DFGScratchRegisterAllocator.h   [plain text]

/*
 * Copyright (C) 2012 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.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#ifndef DFGScratchRegisterAllocator_h
#define DFGScratchRegisterAllocator_h

#include <wtf/Platform.h>

#if ENABLE(DFG_JIT)

#include "DFGRegisterSet.h"
#include "MacroAssembler.h"

namespace JSC { namespace DFG {

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

class ScratchRegisterAllocator {
public:
    ScratchRegisterAllocator(const RegisterSet& usedRegisters)
        : m_usedRegisters(usedRegisters)
        , m_didReuseRegisters(false)
    {
    }
    
    template<typename T>
    void lock(T reg) { m_lockedRegisters.set(reg); }
    
    template<typename BankInfo>
    typename BankInfo::RegisterType allocateScratch()
    {
        // First try to allocate a register that is totally free.
        for (unsigned i = 0; i < BankInfo::numberOfRegisters; ++i) {
            typename BankInfo::RegisterType reg = BankInfo::toRegister(i);
            if (!m_lockedRegisters.get(reg)
                && !m_usedRegisters.get(reg)
                && !m_scratchRegisters.get(reg)) {
                m_scratchRegisters.set(reg);
                return reg;
            }
        }
        
        // Since that failed, try to allocate a register that is not yet
        // locked or used for scratch.
        for (unsigned i = 0; i < BankInfo::numberOfRegisters; ++i) {
            typename BankInfo::RegisterType reg = BankInfo::toRegister(i);
            if (!m_lockedRegisters.get(reg) && !m_scratchRegisters.get(reg)) {
                m_scratchRegisters.set(reg);
                m_didReuseRegisters = true;
                return reg;
            }
        }
        
        // We failed.
        CRASH();
        // Make some silly compilers happy.
        return static_cast<typename BankInfo::RegisterType>(-1);
    }
    
    GPRReg allocateScratchGPR() { return allocateScratch<GPRInfo>(); }
    FPRReg allocateScratchFPR() { return allocateScratch<FPRInfo>(); }
    
    bool didReuseRegisters() const
    {
        return m_didReuseRegisters;
    }
    
    void preserveReusedRegistersByPushing(MacroAssembler& jit)
    {
        if (!m_didReuseRegisters)
            return;
        
        for (unsigned i = 0; i < FPRInfo::numberOfRegisters; ++i) {
            if (m_scratchRegisters.getFPRByIndex(i) && m_usedRegisters.getFPRByIndex(i)) {
                jit.subPtr(MacroAssembler::TrustedImm32(8), MacroAssembler::stackPointerRegister);
                jit.storeDouble(FPRInfo::toRegister(i), MacroAssembler::stackPointerRegister);
            }
        }
        for (unsigned i = 0; i < GPRInfo::numberOfRegisters; ++i) {
            if (m_scratchRegisters.getGPRByIndex(i) && m_usedRegisters.getGPRByIndex(i))
                jit.push(GPRInfo::toRegister(i));
        }
    }
    
    void restoreReusedRegistersByPopping(MacroAssembler& jit)
    {
        if (!m_didReuseRegisters)
            return;
        
        for (unsigned i = GPRInfo::numberOfRegisters; i--;) {
            if (m_scratchRegisters.getGPRByIndex(i) && m_usedRegisters.getGPRByIndex(i))
                jit.pop(GPRInfo::toRegister(i));
        }
        for (unsigned i = FPRInfo::numberOfRegisters; i--;) {
            if (m_scratchRegisters.getFPRByIndex(i) && m_usedRegisters.getFPRByIndex(i)) {
                jit.loadDouble(MacroAssembler::stackPointerRegister, FPRInfo::toRegister(i));
                jit.addPtr(MacroAssembler::TrustedImm32(8), MacroAssembler::stackPointerRegister);
            }
        }
    }
    
    unsigned desiredScratchBufferSize() const { return m_usedRegisters.numberOfSetRegisters() * sizeof(JSValue); }
    
    void preserveUsedRegistersToScratchBuffer(MacroAssembler& jit, ScratchBuffer* scratchBuffer, GPRReg scratchGPR = InvalidGPRReg)
    {
        unsigned count = 0;
        for (unsigned i = GPRInfo::numberOfRegisters; i--;) {
            if (m_usedRegisters.getGPRByIndex(i)) {
#if USE(JSVALUE64)
                jit.store64(GPRInfo::toRegister(i), static_cast<EncodedJSValue*>(scratchBuffer->dataBuffer()) + (count++));
#else
                jit.store32(GPRInfo::toRegister(i), static_cast<EncodedJSValue*>(scratchBuffer->dataBuffer()) + (count++));
#endif
            }
            if (scratchGPR == InvalidGPRReg && !m_lockedRegisters.getGPRByIndex(i) && !m_scratchRegisters.getGPRByIndex(i))
                scratchGPR = GPRInfo::toRegister(i);
        }
        RELEASE_ASSERT(scratchGPR != InvalidGPRReg);
        for (unsigned i = FPRInfo::numberOfRegisters; i--;) {
            if (m_usedRegisters.getFPRByIndex(i)) {
                jit.move(MacroAssembler::TrustedImmPtr(static_cast<EncodedJSValue*>(scratchBuffer->dataBuffer()) + (count++)), scratchGPR);
                jit.storeDouble(FPRInfo::toRegister(i), scratchGPR);
            }
        }
        RELEASE_ASSERT(count * sizeof(JSValue) == desiredScratchBufferSize());
        
        jit.move(MacroAssembler::TrustedImmPtr(scratchBuffer->activeLengthPtr()), scratchGPR);
        jit.storePtr(MacroAssembler::TrustedImmPtr(static_cast<size_t>(count * sizeof(JSValue))), scratchGPR);
    }
    
    void restoreUsedRegistersFromScratchBuffer(MacroAssembler& jit, ScratchBuffer* scratchBuffer, GPRReg scratchGPR = InvalidGPRReg)
    {
        if (scratchGPR == InvalidGPRReg) {
            // Find a scratch register.
            for (unsigned i = GPRInfo::numberOfRegisters; i--;) {
                if (m_lockedRegisters.getGPRByIndex(i) || m_scratchRegisters.getGPRByIndex(i))
                    continue;
                scratchGPR = GPRInfo::toRegister(i);
                break;
            }
        }
        RELEASE_ASSERT(scratchGPR != InvalidGPRReg);
        
        jit.move(MacroAssembler::TrustedImmPtr(scratchBuffer->activeLengthPtr()), scratchGPR);
        jit.storePtr(MacroAssembler::TrustedImmPtr(0), scratchGPR);

        // Restore double registers first.
        unsigned count = m_usedRegisters.numberOfSetGPRs();
        for (unsigned i = FPRInfo::numberOfRegisters; i--;) {
            if (m_usedRegisters.getFPRByIndex(i)) {
                jit.move(MacroAssembler::TrustedImmPtr(static_cast<EncodedJSValue*>(scratchBuffer->dataBuffer()) + (count++)), scratchGPR);
                jit.loadDouble(scratchGPR, FPRInfo::toRegister(i));
            }
        }
        
        count = 0;
        for (unsigned i = GPRInfo::numberOfRegisters; i--;) {
            if (m_usedRegisters.getGPRByIndex(i)) {
#if USE(JSVALUE64)
                jit.load64(static_cast<EncodedJSValue*>(scratchBuffer->dataBuffer()) + (count++), GPRInfo::toRegister(i));
#else
                jit.load32(static_cast<EncodedJSValue*>(scratchBuffer->dataBuffer()) + (count++), GPRInfo::toRegister(i));
#endif
            }
        }
    }
    
private:
    RegisterSet m_usedRegisters;
    RegisterSet m_lockedRegisters;
    RegisterSet m_scratchRegisters;
    bool m_didReuseRegisters;
};

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)

#endif // DFGScratchRegisterAllocator_h