Source/JavaScriptCore/dfg/DFGValueStrength.h

/*
 * Copyright (C) 2014 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
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#ifndef DFGValueStrength_h
#define DFGValueStrength_h

#if ENABLE(DFG_JIT)

#include <wtf/PrintStream.h>

namespace JSC { namespace DFG {

enum ValueStrength {
    // The value is known to the DFG but no optimizations have been performed that require the
    // value to be kept alive. All OSR entry values are fragile until we do some optimization that
    // uses them, like actually constant folding a variable to that value. By convention we say
    // that all non-cells are fragile.
    FragileValue,
    
    // The value has been used for optimization and it arose through inference. We don't want the
    // fact that we optimized the code to result in the GC keeping this value alive unnecessarily,
    // so we'd rather kill the code and recompile than keep the object alive longer.
    WeakValue,
    
    // The code will keep this value alive. This is true of constants that were present in the
    // source. String constants tend to be strong.
    StrongValue
};

inline ValueStrength merge(ValueStrength a, ValueStrength b)
{
    switch (a) {
    case FragileValue:
        return b;
    case WeakValue:
        if (b == StrongValue)
            return StrongValue;
        return WeakValue;
    case StrongValue:
        return StrongValue;
    }
    RELEASE_ASSERT_NOT_REACHED();

    return FragileValue;
}

} } // namespace JSC::DFG

namespace WTF {

void printInternal(PrintStream&, JSC::DFG::ValueStrength);

} // namespace WTF

#endif // ENABLE(DFG_JIT)

#endif // DFGValueStrength_h