webkitgtk-2.4.11webkitgtk-2.4.11

1 files changed, 427 insertions, 617 deletions

diff --git a/Source/JavaScriptCore/runtime/JSString.h b/Source/JavaScriptCore/runtime/JSString.h
index 6dba78621..448ffc484 100644
--- a/Source/JavaScriptCore/runtime/JSString.h
+++ b/Source/JavaScriptCore/runtime/JSString.h
@@ -30,727 +30,537 @@
 #include "PropertySlot.h"
 #include "Structure.h"
 #include <array>
-#include <wtf/text/StringView.h>
 
 namespace JSC {
 
-class JSString;
-class JSRopeString;
-class LLIntOffsetsExtractor;
-
-JSString* jsEmptyString(VM*);
-JSString* jsEmptyString(ExecState*);
-JSString* jsString(VM*, const String&); // returns empty string if passed null string
-JSString* jsString(ExecState*, const String&); // returns empty string if passed null string
-
-JSString* jsSingleCharacterString(VM*, UChar);
-JSString* jsSingleCharacterString(ExecState*, UChar);
-JSString* jsSubstring(VM*, const String&, unsigned offset, unsigned length);
-JSString* jsSubstring(ExecState*, const String&, unsigned offset, unsigned length);
-
-// Non-trivial strings are two or more characters long.
-// These functions are faster than just calling jsString.
-JSString* jsNontrivialString(VM*, const String&);
-JSString* jsNontrivialString(ExecState*, const String&);
-JSString* jsNontrivialString(ExecState*, String&&);
-
-// Should be used for strings that are owned by an object that will
-// likely outlive the JSValue this makes, such as the parse tree or a
-// DOM object that contains a String
-JSString* jsOwnedString(VM*, const String&);
-JSString* jsOwnedString(ExecState*, const String&);
-
-JSRopeString* jsStringBuilder(VM*);
-
-bool isJSString(JSCell*);
-bool isJSString(JSValue);
-JSString* asString(JSValue);
-
-struct StringViewWithUnderlyingString {
-    StringView view;
-    String underlyingString;
-};
-
-class JSString : public JSCell {
-public:
-    friend class JIT;
-    friend class VM;
-    friend class SpecializedThunkJIT;
-    friend class JSRopeString;
-    friend class MarkStack;
-    friend class SlotVisitor;
-    friend struct ThunkHelpers;
-
-    typedef JSCell Base;
-    static const unsigned StructureFlags = Base::StructureFlags | OverridesGetOwnPropertySlot | InterceptsGetOwnPropertySlotByIndexEvenWhenLengthIsNotZero | StructureIsImmortal;
-
-    static const bool needsDestruction = true;
-    static void destroy(JSCell*);
-
-private:
-    JSString(VM& vm, PassRefPtr<StringImpl> value)
-        : JSCell(vm, vm.stringStructure.get())
-        , m_flags(0)
-        , m_value(value)
-    {
-    }
+    class JSString;
+    class JSRopeString;
+    class LLIntOffsetsExtractor;
 
-    JSString(VM& vm)
-        : JSCell(vm, vm.stringStructure.get())
-        , m_flags(0)
-    {
-    }
+    JSString* jsEmptyString(VM*);
+    JSString* jsEmptyString(ExecState*);
+    JSString* jsString(VM*, const String&); // returns empty string if passed null string
+    JSString* jsString(ExecState*, const String&); // returns empty string if passed null string
 
-    void finishCreation(VM& vm, size_t length)
-    {
-        ASSERT(!m_value.isNull());
-        Base::finishCreation(vm);
-        m_length = length;
-        setIs8Bit(m_value.impl()->is8Bit());
-    }
+    JSString* jsSingleCharacterString(VM*, UChar);
+    JSString* jsSingleCharacterString(ExecState*, UChar);
+    JSString* jsSingleCharacterSubstring(ExecState*, const String&, unsigned offset);
+    JSString* jsSubstring(VM*, const String&, unsigned offset, unsigned length);
+    JSString* jsSubstring(ExecState*, const String&, unsigned offset, unsigned length);
 
-    void finishCreation(VM& vm, size_t length, size_t cost)
-    {
-        ASSERT(!m_value.isNull());
-        Base::finishCreation(vm);
-        m_length = length;
-        setIs8Bit(m_value.impl()->is8Bit());
-        Heap::heap(this)->reportExtraMemoryAllocated(cost);
-    }
+    // Non-trivial strings are two or more characters long.
+    // These functions are faster than just calling jsString.
+    JSString* jsNontrivialString(VM*, const String&);
+    JSString* jsNontrivialString(ExecState*, const String&);
 
-protected:
-    void finishCreation(VM& vm)
-    {
-        Base::finishCreation(vm);
-        m_length = 0;
-        setIs8Bit(true);
-    }
+    // Should be used for strings that are owned by an object that will
+    // likely outlive the JSValue this makes, such as the parse tree or a
+    // DOM object that contains a String
+    JSString* jsOwnedString(VM*, const String&);
+    JSString* jsOwnedString(ExecState*, const String&);
 
-public:
-    static JSString* create(VM& vm, PassRefPtr<StringImpl> value)
-    {
-        ASSERT(value);
-        int32_t length = value->length();
-        RELEASE_ASSERT(length >= 0);
-        size_t cost = value->cost();
-        JSString* newString = new (NotNull, allocateCell<JSString>(vm.heap)) JSString(vm, value);
-        newString->finishCreation(vm, length, cost);
-        return newString;
-    }
-    static JSString* createHasOtherOwner(VM& vm, PassRefPtr<StringImpl> value)
-    {
-        ASSERT(value);
-        size_t length = value->length();
-        JSString* newString = new (NotNull, allocateCell<JSString>(vm.heap)) JSString(vm, value);
-        newString->finishCreation(vm, length);
-        return newString;
-    }
+    JSRopeString* jsStringBuilder(VM*);
 
-    Identifier toIdentifier(ExecState*) const;
-    AtomicString toAtomicString(ExecState*) const;
-    RefPtr<AtomicStringImpl> toExistingAtomicString(ExecState*) const;
+    class JSString : public JSCell {
+    public:
+        friend class JIT;
+        friend class VM;
+        friend class SpecializedThunkJIT;
+        friend class JSRopeString;
+        friend class MarkStack;
+        friend class SlotVisitor;
+        friend struct ThunkHelpers;
 
-    class SafeView;
-    SafeView view(ExecState*) const;
-    StringViewWithUnderlyingString viewWithUnderlyingString(ExecState&) const;
+        typedef JSCell Base;
 
-    const String& value(ExecState*) const;
-    const String& tryGetValue() const;
-    const StringImpl* tryGetValueImpl() const;
-    unsigned length() const { return m_length; }
+        static const bool needsDestruction = true;
+        static const bool hasImmortalStructure = true;
+        static void destroy(JSCell*);
 
-    JSValue toPrimitive(ExecState*, PreferredPrimitiveType) const;
-    bool toBoolean() const { return !!m_length; }
-    bool getPrimitiveNumber(ExecState*, double& number, JSValue&) const;
-    JSObject* toObject(ExecState*, JSGlobalObject*) const;
-    double toNumber(ExecState*) const;
+    private:
+        JSString(VM& vm, PassRefPtr<StringImpl> value)
+            : JSCell(vm, vm.stringStructure.get())
+            , m_flags(0)
+            , m_value(value)
+        {
+        }
+
+        JSString(VM& vm)
+            : JSCell(vm, vm.stringStructure.get())
+            , m_flags(0)
+        {
+        }
+
+        void finishCreation(VM& vm, size_t length)
+        {
+            ASSERT(!m_value.isNull());
+            Base::finishCreation(vm);
+            m_length = length;
+            setIs8Bit(m_value.impl()->is8Bit());
+            vm.m_newStringsSinceLastHashCons++;
+        }
 
-    bool getStringPropertySlot(ExecState*, PropertyName, PropertySlot&);
-    bool getStringPropertySlot(ExecState*, unsigned propertyName, PropertySlot&);
-    bool getStringPropertyDescriptor(ExecState*, PropertyName, PropertyDescriptor&);
+        void finishCreation(VM& vm, size_t length, size_t cost)
+        {
+            ASSERT(!m_value.isNull());
+            Base::finishCreation(vm);
+            m_length = length;
+            setIs8Bit(m_value.impl()->is8Bit());
+            Heap::heap(this)->reportExtraMemoryCost(cost);
+            vm.m_newStringsSinceLastHashCons++;
+        }
+
+    protected:
+        void finishCreation(VM& vm)
+        {
+            Base::finishCreation(vm);
+            m_length = 0;
+            setIs8Bit(true);
+            vm.m_newStringsSinceLastHashCons++;
+        }
+            
+    public:
+        static JSString* create(VM& vm, PassRefPtr<StringImpl> value)
+        {
+            ASSERT(value);
+            int32_t length = value->length();
+            RELEASE_ASSERT(length >= 0);
+            size_t cost = value->cost();
+            JSString* newString = new (NotNull, allocateCell<JSString>(vm.heap)) JSString(vm, value);
+            newString->finishCreation(vm, length, cost);
+            return newString;
+        }
+        static JSString* createHasOtherOwner(VM& vm, PassRefPtr<StringImpl> value)
+        {
+            ASSERT(value);
+            size_t length = value->length();
+            JSString* newString = new (NotNull, allocateCell<JSString>(vm.heap)) JSString(vm, value);
+            newString->finishCreation(vm, length);
+            return newString;
+        }
 
-    bool canGetIndex(unsigned i) { return i < m_length; }
-    JSString* getIndex(ExecState*, unsigned);
+        const String& value(ExecState*) const;
+        const String& tryGetValue() const;
+        const StringImpl* tryGetValueImpl() const;
+        unsigned length() { return m_length; }
+
+        JSValue toPrimitive(ExecState*, PreferredPrimitiveType) const;
+        JS_EXPORT_PRIVATE bool toBoolean() const;
+        bool getPrimitiveNumber(ExecState*, double& number, JSValue&) const;
+        JSObject* toObject(ExecState*, JSGlobalObject*) const;
+        double toNumber(ExecState*) const;
+            
+        bool getStringPropertySlot(ExecState*, PropertyName, PropertySlot&);
+        bool getStringPropertySlot(ExecState*, unsigned propertyName, PropertySlot&);
+        bool getStringPropertyDescriptor(ExecState*, PropertyName, PropertyDescriptor&);
+
+        bool canGetIndex(unsigned i) { return i < m_length; }
+        JSString* getIndex(ExecState*, unsigned);
+
+        static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue proto)
+        {
+            return Structure::create(vm, globalObject, proto, TypeInfo(StringType, OverridesGetOwnPropertySlot | InterceptsGetOwnPropertySlotByIndexEvenWhenLengthIsNotZero), info());
+        }
 
-    static Structure* createStructure(VM&, JSGlobalObject*, JSValue);
+        static size_t offsetOfLength() { return OBJECT_OFFSETOF(JSString, m_length); }
+        static size_t offsetOfFlags() { return OBJECT_OFFSETOF(JSString, m_flags); }
+        static size_t offsetOfValue() { return OBJECT_OFFSETOF(JSString, m_value); }
 
-    static size_t offsetOfLength() { return OBJECT_OFFSETOF(JSString, m_length); }
-    static size_t offsetOfFlags() { return OBJECT_OFFSETOF(JSString, m_flags); }
-    static size_t offsetOfValue() { return OBJECT_OFFSETOF(JSString, m_value); }
+        DECLARE_EXPORT_INFO;
 
-    DECLARE_EXPORT_INFO;
+        static void visitChildren(JSCell*, SlotVisitor&);
 
-    static void dumpToStream(const JSCell*, PrintStream&);
-    static size_t estimatedSize(JSCell*);
-    static void visitChildren(JSCell*, SlotVisitor&);
+        enum {
+            HashConsLock = 1u << 2,
+            IsHashConsSingleton = 1u << 1,
+            Is8Bit = 1u
+        };
 
-    enum {
-        Is8Bit = 1u
-    };
+    protected:
+        friend class JSValue;
+            
+        bool isRope() const { return m_value.isNull(); }
+        bool is8Bit() const { return m_flags & Is8Bit; }
+        void setIs8Bit(bool flag)
+        {
+            if (flag)
+                m_flags |= Is8Bit;
+            else
+                m_flags &= ~Is8Bit;
+        }
+        bool shouldTryHashCons();
+        bool isHashConsSingleton() const { return m_flags & IsHashConsSingleton; }
+        void clearHashConsSingleton() { m_flags &= ~IsHashConsSingleton; }
+        void setHashConsSingleton() { m_flags |= IsHashConsSingleton; }
+        bool tryHashConsLock();
+        void releaseHashConsLock();
+
+        unsigned m_flags;
+            
+        // A string is represented either by a String or a rope of fibers.
+        unsigned m_length;
+        mutable String m_value;
 
-protected:
-    friend class JSValue;
+    private:
+        friend class LLIntOffsetsExtractor;
+            
+        static JSValue toThis(JSCell*, ExecState*, ECMAMode);
 
-    bool isRope() const { return m_value.isNull(); }
-    bool isSubstring() const;
-    bool is8Bit() const { return m_flags & Is8Bit; }
-    void setIs8Bit(bool flag) const
-    {
-        if (flag)
-            m_flags |= Is8Bit;
-        else
-            m_flags &= ~Is8Bit;
-    }
+        String& string() { ASSERT(!isRope()); return m_value; }
 
-    mutable unsigned m_flags;
+        friend JSValue jsString(ExecState*, JSString*, JSString*);
+        friend JSString* jsSubstring(ExecState*, JSString*, unsigned offset, unsigned length);
+    };
 
-    // A string is represented either by a String or a rope of fibers.
-    unsigned m_length;
-    mutable String m_value;
+    class JSRopeString : public JSString {
+        friend class JSString;
 
-private:
-    friend class LLIntOffsetsExtractor;
+        friend JSRopeString* jsStringBuilder(VM*);
 
-    static JSValue toThis(JSCell*, ExecState*, ECMAMode);
+        class RopeBuilder {
+        public:
+            RopeBuilder(VM& vm)
+                : m_vm(vm)
+                , m_jsString(jsStringBuilder(&vm))
+                , m_index(0)
+            {
+            }
 
-    String& string() { ASSERT(!isRope()); return m_value; }
-    StringView unsafeView(ExecState&) const;
+            bool append(JSString* jsString)
+            {
+                if (m_index == JSRopeString::s_maxInternalRopeLength)
+                    expand();
+                if (static_cast<int32_t>(m_jsString->length() + jsString->length()) < 0) {
+                    m_jsString = nullptr;
+                    return false;
+                }
+                m_jsString->append(m_vm, m_index++, jsString);
+                return true;
+            }
 
-    friend JSValue jsString(ExecState*, JSString*, JSString*);
-    friend JSString* jsSubstring(ExecState*, JSString*, unsigned offset, unsigned length);
-};
+            JSRopeString* release()
+            {
+                RELEASE_ASSERT(m_jsString);
+                JSRopeString* tmp = m_jsString;
+                m_jsString = 0;
+                return tmp;
+            }
 
-class JSRopeString final : public JSString {
-    friend class JSString;
+            unsigned length() { return m_jsString->m_length; }
 
-    friend JSRopeString* jsStringBuilder(VM*);
+        private:
+            void expand();
+                
+            VM& m_vm;
+            JSRopeString* m_jsString;
+            size_t m_index;
+        };
+            
+    private:
+        JSRopeString(VM& vm)
+            : JSString(vm)
+        {
+        }
 
-public:
-    class RopeBuilder {
-    public:
-        RopeBuilder(VM& vm)
-            : m_vm(vm)
-            , m_jsString(jsStringBuilder(&vm))
-            , m_index(0)
+        void finishCreation(VM& vm, JSString* s1, JSString* s2)
+        {
+            Base::finishCreation(vm);
+            m_length = s1->length() + s2->length();
+            setIs8Bit(s1->is8Bit() && s2->is8Bit());
+            m_fibers[0].set(vm, this, s1);
+            m_fibers[1].set(vm, this, s2);
+        }
+            
+        void finishCreation(VM& vm, JSString* s1, JSString* s2, JSString* s3)
         {
+            Base::finishCreation(vm);
+            m_length = s1->length() + s2->length() + s3->length();
+            setIs8Bit(s1->is8Bit() && s2->is8Bit() &&  s3->is8Bit());
+            m_fibers[0].set(vm, this, s1);
+            m_fibers[1].set(vm, this, s2);
+            m_fibers[2].set(vm, this, s3);
         }
 
-        bool append(JSString* jsString)
+        void finishCreation(VM& vm)
         {
-            if (m_index == JSRopeString::s_maxInternalRopeLength)
-                expand();
-            if (static_cast<int32_t>(m_jsString->length() + jsString->length()) < 0) {
-                m_jsString = nullptr;
-                return false;
-            }
-            m_jsString->append(m_vm, m_index++, jsString);
-            return true;
+            JSString::finishCreation(vm);
         }
 
-        JSRopeString* release()
+        void append(VM& vm, size_t index, JSString* jsString)
         {
-            RELEASE_ASSERT(m_jsString);
-            JSRopeString* tmp = m_jsString;
-            m_jsString = 0;
-            return tmp;
+            m_fibers[index].set(vm, this, jsString);
+            m_length += jsString->m_length;
+            RELEASE_ASSERT(static_cast<int32_t>(m_length) >= 0);
+            setIs8Bit(is8Bit() && jsString->is8Bit());
         }
 
-        unsigned length() const { return m_jsString->m_length; }
+        static JSRopeString* createNull(VM& vm)
+        {
+            JSRopeString* newString = new (NotNull, allocateCell<JSRopeString>(vm.heap)) JSRopeString(vm);
+            newString->finishCreation(vm);
+            return newString;
+        }
 
+    public:
+        static JSString* create(VM& vm, JSString* s1, JSString* s2)
+        {
+            JSRopeString* newString = new (NotNull, allocateCell<JSRopeString>(vm.heap)) JSRopeString(vm);
+            newString->finishCreation(vm, s1, s2);
+            return newString;
+        }
+        static JSString* create(VM& vm, JSString* s1, JSString* s2, JSString* s3)
+        {
+            JSRopeString* newString = new (NotNull, allocateCell<JSRopeString>(vm.heap)) JSRopeString(vm);
+            newString->finishCreation(vm, s1, s2, s3);
+            return newString;
+        }
+
+        void visitFibers(SlotVisitor&);
+            
+        static ptrdiff_t offsetOfFibers() { return OBJECT_OFFSETOF(JSRopeString, m_fibers); }
+
+        static const unsigned s_maxInternalRopeLength = 3;
+            
     private:
-        void expand();
+        friend JSValue jsStringFromRegisterArray(ExecState*, Register*, unsigned);
+        friend JSValue jsStringFromArguments(ExecState*, JSValue);
+
+        JS_EXPORT_PRIVATE void resolveRope(ExecState*) const;
+        void resolveRopeSlowCase8(LChar*) const;
+        void resolveRopeSlowCase(UChar*) const;
+        void outOfMemory(ExecState*) const;
+            
+        JS_EXPORT_PRIVATE JSString* getIndexSlowCase(ExecState*, unsigned);
 
-        VM& m_vm;
-        JSRopeString* m_jsString;
-        size_t m_index;
+        mutable std::array<WriteBarrier<JSString>, s_maxInternalRopeLength> m_fibers;
     };
 
-private:
-    JSRopeString(VM& vm)
-        : JSString(vm)
-    {
-    }
 
-    void finishCreation(VM& vm, JSString* s1, JSString* s2)
+    inline const StringImpl* JSString::tryGetValueImpl() const
     {
-        Base::finishCreation(vm);
-        m_length = s1->length() + s2->length();
-        setIs8Bit(s1->is8Bit() && s2->is8Bit());
-        setIsSubstring(false);
-        fiber(0).set(vm, this, s1);
-        fiber(1).set(vm, this, s2);
-        fiber(2).clear();
+        return m_value.impl();
     }
 
-    void finishCreation(VM& vm, JSString* s1, JSString* s2, JSString* s3)
+    JSString* asString(JSValue);
+
+    inline JSString* asString(JSValue value)
     {
-        Base::finishCreation(vm);
-        m_length = s1->length() + s2->length() + s3->length();
-        setIs8Bit(s1->is8Bit() && s2->is8Bit() &&  s3->is8Bit());
-        setIsSubstring(false);
-        fiber(0).set(vm, this, s1);
-        fiber(1).set(vm, this, s2);
-        fiber(2).set(vm, this, s3);
+        ASSERT(value.asCell()->isString());
+        return jsCast<JSString*>(value.asCell());
     }
 
-    void finishCreation(ExecState& exec, JSString& base, unsigned offset, unsigned length)
+    inline JSString* jsEmptyString(VM* vm)
     {
-        VM& vm = exec.vm();
-        Base::finishCreation(vm);
-        ASSERT(!sumOverflows<int32_t>(offset, length));
-        ASSERT(offset + length <= base.length());
-        m_length = length;
-        setIs8Bit(base.is8Bit());
-        setIsSubstring(true);
-        if (base.isSubstring()) {
-            JSRopeString& baseRope = static_cast<JSRopeString&>(base);
-            substringBase().set(vm, this, baseRope.substringBase().get());
-            substringOffset() = baseRope.substringOffset() + offset;
-        } else {
-            substringBase().set(vm, this, &base);
-            substringOffset() = offset;
-
-            // For now, let's not allow substrings with a rope base.
-            // Resolve non-substring rope bases so we don't have to deal with it.
-            // FIXME: Evaluate if this would be worth adding more branches.
-            if (base.isRope())
-                static_cast<JSRopeString&>(base).resolveRope(&exec);
-        }
+        return vm->smallStrings.emptyString();
     }
 
-    void finishCreation(VM& vm)
+    ALWAYS_INLINE JSString* jsSingleCharacterString(VM* vm, UChar c)
     {
-        JSString::finishCreation(vm);
-        setIsSubstring(false);
-        fiber(0).clear();
-        fiber(1).clear();
-        fiber(2).clear();
+        if (c <= maxSingleCharacterString)
+            return vm->smallStrings.singleCharacterString(c);
+        return JSString::create(*vm, String(&c, 1).impl());
     }
 
-    void append(VM& vm, size_t index, JSString* jsString)
+    ALWAYS_INLINE JSString* jsSingleCharacterSubstring(ExecState* exec, const String& s, unsigned offset)
     {
-        fiber(index).set(vm, this, jsString);
-        m_length += jsString->m_length;
-        RELEASE_ASSERT(static_cast<int32_t>(m_length) >= 0);
-        setIs8Bit(is8Bit() && jsString->is8Bit());
+        VM* vm = &exec->vm();
+        ASSERT(offset < static_cast<unsigned>(s.length()));
+        UChar c = s.characterAt(offset);
+        if (c <= maxSingleCharacterString)
+            return vm->smallStrings.singleCharacterString(c);
+        return JSString::create(*vm, StringImpl::create(s.impl(), offset, 1));
     }
 
-    static JSRopeString* createNull(VM& vm)
+    inline JSString* jsNontrivialString(VM* vm, const String& s)
     {
-        JSRopeString* newString = new (NotNull, allocateCell<JSRopeString>(vm.heap)) JSRopeString(vm);
-        newString->finishCreation(vm);
-        return newString;
+        ASSERT(s.length() > 1);
+        return JSString::create(*vm, s.impl());
     }
 
-public:
-    static JSString* create(VM& vm, JSString* s1, JSString* s2)
+    inline const String& JSString::value(ExecState* exec) const
     {
-        JSRopeString* newString = new (NotNull, allocateCell<JSRopeString>(vm.heap)) JSRopeString(vm);
-        newString->finishCreation(vm, s1, s2);
-        return newString;
+        if (isRope())
+            static_cast<const JSRopeString*>(this)->resolveRope(exec);
+        return m_value;
     }
-    static JSString* create(VM& vm, JSString* s1, JSString* s2, JSString* s3)
+
+    inline const String& JSString::tryGetValue() const
     {
-        JSRopeString* newString = new (NotNull, allocateCell<JSRopeString>(vm.heap)) JSRopeString(vm);
-        newString->finishCreation(vm, s1, s2, s3);
-        return newString;
+        if (isRope())
+            static_cast<const JSRopeString*>(this)->resolveRope(0);
+        return m_value;
     }
 
-    static JSString* create(ExecState& exec, JSString& base, unsigned offset, unsigned length)
+    inline JSString* JSString::getIndex(ExecState* exec, unsigned i)
     {
-        JSRopeString* newString = new (NotNull, allocateCell<JSRopeString>(exec.vm().heap)) JSRopeString(exec.vm());
-        newString->finishCreation(exec, base, offset, length);
-        return newString;
+        ASSERT(canGetIndex(i));
+        if (isRope())
+            return static_cast<JSRopeString*>(this)->getIndexSlowCase(exec, i);
+        ASSERT(i < m_value.length());
+        return jsSingleCharacterSubstring(exec, m_value, i);
     }
 
-    void visitFibers(SlotVisitor&);
-
-    static ptrdiff_t offsetOfFibers() { return OBJECT_OFFSETOF(JSRopeString, u); }
-
-    static const unsigned s_maxInternalRopeLength = 3;
-
-private:
-    friend JSValue jsStringFromRegisterArray(ExecState*, Register*, unsigned);
-    friend JSValue jsStringFromArguments(ExecState*, JSValue);
-
-    JS_EXPORT_PRIVATE void resolveRope(ExecState*) const;
-    JS_EXPORT_PRIVATE void resolveRopeToAtomicString(ExecState*) const;
-    JS_EXPORT_PRIVATE RefPtr<AtomicStringImpl> resolveRopeToExistingAtomicString(ExecState*) const;
-    void resolveRopeSlowCase8(LChar*) const;
-    void resolveRopeSlowCase(UChar*) const;
-    void outOfMemory(ExecState*) const;
-    void resolveRopeInternal8(LChar*) const;
-    void resolveRopeInternal8NoSubstring(LChar*) const;
-    void resolveRopeInternal16(UChar*) const;
-    void resolveRopeInternal16NoSubstring(UChar*) const;
-    void clearFibers() const;
-    StringView unsafeView(ExecState&) const;
-    StringViewWithUnderlyingString viewWithUnderlyingString(ExecState&) const;
-
-    WriteBarrierBase<JSString>& fiber(unsigned i) const
+    inline JSString* jsString(VM* vm, const String& s)
     {
-        ASSERT(!isSubstring());
-        ASSERT(i < s_maxInternalRopeLength);
-        return u[i].string;
+        int size = s.length();
+        if (!size)
+            return vm->smallStrings.emptyString();
+        if (size == 1) {
+            UChar c = s.characterAt(0);
+            if (c <= maxSingleCharacterString)
+                return vm->smallStrings.singleCharacterString(c);
+        }
+        return JSString::create(*vm, s.impl());
     }
 
-    WriteBarrierBase<JSString>& substringBase() const
+    inline JSString* jsSubstring(ExecState* exec, JSString* s, unsigned offset, unsigned length)
     {
-        return u[1].string;
+        ASSERT(offset <= static_cast<unsigned>(s->length()));
+        ASSERT(length <= static_cast<unsigned>(s->length()));
+        ASSERT(offset + length <= static_cast<unsigned>(s->length()));
+        VM* vm = &exec->vm();
+        if (!length)
+            return vm->smallStrings.emptyString();
+        return jsSubstring(vm, s->value(exec), offset, length);
     }
 
-    uintptr_t& substringOffset() const
+    inline JSString* jsSubstring8(VM* vm, const String& s, unsigned offset, unsigned length)
     {
-        return u[2].number;
+        ASSERT(offset <= static_cast<unsigned>(s.length()));
+        ASSERT(length <= static_cast<unsigned>(s.length()));
+        ASSERT(offset + length <= static_cast<unsigned>(s.length()));
+        if (!length)
+            return vm->smallStrings.emptyString();
+        if (length == 1) {
+            UChar c = s.characterAt(offset);
+            if (c <= maxSingleCharacterString)
+                return vm->smallStrings.singleCharacterString(c);
+        }
+        return JSString::createHasOtherOwner(*vm, StringImpl::create8(s.impl(), offset, length));
     }
 
-    static uintptr_t notSubstringSentinel()
+    inline JSString* jsSubstring(VM* vm, const String& s, unsigned offset, unsigned length)
     {
-        return 0;
+        ASSERT(offset <= static_cast<unsigned>(s.length()));
+        ASSERT(length <= static_cast<unsigned>(s.length()));
+        ASSERT(offset + length <= static_cast<unsigned>(s.length()));
+        if (!length)
+            return vm->smallStrings.emptyString();
+        if (length == 1) {
+            UChar c = s.characterAt(offset);
+            if (c <= maxSingleCharacterString)
+                return vm->smallStrings.singleCharacterString(c);
+        }
+        return JSString::createHasOtherOwner(*vm, StringImpl::create(s.impl(), offset, length));
     }
 
-    static uintptr_t substringSentinel()
+    inline JSString* jsOwnedString(VM* vm, const String& s)
     {
-        return 1;
+        int size = s.length();
+        if (!size)
+            return vm->smallStrings.emptyString();
+        if (size == 1) {
+            UChar c = s.characterAt(0);
+            if (c <= maxSingleCharacterString)
+                return vm->smallStrings.singleCharacterString(c);
+        }
+        return JSString::createHasOtherOwner(*vm, s.impl());
     }
 
-    bool isSubstring() const
+    inline JSRopeString* jsStringBuilder(VM* vm)
     {
-        return u[0].number == substringSentinel();
+        return JSRopeString::createNull(*vm);
     }
 
-    void setIsSubstring(bool isSubstring)
+    inline JSString* jsEmptyString(ExecState* exec) { return jsEmptyString(&exec->vm()); }
+    inline JSString* jsString(ExecState* exec, const String& s) { return jsString(&exec->vm(), s); }
+    inline JSString* jsSingleCharacterString(ExecState* exec, UChar c) { return jsSingleCharacterString(&exec->vm(), c); }
+    inline JSString* jsSubstring8(ExecState* exec, const String& s, unsigned offset, unsigned length) { return jsSubstring8(&exec->vm(), s, offset, length); }
+    inline JSString* jsSubstring(ExecState* exec, const String& s, unsigned offset, unsigned length) { return jsSubstring(&exec->vm(), s, offset, length); }
+    inline JSString* jsNontrivialString(ExecState* exec, const String& s) { return jsNontrivialString(&exec->vm(), s); }
+    inline JSString* jsOwnedString(ExecState* exec, const String& s) { return jsOwnedString(&exec->vm(), s); }
+
+    ALWAYS_INLINE bool JSString::getStringPropertySlot(ExecState* exec, PropertyName propertyName, PropertySlot& slot)
     {
-        u[0].number = isSubstring ? substringSentinel() : notSubstringSentinel();
-    }
+        if (propertyName == exec->propertyNames().length) {
+            slot.setValue(this, DontEnum | DontDelete | ReadOnly, jsNumber(m_length));
+            return true;
+        }
 
-    mutable union {
-        uintptr_t number;
-        WriteBarrierBase<JSString> string;
-    } u[s_maxInternalRopeLength];
-};
-
-class JSString::SafeView {
-public:
-    explicit SafeView(ExecState&, const JSString&);
-    StringView get() const;
-
-    bool is8Bit() const { return m_string->is8Bit(); }
-    unsigned length() const { return m_string->length(); }
-    const LChar* characters8() const { return get().characters8(); }
-    const UChar* characters16() const { return get().characters16(); }
-    UChar operator[](unsigned index) const { return get()[index]; }
-
-private:
-    ExecState& m_state;
-
-    // The following pointer is marked "volatile" to make the compiler leave it on the stack
-    // or in a register as long as this object is alive, even after the last use of the pointer.
-    // That's needed to prevent garbage collecting the string and possibly deleting the block
-    // with the characters in it, and then using the StringView after that.
-    const JSString* volatile m_string;
-};
-
-JS_EXPORT_PRIVATE JSString* jsStringWithCacheSlowCase(VM&, StringImpl&);
-
-inline const StringImpl* JSString::tryGetValueImpl() const
-{
-    return m_value.impl();
-}
-
-inline JSString* asString(JSValue value)
-{
-    ASSERT(value.asCell()->isString());
-    return jsCast<JSString*>(value.asCell());
-}
-
-inline JSString* jsEmptyString(VM* vm)
-{
-    return vm->smallStrings.emptyString();
-}
-
-ALWAYS_INLINE JSString* jsSingleCharacterString(VM* vm, UChar c)
-{
-    if (c <= maxSingleCharacterString)
-        return vm->smallStrings.singleCharacterString(c);
-    return JSString::create(*vm, String(&c, 1).impl());
-}
-
-inline JSString* jsNontrivialString(VM* vm, const String& s)
-{
-    ASSERT(s.length() > 1);
-    return JSString::create(*vm, s.impl());
-}
-
-inline JSString* jsNontrivialString(VM* vm, String&& s)
-{
-    ASSERT(s.length() > 1);
-    return JSString::create(*vm, s.releaseImpl());
-}
-
-ALWAYS_INLINE Identifier JSString::toIdentifier(ExecState* exec) const
-{
-    return Identifier::fromString(exec, toAtomicString(exec));
-}
-
-ALWAYS_INLINE AtomicString JSString::toAtomicString(ExecState* exec) const
-{
-    if (isRope())
-        static_cast<const JSRopeString*>(this)->resolveRopeToAtomicString(exec);
-    return AtomicString(m_value);
-}
-
-ALWAYS_INLINE RefPtr<AtomicStringImpl> JSString::toExistingAtomicString(ExecState* exec) const
-{
-    if (isRope())
-        return static_cast<const JSRopeString*>(this)->resolveRopeToExistingAtomicString(exec);
-    if (m_value.impl()->isAtomic())
-        return static_cast<AtomicStringImpl*>(m_value.impl());
-    return AtomicStringImpl::lookUp(m_value.impl());
-}
-
-inline const String& JSString::value(ExecState* exec) const
-{
-    if (isRope())
-        static_cast<const JSRopeString*>(this)->resolveRope(exec);
-    return m_value;
-}
-
-inline const String& JSString::tryGetValue() const
-{
-    if (isRope())
-        static_cast<const JSRopeString*>(this)->resolveRope(0);
-    return m_value;
-}
-
-inline JSString* JSString::getIndex(ExecState* exec, unsigned i)
-{
-    ASSERT(canGetIndex(i));
-    return jsSingleCharacterString(exec, unsafeView(*exec)[i]);
-}
-
-inline JSString* jsString(VM* vm, const String& s)
-{
-    int size = s.length();
-    if (!size)
-        return vm->smallStrings.emptyString();
-    if (size == 1) {
-        UChar c = s.characterAt(0);
-        if (c <= maxSingleCharacterString)
-            return vm->smallStrings.singleCharacterString(c);
-    }
-    return JSString::create(*vm, s.impl());
-}
-
-inline JSString* jsSubstring(ExecState* exec, JSString* s, unsigned offset, unsigned length)
-{
-    ASSERT(offset <= static_cast<unsigned>(s->length()));
-    ASSERT(length <= static_cast<unsigned>(s->length()));
-    ASSERT(offset + length <= static_cast<unsigned>(s->length()));
-    VM& vm = exec->vm();
-    if (!length)
-        return vm.smallStrings.emptyString();
-    if (!offset && length == s->length())
-        return s;
-    return JSRopeString::create(*exec, *s, offset, length);
-}
-
-inline JSString* jsSubstring(VM* vm, const String& s, unsigned offset, unsigned length)
-{
-    ASSERT(offset <= static_cast<unsigned>(s.length()));
-    ASSERT(length <= static_cast<unsigned>(s.length()));
-    ASSERT(offset + length <= static_cast<unsigned>(s.length()));
-    if (!length)
-        return vm->smallStrings.emptyString();
-    if (length == 1) {
-        UChar c = s.characterAt(offset);
-        if (c <= maxSingleCharacterString)
-            return vm->smallStrings.singleCharacterString(c);
-    }
-    return JSString::createHasOtherOwner(*vm, StringImpl::createSubstringSharingImpl(s.impl(), offset, length));
-}
+        unsigned i = propertyName.asIndex();
+        if (i < m_length) {
+            ASSERT(i != PropertyName::NotAnIndex); // No need for an explicit check, the above test would always fail!
+            slot.setValue(this, DontDelete | ReadOnly, getIndex(exec, i));
+            return true;
+        }
 
-inline JSString* jsOwnedString(VM* vm, const String& s)
-{
-    int size = s.length();
-    if (!size)
-        return vm->smallStrings.emptyString();
-    if (size == 1) {
-        UChar c = s.characterAt(0);
-        if (c <= maxSingleCharacterString)
-            return vm->smallStrings.singleCharacterString(c);
-    }
-    return JSString::createHasOtherOwner(*vm, s.impl());
-}
-
-inline JSRopeString* jsStringBuilder(VM* vm)
-{
-    return JSRopeString::createNull(*vm);
-}
-
-inline JSString* jsEmptyString(ExecState* exec) { return jsEmptyString(&exec->vm()); }
-inline JSString* jsString(ExecState* exec, const String& s) { return jsString(&exec->vm(), s); }
-inline JSString* jsSingleCharacterString(ExecState* exec, UChar c) { return jsSingleCharacterString(&exec->vm(), c); }
-inline JSString* jsSubstring(ExecState* exec, const String& s, unsigned offset, unsigned length) { return jsSubstring(&exec->vm(), s, offset, length); }
-inline JSString* jsNontrivialString(ExecState* exec, const String& s) { return jsNontrivialString(&exec->vm(), s); }
-inline JSString* jsNontrivialString(ExecState* exec, String&& s) { return jsNontrivialString(&exec->vm(), WTFMove(s)); }
-inline JSString* jsOwnedString(ExecState* exec, const String& s) { return jsOwnedString(&exec->vm(), s); }
-
-ALWAYS_INLINE JSString* jsStringWithCache(ExecState* exec, const String& s)
-{
-    VM& vm = exec->vm();
-    StringImpl* stringImpl = s.impl();
-    if (!stringImpl || !stringImpl->length())
-        return jsEmptyString(&vm);
-
-    if (stringImpl->length() == 1) {
-        UChar singleCharacter = (*stringImpl)[0u];
-        if (singleCharacter <= maxSingleCharacterString)
-            return vm.smallStrings.singleCharacterString(static_cast<unsigned char>(singleCharacter));
+        return false;
     }
+            
+    ALWAYS_INLINE bool JSString::getStringPropertySlot(ExecState* exec, unsigned propertyName, PropertySlot& slot)
+    {
+        if (propertyName < m_length) {
+            slot.setValue(this, DontDelete | ReadOnly, getIndex(exec, propertyName));
+            return true;
+        }
 
-    if (JSString* lastCachedString = vm.lastCachedString.get()) {
-        if (lastCachedString->tryGetValueImpl() == stringImpl)
-            return lastCachedString;
+        return false;
     }
 
-    return jsStringWithCacheSlowCase(vm, *stringImpl);
-}
-
-ALWAYS_INLINE JSString* jsStringWithCache(ExecState* exec, const AtomicString& s)
-{
-    return jsStringWithCache(exec, s.string());
-}
+    inline bool isJSString(JSValue v) { return v.isCell() && v.asCell()->classInfo() == JSString::info(); }
 
-ALWAYS_INLINE bool JSString::getStringPropertySlot(ExecState* exec, PropertyName propertyName, PropertySlot& slot)
-{
-    if (propertyName == exec->propertyNames().length) {
-        slot.setValue(this, DontEnum | DontDelete | ReadOnly, jsNumber(m_length));
-        return true;
+    // --- JSValue inlines ----------------------------
+        
+    inline bool JSValue::toBoolean(ExecState* exec) const
+    {
+        if (isInt32())
+            return asInt32();
+        if (isDouble())
+            return asDouble() > 0.0 || asDouble() < 0.0; // false for NaN
+        if (isCell())
+            return asCell()->toBoolean(exec);
+        return isTrue(); // false, null, and undefined all convert to false.
     }
 
-    Optional<uint32_t> index = parseIndex(propertyName);
-    if (index && index.value() < m_length) {
-        slot.setValue(this, DontDelete | ReadOnly, getIndex(exec, index.value()));
-        return true;
+    inline JSString* JSValue::toString(ExecState* exec) const
+    {
+        if (isString())
+            return jsCast<JSString*>(asCell());
+        return toStringSlowCase(exec);
     }
 
-    return false;
-}
-
-ALWAYS_INLINE bool JSString::getStringPropertySlot(ExecState* exec, unsigned propertyName, PropertySlot& slot)
-{
-    if (propertyName < m_length) {
-        slot.setValue(this, DontDelete | ReadOnly, getIndex(exec, propertyName));
-        return true;
+    inline String JSValue::toWTFString(ExecState* exec) const
+    {
+        if (isString())
+            return static_cast<JSString*>(asCell())->value(exec);
+        return toWTFStringSlowCase(exec);
     }
 
-    return false;
-}
-
-inline bool isJSString(JSCell* cell)
-{
-    return cell->type() == StringType;
-}
-
-inline bool isJSString(JSValue v)
-{
-    return v.isCell() && isJSString(v.asCell());
-}
-
-ALWAYS_INLINE StringView JSRopeString::unsafeView(ExecState& state) const
-{
-    if (isSubstring()) {
-        if (is8Bit())
-            return StringView(substringBase()->m_value.characters8() + substringOffset(), m_length);
-        return StringView(substringBase()->m_value.characters16() + substringOffset(), m_length);
-    }
-    resolveRope(&state);
-    return m_value;
-}
-
-ALWAYS_INLINE StringViewWithUnderlyingString JSRopeString::viewWithUnderlyingString(ExecState& state) const
-{
-    if (isSubstring()) {
-        auto& base = substringBase()->m_value;
-        if (is8Bit())
-            return { { base.characters8() + substringOffset(), m_length }, base };
-        return { { base.characters16() + substringOffset(), m_length }, base };
+    ALWAYS_INLINE String inlineJSValueNotStringtoString(const JSValue& value, ExecState* exec)
+    {
+        VM& vm = exec->vm();
+        if (value.isInt32())
+            return vm.numericStrings.add(value.asInt32());
+        if (value.isDouble())
+            return vm.numericStrings.add(value.asDouble());
+        if (value.isTrue())
+            return vm.propertyNames->trueKeyword.string();
+        if (value.isFalse())
+            return vm.propertyNames->falseKeyword.string();
+        if (value.isNull())
+            return vm.propertyNames->nullKeyword.string();
+        if (value.isUndefined())
+            return vm.propertyNames->undefinedKeyword.string();
+        return value.toString(exec)->value(exec);
+    }
+
+    ALWAYS_INLINE String JSValue::toWTFStringInline(ExecState* exec) const
+    {
+        if (isString())
+            return static_cast<JSString*>(asCell())->value(exec);
+
+        return inlineJSValueNotStringtoString(*this, exec);
     }
-    resolveRope(&state);
-    return { m_value, m_value };
-}
-
-ALWAYS_INLINE StringView JSString::unsafeView(ExecState& state) const
-{
-    if (isRope())
-        return static_cast<const JSRopeString*>(this)->unsafeView(state);
-    return m_value;
-}
-
-ALWAYS_INLINE StringViewWithUnderlyingString JSString::viewWithUnderlyingString(ExecState& state) const
-{
-    if (isRope())
-        return static_cast<const JSRopeString&>(*this).viewWithUnderlyingString(state);
-    return { m_value, m_value };
-}
-
-inline bool JSString::isSubstring() const
-{
-    return isRope() && static_cast<const JSRopeString*>(this)->isSubstring();
-}
-
-inline JSString::SafeView::SafeView(ExecState& state, const JSString& string)
-    : m_state(state)
-    , m_string(&string)
-{
-}
-
-inline StringView JSString::SafeView::get() const
-{
-    return m_string->unsafeView(m_state);
-}
-
-ALWAYS_INLINE JSString::SafeView JSString::view(ExecState* exec) const
-{
-    return SafeView(*exec, *this);
-}
-
-// --- JSValue inlines ----------------------------
-
-inline bool JSValue::toBoolean(ExecState* exec) const
-{
-    if (isInt32())
-        return asInt32();
-    if (isDouble())
-        return asDouble() > 0.0 || asDouble() < 0.0; // false for NaN
-    if (isCell())
-        return asCell()->toBoolean(exec);
-    return isTrue(); // false, null, and undefined all convert to false.
-}
-
-inline JSString* JSValue::toString(ExecState* exec) const
-{
-    if (isString())
-        return jsCast<JSString*>(asCell());
-    bool returnEmptyStringOnError = true;
-    return toStringSlowCase(exec, returnEmptyStringOnError);
-}
-
-inline JSString* JSValue::toStringOrNull(ExecState* exec) const
-{
-    if (isString())
-        return jsCast<JSString*>(asCell());
-    bool returnEmptyStringOnError = false;
-    return toStringSlowCase(exec, returnEmptyStringOnError);
-}
-
-inline String JSValue::toWTFString(ExecState* exec) const
-{
-    if (isString())
-        return static_cast<JSString*>(asCell())->value(exec);
-    return toWTFStringSlowCase(exec);
-}
 
 } // namespace JSC