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diff --git a/Source/JavaScriptCore/bytecode/UnlinkedModuleProgramCodeBlock.h b/Source/JavaScriptCore/bytecode/UnlinkedModuleProgramCodeBlock.h
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+++ b/Source/JavaScriptCore/bytecode/UnlinkedModuleProgramCodeBlock.h
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+/*
+ * Copyright (C) 2012-2016 Apple Inc. All Rights Reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "UnlinkedGlobalCodeBlock.h"
+
+namespace JSC {
+
+class UnlinkedModuleProgramCodeBlock final : public UnlinkedGlobalCodeBlock {
+public:
+    typedef UnlinkedGlobalCodeBlock Base;
+    static const unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;
+
+    static UnlinkedModuleProgramCodeBlock* create(VM* vm, const ExecutableInfo& info, DebuggerMode debuggerMode)
+    {
+        UnlinkedModuleProgramCodeBlock* instance = new (NotNull, allocateCell<UnlinkedModuleProgramCodeBlock>(vm->heap)) UnlinkedModuleProgramCodeBlock(vm, vm->unlinkedModuleProgramCodeBlockStructure.get(), info, debuggerMode);
+        instance->finishCreation(*vm);
+        return instance;
+    }
+
+    static void destroy(JSCell*);
+
+    static void visitChildren(JSCell*, SlotVisitor&);
+
+    // This offset represents the constant register offset to the stored symbol table that represents the layout of the
+    // module environment. This symbol table is created by the byte code generator since the module environment includes
+    // the top-most lexical captured variables inside the module code. This means that, once the module environment is
+    // allocated and instantiated from this symbol table, it is titely coupled with the specific unlinked module program
+    // code block and the stored symbol table. So before executing the module code, we should not clear the unlinked module
+    // program code block in the module executable. This requirement is met because the garbage collector only clears
+    // unlinked code in (1) unmarked executables and (2) function executables.
+    //
+    // Since the function code may be executed repeatedly and the environment of each function execution is different,
+    // the function code need to allocate and instantiate the environment in the prologue of the function code. On the
+    // other hand, the module code is executed only once. So we can instantiate the module environment outside the module
+    // code. At that time, we construct the module environment by using the symbol table that is held by the module executable.
+    // The symbol table held by the executable is the cloned one from one in the unlinked code block. Instantiating the module
+    // environment before executing and linking the module code is required to link the imported bindings between the modules.
+    //
+    // The unlinked module program code block only holds the pre-cloned symbol table in its constant register pool. It does
+    // not hold the instantiated module environment. So while the module environment requires the specific unlinked module
+    // program code block, the unlinked module code block can be used for the module environment instantiated from this
+    // unlinked code block. There is 1:N relation between the unlinked module code block and the module environments. So the
+    // unlinked module program code block can be cached.
+    //
+    // On the other hand, the linked code block for the module environment includes the resolved references to the imported
+    // bindings. The imported binding references the other module environment, so the linked code block is titly coupled
+    // with the specific set of the module environments. Thus, the linked code block should not be cached.
+    int moduleEnvironmentSymbolTableConstantRegisterOffset() { return m_moduleEnvironmentSymbolTableConstantRegisterOffset; }
+    void setModuleEnvironmentSymbolTableConstantRegisterOffset(int offset)
+    {
+        m_moduleEnvironmentSymbolTableConstantRegisterOffset = offset;
+    }
+
+private:
+    UnlinkedModuleProgramCodeBlock(VM* vm, Structure* structure, const ExecutableInfo& info, DebuggerMode debuggerMode)
+        : Base(vm, structure, ModuleCode, info, debuggerMode)
+    {
+    }
+
+    int m_moduleEnvironmentSymbolTableConstantRegisterOffset { 0 };
+
+public:
+    static Structure* createStructure(VM& vm, JSGlobalObject* globalObject, JSValue proto)
+    {
+        return Structure::create(vm, globalObject, proto, TypeInfo(UnlinkedModuleProgramCodeBlockType, StructureFlags), info());
+    }
+
+    DECLARE_INFO;
+};
+
+}