Source/JavaScriptCore/jit/ScratchRegisterAllocator.h

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 * Redistribution and use in source and binary forms, with or without
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#pragma once

#if ENABLE(JIT)

#include "FPRInfo.h"
#include "RegisterSet.h"

namespace JSC {

class AssemblyHelpers;
struct ScratchBuffer;

// This class provides a low-level register allocator for use in stubs.

class ScratchRegisterAllocator {
public:
    ScratchRegisterAllocator() { }
    ScratchRegisterAllocator(const RegisterSet& usedRegisters);
    ~ScratchRegisterAllocator();

    void lock(GPRReg);
    void lock(FPRReg);
    void lock(JSValueRegs);
    
    template<typename BankInfo>
    typename BankInfo::RegisterType allocateScratch();
    
    GPRReg allocateScratchGPR();
    FPRReg allocateScratchFPR();
    
    bool didReuseRegisters() const
    {
        return !!m_numberOfReusedRegisters;
    }
    
    unsigned numberOfReusedRegisters() const
    {
        return m_numberOfReusedRegisters;
    }

    RegisterSet usedRegisters() const { return m_usedRegisters; }
    
    enum class ExtraStackSpace { SpaceForCCall, NoExtraSpace };

    struct PreservedState {
        PreservedState()
            : numberOfBytesPreserved(std::numeric_limits<unsigned>::max())
            , extraStackSpaceRequirement(ExtraStackSpace::SpaceForCCall)
        { }

        PreservedState(unsigned numberOfBytes, ExtraStackSpace extraStackSpace)
            : numberOfBytesPreserved(numberOfBytes)
            , extraStackSpaceRequirement(extraStackSpace)
        { }

        explicit operator bool() const { return numberOfBytesPreserved != std::numeric_limits<unsigned>::max(); }

        unsigned numberOfBytesPreserved;
        ExtraStackSpace extraStackSpaceRequirement;
    };

    PreservedState preserveReusedRegistersByPushing(AssemblyHelpers& jit, ExtraStackSpace);
    void restoreReusedRegistersByPopping(AssemblyHelpers& jit, const PreservedState&);
    
    RegisterSet usedRegistersForCall() const;
    
    unsigned desiredScratchBufferSizeForCall() const;

    static unsigned preserveRegistersToStackForCall(AssemblyHelpers& jit, const RegisterSet& usedRegisters, unsigned extraPaddingInBytes);
    static void restoreRegistersFromStackForCall(AssemblyHelpers& jit, const RegisterSet& usedRegisters, const RegisterSet& ignore, unsigned numberOfStackBytesUsedForRegisterPreservation, unsigned extraPaddingInBytes);

private:
    RegisterSet m_usedRegisters;
    RegisterSet m_lockedRegisters;
    RegisterSet m_scratchRegisters;
    unsigned m_numberOfReusedRegisters;
};

} // namespace JSC

#endif // ENABLE(JIT)