this methods converts a JSString from holding a string in rope form
+// down to a simple UString representation.  It does so by building up the string
+// backwards, since we want to avoid recursion, we expect that the tree structure
+// representing the rope is likely imbalanced with more nodes down the left side
+// (since appending to the string is likely more common) - and as such resolving
+// in this fashion should minimize work queue size.  (If we built the queue forwards
+// we would likely have to place all of the constituent UString::Reps into the
+// Vector before performing any concatenation, but by working backwards we likely
+// only fill the queue with the number of substrings at any given level in a
+// rope-of-ropes.)
+void JSString::resolveRope() const
+{
+    ASSERT(isRope());
+
+    // Allocate the buffer to hold the final string, position initially points to the end.
+    UChar* buffer = static_cast<UChar*>(fastMalloc(m_length * sizeof(UChar)));
+    UChar* position = buffer + m_length;
+
+    // Start with the current Rope.
+    Vector<Rope::Fiber, 32> workQueue;
+    Rope* rope = m_rope.get();
+    while (true) {
+        // Copy the contents of the current rope into the workQueue, with the last item in 'currentFiber'
+        // (we will be working backwards over the rope).
+        unsigned ropeLengthMinusOne = rope->ropeLength() - 1;
+        for (unsigned i = 0; i < ropeLengthMinusOne; ++i)
+            workQueue.append(rope->fibers(i));
+        Rope::Fiber currentFiber = rope->fibers(ropeLengthMinusOne);
+
+        // Spin backwards over the workQueue (starting with currentFiber),
+        // writing the strings into the buffer.
+        while (currentFiber.isString()) {
+            UString::Rep* string = currentFiber.string();
+            unsigned length = string->len;
+            position -= length;
+            copyChars(position, string->data(), length);
+
+            // Was this the last item in the work queue?
+            if (workQueue.isEmpty())
+                goto breakOutOfTwoLoops;
+            // No! - set the next item up to process.
+            currentFiber = workQueue.last();
+            workQueue.removeLast();
+        }
+
+        // If we get here we fell out of the loop concatenating strings - currentFiber is a rope.
+        // set the 'rope' variable, and continue around the loop.
+        ASSERT(currentFiber.isRope());
+        rope = currentFiber.rope();
+    }
+breakOutOfTwoLoops:
+
+    // Create a string from the UChar buffer, clear the rope RefPtr.
+    ASSERT(buffer == position);
+    m_value = UString::Rep::create(buffer, m_length, false);
+    m_rope.clear();
+
+    ASSERT(!isRope());
+}
+
 JSValue JSString::toPrimitive(ExecState*, PreferredPrimitiveType) const
 {
     return const_cast<JSString*>(this);
 }
 
-bool JSString::getPrimitiveNumber(ExecState*, double& number, JSValue& value)
+bool JSString::getPrimitiveNumber(ExecState*, double& number, JSValue& result)
 {
-    value = this;
-    number = m_value.toDouble();
+    result = this;
+    number = value().toDouble();
     return false;
 }
 
 bool JSString::toBoolean(ExecState*) const
 {
-    return !m_value.isEmpty();
+    return m_length;
 }
 
 double JSString::toNumber(ExecState*) const
 {
-    return m_value.toDouble();
+    return value().toDouble();
 }
 
 UString JSString::toString(ExecState*) const
 {
-    return m_value;
+    return value();
 }
 
 UString JSString::toThisString(ExecState*) const
 {
-    return m_value;
+    return value();
 }
 
 JSString* JSString::toThisJSString(ExecState*)
@@ -106,14 +191,14 @@ bool JSString::getOwnPropertySlot(ExecState* exec, const Identifier& propertyNam
 bool JSString::getStringPropertyDescriptor(ExecState* exec, const Identifier& propertyName, PropertyDescriptor& descriptor)
 {
     if (propertyName == exec->propertyNames().length) {
-        descriptor.setDescriptor(jsNumber(exec, m_value.size()), DontEnum | DontDelete | ReadOnly);
+        descriptor.setDescriptor(jsNumber(exec, m_length), DontEnum | DontDelete | ReadOnly);
         return true;
     }
     
     bool isStrictUInt32;
     unsigned i = propertyName.toStrictUInt32(&isStrictUInt32);
-    if (isStrictUInt32 && i < static_cast<unsigned>(m_value.size())) {
-        descriptor.setDescriptor(jsSingleCharacterSubstring(exec, m_value, i), DontDelete | ReadOnly);
+    if (isStrictUInt32 && i < m_length) {
+        descriptor.setDescriptor(jsSingleCharacterSubstring(exec, value(), i), DontDelete | ReadOnly);
         return true;
     }
     
diff --git a/JavaScriptCore/runtime/JSString.h b/JavaScriptCore/runtime/JSString.h
index 39dfe75..61e8e22 100644
--- a/JavaScriptCore/runtime/JSString.h
+++ b/JavaScriptCore/runtime/JSString.h
@@ -60,12 +60,72 @@ namespace JSC {
     JSString* jsOwnedString(ExecState*, const UString&); 
 
     class JSString : public JSCell {
+    public:
         friend class JIT;
         friend struct VPtrSet;
 
-    public:
+        // A Rope is a string composed of a set of substrings.
+        class Rope : public RefCounted<Rope> {
+        public:
+            // A Rope is composed from a set of smaller strings called Fibers.
+            // Each Fiber in a rope is either UString::Rep or another Rope.
+            class Fiber {
+            public:
+                Fiber() {}
+                Fiber(UString::Rep* string) : m_value(reinterpret_cast<intptr_t>(string)) {}
+                Fiber(Rope* rope) : m_value(reinterpret_cast<intptr_t>(rope) | 1) {}
+
+                bool isRope() { return m_value & 1; }
+                Rope* rope() { return reinterpret_cast<Rope*>(m_value & ~1); }
+                bool isString() { return !isRope(); }
+                UString::Rep* string() { return reinterpret_cast<UString::Rep*>(m_value); }
+
+            private:
+                intptr_t m_value;
+            };
+
+            // Creates a Rope comprising of 'ropeLength' Fibers.
+            // The Rope is constructed in an uninitialized state - initialize must be called for each Fiber in the Rope.
+            static PassRefPtr<Rope> create(unsigned ropeLength) { return adoptRef(new (ropeLength) Rope(ropeLength)); }
+
+            ~Rope();
+
+            void initializeFiber(unsigned index, UString::Rep* string)
+            {
+                string->ref();
+                m_fibers[index] = Fiber(string);
+                m_stringLength += string->len;
+            }
+            void initializeFiber(unsigned index, Rope* rope)
+            {
+                rope->ref();
+                m_fibers[index] = Fiber(rope);
+                m_stringLength += rope->stringLength();
+            }
+            void initializeFiber(unsigned index, JSString* jsString)
+            {
+                if (jsString->isRope())
+                    initializeFiber(index, jsString->rope());
+                else
+                    initializeFiber(index, jsString->string().rep());
+            }
+
+            unsigned ropeLength() { return m_ropeLength; }
+            unsigned stringLength() { return m_stringLength; }
+            Fiber& fibers(unsigned index) { return m_fibers[index]; }
+
+        private:
+            Rope(unsigned ropeLength) : m_ropeLength(ropeLength), m_stringLength(0) {}
+            void* operator new(size_t, unsigned ropeLength) { return fastMalloc(sizeof(Rope) + (ropeLength - 1) * sizeof(UString::Rep*)); }
+            
+            unsigned m_ropeLength;
+            unsigned m_stringLength;
+            Fiber m_fibers[1];
+        };
+
         JSString(JSGlobalData* globalData, const UString& value)
             : JSCell(globalData->stringStructure.get())
+            , m_length(value.size())
             , m_value(value)
         {
             Heap::heap(this)->reportExtraMemoryCost(value.cost());
@@ -74,22 +134,40 @@ namespace JSC {
         enum HasOtherOwnerType { HasOtherOwner };
         JSString(JSGlobalData* globalData, const UString& value, HasOtherOwnerType)
             : JSCell(globalData->stringStructure.get())
+            , m_length(value.size())
             , m_value(value)
         {
         }
         JSString(JSGlobalData* globalData, PassRefPtr<UString::Rep> value, HasOtherOwnerType)
             : JSCell(globalData->stringStructure.get())
+            , m_length(value->size())
             , m_value(value)
         {
         }
+        JSString(JSGlobalData* globalData, PassRefPtr<JSString::Rope> rope)
+            : JSCell(globalData->stringStructure.get())
+            , m_length(rope->stringLength())
+            , m_rope(rope)
+        {
+        }
         
-        const UString& value() const { return m_value; }
+        const UString& value() const
+        {
+            if (m_rope)
+                resolveRope();
+            return m_value;
+        }
+        unsigned length() { return m_length; }
+
+        bool isRope() const { return m_rope; }
+        Rope* rope() { ASSERT(isRope()); return m_rope.get(); }
+        UString& string() { ASSERT(!isRope()); return m_value; }
 
         bool getStringPropertySlot(ExecState*, const Identifier& propertyName, PropertySlot&);
         bool getStringPropertySlot(ExecState*, unsigned propertyName, PropertySlot&);
         bool getStringPropertyDescriptor(ExecState*, const Identifier& propertyName, PropertyDescriptor&);
 
-        bool canGetIndex(unsigned i) { return i < static_cast<unsigned>(m_value.size()); }
+        bool canGetIndex(unsigned i) { return i < m_length; }
         JSString* getIndex(JSGlobalData*, unsigned);
 
         static PassRefPtr<Structure> createStructure(JSValue proto) { return Structure::create(proto, TypeInfo(StringType, OverridesGetOwnPropertySlot | NeedsThisConversion)); }
@@ -101,6 +179,8 @@ namespace JSC {
         {
         }
 
+        void resolveRope() const;
+
         virtual JSValue toPrimitive(ExecState*, PreferredPrimitiveType) const;
         virtual bool getPrimitiveNumber(ExecState*, double& number, JSValue& value);
         virtual bool toBoolean(ExecState*) const;
@@ -117,7 +197,10 @@ namespace JSC {
         virtual bool getOwnPropertySlot(ExecState*, unsigned propertyName, PropertySlot&);
         virtual bool getOwnPropertyDescriptor(ExecState*, const Identifier&, PropertyDescriptor&);
 
-        UString m_value;
+        // A string is represented either by a UString or a Rope.
+        unsigned m_length;
+        mutable UString m_value;
+        mutable RefPtr<Rope> m_rope;
     };
 
     JSString* asString(JSValue);
@@ -146,7 +229,7 @@ namespace JSC {
         UChar c = s.data()[offset];
         if (c <= 0xFF)
             return globalData->smallStrings.singleCharacterString(globalData, c);
-        return new (globalData) JSString(globalData, UString::Rep::create(s.rep(), offset, 1));
+        return new (globalData) JSString(globalData, UString(UString::Rep::create(s.rep(), offset, 1)));
     }
 
     inline JSString* jsNontrivialString(JSGlobalData* globalData, const char* s)
@@ -166,7 +249,7 @@ namespace JSC {
     inline JSString* JSString::getIndex(JSGlobalData* globalData, unsigned i)
     {
         ASSERT(canGetIndex(i));
-        return jsSingleCharacterSubstring(globalData, m_value, i);
+        return jsSingleCharacterSubstring(globalData, value(), i);
     }
 
     inline JSString* jsString(JSGlobalData* globalData, const UString& s)
@@ -194,7 +277,7 @@ namespace JSC {
             if (c <= 0xFF)
                 return globalData->smallStrings.singleCharacterString(globalData, c);
         }
-        return new (globalData) JSString(globalData, UString::Rep::create(s.rep(), offset, length));
+        return new (globalData) JSString(globalData, UString(UString::Rep::create(s.rep(), offset, length)));
     }
 
     inline JSString* jsOwnedString(JSGlobalData* globalData, const UString& s)
@@ -222,14 +305,14 @@ namespace JSC {
     ALWAYS_INLINE bool JSString::getStringPropertySlot(ExecState* exec, const Identifier& propertyName, PropertySlot& slot)
     {
         if (propertyName == exec->propertyNames().length) {
-            slot.setValue(jsNumber(exec, m_value.size()));
+            slot.setValue(jsNumber(exec, m_length));
             return true;
         }
 
         bool isStrictUInt32;
         unsigned i = propertyName.toStrictUInt32(&isStrictUInt32);
-        if (isStrictUInt32 && i < static_cast<unsigned>(m_value.size())) {
-            slot.setValue(jsSingleCharacterSubstring(exec, m_value, i));
+        if (isStrictUInt32 && i < m_length) {
+            slot.setValue(jsSingleCharacterSubstring(exec, value(), i));
             return true;
         }
 
@@ -238,8 +321,8 @@ namespace JSC {
         
     ALWAYS_INLINE bool JSString::getStringPropertySlot(ExecState* exec, unsigned propertyName, PropertySlot& slot)
     {
-        if (propertyName < static_cast<unsigned>(m_value.size())) {
-            slot.setValue(jsSingleCharacterSubstring(exec, m_value, propertyName));
+        if (propertyName < m_length) {
+            slot.setValue(jsSingleCharacterSubstring(exec, value(), propertyName));
             return true;
         }
 
diff --git a/JavaScriptCore/runtime/Operations.h b/JavaScriptCore/runtime/Operations.h
index 3bfb982..fe9819c 100644
--- a/JavaScriptCore/runtime/Operations.h
+++ b/JavaScriptCore/runtime/Operations.h
@@ -204,6 +204,14 @@ namespace JSC {
         
         bool leftIsString = v1.isString();
         if (leftIsString && v2.isString()) {
+            if (asString(v1)->isRope() || asString(v2)->isRope()) {
+                RefPtr<JSString::Rope> rope = JSString::Rope::create(2);
+                rope->initializeFiber(0, asString(v1));
+                rope->initializeFiber(1, asString(v2));
+                JSGlobalData* globalData = &callFrame->globalData();
+                return new (globalData) JSString(globalData, rope.release());
+            }
+
             RefPtr<UString::Rep> value = concatenate(asString(v1)->value().rep(), asString(v2)->value().rep());
             if (!value)
                 return throwOutOfMemoryError(callFrame);
@@ -298,47 +306,19 @@ namespace JSC {
     {
         ASSERT(count >= 3);
 
-        // Estimate the amount of space required to hold the entire string.  If all
-        // arguments are strings, we can easily calculate the exact amount of space
-        // required.  For any other arguments, for now let's assume they may require
-        // 11 UChars of storage.  This is enouch to hold any int, and likely is also
-        // reasonable for the other immediates.  We may want to come back and tune
-        // this value at some point.
-        unsigned bufferSize = 0;
-        for (unsigned i = 0; i < count; ++i) {
-            JSValue v = strings[i].jsValue();
-            if (LIKELY(v.isString()))
-                bufferSize += asString(v)->value().size();
-            else
-                bufferSize += 11;
-        }
+        RefPtr<JSString::Rope> rope = JSString::Rope::create(count);
 
-        // Allocate an output string to store the result.
-        // If the first argument is a String, and if it has the capacity (or can grow
-        // its capacity) to hold the entire result then use this as a base to concatenate
-        // onto.  Otherwise, allocate a new empty output buffer.
-        JSValue firstValue = strings[0].jsValue();
-        RefPtr<UString::Rep> resultRep;
-        if (firstValue.isString() && (resultRep = asString(firstValue)->value().rep())->reserveCapacity(bufferSize)) {
-            // We're going to concatenate onto the first string - remove it from the list of items to be appended.
-            ++strings;
-            --count;
-        } else
-            resultRep = UString::Rep::createEmptyBuffer(bufferSize);
-        UString result(resultRep);
-
-        // Loop over the operands, writing them into the output buffer.
         for (unsigned i = 0; i < count; ++i) {
             JSValue v = strings[i].jsValue();
             if (LIKELY(v.isString()))
-                result.append(asString(v)->value());
+                rope->initializeFiber(i, asString(v));
             else
-                result.append(v.toString(callFrame));
+                rope->initializeFiber(i, v.toString(callFrame).rep());
         }
 
-        return jsString(callFrame, result);
+        JSGlobalData* globalData = &callFrame->globalData();
+        return new (globalData) JSString(globalData, rope.release());
     }
-
 } // namespace JSC
 
 #endif // Operations_h
diff --git a/JavaScriptCore/runtime/StringObject.cpp b/JavaScriptCore/runtime/StringObject.cpp
index 7216d3a..9455c36 100644
--- a/JavaScriptCore/runtime/StringObject.cpp
+++ b/JavaScriptCore/runtime/StringObject.cpp
@@ -84,7 +84,7 @@ bool StringObject::deleteProperty(ExecState* exec, const Identifier& propertyNam
 
 void StringObject::getOwnPropertyNames(ExecState* exec, PropertyNameArray& propertyNames)
 {
-    int size = internalValue()->value().size();
+    int size = internalValue()->length();
     for (int i = 0; i < size; ++i)
         propertyNames.add(Identifier(exec, UString::from(i)));
     return JSObject::getOwnPropertyNames(exec, propertyNames);

-- 
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