gecko/js/src/nanojit/LIR.h

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#ifndef __nanojit_LIR__
#define __nanojit_LIR__

/**
 * Fundamentally, the arguments to the various operands can be grouped along
 * two dimensions.  One dimension is size: can the arguments fit into a 32-bit
 * register, or not?  The other dimension is whether the argument is an integer
 * (including pointers) or a floating-point value.  In all comments below,
 * "integer" means integer of any size, including 64-bit, unless otherwise
 * specified.  All floating-point values are always 64-bit.  Below, "quad" is
 * used for a 64-bit value that might be either integer or floating-point.
 */
namespace nanojit
{
    using namespace MMgc;

    enum LOpcode
#if defined(_MSC_VER) && _MSC_VER >= 1400
          : unsigned
#endif
    {
        // flags; upper bits reserved
        LIR64    = 0x40,            // result is double or quad

#define OPDEF(op, number, args, repkind) \
        LIR_##op = (number),
#define OPDEF64(op, number, args, repkind) \
        LIR_##op = ((number) | LIR64),
#include "LIRopcode.tbl"
        LIR_sentinel
#undef OPDEF
#undef OPDEF64
    };

#ifdef NANOJIT_64BIT
#  define PTR_SIZE(a,b)  b
#else
#  define PTR_SIZE(a,b)  a
#endif

    #if defined NANOJIT_64BIT
    #define LIR_ldp     LIR_ldq
    #define LIR_piadd   LIR_qiadd
    #define LIR_piand   LIR_qiand
    #define LIR_pilsh   LIR_qilsh
    #define LIR_pcmov    LIR_qcmov
    #define LIR_pior    LIR_qior
    #else
    #define LIR_ldp     LIR_ld
    #define LIR_piadd   LIR_add
    #define LIR_piand   LIR_and
    #define LIR_pilsh   LIR_lsh
    #define LIR_pcmov    LIR_cmov
    #define LIR_pior    LIR_or
    #endif

    struct GuardRecord;
    struct SideExit;
    struct Page;

    enum AbiKind {
        ABI_FASTCALL,
        ABI_THISCALL,
        ABI_STDCALL,
        ABI_CDECL
    };

    enum ArgSize {
        ARGSIZE_NONE = 0,
        ARGSIZE_F = 1,      // double (64bit)
        ARGSIZE_I = 2,      // int32_t
        ARGSIZE_Q = 3,      // uint64_t
        ARGSIZE_U = 6,      // uint32_t
        ARGSIZE_MASK_ANY = 7,
        ARGSIZE_MASK_INT = 2,
        ARGSIZE_SHIFT = 3,

        // aliases
        ARGSIZE_P = PTR_SIZE(ARGSIZE_I, ARGSIZE_Q), // pointer
        ARGSIZE_LO = ARGSIZE_I, // int32_t
        ARGSIZE_B = ARGSIZE_I, // bool
        ARGSIZE_V = ARGSIZE_NONE  // void
    };

    enum IndirectCall {
        CALL_INDIRECT = 0
    };

    struct CallInfo
    {
        uintptr_t   _address;
        uint32_t    _argtypes:27;    // 9 3-bit fields indicating arg type, by ARGSIZE above (including ret type): a1 a2 a3 a4 a5 ret
        uint8_t     _cse:1;          // true if no side effects
        uint8_t     _fold:1;         // true if no side effects
        AbiKind     _abi:3;
        verbose_only ( const char* _name; )

        uint32_t FASTCALL _count_args(uint32_t mask) const;
        uint32_t get_sizes(ArgSize*) const;

        inline bool isIndirect() const {
            return _address < 256;
        }
        inline uint32_t count_args() const {
            return _count_args(ARGSIZE_MASK_ANY);
        }
        inline uint32_t count_iargs() const {
            return _count_args(ARGSIZE_MASK_INT);
        }
        // fargs = args - iargs
    };

    /*
     * Record for extra data used to compile switches as jump tables.
     */
    struct SwitchInfo
    {
        NIns**      table;       // Jump table; a jump address is NIns*
        uint32_t    count;       // Number of table entries
        // Index value at last execution of the switch. The index value
        // is the offset into the jump table. Thus it is computed as
        // (switch expression) - (lowest case value).
        uint32_t    index;
    };

    inline bool isCseOpcode(LOpcode op) {
        op = LOpcode(op & ~LIR64);
        return op >= LIR_int && op <= LIR_uge;
    }
    inline bool isRetOpcode(LOpcode op) {
        return (op & ~LIR64) == LIR_ret;
    }

    // The opcode is not logically part of the Reservation, but we include it
    // in this struct to ensure that opcode plus the Reservation fits in a
    // single word.  Yuk.
    struct Reservation
    {
        uint32_t arIndex:16;    // index into stack frame.  displ is -4*arIndex
        Register reg:7;         // register UnknownReg implies not in register
        uint32_t used:1;        // when set, the reservation is active
        LOpcode  opcode:8;

        inline void init() {
            reg = UnknownReg;
            arIndex = 0;
            used = 1;
        }

        inline void clear() {
            used = 0;
        }
    };

    //-----------------------------------------------------------------------
    // Low-level instructions.  This is a bit complicated, because we have a
    // variable-width representation to minimise space usage.
    //
    // - Instruction size is always an integral multiple of word size.
    //
    // - Every instruction has at least one word, holding the opcode and the
    //   reservation info.  That word is in class LIns.
    //
    // - Beyond that, most instructions have 1, 2 or 3 extra words.  These
    //   extra words are in classes LInsOp1, LInsOp2, etc (collectively called
    //   "LInsXYZ" in what follows).  Each LInsXYZ class also contains a word,
    //   accessible by the 'ins' member, which holds the LIns data;  its type
    //   is void* (which is the same size as LIns) rather than LIns to avoid a
    //   recursive dependency between LIns and LInsXYZ.
    //
    // - LIR is written forward, but read backwards.  When reading backwards,
    //   in order to find the opcode, it must be in a predictable place in the
    //   LInsXYZ isn't affected by instruction width.  Therefore, the LIns
    //   word (which contains the opcode) is always the *last* word in an
    //   instruction.
    //
    // - Each instruction is created by casting pre-allocated bytes from a
    //   LirBuffer to the LInsXYZ type.  Therefore there are no constructors
    //   for LIns or LInsXYZ.
    //
    // - The standard handle for an instruction is a LIns*.  This actually
    //   points to the LIns word, ie. to the final word in the instruction.
    //   This is a bit odd, but it allows the instruction's opcode to be
    //   easily accessed.  Once you've looked at the opcode and know what kind
    //   of instruction it is, if you want to access any of the other words,
    //   you need to use toLInsXYZ(), which takes the LIns* and gives you an
    //   LInsXYZ*, ie. the pointer to the actual start of the instruction's
    //   bytes.  From there you can access the instruction-specific extra
    //   words.
    //
    // - However, from outside class LIns, LInsXYZ isn't visible, nor is
    //   toLInsXYZ() -- from outside LIns, all LIR instructions are handled
    //   via LIns pointers and get/set methods are used for all LIns/LInsXYZ
    //   accesses.  In fact, all data members in LInsXYZ are private and can
    //   only be accessed by LIns, which is a friend class.  The only thing
    //   anyone outside LIns can do with a LInsXYZ is call getLIns().
    //
    // - An example Op2 instruction and the likely pointers to it (each line
    //   represents a word, and pointers to a line point to the start of the
    //   word on that line):
    //
    //      [ oprnd_2         <-- LInsOp2* insOp2 == toLInsOp2(ins)
    //        oprnd_1
    //        opcode + resv ] <-- LIns* ins
    //
    // - LIR_skip instructions are more complicated.  They allow an arbitrary
    //   blob of data (the "payload") to be placed in the LIR stream.  The
    //   size of the payload is always a multiple of the word size.  A skip
    //   instruction's operand points to the previous instruction, which lets
    //   the payload be skipped over when reading backwards.  Here's an
    //   example of a skip instruction with a 3-word payload preceded by an
    //   LInsOp1:
    //
    //      [ oprnd_1
    //  +->   opcode + resv           ]
    //  |   [ data
    //  |     data
    //  |     data
    //  +---- prevLIns                  <-- LInsSk* insSk == toLInsSk(ins)
    //        opcode==LIR_skip + resv ] <-- LIns* ins
    //
    //   Skips are also used to link code pages.  If the first instruction on
    //   a page isn't a LIR_start, it will be a skip, and the skip's operand
    //   will point to the last LIns on the previous page.  In this case there
    //   isn't a payload as such;  in fact, the previous page might be at a
    //   higher address, ie. the operand might point forward rather than
    //   backward.
    //
    //   LInsSk has the same layout as LInsOp1, but we represent it as a
    //   different class because there are some places where we treat
    //   skips specially and so having it separate seems like a good idea.
    //
    // - Call instructions (LIR_call, LIR_fcall, LIR_calli, LIR_fcalli) are
    //   also more complicated.  They are preceded by the arguments to the
    //   call, which are laid out in reverse order.  For example, a call with
    //   3 args will look like this:
    //
    //      [ arg #2
    //        arg #1
    //        arg #0
    //        argc            <-- LInsC insC == toLInsC(ins)
    //        ci
    //        opcode + resv ] <-- LIns* ins
    //
    // - Various things about the size and layout of LIns and LInsXYZ are
    //   statically checked in staticSanityCheck().  In particular, this is
    //   worthwhile because there's nothing that guarantees that all the
    //   LInsXYZ classes have a size that is a multiple of word size (but in
    //   practice all sane compilers use a layout that results in this).  We
    //   also check that every LInsXYZ is word-aligned in
    //   LirBuffer::makeRoom();  this seems sensible to avoid potential
    //   slowdowns due to misalignment.  It relies on pages themselves being
    //   word-aligned, which is extremely likely.
    //
    // - There is an enum, LInsRepKind, with one member for each of the
    //   LInsXYZ kinds.  Each opcode is categorised with its LInsRepKind value
    //   in LIRopcode.tbl, and this is used in various places.
    //-----------------------------------------------------------------------

    enum LInsRepKind {
        // LRK_XYZ corresponds to class LInsXYZ.
        LRK_Op0,
        LRK_Op1,
        LRK_Op2,
        LRK_Op3,
        LRK_Ld,
        LRK_Sti,
        LRK_Sk,
        LRK_C,
        LRK_P,
        LRK_I,
        LRK_I64,
        LRK_None    // this one is used for unused opcode numbers
    };

    // 0-operand form.  Used for LIR_start and LIR_label.
    class LInsOp0
    {
    private:
        friend class LIns;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // 1-operand form.  Used for LIR_ret, LIR_ov, unary arithmetic/logic ops,
    // etc.
    class LInsOp1
    {
    private:
        friend class LIns;

        LIns*       oprnd_1;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // 2-operand form.  Used for loads, guards, branches, comparisons, binary
    // arithmetic/logic ops, etc.
    class LInsOp2
    {
    private:
        friend class LIns;

        LIns*       oprnd_2;

        LIns*       oprnd_1;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // 3-operand form.  Used for conditional moves.
    class LInsOp3
    {
    private:
        friend class LIns;

        LIns*       oprnd_3;

        LIns*       oprnd_2;

        LIns*       oprnd_1;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used for all loads.
    class LInsLd
    {
    private:
        friend class LIns;

        int32_t     disp;

        LIns*       oprnd_1;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used for LIR_sti and LIR_stqi.
    class LInsSti
    {
    private:
        friend class LIns;

        int32_t     disp;

        LIns*       oprnd_2;

        LIns*       oprnd_1;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used for LIR_skip.
    class LInsSk
    {
    private:
        friend class LIns;

        LIns*       prevLIns;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used for all variants of LIR_call.
    class LInsC
    {
    private:
        friend class LIns;

        uintptr_t   argc:8;

        const CallInfo* ci;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used for LIR_iparam.
    class LInsP
    {
    private:
        friend class LIns;

        uintptr_t   arg:8;
        uintptr_t   kind:8;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used for LIR_int and LIR_ialloc.
    class LInsI
    {
    private:
        friend class LIns;

        int32_t     imm32;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used for LIR_quad.
    class LInsI64
    {
    private:
        friend class LIns;

        int32_t     imm64_0;

        int32_t     imm64_1;

        void*       ins;

    public:
        LIns* getLIns() { return (LIns*)&ins; };
    };

    // Used only as a placeholder for OPDEF macros for unused opcodes in
    // LIRopcode.tbl.
    class LInsNone
    {
    };

    class LIns
    {
    private:
        // Last word: fields shared by all LIns kinds.  The reservation fields
        // are read/written during assembly.
        Reservation lastWord;

        // LIns-to-LInsXYZ converters.
        LInsOp0* toLInsOp0() const { return (LInsOp0*)( uintptr_t(this+1) - sizeof(LInsOp0) ); }
        LInsOp1* toLInsOp1() const { return (LInsOp1*)( uintptr_t(this+1) - sizeof(LInsOp1) ); }
        LInsOp2* toLInsOp2() const { return (LInsOp2*)( uintptr_t(this+1) - sizeof(LInsOp2) ); }
        LInsOp3* toLInsOp3() const { return (LInsOp3*)( uintptr_t(this+1) - sizeof(LInsOp3) ); }
        LInsLd*  toLInsLd()  const { return (LInsLd* )( uintptr_t(this+1) - sizeof(LInsLd ) ); }
        LInsSti* toLInsSti() const { return (LInsSti*)( uintptr_t(this+1) - sizeof(LInsSti) ); }
        LInsSk*  toLInsSk()  const { return (LInsSk* )( uintptr_t(this+1) - sizeof(LInsSk ) ); }
        LInsC*   toLInsC()   const { return (LInsC*  )( uintptr_t(this+1) - sizeof(LInsC  ) ); }
        LInsP*   toLInsP()   const { return (LInsP*  )( uintptr_t(this+1) - sizeof(LInsP  ) ); }
        LInsI*   toLInsI()   const { return (LInsI*  )( uintptr_t(this+1) - sizeof(LInsI  ) ); }
        LInsI64* toLInsI64() const { return (LInsI64*)( uintptr_t(this+1) - sizeof(LInsI64) ); }

        // This is never called, but that's ok because it contains only static
        // assertions.
        void staticSanityCheck()
        {
            // LIns must be word-sized.
            NanoStaticAssert(sizeof(LIns) == 1*sizeof(void*));

            // LInsXYZ have expected sizes too.
            NanoStaticAssert(sizeof(LInsOp0) == 1*sizeof(void*));
            NanoStaticAssert(sizeof(LInsOp1) == 2*sizeof(void*));
            NanoStaticAssert(sizeof(LInsOp2) == 3*sizeof(void*));
            NanoStaticAssert(sizeof(LInsOp3) == 4*sizeof(void*));
            NanoStaticAssert(sizeof(LInsLd)  == 3*sizeof(void*));
            NanoStaticAssert(sizeof(LInsSti) == 4*sizeof(void*));
            NanoStaticAssert(sizeof(LInsSk)  == 2*sizeof(void*));
            NanoStaticAssert(sizeof(LInsC)   == 3*sizeof(void*));
            NanoStaticAssert(sizeof(LInsP)   == 2*sizeof(void*));
            NanoStaticAssert(sizeof(LInsI)   == 2*sizeof(void*));
        #if defined NANOJIT_64BIT
            NanoStaticAssert(sizeof(LInsI64) == 2*sizeof(void*));
        #else
            NanoStaticAssert(sizeof(LInsI64) == 3*sizeof(void*));
        #endif

            // oprnd_1 must be in the same position in LIns{Op1,Op2,Op3,Ld,Sti}
            // because oprnd1() is used for all of them.
            NanoStaticAssert( (offsetof(LInsOp1, ins) - offsetof(LInsOp1, oprnd_1)) ==
                              (offsetof(LInsOp2, ins) - offsetof(LInsOp2, oprnd_1)) );
            NanoStaticAssert( (offsetof(LInsOp2, ins) - offsetof(LInsOp2, oprnd_1)) ==
                              (offsetof(LInsOp3, ins) - offsetof(LInsOp3, oprnd_1)) );
            NanoStaticAssert( (offsetof(LInsOp3, ins) - offsetof(LInsOp3, oprnd_1)) ==
                              (offsetof(LInsLd,  ins) - offsetof(LInsLd,  oprnd_1)) );
            NanoStaticAssert( (offsetof(LInsLd,  ins) - offsetof(LInsLd,  oprnd_1)) ==
                              (offsetof(LInsSti, ins) - offsetof(LInsSti, oprnd_1)) );

            // oprnd_2 must be in the same position in LIns{Op2,Op3,Sti}
            // because oprnd2() is used for both of them.
            NanoStaticAssert( (offsetof(LInsOp2, ins) - offsetof(LInsOp2, oprnd_2)) ==
                              (offsetof(LInsOp3, ins) - offsetof(LInsOp3, oprnd_2)) );
            NanoStaticAssert( (offsetof(LInsOp3, ins) - offsetof(LInsOp3, oprnd_2)) ==
                              (offsetof(LInsSti, ins) - offsetof(LInsSti, oprnd_2)) );
        }

    public:
        void initLInsOp0(LOpcode opcode) {
            lastWord.clear();
            lastWord.opcode = opcode;
            NanoAssert(isLInsOp0());
        }
        void initLInsOp1(LOpcode opcode, LIns* oprnd1) {
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsOp1()->oprnd_1 = oprnd1;
            NanoAssert(isLInsOp1());
        }
        void initLInsOp2(LOpcode opcode, LIns* oprnd1, LIns* oprnd2) {
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsOp2()->oprnd_1 = oprnd1;
            toLInsOp2()->oprnd_2 = oprnd2;
            NanoAssert(isLInsOp2());
        }
        void initLInsOp3(LOpcode opcode, LIns* oprnd1, LIns* oprnd2, LIns* oprnd3) {
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsOp3()->oprnd_1 = oprnd1;
            toLInsOp3()->oprnd_2 = oprnd2;
            toLInsOp3()->oprnd_3 = oprnd3;
            NanoAssert(isLInsOp3());
        }
        void initLInsLd(LOpcode opcode, LIns* val, int32_t d) {
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsLd()->oprnd_1 = val;
            toLInsLd()->disp = d;
            NanoAssert(isLInsLd());
        }
        void initLInsSti(LOpcode opcode, LIns* val, LIns* base, int32_t d) {
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsSti()->oprnd_1 = val;
            toLInsSti()->oprnd_2 = base;
            toLInsSti()->disp = d;
            NanoAssert(isLInsSti());
        }
        void initLInsSk(LIns* prevLIns) {
            lastWord.clear();
            lastWord.opcode = LIR_skip;
            toLInsSk()->prevLIns = prevLIns;
            NanoAssert(isLInsSk());
        }
        // Nb: this does NOT initialise the arguments.  That must be done
        // separately.
        void initLInsC(LOpcode opcode, int32_t argc, const CallInfo* ci) {
            NanoAssert(isU8(argc));
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsC()->argc = argc;
            toLInsC()->ci = ci;
            NanoAssert(isLInsC());
        }
        void initLInsP(int32_t arg, int32_t kind) {
            lastWord.clear();
            lastWord.opcode = LIR_iparam;
            NanoAssert(isU8(arg) && isU8(kind));
            toLInsP()->arg = arg;
            toLInsP()->kind = kind;
            NanoAssert(isLInsP());
        }
        void initLInsI(LOpcode opcode, int32_t imm32) {
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsI()->imm32 = imm32;
            NanoAssert(isLInsI());
        }
        void initLInsI64(LOpcode opcode, int64_t imm64) {
            lastWord.clear();
            lastWord.opcode = opcode;
            toLInsI64()->imm64_0 = int32_t(imm64);
            toLInsI64()->imm64_1 = int32_t(imm64 >> 32);
            NanoAssert(isLInsI64());
        }

        LIns* oprnd1() const {
            NanoAssert(isLInsOp1() || isLInsOp2() || isLInsOp3() || isLInsLd() || isLInsSti());
            return toLInsOp2()->oprnd_1;
        }
        LIns* oprnd2() const {
            NanoAssert(isLInsOp2() || isLInsOp3() || isLInsSti());
            return toLInsOp2()->oprnd_2;
        }
        LIns* oprnd3() const {
            NanoAssert(isLInsOp3());
            return toLInsOp3()->oprnd_3;
        }

        LIns* prevLIns() const {
            NanoAssert(isLInsSk());
            return toLInsSk()->prevLIns;
        }

        inline LOpcode opcode()    const { return lastWord.opcode; }
        inline uint8_t paramArg()  const { NanoAssert(isop(LIR_iparam)); return toLInsP()->arg; }
        inline uint8_t paramKind() const { NanoAssert(isop(LIR_iparam)); return toLInsP()->kind; }
        inline int32_t imm32()     const { NanoAssert(isconst());  return toLInsI()->imm32; }
        inline int32_t imm64_0()   const { NanoAssert(isconstq()); return toLInsI64()->imm64_0; }
        inline int32_t imm64_1()   const { NanoAssert(isconstq()); return toLInsI64()->imm64_1; }
        uint64_t       imm64()     const;
        double         imm64f()    const;
        Reservation*   resv()            { return &lastWord; }
        void*          payload()   const;
        inline Page*   page()            { return (Page*) alignTo(this,NJ_PAGE_SIZE); }
        inline int32_t size()      const {
            NanoAssert(isop(LIR_ialloc));
            return toLInsI()->imm32 << 2;
        }

        LIns* arg(uint32_t i);

        inline int32_t disp() const
        {
            if (isLInsSti()) {
                return toLInsSti()->disp;
            } else {
                NanoAssert(isLInsLd());
                return toLInsLd()->disp;
            }
        }

        inline void* constvalp() const
        {
        #ifdef AVMPLUS_64BIT
            return (void*)imm64();
        #else
            return (void*)imm32();
        #endif
        }

        bool isCse() const;
        bool isRet() const { return nanojit::isRetOpcode(opcode()); }
        bool isop(LOpcode o) const { return opcode() == o; }
        // isLInsXYZ() returns true if the instruction has the LInsXYZ form.
        // Note that there is some overlap with other predicates, eg.
        // isStore()==isLInsSti(), isCall()==isLInsC(), but that's ok;  these
        // ones are used only to check that opcodes are appropriate for
        // instruction layouts, the others are used for non-debugging
        // purposes.
        bool isLInsOp0() const;
        bool isLInsOp1() const;
        bool isLInsOp2() const;
        bool isLInsOp3() const;
        bool isLInsSti() const;
        bool isLInsLd()  const;
        bool isLInsSk()  const;
        bool isLInsC()   const;
        bool isLInsP()   const;
        bool isLInsI()   const;
        bool isLInsI64() const;
        bool isQuad() const;
        bool isCond() const;
        bool isFloat() const;
        bool isCmp() const;
        bool isCall() const {
            LOpcode op = LOpcode(opcode() & ~LIR64);
            return op == LIR_call;
        }
        bool isStore() const {
            LOpcode op = LOpcode(opcode() & ~LIR64);
            return op == LIR_sti;
        }
        bool isLoad() const {
            LOpcode op = opcode();
            return op == LIR_ldq  || op == LIR_ld || op == LIR_ldc ||
                   op == LIR_ldqc || op == LIR_ldcs || op == LIR_ldcb;
        }
        bool isGuard() const {
            LOpcode op = opcode();
            return op == LIR_x || op == LIR_xf || op == LIR_xt ||
                   op == LIR_loop || op == LIR_xbarrier || op == LIR_xtbl;
        }
        // True if the instruction is a 32-bit or smaller constant integer.
        bool isconst() const { return opcode() == LIR_int; }
        // True if the instruction is a 32-bit or smaller constant integer and
        // has the value val when treated as a 32-bit signed integer.
        bool isconstval(int32_t val) const;
        // True if the instruction is a constant quad value.
        bool isconstq() const;
        // True if the instruction is a constant pointer value.
        bool isconstp() const;
        bool isBranch() const {
            return isop(LIR_jt) || isop(LIR_jf) || isop(LIR_j);
        }

        // Return true if removal of 'ins' from a LIR fragment could
        // possibly change the behaviour of that fragment, even if any
        // value computed by 'ins' is not used later in the fragment.
        // In other words, can 'ins' possible alter control flow or memory?
        // Note, this assumes that loads will never fault and hence cannot
        // affect the control flow.
        bool isStmt() {
            return isGuard() || isBranch() ||
                   (isCall() && !isCse()) ||
                   isStore() ||
                   isop(LIR_loop) || isop(LIR_label) || isop(LIR_live) ||
                   isRet();
        }

        void setTarget(LIns* t);
        LIns* getTarget();

        GuardRecord *record();

        inline uint32_t argc() const {
            NanoAssert(isCall());
            return toLInsC()->argc;
        }
        const CallInfo *callInfo() const;
    };

    typedef LIns* LInsp;

    LIns* FASTCALL callArgN(LInsp i, uint32_t n);
    extern const uint8_t operandCount[];

    class Fragmento;    // @todo remove this ; needed for minbuild for some reason?!?  Should not be compiling this code at all

    // make it a GCObject so we can explicitly delete it early
    class LirWriter : public GCObject
    {
    public:
        LirWriter *out;

        virtual ~LirWriter() {}
        LirWriter(LirWriter* out)
            : out(out) {}

        virtual LInsp ins0(LOpcode v) {
            return out->ins0(v);
        }
        virtual LInsp ins1(LOpcode v, LIns* a) {
            return out->ins1(v, a);
        }
        virtual LInsp ins2(LOpcode v, LIns* a, LIns* b) {
            return out->ins2(v, a, b);
        }
        virtual LInsp ins3(LOpcode v, LIns* a, LIns* b, LIns* c) {
            return out->ins3(v, a, b, c);
        }
        virtual LInsp insGuard(LOpcode v, LIns *c, LIns *x) {
            return out->insGuard(v, c, x);
        }
        virtual LInsp insBranch(LOpcode v, LInsp condition, LInsp to) {
            return out->insBranch(v, condition, to);
        }
        // arg: 0=first, 1=second, ...
        // kind: 0=arg 1=saved-reg
        virtual LInsp insParam(int32_t arg, int32_t kind) {
            return out->insParam(arg, kind);
        }
        virtual LInsp insImm(int32_t imm) {
            return out->insImm(imm);
        }
        virtual LInsp insImmq(uint64_t imm) {
            return out->insImmq(imm);
        }
        virtual LInsp insLoad(LOpcode op, LIns* base, int32_t d) {
            return out->insLoad(op, base, d);
        }
        virtual LInsp insStorei(LIns* value, LIns* base, int32_t d) {
            return out->insStorei(value, base, d);
        }
        virtual LInsp insCall(const CallInfo *call, LInsp args[]) {
            return out->insCall(call, args);
        }
        virtual LInsp insAlloc(int32_t size) {
            NanoAssert(size != 0);
            return out->insAlloc(size);
        }
        virtual LInsp insSkip(size_t size) {
            return out->insSkip(size);
        }

        // convenience functions

        // Inserts a conditional to execute and branches to execute if
        // the condition is true and false respectively.
        LIns*        ins_choose(LIns* cond, LIns* iftrue, LIns* iffalse);
        // Inserts an integer comparison to 0
        LIns*        ins_eq0(LIns* oprnd1);
        // Inserts a binary operation where the second operand is an
        // integer immediate.
        LIns*       ins2i(LOpcode op, LIns *oprnd1, int32_t);
        LIns*        qjoin(LInsp lo, LInsp hi);
        LIns*        insImmPtr(const void *ptr);
        LIns*        insImmf(double f);
    };


    // Each page has a header;  the rest of it holds code.
    #define NJ_PAGE_CODE_AREA_SZB       (NJ_PAGE_SIZE - sizeof(PageHeader))

    // The first instruction on a page is always a start instruction, or a
    // payload-less skip instruction linking to the previous page.  The
    // biggest possible instruction would take up the entire rest of the page.
    #define NJ_MAX_LINS_SZB             (NJ_PAGE_CODE_AREA_SZB - sizeof(LInsSk))

    // The maximum skip payload size is determined by the maximum instruction
    // size.  We require that a skip's payload be adjacent to the skip LIns
    // itself.
    #define NJ_MAX_SKIP_PAYLOAD_SZB     (NJ_MAX_LINS_SZB - sizeof(LInsSk))


#ifdef NJ_VERBOSE
    extern const char* lirNames[];

    /**
     * map address ranges to meaningful names.
     */
    class LabelMap MMGC_SUBCLASS_DECL
    {
        class Entry MMGC_SUBCLASS_DECL
        {
        public:
            Entry(int) : name(0), size(0), align(0) {}
            Entry(avmplus::String *n, size_t s, size_t a) : name(n),size(s),align(a) {}
            ~Entry();
            DRCWB(avmplus::String*) name;
            size_t size:29, align:3;
        };
        avmplus::SortedMap<const void*, Entry*, avmplus::LIST_GCObjects> names;
        bool addrs, pad[3];
        char buf[1000], *end;
        void formatAddr(const void *p, char *buf);
    public:
        avmplus::AvmCore *core;
        LabelMap(avmplus::AvmCore *);
        ~LabelMap();
        void add(const void *p, size_t size, size_t align, const char *name);
        void add(const void *p, size_t size, size_t align, avmplus::String*);
        const char *dup(const char *);
        const char *format(const void *p);
        void clear();
    };

    class LirNameMap MMGC_SUBCLASS_DECL
    {
        template <class Key>
        class CountMap: public avmplus::SortedMap<Key, int, avmplus::LIST_NonGCObjects> {
        public:
            CountMap(GC*gc) : avmplus::SortedMap<Key, int, avmplus::LIST_NonGCObjects>(gc) {}
            int add(Key k) {
                int c = 1;
                if (containsKey(k)) {
                    c = 1+get(k);
                }
                put(k,c);
                return c;
            }
        };
        CountMap<int> lircounts;
        CountMap<const CallInfo *> funccounts;

        class Entry MMGC_SUBCLASS_DECL
        {
        public:
            Entry(int) : name(0) {}
            Entry(avmplus::String *n) : name(n) {}
            ~Entry();
            DRCWB(avmplus::String*) name;
        };
        avmplus::SortedMap<LInsp, Entry*, avmplus::LIST_GCObjects> names;
        LabelMap *labels;
        void formatImm(int32_t c, char *buf);
    public:

        LirNameMap(GC *gc, LabelMap *r)
            : lircounts(gc),
            funccounts(gc),
            names(gc),
            labels(r)
        {}
        ~LirNameMap();

        void addName(LInsp i, const char *s);
        bool addName(LInsp i, avmplus::String *s);
        void copyName(LInsp i, const char *s, int suffix);
        const char *formatRef(LIns *ref);
        const char *formatIns(LInsp i);
        void formatGuard(LInsp i, char *buf);
    };


    class VerboseWriter : public LirWriter
    {
        InsList code;
        DWB(LirNameMap*) names;
        LogControl* logc;
    public:
        VerboseWriter(GC *gc, LirWriter *out,
                      LirNameMap* names, LogControl* logc)
            : LirWriter(out), code(gc), names(names), logc(logc)
        {}

        LInsp add(LInsp i) {
            if (i)
                code.add(i);
            return i;
        }

        LInsp add_flush(LInsp i) {
            if ((i = add(i)) != 0)
                flush();
            return i;
        }

        void flush()
        {
            int n = code.size();
            if (n) {
                for (int i=0; i < n; i++)
                    logc->printf("    %s\n",names->formatIns(code[i]));
                code.clear();
                if (n > 1)
                    logc->printf("\n");
            }
        }

        LIns* insGuard(LOpcode op, LInsp cond, LIns *x) {
            return add_flush(out->insGuard(op,cond,x));
        }

        LIns* insBranch(LOpcode v, LInsp condition, LInsp to) {
            return add_flush(out->insBranch(v, condition, to));
        }

        LIns* ins0(LOpcode v) {
            if (v == LIR_label || v == LIR_start) {
                flush();
            }
            return add(out->ins0(v));
        }

        LIns* ins1(LOpcode v, LInsp a) {
            return isRetOpcode(v) ? add_flush(out->ins1(v, a)) : add(out->ins1(v, a));
        }
        LIns* ins2(LOpcode v, LInsp a, LInsp b) {
            return add(out->ins2(v, a, b));
        }
        LIns* ins3(LOpcode v, LInsp a, LInsp b, LInsp c) {
            return add(out->ins3(v, a, b, c));
        }
        LIns* insCall(const CallInfo *call, LInsp args[]) {
            return add_flush(out->insCall(call, args));
        }
        LIns* insParam(int32_t i, int32_t kind) {
            return add(out->insParam(i, kind));
        }
        LIns* insLoad(LOpcode v, LInsp base, int32_t disp) {
            return add(out->insLoad(v, base, disp));
        }
        LIns* insStorei(LInsp v, LInsp b, int32_t d) {
            return add(out->insStorei(v, b, d));
        }
        LIns* insAlloc(int32_t size) {
            return add(out->insAlloc(size));
        }
        LIns* insImm(int32_t imm) {
            return add(out->insImm(imm));
        }
        LIns* insImmq(uint64_t imm) {
            return add(out->insImmq(imm));
        }
    };

#endif

    class ExprFilter: public LirWriter
    {
    public:
        ExprFilter(LirWriter *out) : LirWriter(out) {}
        LIns* ins1(LOpcode v, LIns* a);
        LIns* ins2(LOpcode v, LIns* a, LIns* b);
        LIns* ins3(LOpcode v, LIns* a, LIns* b, LIns* c);
        LIns* insGuard(LOpcode, LIns *cond, LIns *);
        LIns* insBranch(LOpcode, LIns *cond, LIns *target);
    };

    // @todo, this could be replaced by a generic HashMap or HashSet, if we had one
    class LInsHashSet
    {
        // must be a power of 2.
        // don't start too small, or we'll waste time growing and rehashing.
        // don't start too large, will waste memory.
        static const uint32_t kInitialCap = 64;

        LInsp *m_list; // explicit WB's are used, no DWB needed.
        uint32_t m_used, m_cap;
        GC* m_gc;

        static uint32_t FASTCALL hashcode(LInsp i);
        uint32_t FASTCALL find(LInsp name, uint32_t hash, const LInsp *list, uint32_t cap);
        static bool FASTCALL equals(LInsp a, LInsp b);
        void FASTCALL grow();

    public:
        LInsHashSet(GC* gc);
        ~LInsHashSet();
        LInsp find32(int32_t a, uint32_t &i);
        LInsp find64(uint64_t a, uint32_t &i);
        LInsp find1(LOpcode v, LInsp a, uint32_t &i);
        LInsp find2(LOpcode v, LInsp a, LInsp b, uint32_t &i);
        LInsp find3(LOpcode v, LInsp a, LInsp b, LInsp c, uint32_t &i);
        LInsp findLoad(LOpcode v, LInsp a, int32_t b, uint32_t &i);
        LInsp findcall(const CallInfo *call, uint32_t argc, LInsp args[], uint32_t &i);
        LInsp add(LInsp i, uint32_t k);
        void replace(LInsp i);
        void clear();

        static uint32_t FASTCALL hashimm(int32_t);
        static uint32_t FASTCALL hashimmq(uint64_t);
        static uint32_t FASTCALL hash1(LOpcode v, LInsp);
        static uint32_t FASTCALL hash2(LOpcode v, LInsp, LInsp);
        static uint32_t FASTCALL hash3(LOpcode v, LInsp, LInsp, LInsp);
        static uint32_t FASTCALL hashLoad(LOpcode v, LInsp, int32_t);
        static uint32_t FASTCALL hashcall(const CallInfo *call, uint32_t argc, LInsp args[]);
    };

    class CseFilter: public LirWriter
    {
    public:
        LInsHashSet exprs;
        CseFilter(LirWriter *out, GC *gc);
        LIns* insImm(int32_t imm);
        LIns* insImmq(uint64_t q);
        LIns* ins0(LOpcode v);
        LIns* ins1(LOpcode v, LInsp);
        LIns* ins2(LOpcode v, LInsp, LInsp);
        LIns* ins3(LOpcode v, LInsp, LInsp, LInsp);
        LIns* insLoad(LOpcode op, LInsp cond, int32_t d);
        LIns* insCall(const CallInfo *call, LInsp args[]);
        LIns* insGuard(LOpcode op, LInsp cond, LIns *x);
    };

    class LirBuffer : public GCFinalizedObject
    {
        public:
            DWB(Fragmento*)        _frago;
            LirBuffer(Fragmento* frago);
            virtual ~LirBuffer();
            void        clear();
            void        rewind();
            uintptr_t   makeRoom(size_t szB);   // make room for an instruction
            bool        outOMem() { return _noMem != 0; }

            debug_only (void validate() const;)
            verbose_only(DWB(LirNameMap*) names;)

            int32_t insCount();
            size_t  byteCount();

            // stats
            struct
            {
                uint32_t lir;    // # instructions
            }
            _stats;

            AbiKind abi;
            LInsp state,param1,sp,rp;
            LInsp savedRegs[NumSavedRegs];
            bool explicitSavedRegs;

        protected:
            Page*        pageAlloc();
            void        moveToNewPage(uintptr_t addrOfLastLInsOnCurrentPage);

            PageList    _pages;
            Page*        _nextPage; // allocated in preperation of a needing to growing the buffer
            uintptr_t   _unused;    // next unused instruction slot
            int            _noMem;        // set if ran out of memory when writing to buffer
    };

    class LirBufWriter : public LirWriter
    {
        DWB(LirBuffer*)    _buf;        // underlying buffer housing the instructions

        public:
            LirBufWriter(LirBuffer* buf)
                : LirWriter(0), _buf(buf) {
            }

            // LirWriter interface
            LInsp   insLoad(LOpcode op, LInsp base, int32_t disp);
            LInsp    insStorei(LInsp o1, LInsp o2, int32_t disp);
            LInsp    ins0(LOpcode op);
            LInsp    ins1(LOpcode op, LInsp o1);
            LInsp    ins2(LOpcode op, LInsp o1, LInsp o2);
            LInsp    ins3(LOpcode op, LInsp o1, LInsp o2, LInsp o3);
            LInsp    insParam(int32_t i, int32_t kind);
            LInsp    insImm(int32_t imm);
            LInsp    insImmq(uint64_t imm);
            LInsp    insCall(const CallInfo *call, LInsp args[]);
            LInsp    insGuard(LOpcode op, LInsp cond, LIns *x);
            LInsp    insBranch(LOpcode v, LInsp condition, LInsp to);
            LInsp   insAlloc(int32_t size);
            LInsp   insSkip(size_t);
    };

    class LirFilter
    {
    public:
        LirFilter *in;
        LirFilter(LirFilter *in) : in(in) {}
        virtual ~LirFilter(){}

        virtual LInsp read() {
            return in->read();
        }
        virtual LInsp pos() {
            return in->pos();
        }
    };

    // concrete
    class LirReader : public LirFilter
    {
        LInsp _i; // current instruction that this decoder is operating on.

    public:
        LirReader(LInsp i) : LirFilter(0), _i(i) { }
        virtual ~LirReader() {}

        // LirReader i/f
        LInsp read(); // advance to the prior instruction
        LInsp pos() {
            return _i;
        }
        void setpos(LIns *i) {
            _i = i;
        }
    };

    class Assembler;

    void compile(Assembler *assm, Fragment *frag);
    verbose_only(void live(GC *gc, LirBuffer *lirbuf);)

    class StackFilter: public LirFilter
    {
        GC *gc;
        LirBuffer *lirbuf;
        LInsp sp;
        avmplus::BitSet stk;
        int top;
        int getTop(LInsp br);
    public:
        StackFilter(LirFilter *in, GC *gc, LirBuffer *lirbuf, LInsp sp);
        virtual ~StackFilter() {}
        LInsp read();
    };

    class CseReader: public LirFilter
    {
        LInsHashSet *exprs;
    public:
        CseReader(LirFilter *in, LInsHashSet *exprs);
        LInsp read();
    };

    // eliminate redundant loads by watching for stores & mutator calls
    class LoadFilter: public LirWriter
    {
    public:
        LInsp sp, rp;
        LInsHashSet exprs;
        void clear(LInsp p);
    public:
        LoadFilter(LirWriter *out, GC *gc)
            : LirWriter(out), exprs(gc) { }

        LInsp ins0(LOpcode);
        LInsp insLoad(LOpcode, LInsp base, int32_t disp);
        LInsp insStorei(LInsp v, LInsp b, int32_t d);
        LInsp insCall(const CallInfo *call, LInsp args[]);
    };
}
#endif // __nanojit_LIR__