// -*- mode:c++ -*-
// Copyright (c) 2010-2014, 2016-2018, 2021-2022 Arm Limited
// All rights reserved
//
// The license below extends only to copyright in the software and shall
// not be construed as granting a license to any other intellectual
// property including but not limited to intellectual property relating
// to a hardware implementation of the functionality of the software
// licensed hereunder.  You may use the software subject to the license
// terms below provided that you ensure that this notice is replicated
// unmodified and in its entirety in all distributions of the software,
// modified or unmodified, in source code or in binary form.
//
// Copyright (c) 2007-2008 The Florida State University
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met: redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer;
// 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;
// neither the name of the copyright holders nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "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 THE COPYRIGHT
// OWNER 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.

def operand_types {{
    'sb' : 'int8_t',
    'ub' : 'uint8_t',
    'sh' : 'int16_t',
    'uh' : 'uint16_t',
    'sw' : 'int32_t',
    'uw' : 'uint32_t',
    'sd' : 'int64_t',
    'ud' : 'uint64_t',
    'pint' : 'ArmISA::PackedIntReg',
    'sq' : '__int128_t',
    'uq' : '__uint128_t',
    'tud' : 'std::array<uint64_t, 2>',
    'sf' : 'float',
    'df' : 'double',
    'vc' : 'ArmISA::VecRegContainer',
    # For operations that are implemented as a template
    'x' : 'TPElem',
    'xs' : 'TPSElem',
    'xd' : 'TPDElem',
    'pc' : 'ArmISA::VecPredRegContainer',
    'pb' : 'uint8_t'
}};

let {{
    cntrlNsBankedWrite = '''
        xc->setMiscReg(snsBankedIndex(dest, xc->tcBase()), %(final_val)s)
    '''

    #PCState operands need to have a sorting index (the number at the end)
    #less than all the integer registers which might update the PC. That way
    #if the flag bits of the pc state are updated and a branch happens through
    #R15, the updates are layered properly and the R15 update isn't lost.
    srtNormal = 5
    srtCpsr = 4
    srtBase = 3
    srtPC = 2
    srtMode = 1
    srtEPC = 0

    class VectorElem(VecElemOp):
        def __init__(self, idx):
            flat_idx = f'((({idx}) / 4) * NumVecElemPerVecReg) + ({idx}) % 4'
            super().__init__('sf', flat_idx, 'IsVectorElem', srtNormal)

    class VectorReg(VecRegOp):
        def __init__(self, idx, base, suffix=''):
            elems = {
                base + 'P0' + suffix : ('0', 'sf'),
                base + 'P1' + suffix : ('1', 'sf'),
                base + 'P2' + suffix : ('2', 'sf'),
                base + 'P3' + suffix : ('3', 'sf'),
                base + 'S' + suffix : ('0', 'sf'),
                base + 'D' + suffix : ('0', 'df'),
                base + 'Q' + suffix : ('0', 'tud')
            }
            super().__init__('vc', (idx, elems), 'IsVector', srtNormal)

    class VecPredReg(VecPredRegOp):
        def __init__(self, idx):
            super().__init__('pc', idx, sort_pri=srtNormal)

    class IntRegNPC(IntRegOp):
        @overrideInOperand
        def regId(self):
            return f'gem5::ArmISA::couldBeZero({self.reg_spec}) ? RegId() : ' \
                   f'RegId({self.reg_class}, {self.reg_spec})'
        def __init__(self, idx, ctype='uw', id=srtNormal):
            super().__init__(ctype, idx, 'IsInteger', id)

    class IntReg(IntRegNPC):
        @overrideInOperand
        def makeRead(self):
            '''Maybe PC read'''
            return f'{self.base_name} = ({self.reg_spec} == int_reg::Pc) ? ' \
                   f'readPC(xc) : xc->getRegOperand(' \
                   f'this, {self.src_reg_idx});\n'
        @overrideInOperand
        def makeWrite(self):
            '''Maybe PC write'''
            return f'''
            if ({self.reg_spec} == int_reg::Pc)
                setNextPC(xc, {self.base_name});
            else
                xc->setRegOperand(this, {self.dest_reg_idx}, {self.base_name});
            if (traceData)
                traceData->setData({self.base_name});
            '''

    class PIntReg(IntReg):
        def __init__(self, idx):
            super().__init__(idx, ctype='pint')

    class IntRegAPC(IntReg):
        @overrideInOperand
        def makeRead(self):
            '''Maybe aligned PC read'''
            return f'{self.base_name} = ({self.reg_spec} == int_reg::Pc) ? ' \
                   f'(roundDown(readPC(xc), 4)) : ' \
                   f'xc->getRegOperand(this, {self.src_reg_idx});\n'

    class IntRegIWPC(IntReg):
        @overrideInOperand
        def makeWrite(self):
            '''Maybe interworking PC write'''
            return f'''
            if ({self.reg_spec} == int_reg::Pc)
                setIWNextPC(xc, {self.base_name});
            else
                xc->setRegOperand(this, {self.dest_reg_idx}, {self.base_name});
            if (traceData)
                traceData->setData({self.base_name});
            '''

    class IntRegAIWPC(IntReg):
        @overrideInOperand
        def makeWrite(self):
            '''Maybe aligned interworking PC write'''
            return f'''
            if ({self.reg_spec} == int_reg::Pc) {"{"}
                if ((bool)THUMB)
                    setNextPC(xc, {self.base_name});
                else
                    setIWNextPC(xc, {self.base_name});
            {"}"} else {"{"}
                xc->setRegOperand(this, {self.dest_reg_idx}, {self.base_name});
            {"}"}
            if (traceData)
                traceData->setData({self.base_name});
            '''

    class IntReg64(IntRegOp):
        @overrideInOperand
        def regId(self):
            return f'gem5::ArmISA::couldBeZero({self.reg_spec}) ? RegId() : ' \
                   f'RegId({self.reg_class}, {self.reg_spec})'
        @overrideInOperand
        def makeRead(self):
            '''aarch64 read'''
            return f'{self.base_name} = ' \
                   f'(xc->getRegOperand(this, {self.src_reg_idx})) & ' \
                   f'mask(intWidth);\n'
        @overrideInOperand
        def makeWrite(self):
            '''aarch64 write'''
            return f'''
            xc->setRegOperand(this, {self.dest_reg_idx}, {self.base_name} &
                mask(intWidth));
            if (traceData)
                traceData->setData({self.base_name});
            '''
        def __init__(self, idx, id=srtNormal):
            super().__init__('ud', idx, 'IsInteger', id)

    class IntRegX64(IntReg64):
        @overrideInOperand
        def makeRead(self):
            '''Maybe masked to 32 bit read'''
            return f'{self.base_name} = ' \
                   f'(xc->getRegOperand(this, {self.src_reg_idx}) & ' \
                    'mask(aarch64 ? 64 : 32));\n'
        @overrideInOperand
        def makeWrite(self):
            '''Maybe masked to 32 bit write'''
            return f'''
            xc->setRegOperand(this, {self.dest_reg_idx}, {self.base_name} &
                    mask(aarch64 ? 64 : 32));
            if (traceData)
                traceData->setData({self.base_name});
            '''

    class IntRegW64(IntReg64):
        @overrideInOperand
        def makeRead(self):
            '''Masked to 32 bit read'''
            return f'{self.base_name} = ' \
                   f'(xc->getRegOperand(this, {self.src_reg_idx})) & ' \
                   f'mask(32);\n'
        @overrideInOperand
        def makeWrite(self):
            '''Masked to 32 bit write'''
            return f'''
            xc->setRegOperand(this, {self.dest_reg_idx}, {self.base_name} &
                    mask(32));
            if (traceData)
                traceData->setData({self.base_name});
            '''

    class CCReg(CCRegOp):
        def __init__(self, idx):
            super().__init__('uw', idx, sort_pri=srtNormal)

    class CntrlReg(ControlRegOp):
        def __init__(self, idx, id=srtNormal, ctype='uw', flags=None):
            super().__init__(ctype, idx, flags, id)

    class CntrlReg64(CntrlReg):
        def __init__(self, idx, id=srtNormal, ctype='ud'):
            super().__init__(idx, id, ctype)

    class CntrlNsBankedReg(CntrlReg):
        @overrideInOperand
        def makeRead(self):
            return f'{self.base_name} = ' \
                   f'xc->readMiscReg(snsBankedIndex(op1, xc->tcBase()));\n'
        @overrideInOperand
        def makeWrite(self):
            return f'''
            xc->setMiscReg(snsBankedIndex(dest, xc->tcBase()),
                           {self.base_name});
            if (traceData)
                traceData->setData({self.base_name});
            '''
        def __init__(self, idx, id=srtNormal, ctype='uw'):
            super().__init__(idx, id, ctype, (None, None, 'IsControl'))

    class CntrlNsBankedReg64(CntrlNsBankedReg):
        def __init__(self, idx, id=srtNormal, ctype='ud'):
            super().__init__(idx, id, ctype)

    class CntrlRegNC(CntrlReg):
        pass

    class PCStateReg(PCStateOp):
        def __init__(self, idx, id):
            super().__init__('ud', idx, (None, None, 'IsControl'), id)
}};

def operands {{
    #Abstracted integer reg operands
    'Dest': IntReg('dest'),
    'Dest64': IntReg64('dest'),
    'XDest': IntRegX64('dest'),
    'WDest': IntRegW64('dest'),
    'IWDest': IntRegIWPC('dest'),
    'AIWDest': IntRegAIWPC('dest'),
    'Dest2': IntReg('dest2'),
    'XDest2': IntRegX64('dest2'),
    'IWDest2': IntRegIWPC('dest2'),
    'Result': IntReg('result'),
    'XResult': IntRegX64('result'),
    'XResult2': IntRegX64('result2'),
    'XBase': IntRegX64('base', id=srtBase),
    'Base': IntRegAPC('base', id=srtBase),
    'XOffset': IntRegX64('offset'),
    'Index': IntReg('index'),
    'Shift': IntReg('shift'),
    'Op1': IntReg('op1'),
    'Op2': IntReg('op2'),
    'Op3': IntReg('op3'),
    'Op164': IntReg64('op1'),
    'Op264': IntReg64('op2'),
    'Op364': IntReg64('op3'),
    'XOp1': IntRegX64('op1'),
    'XOp2': IntRegX64('op2'),
    'XOp3': IntRegX64('op3'),
    'WOp1': IntRegW64('op1'),
    'WOp2': IntRegW64('op2'),
    'WOp3': IntRegW64('op3'),
    'Reg0': IntReg('reg0'),
    'Reg1': IntReg('reg1'),
    'Reg2': IntReg('reg2'),
    'Reg3': IntReg('reg3'),
    'PInt0': PIntReg('reg0'),
    'PInt1': PIntReg('reg1'),
    'PInt2': PIntReg('reg2'),
    'PInt3': PIntReg('reg3'),

    #Fixed index integer reg operands
    'SpMode': IntRegNPC('int_reg::regInMode((OperatingMode)regMode, '
                        'int_reg::Sp)'),
    'DecodedBankedIntReg':
        IntRegNPC('decodeMrsMsrBankedIntRegIndex(byteMask, r)'),
    'LR': IntRegNPC('int_reg::Lr'),
    'XLR': IntRegX64('int_reg::X30'),
    'R7': IntRegNPC('7'),
    # First four arguments are passed in registers
    'R0': IntRegNPC('0'),
    'R1': IntRegNPC('1'),
    'R2': IntRegNPC('2'),
    'R3': IntRegNPC('3'),
    'R4': IntRegNPC('4'),
    'R5': IntRegNPC('5'),
    'X0': IntRegX64('0'),
    'X1': IntRegX64('1'),
    'X2': IntRegX64('2'),
    'X3': IntRegX64('3'),
    'X4': IntRegX64('4'),
    'X5': IntRegX64('5'),

    # Condition code registers
    'CondCodesNZ': CCReg('cc_reg::Nz'),
    'CondCodesC': CCReg('cc_reg::C'),
    'CondCodesV': CCReg('cc_reg::V'),
    'CondCodesGE': CCReg('cc_reg::Ge'),
    'OptCondCodesNZ': CCReg(
            '''((condCode == COND_AL || condCode == COND_UC ||
                 condCode == COND_CC || condCode == COND_CS ||
                 condCode == COND_VS || condCode == COND_VC) ?
                cc_reg::Zero : cc_reg::Nz)'''),
    'OptCondCodesC': CCReg(
             '''((condCode == COND_HI || condCode == COND_LS ||
                condCode == COND_CS || condCode == COND_CC) ?
               cc_reg::C : cc_reg::Zero)'''),
    'OptShiftRmCondCodesC': CCReg(
            '''((condCode == COND_HI || condCode == COND_LS ||
                 condCode == COND_CS || condCode == COND_CC ||
                 shiftType == ROR) ?
                cc_reg::C : cc_reg::Zero)'''),
    'OptCondCodesV': CCReg(
            '''((condCode == COND_VS || condCode == COND_VC ||
                 condCode == COND_GE || condCode == COND_LT ||
                 condCode == COND_GT || condCode == COND_LE) ?
                cc_reg::V : cc_reg::Zero)'''),
    'FpCondCodes': CCReg('cc_reg::Fp'),

    #Abstracted floating point reg operands
    'FpDest': VectorElem('dest'),
    'FpDestP0': VectorElem('dest + 0'),
    'FpDestP1': VectorElem('dest + 1'),
    'FpDestP2': VectorElem('dest + 2'),
    'FpDestP3': VectorElem('dest + 3'),
    'FpDestP4': VectorElem('dest + 4'),
    'FpDestP5': VectorElem('dest + 5'),
    'FpDestP6': VectorElem('dest + 6'),
    'FpDestP7': VectorElem('dest + 7'),

    'FpDestS0P0': VectorElem('dest + step * 0 + 0'),
    'FpDestS0P1': VectorElem('dest + step * 0 + 1'),
    'FpDestS1P0': VectorElem('dest + step * 1 + 0'),
    'FpDestS1P1': VectorElem('dest + step * 1 + 1'),
    'FpDestS2P0': VectorElem('dest + step * 2 + 0'),
    'FpDestS2P1': VectorElem('dest + step * 2 + 1'),
    'FpDestS3P0': VectorElem('dest + step * 3 + 0'),
    'FpDestS3P1': VectorElem('dest + step * 3 + 1'),

    'FpDest2': VectorElem('dest2'),
    'FpDest2P0': VectorElem('dest2 + 0'),
    'FpDest2P1': VectorElem('dest2 + 1'),
    'FpDest2P2': VectorElem('dest2 + 2'),
    'FpDest2P3': VectorElem('dest2 + 3'),

    'FpOp1': VectorElem('op1'),
    'FpOp1P0': VectorElem('op1 + 0'),
    'FpOp1P1': VectorElem('op1 + 1'),
    'FpOp1P2': VectorElem('op1 + 2'),
    'FpOp1P3': VectorElem('op1 + 3'),
    'FpOp1P4': VectorElem('op1 + 4'),
    'FpOp1P5': VectorElem('op1 + 5'),
    'FpOp1P6': VectorElem('op1 + 6'),
    'FpOp1P7': VectorElem('op1 + 7'),

    'FpOp1S0P0': VectorElem('op1 + step * 0 + 0'),
    'FpOp1S0P1': VectorElem('op1 + step * 0 + 1'),
    'FpOp1S1P0': VectorElem('op1 + step * 1 + 0'),
    'FpOp1S1P1': VectorElem('op1 + step * 1 + 1'),
    'FpOp1S2P0': VectorElem('op1 + step * 2 + 0'),
    'FpOp1S2P1': VectorElem('op1 + step * 2 + 1'),
    'FpOp1S3P0': VectorElem('op1 + step * 3 + 0'),
    'FpOp1S3P1': VectorElem('op1 + step * 3 + 1'),

    'FpOp2': VectorElem('op2'),
    'FpOp2P0': VectorElem('op2 + 0'),
    'FpOp2P1': VectorElem('op2 + 1'),
    'FpOp2P2': VectorElem('op2 + 2'),
    'FpOp2P3': VectorElem('op2 + 3'),

    # Create AArch64 unpacked view of the FP registers
    # Name   ::= 'AA64Vec' OpSpec [LaneSpec]
    # OpSpec ::= IOSpec [Index] [Plus]
    # IOSpec ::= 'S' | 'D'
    # Index  ::= '0' | ... | '9'
    # Plus  ::= [PlusAmount] ['l']
    # PlusAmount ::= 'p' [PlusAmount]
    # LaneSpec ::= 'L' Index
    #
    # All the constituents are hierarchically defined as part of the Vector
    # Register they belong to

    'AA64FpOp1': VectorReg('op1', 'AA64FpOp1'),
    'AA64FpOp2': VectorReg('op2', 'AA64FpOp2'),
    'AA64FpOp3': VectorReg('op3', 'AA64FpOp3'),
    'AA64FpDest': VectorReg('dest', 'AA64FpDest'),
    'AA64FpDest2': VectorReg('dest2', 'AA64FpDest2'),
    'AA64FpOp1V0': VectorReg('op1', 'AA64FpOp1', 'V0'),
    'AA64FpOp1V1': VectorReg('op1 + 1', 'AA64FpOp1', 'V1'),
    'AA64FpOp1V2': VectorReg('op1 + 2', 'AA64FpOp1', 'V2'),
    'AA64FpOp1V3': VectorReg('op1 + 3', 'AA64FpOp1', 'V3'),
    'AA64FpOp1V0S': VectorReg('(op1 + 0) % 32', 'AA64FpOp1', 'V0S'),
    'AA64FpOp1V1S': VectorReg('(op1 + 1) % 32', 'AA64FpOp1', 'V1S'),
    'AA64FpOp1V2S': VectorReg('(op1 + 2) % 32', 'AA64FpOp1', 'V2S'),
    'AA64FpOp1V3S': VectorReg('(op1 + 3) % 32', 'AA64FpOp1', 'V3S'),
    'AA64FpDestV0': VectorReg('(dest + 0)', 'AA64FpDest', 'V0'),
    'AA64FpDestV1': VectorReg('(dest + 1)', 'AA64FpDest', 'V1'),
    'AA64FpDestV0L': VectorReg('(dest + 0) % 32', 'AA64FpDest', 'V0L'),
    'AA64FpDestV1L': VectorReg('(dest + 1) % 32', 'AA64FpDest', 'V1L'),

    # Temporary registers for SVE interleaving
    'AA64IntrlvReg0': VectorReg('INTRLVREG0', 'AA64FpIntrlvReg0'),
    'AA64IntrlvReg1': VectorReg('INTRLVREG1', 'AA64FpIntrlvReg1'),
    'AA64IntrlvReg2': VectorReg('INTRLVREG2', 'AA64FpIntrlvReg2'),
    'AA64IntrlvReg3': VectorReg('INTRLVREG3', 'AA64FpIntrlvReg3'),
    'AA64FpDestMerge': VectorReg('dest', 'AA64FpDestMerge'),
    'AA64FpBase': VectorReg('base', 'AA64FpBase'),
    'AA64FpOffset': VectorReg('offset', 'AA64FpOffset'),
    'AA64FpUreg0': VectorReg('VECREG_UREG0', 'AA64FpUreg0'),

    # Predicate register operands
    'GpOp': VecPredReg('gp'),
    'POp1': VecPredReg('op1'),
    'POp2': VecPredReg('op2'),
    'PDest': VecPredReg('dest'),
    'PDestMerge': VecPredReg('dest'),
    'Ffr': VecPredReg('PREDREG_FFR'),
    'FfrAux': VecPredReg('PREDREG_FFR'),
    'PUreg0': VecPredReg('PREDREG_UREG0'),

    #Abstracted control reg operands
    'MiscDest': CntrlReg('dest'),
    'MiscOp1': CntrlReg('op1'),
    'MiscNsBankedDest': CntrlNsBankedReg('dest'),
    'MiscNsBankedOp1': CntrlNsBankedReg('op1'),
    'MiscNsBankedDest64': CntrlNsBankedReg64('dest'),
    'MiscNsBankedOp164': CntrlNsBankedReg64('op1'),

    #Fixed index control regs
    'Cpsr': CntrlReg('MISCREG_CPSR', srtCpsr),
    'CpsrQ': CntrlReg('MISCREG_CPSR_Q', srtCpsr),
    'Spsr': CntrlRegNC('MISCREG_SPSR'),
    'Fpsr': CntrlRegNC('MISCREG_FPSR'),
    'Fpsid': CntrlRegNC('MISCREG_FPSID'),
    'Fpscr': CntrlRegNC('MISCREG_FPSCR'),
    'FpscrQc': CntrlRegNC('MISCREG_FPSCR_QC'),
    'FpscrExc': CntrlRegNC('MISCREG_FPSCR_EXC'),
    'Cpacr': CntrlReg('MISCREG_CPACR'),
    'Cpacr64': CntrlReg64('MISCREG_CPACR_EL1'),
    'Fpexc': CntrlRegNC('MISCREG_FPEXC'),
    'Nsacr': CntrlReg('MISCREG_NSACR'),
    'ElrHyp': CntrlRegNC('MISCREG_ELR_HYP'),
    'Hcr': CntrlReg('MISCREG_HCR'),
    'Hcr64': CntrlReg64('MISCREG_HCR_EL2'),
    'CptrEl264': CntrlReg64('MISCREG_CPTR_EL2'),
    'CptrEl364': CntrlReg64('MISCREG_CPTR_EL3'),
    'Hstr': CntrlReg('MISCREG_HSTR'),
    'Scr': CntrlReg('MISCREG_SCR'),
    'Scr64': CntrlReg64('MISCREG_SCR_EL3'),
    'Sctlr': CntrlRegNC('MISCREG_SCTLR'),
    'SevMailbox': CntrlRegNC('MISCREG_SEV_MAILBOX'),
    'LLSCLock': CntrlRegNC('MISCREG_LOCKFLAG'),
    'Dczid' : CntrlRegNC('MISCREG_DCZID_EL0'),
    'PendingDvm': CntrlRegNC('MISCREG_TLBINEEDSYNC'),

    #Register fields for microops
    'URa' : IntReg('ura'),
    'XURa' : IntRegX64('ura'),
    'WURa' : IntRegW64('ura'),
    'IWRa' : IntRegIWPC('ura'),
    'Fa' : VectorElem('ura'),
    'URb' : IntReg('urb'),
    'XURb' : IntRegX64('urb'),
    'URc' : IntReg('urc'),
    'XURc' : IntRegX64('urc'),

    #Memory Operand
    'Mem': MemOp('uw', None, (None, 'IsLoad', 'IsStore'), srtNormal),

    #PCState fields
    'RawPC': PCStateReg('pc', srtPC),
    'PC': PCStateReg('instPC', srtPC),
    'NPC': PCStateReg('instNPC', srtPC),
    'pNPC': PCStateReg('instNPC', srtEPC),
    'IWNPC': PCStateReg('instIWNPC', srtPC),
    'Thumb': PCStateReg('thumb', srtPC),
    'NextThumb': PCStateReg('nextThumb', srtMode),
    'NextJazelle': PCStateReg('nextJazelle', srtMode),
    'NextItState': PCStateReg('nextItstate', srtMode),
    'Itstate': PCStateReg('itstate', srtMode),
    'NextAArch64': PCStateReg('nextAArch64', srtMode),

    #Register operands depending on a field in the instruction encoding. These
    #should be avoided since they may not be portable across different
    #encodings of the same instruction.
    'Rd': IntReg('RD'),
    'Rm': IntReg('RM'),
    'Rs': IntReg('RS'),
    'Rn': IntReg('RN'),
    'Rt': IntReg('RT')
}};