Source/JavaScriptCore/runtime/JSEnvironmentRecord.h

/*
 * Copyright (C) 2007, 2008, 2012, 2015 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. 
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 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission. 
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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#ifndef JSEnvironmentRecord_h
#define JSEnvironmentRecord_h

#include "JSObject.h"
#include "JSSymbolTableObject.h"
#include "Register.h"
#include "SymbolTable.h"

namespace JSC {

class LLIntOffsetsExtractor;
class Register;

class JSEnvironmentRecord : public JSSymbolTableObject {
    friend class JIT;
    friend class LLIntOffsetsExtractor;

public:
    typedef JSSymbolTableObject Base;
    static const unsigned StructureFlags = Base::StructureFlags;

    WriteBarrierBase<Unknown>* variables()
    {
        return bitwise_cast<WriteBarrierBase<Unknown>*>(bitwise_cast<char*>(this) + offsetOfVariables());
    }
    
    bool isValidScopeOffset(ScopeOffset offset)
    {
        return !!offset && offset.offset() < symbolTable()->scopeSize();
    }
    
    WriteBarrierBase<Unknown>& variableAt(ScopeOffset offset)
    {
        ASSERT(isValidScopeOffset(offset));
        return variables()[offset.offset()];
    }

    static size_t offsetOfVariables()
    {
        return WTF::roundUpToMultipleOf<sizeof(WriteBarrier<Unknown>)>(sizeof(JSEnvironmentRecord));
    }
    
    static ptrdiff_t offsetOfVariable(ScopeOffset offset)
    {
        return offsetOfVariables() + offset.offset() * sizeof(WriteBarrier<Unknown>);
    }

    DECLARE_INFO;

    static size_t allocationSizeForScopeSize(unsigned scopeSize)
    {
        return offsetOfVariables() + scopeSize * sizeof(WriteBarrier<Unknown>);
    }
    
    static size_t allocationSize(SymbolTable* symbolTable)
    {
        return allocationSizeForScopeSize(symbolTable->scopeSize());
    }
    
protected:
    JSEnvironmentRecord(
        VM& vm,
        Structure* structure,
        JSScope* scope,
        SymbolTable* symbolTable)
        : Base(vm, structure, scope, symbolTable)
    {
    }
    
    void finishCreationUninitialized(VM& vm)
    {
        Base::finishCreation(vm);
    }
    
    void finishCreation(VM& vm, JSValue value)
    {
        finishCreationUninitialized(vm);
        ASSERT(value == jsUndefined() || value == jsTDZValue());
        for (unsigned i = symbolTable()->scopeSize(); i--;) {
            // Filling this with undefined/TDZEmptyValue is useful because that's what variables start out as.
            variableAt(ScopeOffset(i)).setStartingValue(value);
        }
    }

    static void visitChildren(JSCell*, SlotVisitor&);
};

} // namespace JSC

#endif // JSEnvironmentRecord_h