path: root/src/3rdparty/webkit/JavaScriptCore/assembler/ARMv7Assembler.h

/*
 * Copyright (C) 2009 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 ARMAssembler_h
#define ARMAssembler_h

#include <wtf/Platform.h>

#if ENABLE(ASSEMBLER) && PLATFORM_ARM_ARCH(7)

#include "AssemblerBuffer.h"
#include <wtf/Assertions.h>
#include <wtf/Vector.h>
#include <stdint.h>

namespace JSC {

namespace ARM {
    typedef enum {
        r0,
        r1,
        r2,
        r3,
        r4,
        r5,
        r6,
        r7, wr = r7,   // thumb work register
        r8,
        r9, sb = r9,   // static base
        r10, sl = r10, // stack limit
        r11, fp = r11, // frame pointer
        r12, ip = r12,
        r13, sp = r13,
        r14, lr = r14,
        r15, pc = r15,
    } RegisterID;

    // s0 == d0 == q0
    // s4 == d2 == q1
    // etc
    typedef enum {
        s0 = 0,
        s1 = 1,
        s2 = 2,
        s3 = 3,
        s4 = 4,
        s5 = 5,
        s6 = 6,
        s7 = 7,
        s8 = 8,
        s9 = 9,
        s10 = 10,
        s11 = 11,
        s12 = 12,
        s13 = 13,
        s14 = 14,
        s15 = 15,
        s16 = 16,
        s17 = 17,
        s18 = 18,
        s19 = 19,
        s20 = 20,
        s21 = 21,
        s22 = 22,
        s23 = 23,
        s24 = 24,
        s25 = 25,
        s26 = 26,
        s27 = 27,
        s28 = 28,
        s29 = 29,
        s30 = 30,
        s31 = 31,
        d0 = 0 << 1,
        d1 = 1 << 1,
        d2 = 2 << 1,
        d3 = 3 << 1,
        d4 = 4 << 1,
        d5 = 5 << 1,
        d6 = 6 << 1,
        d7 = 7 << 1,
        d8 = 8 << 1,
        d9 = 9 << 1,
        d10 = 10 << 1,
        d11 = 11 << 1,
        d12 = 12 << 1,
        d13 = 13 << 1,
        d14 = 14 << 1,
        d15 = 15 << 1,
        d16 = 16 << 1,
        d17 = 17 << 1,
        d18 = 18 << 1,
        d19 = 19 << 1,
        d20 = 20 << 1,
        d21 = 21 << 1,
        d22 = 22 << 1,
        d23 = 23 << 1,
        d24 = 24 << 1,
        d25 = 25 << 1,
        d26 = 26 << 1,
        d27 = 27 << 1,
        d28 = 28 << 1,
        d29 = 29 << 1,
        d30 = 30 << 1,
        d31 = 31 << 1,
        q0 = 0 << 2,
        q1 = 1 << 2,
        q2 = 2 << 2,
        q3 = 3 << 2,
        q4 = 4 << 2,
        q5 = 5 << 2,
        q6 = 6 << 2,
        q7 = 7 << 2,
        q8 = 8 << 2,
        q9 = 9 << 2,
        q10 = 10 << 2,
        q11 = 11 << 2,
        q12 = 12 << 2,
        q13 = 13 << 2,
        q14 = 14 << 2,
        q15 = 15 << 2,
        q16 = 16 << 2,
        q17 = 17 << 2,
        q18 = 18 << 2,
        q19 = 19 << 2,
        q20 = 20 << 2,
        q21 = 21 << 2,
        q22 = 22 << 2,
        q23 = 23 << 2,
        q24 = 24 << 2,
        q25 = 25 << 2,
        q26 = 26 << 2,
        q27 = 27 << 2,
        q28 = 28 << 2,
        q29 = 29 << 2,
        q30 = 30 << 2,
        q31 = 31 << 2,
    } FPRegisterID;
}

class ARMv7Assembler;
class ARMThumbImmediate {
    friend class ARMv7Assembler;

    typedef uint8_t ThumbImmediateType;
    static const ThumbImmediateType TypeInvalid = 0;
    static const ThumbImmediateType TypeEncoded = 1;
    static const ThumbImmediateType TypeUInt16 = 2;

    typedef union {
        int16_t asInt;
        struct {
            unsigned imm8 : 8;
            unsigned imm3 : 3;
            unsigned i    : 1;
            unsigned imm4 : 4;
        };
        // If this is an encoded immediate, then it may describe a shift, or a pattern.
        struct {
            unsigned shiftValue7 : 7;
            unsigned shiftAmount : 5;
        };
        struct {
            unsigned immediate   : 8;
            unsigned pattern     : 4;
        };
    } ThumbImmediateValue;

    // byte0 contains least significant bit; not using an array to make client code endian agnostic.
    typedef union {
        int32_t asInt;
        struct {
            uint8_t byte0;
            uint8_t byte1;
            uint8_t byte2;
            uint8_t byte3;
        };
    } PatternBytes;

    ALWAYS_INLINE static int32_t countLeadingZerosPartial(uint32_t& value, int32_t& zeros, const int N)
    {
        if (value & ~((1<<N)-1)) /* check for any of the top N bits (of 2N bits) are set */ \
            value >>= N;         /* if any were set, lose the bottom N */ \
        else                     /* if none of the top N bits are set, */ \
            zeros += N;          /* then we have identified N leading zeros */
    }

    static int32_t countLeadingZeros(uint32_t value)
    {
        if (!value)
            return 32;

        int32_t zeros = 0;
        countLeadingZerosPartial(value, zeros, 16);
        countLeadingZerosPartial(value, zeros, 8);
        countLeadingZerosPartial(value, zeros, 4);
        countLeadingZerosPartial(value, zeros, 2);
        countLeadingZerosPartial(value, zeros, 1);
        return zeros;
    }

    ARMThumbImmediate()
        : m_type(TypeInvalid)
    {
        m_value.asInt = 0;
    }
        
    ARMThumbImmediate(ThumbImmediateType type, ThumbImmediateValue value)
        : m_type(type)
        , m_value(value)
    {
    }

    ARMThumbImmediate(ThumbImmediateType type, uint16_t value)
        : m_type(TypeUInt16)
    {
        m_value.asInt = value;
    }

public:
    static ARMThumbImmediate makeEncodedImm(uint32_t value)
    {
        ThumbImmediateValue encoding;
        encoding.asInt = 0;

        // okay, these are easy.
        if (value < 256) {
            encoding.immediate = value;
            encoding.pattern = 0;
            return ARMThumbImmediate(TypeEncoded, encoding);
        }

        int32_t leadingZeros = countLeadingZeros(value);
        // if there were 24 or more leading zeros, then we'd have hit the (value < 256) case.
        ASSERT(leadingZeros < 24);

        // Given a number with bit fields Z:B:C, where count(Z)+count(B)+count(C) == 32,
        // Z are the bits known zero, B is the 8-bit immediate, C are the bits to check for
        // zero.  count(B) == 8, so the count of bits to be checked is 24 - count(Z).
        int32_t rightShiftAmount = 24 - leadingZeros;
        if (value == ((value >> rightShiftAmount) << rightShiftAmount)) {
            // Shift the value down to the low byte position.  The assign to 
            // shiftValue7 drops the implicit top bit.
            encoding.shiftValue7 = value >> rightShiftAmount;
            // The endoded shift amount is the magnitude of a right rotate.
            encoding.shiftAmount = 8 + leadingZeros;
            return ARMThumbImmediate(TypeEncoded, encoding);
        }
        
        PatternBytes bytes;
        bytes.asInt = value;

        if ((bytes.byte0 == bytes.byte1) && (bytes.byte0 == bytes.byte2) && (bytes.byte0 == bytes.byte3)) {
            encoding.immediate = bytes.byte0;
            encoding.pattern = 3;
            return ARMThumbImmediate(TypeEncoded, encoding);
        }

        if ((bytes.byte0 == bytes.byte2) && !(bytes.byte1 | bytes.byte3)) {
            encoding.immediate = bytes.byte0;
            encoding.pattern = 1;
            return ARMThumbImmediate(TypeEncoded, encoding);
        }

        if ((bytes.byte1 == bytes.byte3) && !(bytes.byte0 | bytes.byte2)) {
            encoding.immediate = bytes.byte0;
            encoding.pattern = 2;
            return ARMThumbImmediate(TypeEncoded, encoding);
        }

        return ARMThumbImmediate();
    }

    static ARMThumbImmediate makeUInt12(int32_t value)
    {
        return (!(value & 0xfffff000))
            ? ARMThumbImmediate(TypeUInt16, (uint16_t)value)
            : ARMThumbImmediate();
    }

    static ARMThumbImmediate makeUInt12OrEncodedImm(int32_t value)
    {
        // If this is not a 12-bit unsigned it, try making an encoded immediate.
        return (!(value & 0xfffff000))
            ? ARMThumbImmediate(TypeUInt16, (uint16_t)value)
            : makeEncodedImm(value);
    }

    // The 'make' methods, above, return a !isValid() value if the argument
    // cannot be represented as the requested type.  This methods  is called
    // 'get' since the argument can always be represented.
    static ARMThumbImmediate makeUInt16(uint16_t value)
    {
        return ARMThumbImmediate(TypeUInt16, value);
    }
    
    bool isValid()
    {
        return m_type != TypeInvalid;
    }

    // These methods rely on the format of encoded byte values.
    bool isUInt3() { return !(m_value.asInt & 0xfff8); }
    bool isUInt4() { return !(m_value.asInt & 0xfff0); }
    bool isUInt5() { return !(m_value.asInt & 0xffe0); }
    bool isUInt6() { return !(m_value.asInt & 0xffc0); }
    bool isUInt7() { return !(m_value.asInt & 0xff80); }
    bool isUInt8() { return !(m_value.asInt & 0xff00); }
    bool isUInt9() { return (m_type == TypeUInt16) && !(m_value.asInt & 0xfe00); }
    bool isUInt10() { return (m_type == TypeUInt16) && !(m_value.asInt & 0xfc00); }
    bool isUInt12() { return (m_type == TypeUInt16) && !(m_value.asInt & 0xf000); }
    bool isUInt16() { return m_type == TypeUInt16; }
    uint8_t getUInt3() { ASSERT(isUInt3()); return m_value.asInt; }
    uint8_t getUInt4() { ASSERT(isUInt4()); return m_value.asInt; }
    uint8_t getUInt5() { ASSERT(isUInt5()); return m_value.asInt; }
    uint8_t getUInt6() { ASSERT(isUInt6()); return m_value.asInt; }
    uint8_t getUInt7() { ASSERT(isUInt7()); return m_value.asInt; }
    uint8_t getUInt8() { ASSERT(isUInt8()); return m_value.asInt; }
    uint8_t getUInt9() { ASSERT(isUInt9()); return m_value.asInt; }
    uint8_t getUInt10() { ASSERT(isUInt10()); return m_value.asInt; }
    uint16_t getUInt12() { ASSERT(isUInt12()); return m_value.asInt; }
    uint16_t getUInt16() { ASSERT(isUInt16()); return m_value.asInt; }

    bool isEncodedImm() { return m_type == TypeEncoded; }

private:
    ThumbImmediateType m_type;
    ThumbImmediateValue m_value;
};


typedef enum {
    SRType_LSL,
    SRType_LSR,
    SRType_ASR,
    SRType_ROR,

    SRType_RRX = SRType_ROR
} ARMShiftType;

class ARMv7Assembler;
class ShiftTypeAndAmount {
    friend class ARMv7Assembler;

public:
    ShiftTypeAndAmount()
    {
        m_u.type = (ARMShiftType)0;
        m_u.amount = 0;
    }
    
    ShiftTypeAndAmount(ARMShiftType type, unsigned amount)
    {
        m_u.type = type;
        m_u.amount = amount & 31;
    }
    
    unsigned lo4() { return m_u.lo4; }
    unsigned hi4() { return m_u.hi4; }
    
private:
    union {
        struct {
            unsigned lo4 : 4;
            unsigned hi4 : 4;
        };
        struct {
            unsigned type   : 2;
            unsigned amount : 5;
        };
    } m_u;
};


/*
Some features of the Thumb instruction set are deprecated in ARMv7. Deprecated features affecting 
instructions supported by ARMv7-M are as follows: 
• use of the PC as <Rd> or <Rm> in a 16-bit ADD (SP plus register) instruction 
• use of the SP as <Rm> in a 16-bit ADD (SP plus register) instruction 
• use of the SP as <Rm> in a 16-bit CMP (register) instruction 
• use of MOV (register) instructions in which <Rd> is the SP or PC and <Rm> is also the SP or PC. 
• use of <Rn> as the lowest-numbered register in the register list of a 16-bit STM instruction with base 
register writeback 
*/

class ARMv7Assembler {
public:
    typedef ARM::RegisterID RegisterID;
    typedef ARM::FPRegisterID FPRegisterID;

    // (HS, LO, HI, LS) -> (AE, B, A, BE)
    // (VS, VC) -> (O, NO)
    typedef enum {
        ConditionEQ,
        ConditionNE,
        ConditionHS,
        ConditionLO,
        ConditionMI,
        ConditionPL,
        ConditionVS,
        ConditionVC,
        ConditionHI,
        ConditionLS,
        ConditionGE,
        ConditionLT,
        ConditionGT,
        ConditionLE,
        ConditionAL,

        ConditionCS = ConditionHS,
        ConditionCC = ConditionLO,
    } Condition;

    class JmpSrc {
        friend class ARMv7Assembler;
        friend class ARMInstructionFormatter;
    public:
        JmpSrc()
            : m_offset(-1)
        {
        }

    private:
        JmpSrc(int offset)
            : m_offset(offset)
        {
        }

        int m_offset;
    };
    
    class JmpDst {
        friend class ARMv7Assembler;
        friend class ARMInstructionFormatter;
    public:
        JmpDst()
            : m_offset(-1)
            , m_used(false)
        {
        }

        bool isUsed() const { return m_used; }
        void used() { m_used = true; }
    private:
        JmpDst(int offset)
            : m_offset(offset)
            , m_used(false)
        {
            ASSERT(m_offset == offset);
        }

        int m_offset : 31;
        int m_used : 1;
    };

private:

    // ARMv7, Appx-A.6.3
    bool BadReg(RegisterID reg)
    {
        return (reg == ARM::sp) || (reg == ARM::pc);
    }

    bool isSingleRegister(FPRegisterID reg)
    {
        // Check that the high bit isn't set (q16+), and that the low bit isn't (s1, s3, etc).
        return !(reg & ~31);
    }

    bool isDoubleRegister(FPRegisterID reg)
    {
        // Check that the high bit isn't set (q16+), and that the low bit isn't (s1, s3, etc).
        return !(reg & ~(31 << 1));
    }

    bool isQuadRegister(FPRegisterID reg)
    {
        return !(reg & ~(31 << 2));
    }

    uint32_t singleRegisterNum(FPRegisterID reg)
    {
        ASSERT(isSingleRegister(reg));
        return reg;
    }

    uint32_t doubleRegisterNum(FPRegisterID reg)
    {
        ASSERT(isDoubleRegister(reg));
        return reg >> 1;
    }

    uint32_t quadRegisterNum(FPRegisterID reg)
    {
        ASSERT(isQuadRegister(reg));
        return reg >> 2;
    }

    uint32_t singleRegisterMask(FPRegisterID rd, int highBitsShift, int lowBitShift)
    {
        uint32_t rdNum = singleRegisterNum(rd);
        uint32_t rdMask = (rdNum >> 1) << highBitsShift;
        if (rdNum & 1)
            rdMask |= 1 << lowBitShift;
        return rdMask;
    }

    uint32_t doubleRegisterMask(FPRegisterID rd, int highBitShift, int lowBitsShift)
    {
        uint32_t rdNum = doubleRegisterNum(rd);
        uint32_t rdMask = (rdNum & 0xf) << lowBitsShift;
        if (rdNum & 16)
            rdMask |= 1 << highBitShift;
        return rdMask;
    }

    typedef enum {
        OP_ADD_reg_T1       = 0x1800,
        OP_ADD_S_reg_T1     = 0x1800,
        OP_SUB_reg_T1       = 0x1A00,
        OP_SUB_S_reg_T1     = 0x1A00,
        OP_ADD_imm_T1       = 0x1C00,
        OP_ADD_S_imm_T1     = 0x1C00,
        OP_SUB_imm_T1       = 0x1E00,
        OP_SUB_S_imm_T1     = 0x1E00,
        OP_MOV_imm_T1       = 0x2000,
        OP_CMP_imm_T1       = 0x2800,
        OP_ADD_imm_T2       = 0x3000,
        OP_ADD_S_imm_T2     = 0x3000,
        OP_SUB_imm_T2       = 0x3800,
        OP_SUB_S_imm_T2     = 0x3800,
        OP_AND_reg_T1       = 0x4000,
        OP_EOR_reg_T1       = 0x4040,
        OP_TST_reg_T1       = 0x4200,
        OP_CMP_reg_T1       = 0x4280,
        OP_ORR_reg_T1       = 0x4300,
        OP_MVN_reg_T1       = 0x43C0,
        OP_ADD_reg_T2       = 0x4400,
        OP_MOV_reg_T1       = 0x4600,
        OP_BLX              = 0x4700,
        OP_BX               = 0x4700,
        OP_LDRH_reg_T1      = 0x5A00,
        OP_STR_reg_T1       = 0x5000,
        OP_LDR_reg_T1       = 0x5800,
        OP_STR_imm_T1       = 0x6000,
        OP_LDR_imm_T1       = 0x6800,
        OP_LDRH_imm_T1      = 0x8800,
        OP_STR_imm_T2       = 0x9000,
        OP_LDR_imm_T2       = 0x9800,
        OP_ADD_SP_imm_T1    = 0xA800,
        OP_ADD_SP_imm_T2    = 0xB000,
        OP_SUB_SP_imm_T1    = 0xB080,
        OP_BKPT             = 0xBE00,
        OP_IT               = 0xBF00,
    } OpcodeID;

    typedef enum {
        OP_AND_reg_T2   = 0xEA00,
        OP_TST_reg_T2   = 0xEA10,
        OP_ORR_reg_T2   = 0xEA40,
        OP_ASR_imm_T1   = 0xEA4F,
        OP_LSL_imm_T1   = 0xEA4F,
        OP_LSR_imm_T1   = 0xEA4F,
        OP_ROR_imm_T1   = 0xEA4F,
        OP_MVN_reg_T2   = 0xEA6F,
        OP_EOR_reg_T2   = 0xEA80,
        OP_ADD_reg_T3   = 0xEB00,
        OP_ADD_S_reg_T3 = 0xEB10,
        OP_SUB_reg_T2   = 0xEBA0,
        OP_SUB_S_reg_T2 = 0xEBB0,
        OP_CMP_reg_T2   = 0xEBB0,
        OP_B_T4a        = 0xF000,
        OP_AND_imm_T1   = 0xF000,
        OP_TST_imm      = 0xF010,
        OP_ORR_imm_T1   = 0xF040,
        OP_MOV_imm_T2   = 0xF040,
        OP_MVN_imm      = 0xF060,
        OP_EOR_imm_T1   = 0xF080,
        OP_ADD_imm_T3   = 0xF100,
        OP_ADD_S_imm_T3 = 0xF110,
        OP_CMN_imm      = 0xF110,
        OP_SUB_imm_T3   = 0xF1A0,
        OP_SUB_S_imm_T3 = 0xF1B0,
        OP_CMP_imm_T2   = 0xF1B0,
        OP_ADD_imm_T4   = 0xF200,
        OP_MOV_imm_T3   = 0xF240,
        OP_SUB_imm_T4   = 0xF2A0,
        OP_MOVT         = 0xF2C0,
        OP_LDRH_reg_T2  = 0xF830,
        OP_LDRH_imm_T3  = 0xF830,
        OP_STR_imm_T4   = 0xF840,
        OP_STR_reg_T2   = 0xF840,
        OP_LDR_imm_T4   = 0xF850,
        OP_LDR_reg_T2   = 0xF850,
        OP_LDRH_imm_T2  = 0xF8B0,
        OP_STR_imm_T3   = 0xF8C0,
        OP_LDR_imm_T3   = 0xF8D0,
        OP_LSL_reg_T2   = 0xFA00,
        OP_LSR_reg_T2   = 0xFA20,
        OP_ASR_reg_T2   = 0xFA40,
        OP_ROR_reg_T2   = 0xFA60,
        OP_SMULL_T1     = 0xFB80,
    } OpcodeID1;

    typedef enum {
        OP_B_T4b        = 0x9000,
    } OpcodeID2;

    struct FourFours {
        FourFours(unsigned f3, unsigned f2, unsigned f1, unsigned f0)
        {
            m_u.f0 = f0;
            m_u.f1 = f1;
            m_u.f2 = f2;
            m_u.f3 = f3;
        }

        union {
            unsigned value;
            struct {
                unsigned f0 : 4;
                unsigned f1 : 4;
                unsigned f2 : 4;
                unsigned f3 : 4;
            };
        } m_u;
    };

    class ARMInstructionFormatter;

    // false means else!
    bool ifThenElseConditionBit(Condition condition, bool isIf)
    {
        return isIf ? (condition & 1) : !(condition & 1);
    }
    uint8_t ifThenElse(Condition condition, bool inst2if, bool inst3if, bool inst4if)
    {
        int mask = (ifThenElseConditionBit(condition, inst2if) << 3)
            | (ifThenElseConditionBit(condition, inst3if) << 2)
            | (ifThenElseConditionBit(condition, inst4if) << 1)
            | 1;
        ASSERT((condition != ConditionAL) || (mask & (mask - 1)));
        return (condition << 4) | mask;
    }
    uint8_t ifThenElse(Condition condition, bool inst2if, bool inst3if)
    {
        int mask = (ifThenElseConditionBit(condition, inst2if) << 3)
            | (ifThenElseConditionBit(condition, inst3if) << 2)
            | 2;
        ASSERT((condition != ConditionAL) || (mask & (mask - 1)));
        return (condition << 4) | mask;
    }
    uint8_t ifThenElse(Condition condition, bool inst2if)
    {
        int mask = (ifThenElseConditionBit(condition, inst2if) << 3)
            | 4;
        ASSERT((condition != ConditionAL) || (mask & (mask - 1)));
        return (condition << 4) | mask;
    }

    uint8_t ifThenElse(Condition condition)
    {
        int mask = 8;
        ASSERT((condition != ConditionAL) || (mask & (mask - 1)));
        return (condition << 4) | mask;
    }

public:

    void add(RegisterID rd, RegisterID rn, ARMThumbImmediate imm)
    {
        // Rd can only be SP if Rn is also SP.
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(imm.isValid());

        if (rn == ARM::sp) {
            if (!(rd & 8) && imm.isUInt10()) {
                m_formatter.oneWordOp5Reg3Imm8(OP_ADD_SP_imm_T1, rd, imm.getUInt10() >> 2);
                return;
            } else if ((rd == ARM::sp) && imm.isUInt9()) {
                m_formatter.oneWordOp9Imm7(OP_ADD_SP_imm_T2, imm.getUInt9() >> 2);
                return;
            }
        } else if (!((rd | rn) & 8)) {
            if (imm.isUInt3()) {
                m_formatter.oneWordOp7Reg3Reg3Reg3(OP_ADD_imm_T1, (RegisterID)imm.getUInt3(), rn, rd);
                return;
            } else if ((rd == rn) && imm.isUInt8()) {
                m_formatter.oneWordOp5Reg3Imm8(OP_ADD_imm_T2, rd, imm.getUInt8());
                return;
            }
        }

        if (imm.isEncodedImm())
            m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_ADD_imm_T3, rn, rd, imm);
        else {
            ASSERT(imm.isUInt12());
            m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_ADD_imm_T4, rn, rd, imm);
        }
    }

    void add(RegisterID rd, RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_ADD_reg_T3, rn, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    // NOTE: In an IT block, add doesn't modify the flags register.
    void add(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        if (rd == rn)
            m_formatter.oneWordOp8RegReg143(OP_ADD_reg_T2, rm, rd);
        else if (rd == rm)
            m_formatter.oneWordOp8RegReg143(OP_ADD_reg_T2, rn, rd);
        else if (!((rd | rn | rm) & 8))
            m_formatter.oneWordOp7Reg3Reg3Reg3(OP_ADD_reg_T1, rm, rn, rd);
        else
            add(rd, rn, rm, ShiftTypeAndAmount());
    }

    // Not allowed in an IT (if then) block.
    void add_S(RegisterID rd, RegisterID rn, ARMThumbImmediate imm)
    {
        // Rd can only be SP if Rn is also SP.
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(imm.isEncodedImm());

        if (!((rd | rn) & 8)) {
            if (imm.isUInt3()) {
                m_formatter.oneWordOp7Reg3Reg3Reg3(OP_ADD_S_imm_T1, (RegisterID)imm.getUInt3(), rn, rd);
                return;
            } else if ((rd == rn) && imm.isUInt8()) {
                m_formatter.oneWordOp5Reg3Imm8(OP_ADD_S_imm_T2, rd, imm.getUInt8());
                return;
            }
        }

        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_ADD_S_imm_T3, rn, rd, imm);
    }

    // Not allowed in an IT (if then) block?
    void add_S(RegisterID rd, RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_ADD_S_reg_T3, rn, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    // Not allowed in an IT (if then) block.
    void add_S(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        if (!((rd | rn | rm) & 8))
            m_formatter.oneWordOp7Reg3Reg3Reg3(OP_ADD_S_reg_T1, rm, rn, rd);
        else
            add_S(rd, rn, rm, ShiftTypeAndAmount());
    }

    void ARM_and(RegisterID rd, RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(imm.isEncodedImm());
        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_AND_imm_T1, rn, rd, imm);
    }

    void ARM_and(RegisterID rd, RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_AND_reg_T2, rn, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    void ARM_and(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        if ((rd == rn) && !((rd | rm) & 8))
            m_formatter.oneWordOp10Reg3Reg3(OP_AND_reg_T1, rm, rd);
        else if ((rd == rm) && !((rd | rn) & 8))
            m_formatter.oneWordOp10Reg3Reg3(OP_AND_reg_T1, rn, rd);
        else
            ARM_and(rd, rn, rm, ShiftTypeAndAmount());
    }

    void asr(RegisterID rd, RegisterID rm, int32_t shiftAmount)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rm));
        ShiftTypeAndAmount shift(SRType_ASR, shiftAmount);
        m_formatter.twoWordOp16FourFours(OP_ASR_imm_T1, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    void asr(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_ASR_reg_T2, rn, FourFours(0xf, rd, 0, rm));
    }

    // Only allowed in IT (if then) block if last instruction.
    JmpSrc b()
    {
        m_formatter.twoWordOp16Op16(OP_B_T4a, OP_B_T4b);
        return JmpSrc(m_formatter.size());
    }
    
    // Only allowed in IT (if then) block if last instruction.
    JmpSrc blx(RegisterID rm)
    {
        ASSERT(rm != ARM::pc);
        m_formatter.oneWordOp8RegReg143(OP_BLX, rm, (RegisterID)8);
        return JmpSrc(m_formatter.size());
    }

    // Only allowed in IT (if then) block if last instruction.
    JmpSrc bx(RegisterID rm)
    {
        m_formatter.oneWordOp8RegReg143(OP_BX, rm, (RegisterID)0);
        return JmpSrc(m_formatter.size());
    }

    void bkpt(uint8_t imm=0)
    {
        m_formatter.oneWordOp8Imm8(OP_BKPT, imm);
    }

    void cmn(RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(rn != ARM::pc);
        ASSERT(imm.isEncodedImm());

        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_CMN_imm, rn, (RegisterID)0xf, imm);
    }

    void cmp(RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(rn != ARM::pc);
        ASSERT(imm.isEncodedImm());

        if (!(rn & 8) && imm.isUInt8())
            m_formatter.oneWordOp5Reg3Imm8(OP_CMP_imm_T1, rn, imm.getUInt8());
        else
            m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_CMP_imm_T2, rn, (RegisterID)0xf, imm);
    }

    void cmp(RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT(rn != ARM::pc);
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_CMP_reg_T2, rn, FourFours(shift.hi4(), 0xf, shift.lo4(), rm));
    }

    void cmp(RegisterID rn, RegisterID rm)
    {
        if ((rn | rm) & 8)
            cmp(rn, rm, ShiftTypeAndAmount());
        else
            m_formatter.oneWordOp10Reg3Reg3(OP_CMP_reg_T1, rm, rn);
    }

    // xor is not spelled with an 'e'. :-(
    void eor(RegisterID rd, RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(imm.isEncodedImm());
        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_EOR_imm_T1, rn, rd, imm);
    }

    // xor is not spelled with an 'e'. :-(
    void eor(RegisterID rd, RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_EOR_reg_T2, rn, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    // xor is not spelled with an 'e'. :-(
    void eor(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        if ((rd == rn) && !((rd | rm) & 8))
            m_formatter.oneWordOp10Reg3Reg3(OP_EOR_reg_T1, rm, rd);
        else if ((rd == rm) && !((rd | rn) & 8))
            m_formatter.oneWordOp10Reg3Reg3(OP_EOR_reg_T1, rn, rd);
        else
            eor(rd, rn, rm, ShiftTypeAndAmount());
    }

    void it(Condition cond)
    {
        m_formatter.oneWordOp8Imm8(OP_IT, ifThenElse(cond));
    }

    void it(Condition cond, bool inst2if)
    {
        m_formatter.oneWordOp8Imm8(OP_IT, ifThenElse(cond, inst2if));
    }

    void it(Condition cond, bool inst2if, bool inst3if)
    {
        m_formatter.oneWordOp8Imm8(OP_IT, ifThenElse(cond, inst2if, inst3if));
    }

    void it(Condition cond, bool inst2if, bool inst3if, bool inst4if)
    {
        m_formatter.oneWordOp8Imm8(OP_IT, ifThenElse(cond, inst2if, inst3if, inst4if));
    }

    // rt == ARM::pc only allowed if last instruction in IT (if then) block.
    void ldr(RegisterID rt, RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(rn != ARM::pc); // LDR (literal)
        ASSERT(imm.isUInt12());

        if (!((rt | rn) & 8) && imm.isUInt7())
            m_formatter.oneWordOp5Imm5Reg3Reg3(OP_LDR_imm_T1, imm.getUInt7() >> 2, rn, rt);
        else if ((rn == ARM::sp) && !(rt & 8) && imm.isUInt10())
            m_formatter.oneWordOp5Reg3Imm8(OP_LDR_imm_T2, rt, imm.getUInt10() >> 2);
        else
            m_formatter.twoWordOp12Reg4Reg4Imm12(OP_LDR_imm_T3, rn, rt, imm.getUInt12());
    }

    // If index is set, this is a regular offset or a pre-indexed load;
    // if index is not set then is is a post-index load.
    //
    // If wback is set rn is updated - this is a pre or post index load,
    // if wback is not set this is a regular offset memory access.
    //
    // (-255 <= offset <= 255)
    // _reg = REG[rn]
    // _tmp = _reg + offset
    // MEM[index ? _tmp : _reg] = REG[rt]
    // if (wback) REG[rn] = _tmp
    void ldr(RegisterID rt, RegisterID rn, int offset, bool index, bool wback)
    {
        ASSERT(rt != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(index || wback);
        ASSERT(!wback | (rt != rn));
    
        bool add = true;
        if (offset < 0) {
            add = false;
            offset = -offset;
        }
        ASSERT((offset & ~0xff) == 0);
        
        offset |= (wback << 8);
        offset |= (add   << 9);
        offset |= (index << 10);
        offset |= (1 << 11);
        
        m_formatter.twoWordOp12Reg4Reg4Imm12(OP_LDR_imm_T4, rn, rt, offset);
    }

    // rt == ARM::pc only allowed if last instruction in IT (if then) block.
    void ldr(RegisterID rt, RegisterID rn, RegisterID rm, unsigned shift=0)
    {
        ASSERT(rn != ARM::pc); // LDR (literal)
        ASSERT(!BadReg(rm));
        ASSERT(shift <= 3);

        if (!shift && !((rt | rn | rm) & 8))
            m_formatter.oneWordOp7Reg3Reg3Reg3(OP_LDR_reg_T1, rm, rn, rt);
        else
            m_formatter.twoWordOp12Reg4FourFours(OP_LDR_reg_T2, rn, FourFours(rt, 0, shift, rm));
    }

    // rt == ARM::pc only allowed if last instruction in IT (if then) block.
    void ldrh(RegisterID rt, RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(rn != ARM::pc); // LDR (literal)
        ASSERT(imm.isUInt12());

        if (!((rt | rn) & 8) && imm.isUInt6())
            m_formatter.oneWordOp5Imm5Reg3Reg3(OP_LDRH_imm_T1, imm.getUInt6() >> 2, rn, rt);
        else
            m_formatter.twoWordOp12Reg4Reg4Imm12(OP_LDRH_imm_T2, rn, rt, imm.getUInt12());
    }

    // If index is set, this is a regular offset or a pre-indexed load;
    // if index is not set then is is a post-index load.
    //
    // If wback is set rn is updated - this is a pre or post index load,
    // if wback is not set this is a regular offset memory access.
    //
    // (-255 <= offset <= 255)
    // _reg = REG[rn]
    // _tmp = _reg + offset
    // MEM[index ? _tmp : _reg] = REG[rt]
    // if (wback) REG[rn] = _tmp
    void ldrh(RegisterID rt, RegisterID rn, int offset, bool index, bool wback)
    {
        ASSERT(rt != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(index || wback);
        ASSERT(!wback | (rt != rn));
    
        bool add = true;
        if (offset < 0) {
            add = false;
            offset = -offset;
        }
        ASSERT((offset & ~0xff) == 0);
        
        offset |= (wback << 8);
        offset |= (add   << 9);
        offset |= (index << 10);
        offset |= (1 << 11);
        
        m_formatter.twoWordOp12Reg4Reg4Imm12(OP_LDRH_imm_T3, rn, rt, offset);
    }

    void ldrh(RegisterID rt, RegisterID rn, RegisterID rm, unsigned shift=0)
    {
        ASSERT(!BadReg(rt));   // Memory hint
        ASSERT(rn != ARM::pc); // LDRH (literal)
        ASSERT(!BadReg(rm));
        ASSERT(shift <= 3);

        if (!shift && !((rt | rn | rm) & 8))
            m_formatter.oneWordOp7Reg3Reg3Reg3(OP_LDRH_reg_T1, rm, rn, rt);
        else
            m_formatter.twoWordOp12Reg4FourFours(OP_LDRH_reg_T2, rn, FourFours(rt, 0, shift, rm));
    }

    void lsl(RegisterID rd, RegisterID rm, int32_t shiftAmount)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rm));
        ShiftTypeAndAmount shift(SRType_LSL, shiftAmount);
        m_formatter.twoWordOp16FourFours(OP_LSL_imm_T1, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    void lsl(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_LSL_reg_T2, rn, FourFours(0xf, rd, 0, rm));
    }

    void lsr(RegisterID rd, RegisterID rm, int32_t shiftAmount)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rm));
        ShiftTypeAndAmount shift(SRType_LSR, shiftAmount);
        m_formatter.twoWordOp16FourFours(OP_LSR_imm_T1, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    void lsr(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_LSR_reg_T2, rn, FourFours(0xf, rd, 0, rm));
    }

    void movT3(RegisterID rd, ARMThumbImmediate imm)
    {
        ASSERT(imm.isValid());
        ASSERT(!imm.isEncodedImm());
        ASSERT(!BadReg(rd));
        
        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_MOV_imm_T3, imm.m_value.imm4, rd, imm);
    }

     void mov(RegisterID rd, ARMThumbImmediate imm)
    {
        ASSERT(imm.isValid());
        ASSERT(!BadReg(rd));
        
        if ((rd < 8) && imm.isUInt8())
            m_formatter.oneWordOp5Reg3Imm8(OP_MOV_imm_T1, rd, imm.getUInt8());
        else if (imm.isEncodedImm())
            m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_MOV_imm_T2, 0xf, rd, imm);
        else
            movT3(rd, imm);
    }

   void mov(RegisterID rd, RegisterID rm)
    {
        m_formatter.oneWordOp8RegReg143(OP_MOV_reg_T1, rm, rd);
    }

    void movt(RegisterID rd, ARMThumbImmediate imm)
    {
        ASSERT(imm.isUInt16());
        ASSERT(!BadReg(rd));
        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_MOVT, imm.m_value.imm4, rd, imm);
    }

    void mvn(RegisterID rd, ARMThumbImmediate imm)
    {
        ASSERT(imm.isEncodedImm());
        ASSERT(!BadReg(rd));
        
        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_MVN_imm, 0xf, rd, imm);
    }

    void mvn(RegisterID rd, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp16FourFours(OP_MVN_reg_T2, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    void mvn(RegisterID rd, RegisterID rm)
    {
        if (!((rd | rm) & 8))
            m_formatter.oneWordOp10Reg3Reg3(OP_MVN_reg_T1, rm, rd);
        else
            mvn(rd, rm, ShiftTypeAndAmount());
    }

    void orr(RegisterID rd, RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(imm.isEncodedImm());
        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_ORR_imm_T1, rn, rd, imm);
    }

    void orr(RegisterID rd, RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_ORR_reg_T2, rn, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    void orr(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        if ((rd == rn) && !((rd | rm) & 8))
            m_formatter.oneWordOp10Reg3Reg3(OP_ORR_reg_T1, rm, rd);
        else if ((rd == rm) && !((rd | rn) & 8))
            m_formatter.oneWordOp10Reg3Reg3(OP_ORR_reg_T1, rn, rd);
        else
            orr(rd, rn, rm, ShiftTypeAndAmount());
    }

    void ror(RegisterID rd, RegisterID rm, int32_t shiftAmount)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rm));
        ShiftTypeAndAmount shift(SRType_ROR, shiftAmount);
        m_formatter.twoWordOp16FourFours(OP_ROR_imm_T1, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    void ror(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        ASSERT(!BadReg(rd));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_ROR_reg_T2, rn, FourFours(0xf, rd, 0, rm));
    }

    void smull(RegisterID rdLo, RegisterID rdHi, RegisterID rn, RegisterID rm)
    {
        ASSERT(!BadReg(rdLo));
        ASSERT(!BadReg(rdHi));
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        ASSERT(rdLo != rdHi);
        m_formatter.twoWordOp12Reg4FourFours(OP_SMULL_T1, rn, FourFours(rdLo, rdHi, 0, rm));
    }

    // rt == ARM::pc only allowed if last instruction in IT (if then) block.
    void str(RegisterID rt, RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(rt != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(imm.isUInt12());

        if (!((rt | rn) & 8) && imm.isUInt7())
            m_formatter.oneWordOp5Imm5Reg3Reg3(OP_STR_imm_T1, imm.getUInt7() >> 2, rn, rt);
        else if ((rn == ARM::sp) && !(rt & 8) && imm.isUInt10())
            m_formatter.oneWordOp5Reg3Imm8(OP_STR_imm_T2, rt, imm.getUInt10() >> 2);
        else
            m_formatter.twoWordOp12Reg4Reg4Imm12(OP_STR_imm_T3, rn, rt, imm.getUInt12());
    }

    // If index is set, this is a regular offset or a pre-indexed store;
    // if index is not set then is is a post-index store.
    //
    // If wback is set rn is updated - this is a pre or post index store,
    // if wback is not set this is a regular offset memory access.
    //
    // (-255 <= offset <= 255)
    // _reg = REG[rn]
    // _tmp = _reg + offset
    // MEM[index ? _tmp : _reg] = REG[rt]
    // if (wback) REG[rn] = _tmp
    void str(RegisterID rt, RegisterID rn, int offset, bool index, bool wback)
    {
        ASSERT(rt != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(index || wback);
        ASSERT(!wback | (rt != rn));
    
        bool add = true;
        if (offset < 0) {
            add = false;
            offset = -offset;
        }
        ASSERT((offset & ~0xff) == 0);
        
        offset |= (wback << 8);
        offset |= (add   << 9);
        offset |= (index << 10);
        offset |= (1 << 11);
        
        m_formatter.twoWordOp12Reg4Reg4Imm12(OP_STR_imm_T4, rn, rt, offset);
    }

    // rt == ARM::pc only allowed if last instruction in IT (if then) block.
    void str(RegisterID rt, RegisterID rn, RegisterID rm, unsigned shift=0)
    {
        ASSERT(rn != ARM::pc);
        ASSERT(!BadReg(rm));
        ASSERT(shift <= 3);

        if (!shift && !((rt | rn | rm) & 8))
            m_formatter.oneWordOp7Reg3Reg3Reg3(OP_STR_reg_T1, rm, rn, rt);
        else
            m_formatter.twoWordOp12Reg4FourFours(OP_STR_reg_T2, rn, FourFours(rt, 0, shift, rm));
    }

    void sub(RegisterID rd, RegisterID rn, ARMThumbImmediate imm)
    {
        // Rd can only be SP if Rn is also SP.
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(imm.isValid());

        if ((rn == ARM::sp) && (rd == ARM::sp) && imm.isUInt9()) {
            m_formatter.oneWordOp9Imm7(OP_SUB_SP_imm_T1, imm.getUInt9() >> 2);
            return;
        } else if (!((rd | rn) & 8)) {
            if (imm.isUInt3()) {
                m_formatter.oneWordOp7Reg3Reg3Reg3(OP_SUB_imm_T1, (RegisterID)imm.getUInt3(), rn, rd);
                return;
            } else if ((rd == rn) && imm.isUInt8()) {
                m_formatter.oneWordOp5Reg3Imm8(OP_SUB_imm_T2, rd, imm.getUInt8());
                return;
            }
        }

        if (imm.isEncodedImm())
            m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_SUB_imm_T3, rn, rd, imm);
        else {
            ASSERT(imm.isUInt12());
            m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_SUB_imm_T4, rn, rd, imm);
        }
    }

    void sub(RegisterID rd, RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_SUB_reg_T2, rn, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    // NOTE: In an IT block, add doesn't modify the flags register.
    void sub(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        if (!((rd | rn | rm) & 8))
            m_formatter.oneWordOp7Reg3Reg3Reg3(OP_SUB_reg_T1, rm, rn, rd);
        else
            sub(rd, rn, rm, ShiftTypeAndAmount());
    }

    // Not allowed in an IT (if then) block.
    void sub_S(RegisterID rd, RegisterID rn, ARMThumbImmediate imm)
    {
        // Rd can only be SP if Rn is also SP.
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(imm.isValid());

        if ((rn == ARM::sp) && (rd == ARM::sp) && imm.isUInt9()) {
            m_formatter.oneWordOp9Imm7(OP_SUB_SP_imm_T1, imm.getUInt9() >> 2);
            return;
        } else if (!((rd | rn) & 8)) {
            if (imm.isUInt3()) {
                m_formatter.oneWordOp7Reg3Reg3Reg3(OP_SUB_S_imm_T1, (RegisterID)imm.getUInt3(), rn, rd);
                return;
            } else if ((rd == rn) && imm.isUInt8()) {
                m_formatter.oneWordOp5Reg3Imm8(OP_SUB_S_imm_T2, rd, imm.getUInt8());
                return;
            }
        }

        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_SUB_S_imm_T3, rn, rd, imm);
    }

    // Not allowed in an IT (if then) block?
    void sub_S(RegisterID rd, RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT((rd != ARM::sp) || (rn == ARM::sp));
        ASSERT(rd != ARM::pc);
        ASSERT(rn != ARM::pc);
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_SUB_S_reg_T2, rn, FourFours(shift.hi4(), rd, shift.lo4(), rm));
    }

    // Not allowed in an IT (if then) block.
    void sub_S(RegisterID rd, RegisterID rn, RegisterID rm)
    {
        if (!((rd | rn | rm) & 8))
            m_formatter.oneWordOp7Reg3Reg3Reg3(OP_SUB_S_reg_T1, rm, rn, rd);
        else
            sub_S(rd, rn, rm, ShiftTypeAndAmount());
    }

    void tst(RegisterID rn, ARMThumbImmediate imm)
    {
        ASSERT(!BadReg(rn));
        ASSERT(imm.isEncodedImm());

        m_formatter.twoWordOp5i6Imm4Reg4EncodedImm(OP_TST_imm, rn, (RegisterID)0xf, imm);
    }

    void tst(RegisterID rn, RegisterID rm, ShiftTypeAndAmount shift)
    {
        ASSERT(!BadReg(rn));
        ASSERT(!BadReg(rm));
        m_formatter.twoWordOp12Reg4FourFours(OP_TST_reg_T2, rn, FourFours(shift.hi4(), 0xf, shift.lo4(), rm));
    }

    void tst(RegisterID rn, RegisterID rm)
    {
        if ((rn | rm) & 8)
            tst(rn, rm, ShiftTypeAndAmount());
        else
            m_formatter.oneWordOp10Reg3Reg3(OP_TST_reg_T1, rm, rn);
    }

    void vadd_F64(FPRegisterID rd, FPRegisterID rn, FPRegisterID rm)
    {
        m_formatter.vfpOp(0x0b00ee30 | doubleRegisterMask(rd, 6, 28) | doubleRegisterMask(rn, 23, 0) | doubleRegisterMask(rm, 21, 16));
    }

    void vcmp_F64(FPRegisterID rd, FPRegisterID rm)
    {
        m_formatter.vfpOp(0x0bc0eeb4 | doubleRegisterMask(rd, 6, 28) | doubleRegisterMask(rm, 21, 16));
    }

    void vcvt_F64_S32(FPRegisterID fd, FPRegisterID sm)
    {
        m_formatter.vfpOp(0x0bc0eeb8 | doubleRegisterMask(fd, 6, 28) | singleRegisterMask(sm, 16, 21));
    }

    void vcvt_S32_F64(FPRegisterID sd, FPRegisterID fm)
    {
        m_formatter.vfpOp(0x0bc0eebd | singleRegisterMask(sd, 28, 6) | doubleRegisterMask(fm, 21, 16));
    }

    void vldr(FPRegisterID rd, RegisterID rn, int32_t imm)
    {
        vmem(rd, rn, imm, true);
    }

    void vmov(RegisterID rd, FPRegisterID sn)
    {
        m_formatter.vfpOp(0x0a10ee10 | (rd << 28) | singleRegisterMask(sn, 0, 23));
    }

    void vmov(FPRegisterID sn, RegisterID rd)
    {
        m_formatter.vfpOp(0x0a10ee00 | (rd << 28) | singleRegisterMask(sn, 0, 23));
    }

    // move FPSCR flags to APSR.
    void vmrs_APSR_nzcv_FPSCR()
    {
        m_formatter.vfpOp(0xfa10eef1);
    }

    void vmul_F64(FPRegisterID rd, FPRegisterID rn, FPRegisterID rm)
    {
        m_formatter.vfpOp(0x0b00ee20 | doubleRegisterMask(rd, 6, 28) | doubleRegisterMask(rn, 23, 0) | doubleRegisterMask(rm, 21, 16));
    }

    void vstr(FPRegisterID rd, RegisterID rn, int32_t imm)
    {
        vmem(rd, rn, imm, false);
    }

    void vsub_F64(FPRegisterID rd, FPRegisterID rn, FPRegisterID rm)
    {
        m_formatter.vfpOp(0x0b40ee30 | doubleRegisterMask(rd, 6, 28) | doubleRegisterMask(rn, 23, 0) | doubleRegisterMask(rm, 21, 16));
    }


    JmpDst label()
    {
        return JmpDst(m_formatter.size());
    }
    
    JmpDst align(int alignment)
    {
        while (!m_formatter.isAligned(alignment))
            bkpt();

        return label();
    }
    
    static void* getRelocatedAddress(void* code, JmpSrc jump)
    {
        ASSERT(jump.m_offset != -1);

        return reinterpret_cast<void*>(reinterpret_cast<ptrdiff_t>(code) + jump.m_offset);
    }
    
    static void* getRelocatedAddress(void* code, JmpDst destination)
    {
        ASSERT(destination.m_offset != -1);

        return reinterpret_cast<void*>(reinterpret_cast<ptrdiff_t>(code) + destination.m_offset);
    }
    
    static int getDifferenceBetweenLabels(JmpDst src, JmpDst dst)
    {
        return dst.m_offset - src.m_offset;
    }
    
    static int getDifferenceBetweenLabels(JmpDst src, JmpSrc dst)
    {
        return dst.m_offset - src.m_offset;
    }
    
    static int getDifferenceBetweenLabels(JmpSrc src, JmpDst dst)
    {
        return dst.m_offset - src.m_offset;
    }
    
    // Assembler admin methods:

    size_t size() const
    {
        return m_formatter.size();
    }

    void* executableCopy(ExecutablePool* allocator)
    {
        void* copy = m_formatter.executableCopy(allocator);
        ASSERT(copy);
        return copy;
    }

    static unsigned getCallReturnOffset(JmpSrc call)
    {
        ASSERT(call.m_offset >= 0);
        return call.m_offset;
    }

    // Linking & patching:
    //
    // 'link' and 'patch' methods are for use on unprotected code - such as the code
    // within the AssemblerBuffer, and code being patched by the patch buffer.  Once
    // code has been finalized it is (platform support permitting) within a non-
    // writable region of memory; to modify the code in an execute-only execuable
    // pool the 'repatch' and 'relink' methods should be used.

    void linkJump(JmpSrc from, JmpDst to)
    {
        ASSERT(to.m_offset != -1);
        ASSERT(from.m_offset != -1);

        uint16_t* location = reinterpret_cast<uint16_t*>(reinterpret_cast<intptr_t>(m_formatter.data()) + from.m_offset);
        intptr_t relative = to.m_offset - from.m_offset;

        linkWithOffset(location, relative);
    }

    static void linkJump(void* code, JmpSrc from, void* to)
    {
        ASSERT(from.m_offset != -1);
        
        uint16_t* location = reinterpret_cast<uint16_t*>(reinterpret_cast<intptr_t>(code) + from.m_offset);
        intptr_t relative = reinterpret_cast<intptr_t>(to) - reinterpret_cast<intptr_t>(location);

        linkWithOffset(location, relative);
    }

    // bah, this mathod should really be static, since it is used by the LinkBuffer.
    // return a bool saying whether the link was successful?
    static void linkCall(void* code, JmpSrc from, void* to)
    {
        ASSERT(!(reinterpret_cast<intptr_t>(code) & 1));
        ASSERT(from.m_offset != -1);
        ASSERT(reinterpret_cast<intptr_t>(to) & 1);

        patchPointer(reinterpret_cast<uint16_t*>(reinterpret_cast<intptr_t>(code) + from.m_offset) - 1, to);
    }

    static void patchPointer(void* code, JmpDst where, void* value)
    {
        patchPointer(reinterpret_cast<char*>(code) + where.m_offset, value);
    }

    static void relinkJump(void* from, void* to)
    {
        ExecutableAllocator::MakeWritable unprotect(reinterpret_cast<uint16_t*>(from) - 2, 2 * sizeof(uint16_t));

        ASSERT(!(reinterpret_cast<intptr_t>(from) & 1));
        ASSERT(!(reinterpret_cast<intptr_t>(to) & 1));

        intptr_t relative = reinterpret_cast<intptr_t>(to) - reinterpret_cast<intptr_t>(from);
        linkWithOffset(reinterpret_cast<uint16_t*>(from), relative);
    }
    
    static void relinkCall(void* from, void* to)
    {
        ExecutableAllocator::MakeWritable unprotect(reinterpret_cast<uint16_t*>(from) - 5, 4 * sizeof(uint16_t));

        ASSERT(!(reinterpret_cast<intptr_t>(from) & 1));
        ASSERT(reinterpret_cast<intptr_t>(to) & 1);

        patchPointer(reinterpret_cast<uint16_t*>(from) - 1, to);
    }

    static void repatchInt32(void* where, int32_t value)
    {
        ExecutableAllocator::MakeWritable unprotect(reinterpret_cast<uint16_t*>(where) - 4, 4 * sizeof(uint16_t));

        ASSERT(!(reinterpret_cast<intptr_t>(where) & 1));
        
        patchInt32(where, value);
    }

    static void repatchPointer(void* where, void* value)
    {
        ExecutableAllocator::MakeWritable unprotect(reinterpret_cast<uint16_t*>(where) - 4, 4 * sizeof(uint16_t));

        ASSERT(!(reinterpret_cast<intptr_t>(where) & 1));
        
        patchPointer(where, value);
    }

    static void repatchLoadPtrToLEA(void* where)
    {
        ASSERT(!(reinterpret_cast<intptr_t>(where) & 1));

        uint16_t* loadOp = reinterpret_cast<uint16_t*>(where) + 4;
        ASSERT((*loadOp & 0xfff0) == OP_LDR_reg_T2);

        ExecutableAllocator::MakeWritable unprotect(loadOp, sizeof(uint16_t));
        *loadOp = OP_ADD_reg_T3 | (*loadOp & 0xf);
    }

private:

    // Arm vfp addresses can be offset by a 9-bit ones-comp immediate, left shifted by 2.
    // (i.e. +/-(0..255) 32-bit words)
    void vmem(FPRegisterID rd, RegisterID rn, int32_t imm, bool isLoad)
    {
        bool up;
        uint32_t offset;
        if (imm < 0) {
            offset = -imm;
            up = false;
        } else {
            offset = imm;
            up = true;
        }

        // offset is effectively leftshifted by 2 already (the bottom two bits are zero, and not
        // reperesented in the instruction.  Left shift by 14, to mov it into position 0x00AA0000.
        ASSERT((offset & ~(0xff << 2)) == 0);
        offset <<= 14;

        m_formatter.vfpOp(0x0b00ed00 | offset | (up << 7) | (isLoad << 4) | doubleRegisterMask(rd, 6, 28) | rn);
    }

    static void patchInt32(void* code, uint32_t value)
    {
        uint16_t* location = reinterpret_cast<uint16_t*>(code);

        ExecutableAllocator::MakeWritable unprotect(location - 4, 4 * sizeof(uint16_t));

        uint16_t lo16 = value;
        uint16_t hi16 = value >> 16;

        spliceHi5(location - 4, lo16);
        spliceLo11(location - 3, lo16);
        spliceHi5(location - 2, hi16);
        spliceLo11(location - 1, hi16);
    }

    static void patchPointer(void* code, void* value)
    {
        patchInt32(code, reinterpret_cast<uint32_t>(value));
    }

    // Linking & patching:
    // This method assumes that the JmpSrc being linked is a T4 b instruction.
    static void linkWithOffset(uint16_t* instruction, intptr_t relative)
    {
        // Currently branches > 16m = mostly deathy.
        if (((relative << 7) >> 7) != relative) {
            // FIXME: This CRASH means we cannot turn the JIT on by default on arm-v7.
            fprintf(stderr, "Error: Cannot link T4b.\n");
            CRASH();
        }
        
        // ARM encoding for the top two bits below the sign bit is 'peculiar'.
        if (relative >= 0)
            relative ^= 0xC00000;

        // All branch offsets should be an even distance.
        ASSERT(!(relative & 1));

        int word1 = ((relative & 0x1000000) >> 14) | ((relative & 0x3ff000) >> 12);
        int word2 = ((relative & 0x800000) >> 10) | ((relative & 0x400000) >> 11) | ((relative & 0xffe) >> 1);

        instruction[-2] = OP_B_T4a | word1;
        instruction[-1] = OP_B_T4b | word2;
    }

    // These functions can be used to splice 16-bit immediates back into previously generated instructions.
    static void spliceHi5(uint16_t* where, uint16_t what)
    {
        uint16_t pattern = (what >> 12) | ((what & 0x0800) >> 1);
        *where = (*where & 0xFBF0) | pattern;
    }
    static void spliceLo11(uint16_t* where, uint16_t what)
    {
        uint16_t pattern = ((what & 0x0700) << 4) | (what & 0x00FF);
        *where = (*where & 0x8F00) | pattern;
    }

    class ARMInstructionFormatter {
    public:
        void oneWordOp5Reg3Imm8(OpcodeID op, RegisterID rd, uint8_t imm)
        {
            m_buffer.putShort(op | (rd << 8) | imm);
        }
        
        void oneWordOp5Imm5Reg3Reg3(OpcodeID op, uint8_t imm, RegisterID reg1, RegisterID reg2)
        {
            m_buffer.putShort(op | (imm << 6) | (reg1 << 3) | reg2);
        }

        void oneWordOp7Reg3Reg3Reg3(OpcodeID op, RegisterID reg1, RegisterID reg2, RegisterID reg3)
        {
            m_buffer.putShort(op | (reg1 << 6) | (reg2 << 3) | reg3);
        }

        void oneWordOp8Imm8(OpcodeID op, uint8_t imm)
        {
            m_buffer.putShort(op | imm);
        }

        void oneWordOp8RegReg143(OpcodeID op, RegisterID reg1, RegisterID reg2)
        {
            m_buffer.putShort(op | ((reg2 & 8) << 4) | (reg1 << 3) | (reg2 & 7));
        }
        void oneWordOp9Imm7(OpcodeID op, uint8_t imm)
        {
            m_buffer.putShort(op | imm);
        }

        void oneWordOp10Reg3Reg3(OpcodeID op, RegisterID reg1, RegisterID reg2)
        {
            m_buffer.putShort(op | (reg1 << 3) | reg2);
        }

        void twoWordOp12Reg4FourFours(OpcodeID1 op, RegisterID reg, FourFours ff)
        {
            m_buffer.putShort(op | reg);
            m_buffer.putShort(ff.m_u.value);
        }
        
        void twoWordOp16FourFours(OpcodeID1 op, FourFours ff)
        {
            m_buffer.putShort(op);
            m_buffer.putShort(ff.m_u.value);
        }
        
        void twoWordOp16Op16(OpcodeID1 op1, OpcodeID2 op2)
        {
            m_buffer.putShort(op1);
            m_buffer.putShort(op2);
        }

        void twoWordOp5i6Imm4Reg4EncodedImm(OpcodeID1 op, int imm4, RegisterID rd, ARMThumbImmediate imm)
        {
            m_buffer.putShort(op | (imm.m_value.i << 10) | imm4);
            m_buffer.putShort((imm.m_value.imm3 << 12) | (rd << 8) | imm.m_value.imm8);
        }

        void twoWordOp12Reg4Reg4Imm12(OpcodeID1 op, RegisterID reg1, RegisterID reg2, uint16_t imm)
        {
            m_buffer.putShort(op | reg1);
            m_buffer.putShort((reg2 << 12) | imm);
        }

        void vfpOp(int32_t op)
        {
            m_buffer.putInt(op);
        }


        // Administrative methods:

        size_t size() const { return m_buffer.size(); }
        bool isAligned(int alignment) const { return m_buffer.isAligned(alignment); }
        void* data() const { return m_buffer.data(); }
        void* executableCopy(ExecutablePool* allocator) { return m_buffer.executableCopy(allocator); }

    private:
        AssemblerBuffer m_buffer;
    } m_formatter;
};

} // namespace JSC

#endif // ENABLE(ASSEMBLER) && PLATFORM_ARM_ARCH(7)

#endif // ARMAssembler_h