Source/JavaScriptCore/bytecode/FullBytecodeLiveness.h

/*
 * Copyright (C) 2013, 2015 Apple Inc. All rights reserved.
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#pragma once

#include "BytecodeLivenessAnalysis.h"
#include "Operands.h"
#include <wtf/FastBitVector.h>

namespace JSC {

class BytecodeLivenessAnalysis;
class CodeBlock;

// Note: Full bytecode liveness does not track any information about the liveness of temps.
// If you want tmp liveness for a checkpoint ask tmpLivenessForCheckpoint.
class FullBytecodeLiveness {
    WTF_MAKE_FAST_ALLOCATED;
public:
    const FastBitVector& getLiveness(BytecodeIndex bytecodeIndex, LivenessCalculationPoint point) const
    {
        // We don't have to worry about overflowing into the next bytecodeoffset in our vectors because we
        // static assert that bytecode length is greater than the number of checkpoints in BytecodeStructs.h
        switch (point) {
        case LivenessCalculationPoint::BeforeUse:
            return m_usesBefore[toIndex(bytecodeIndex)];
        case LivenessCalculationPoint::AfterUse:
            return m_usesAfter[toIndex(bytecodeIndex)];
        }
        RELEASE_ASSERT_NOT_REACHED();
    }
    
    bool virtualRegisterIsLive(VirtualRegister reg, BytecodeIndex bytecodeIndex, LivenessCalculationPoint point) const
    {
        return virtualRegisterIsAlwaysLive(reg) || virtualRegisterThatIsNotAlwaysLiveIsLive(getLiveness(bytecodeIndex, point), reg);
    }
    
private:
    friend class BytecodeLivenessAnalysis;
    
    static size_t toIndex(BytecodeIndex bytecodeIndex) { return bytecodeIndex.offset() + bytecodeIndex.checkpoint(); }

    // FIXME: Use FastBitVector's view mechanism to make them compact.
    // https://bugs.webkit.org/show_bug.cgi?id=204427
    Vector<FastBitVector, 0, UnsafeVectorOverflow> m_usesBefore;
    Vector<FastBitVector, 0, UnsafeVectorOverflow> m_usesAfter;
};

} // namespace JSC