Source/JavaScriptCore/bytecode/UnlinkedModuleProgramCodeBlock.h

/*
 * Copyright (C) 2012-2017 Apple Inc. All Rights Reserved.
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 * Redistribution and use in source and binary forms, with or without
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#pragma once

#include "UnlinkedGlobalCodeBlock.h"

namespace JSC {

class Decoder;
class CachedModuleCodeBlock;

class UnlinkedModuleProgramCodeBlock final : public UnlinkedGlobalCodeBlock {
public:
    typedef UnlinkedGlobalCodeBlock Base;
    static const unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;

    static UnlinkedModuleProgramCodeBlock* create(VM* vm, const ExecutableInfo& info, OptionSet<CodeGenerationMode> codeGenerationMode)
    {
        UnlinkedModuleProgramCodeBlock* instance = new (NotNull, allocateCell<UnlinkedModuleProgramCodeBlock>(vm->heap)) UnlinkedModuleProgramCodeBlock(vm, vm->unlinkedModuleProgramCodeBlockStructure.get(), info, codeGenerationMode);
        instance->finishCreation(*vm);
        return instance;
    }

    static void destroy(JSCell*);

    // 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:
    friend CachedModuleCodeBlock;

    UnlinkedModuleProgramCodeBlock(VM* vm, Structure* structure, const ExecutableInfo& info, OptionSet<CodeGenerationMode> codeGenerationMode)
        : Base(vm, structure, ModuleCode, info, codeGenerationMode)
    {
    }

    UnlinkedModuleProgramCodeBlock(Decoder&, const CachedModuleCodeBlock&);

    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;
};

}