text: /*
  ** $Id: lcode.c,v 2.112.1.1 2017/04/19 17:20:42 roberto Exp $
  ** Code generator for Lua
  ** See Copyright Notice in lua.h
  */
  
  #define lcode_c
  #define LUA_CORE
  
  
  
  #include "lprefix.h"
  
  
  #include <math.h>
  #include <stdlib.h>
  
  #include "lua.h"
  
  #include "lcode.h"
  #include "ldebug.h"
  #include "ldo.h"
  #include "lgc.h"
  #include "llex.h"
  #include "lmem.h"
  #include "lobject.h"
  #include "lopcodes.h"
  #include "lparser.h"
  #include "lstring.h"
  #include "ltable.h"
  #include "lvm.h"
  
  
  
  /* Maximum number of registers in a Lua function (must fit in 8 bits) */
  #define MAXREGS		255
  
  
  #define hasjumps(e)	((e)->t != (e)->f)
  
  
  /*
  ** If expression is a numeric constant, fills 'v' with its value
  ** and returns 1. Otherwise, returns 0.
  */
  static int tonumeral(const expdesc *e, TValue *v) {
    if (hasjumps(e))
      return 0;  /* not a numeral */
    switch (e->k) {
      case VKINT:
        if (v) setivalue(v, e->u.ival);
        return 1;
      case VKFLT:
        if (v) setfltvalue(v, e->u.nval);
        return 1;
      default: return 0;
    }
  }
  
  
  /*
  ** Create a OP_LOADNIL instruction, but try to optimize: if the previous
  ** instruction is also OP_LOADNIL and ranges are compatible, adjust
  ** range of previous instruction instead of emitting a new one. (For
  ** instance, 'local a; local b' will generate a single opcode.)
  */
  void luaK_nil (FuncState *fs, int from, int n) {
    Instruction *previous;
    int l = from + n - 1;  /* last register to set nil */
    if (fs->pc > fs->lasttarget) {  /* no jumps to current position? */
      previous = &fs->f->code[fs->pc-1];
      if (GET_OPCODE(*previous) == OP_LOADNIL) {  /* previous is LOADNIL? */
        int pfrom = GETARG_A(*previous);  /* get previous range */
        int pl = pfrom + GETARG_B(*previous);
        if ((pfrom <= from && from <= pl + 1) ||
            (from <= pfrom && pfrom <= l + 1)) {  /* can connect both? */
          if (pfrom < from) from = pfrom;  /* from = min(from, pfrom) */
          if (pl > l) l = pl;  /* l = max(l, pl) */
          SETARG_A(*previous, from);
          SETARG_B(*previous, l - from);
          return;
        }
      }  /* else go through */
    }
    luaK_codeABC(fs, OP_LOADNIL, from, n - 1, 0);  /* else no optimization */
  }
  
  
  /*
  ** Gets the destination address of a jump instruction. Used to traverse
  ** a list of jumps.
  */
  static int getjump (FuncState *fs, int pc) {
    int offset = GETARG_sBx(fs->f->code[pc]);
    if (offset == NO_JUMP)  /* point to itself represents end of list */
      return NO_JUMP;  /* end of list */
    else
      return (pc+1)+offset;  /* turn offset into absolute position */
  }
  
  
  /*
  ** Fix jump instruction at position 'pc' to jump to 'dest'.
  ** (Jump addresses are relative in Lua)
  */
  static void fixjump (FuncState *fs, int pc, int dest) {
    Instruction *jmp = &fs->f->code[pc];
    int offset = dest - (pc + 1);
    lua_assert(dest != NO_JUMP);
    if (abs(offset) > MAXARG_sBx)
      luaX_syntaxerror(fs->ls, "control structure too long");
    SETARG_sBx(*jmp, offset);
  }
  
  
  /*
  ** Concatenate jump-list 'l2' into jump-list 'l1'
  */
  void luaK_concat (FuncState *fs, int *l1, int l2) {
    if (l2 == NO_JUMP) return;  /* nothing to concatenate? */
    else if (*l1 == NO_JUMP)  /* no original list? */
      *l1 = l2;  /* 'l1' points to 'l2' */
    else {
      int list = *l1;
      int next;
      while ((next = getjump(fs, list)) != NO_JUMP)  /* find last element */
        list = next;
      fixjump(fs, list, l2);  /* last element links to 'l2' */
    }
  }
  
  
  /*
  ** Create a jump instruction and return its position, so its destination
  ** can be fixed later (with 'fixjump'). If there are jumps to
  ** this position (kept in 'jpc'), link them all together so that
  ** 'patchlistaux' will fix all them directly to the final destination.
  */
  int luaK_jump (FuncState *fs) {
    int jpc = fs->jpc;  /* save list of jumps to here */
    int j;
    fs->jpc = NO_JUMP;  /* no more jumps to here */
    j = luaK_codeAsBx(fs, OP_JMP, 0, NO_JUMP);
    luaK_concat(fs, &j, jpc);  /* keep them on hold */
    return j;
  }
  
  
  /*
  ** Code a 'return' instruction
  */
  void luaK_ret (FuncState *fs, int first, int nret) {
    luaK_codeABC(fs, OP_RETURN, first, nret+1, 0);
  }
  
  
  /*
  ** Code a "conditional jump", that is, a test or comparison opcode
  ** followed by a jump. Return jump position.
  */
  static int condjump (FuncState *fs, OpCode op, int A, int B, int C) {
    luaK_codeABC(fs, op, A, B, C);
    return luaK_jump(fs);
  }
  
  
  /*
  ** returns current 'pc' and marks it as a jump target (to avoid wrong
  ** optimizations with consecutive instructions not in the same basic block).
  */
  int luaK_getlabel (FuncState *fs) {
    fs->lasttarget = fs->pc;
    return fs->pc;
  }
  
  
  /*
  ** Returns the position of the instruction "controlling" a given
  ** jump (that is, its condition), or the jump itself if it is
  ** unconditional.
  */
  static Instruction *getjumpcontrol (FuncState *fs, int pc) {
    Instruction *pi = &fs->f->code[pc];
    if (pc >= 1 && testTMode(GET_OPCODE(*(pi-1))))
      return pi-1;
    else
      return pi;
  }
  
  
  /*
  ** Patch destination register for a TESTSET instruction.
  ** If instruction in position 'node' is not a TESTSET, return 0 ("fails").
  ** Otherwise, if 'reg' is not 'NO_REG', set it as the destination
  ** register. Otherwise, change instruction to a simple 'TEST' (produces
  ** no register value)
  */
  static int patchtestreg (FuncState *fs, int node, int reg) {
    Instruction *i = getjumpcontrol(fs, node);
    if (GET_OPCODE(*i) != OP_TESTSET)
      return 0;  /* cannot patch other instructions */
    if (reg != NO_REG && reg != GETARG_B(*i))
      SETARG_A(*i, reg);
    else {
       /* no register to put value or register already has the value;
          change instruction to simple test */
      *i = CREATE_ABC(OP_TEST, GETARG_B(*i), 0, GETARG_C(*i));
    }
    return 1;
  }
  
  
  /*
  ** Traverse a list of tests ensuring no one produces a value
  */
  static void removevalues (FuncState *fs, int list) {
    for (; list != NO_JUMP; list = getjump(fs, list))
        patchtestreg(fs, list, NO_REG);
  }
  
  
  /*
  ** Traverse a list of tests, patching their destination address and
  ** registers: tests producing values jump to 'vtarget' (and put their
  ** values in 'reg'), other tests jump to 'dtarget'.
  */
  static void patchlistaux (FuncState *fs, int list, int vtarget, int reg,
                            int dtarget) {
    while (list != NO_JUMP) {
      int next = getjump(fs, list);
      if (patchtestreg(fs, list, reg))
        fixjump(fs, list, vtarget);
      else
        fixjump(fs, list, dtarget);  /* jump to default target */
      list = next;
    }
  }
  
  
  /*
  ** Ensure all pending jumps to current position are fixed (jumping
  ** to current position with no values) and reset list of pending
  ** jumps
  */
  static void dischargejpc (FuncState *fs) {
    patchlistaux(fs, fs->jpc, fs->pc, NO_REG, fs->pc);
    fs->jpc = NO_JUMP;
  }
  
  
  /*
  ** Add elements in 'list' to list of pending jumps to "here"
  ** (current position)
  */
  void luaK_patchtohere (FuncState *fs, int list) {
    luaK_getlabel(fs);  /* mark "here" as a jump target */
    luaK_concat(fs, &fs->jpc, list);
  }
  
  
  /*
  ** Path all jumps in 'list' to jump to 'target'.
  ** (The assert means that we cannot fix a jump to a forward address
  ** because we only know addresses once code is generated.)
  */
  void luaK_patchlist (FuncState *fs, int list, int target) {
    if (target == fs->pc)  /* 'target' is current position? */
      luaK_patchtohere(fs, list);  /* add list to pending jumps */
    else {
      lua_assert(target < fs->pc);
      patchlistaux(fs, list, target, NO_REG, target);
    }
  }
  
  
  /*
  ** Path all jumps in 'list' to close upvalues up to given 'level'
  ** (The assertion checks that jumps either were closing nothing
  ** or were closing higher levels, from inner blocks.)
  */
  void luaK_patchclose (FuncState *fs, int list, int level) {
    level++;  /* argument is +1 to reserve 0 as non-op */
    for (; list != NO_JUMP; list = getjump(fs, list)) {
      lua_assert(GET_OPCODE(fs->f->code[list]) == OP_JMP &&
                  (GETARG_A(fs->f->code[list]) == 0 ||
                   GETARG_A(fs->f->code[list]) >= level));
      SETARG_A(fs->f->code[list], level);
    }
  }
  
  
  /*
  ** Emit instruction 'i', checking for array sizes and saving also its
  ** line information. Return 'i' position.
  */
  static int luaK_code (FuncState *fs, Instruction i) {
    Proto *f = fs->f;
    dischargejpc(fs);  /* 'pc' will change */
    /* put new instruction in code array */
    luaM_growvector(fs->ls->L, f->code, fs->pc, f->sizecode, Instruction,
                    MAX_INT, "opcodes");
    f->code[fs->pc] = i;
    /* save corresponding line information */
    luaM_growvector(fs->ls->L, f->lineinfo, fs->pc, f->sizelineinfo, int,
                    MAX_INT, "opcodes");
    f->lineinfo[fs->pc] = fs->ls->lastline;
    return fs->pc++;
  }
  
  
  /*
  ** Format and emit an 'iABC' instruction. (Assertions check consistency
  ** of parameters versus opcode.)
  */
  int luaK_codeABC (FuncState *fs, OpCode o, int a, int b, int c) {
    lua_assert(getOpMode(o) == iABC);
    lua_assert(getBMode(o) != OpArgN || b == 0);
    lua_assert(getCMode(o) != OpArgN || c == 0);
    lua_assert(a <= MAXARG_A && b <= MAXARG_B && c <= MAXARG_C);
    return luaK_code(fs, CREATE_ABC(o, a, b, c));
  }
  
  
  /*
  ** Format and emit an 'iABx' instruction.
  */
  int luaK_codeABx (FuncState *fs, OpCode o, int a, unsigned int bc) {
    lua_assert(getOpMode(o) == iABx || getOpMode(o) == iAsBx);
    lua_assert(getCMode(o) == OpArgN);
    lua_assert(a <= MAXARG_A && bc <= MAXARG_Bx);
    return luaK_code(fs, CREATE_ABx(o, a, bc));
  }
  
  
  /*
  ** Emit an "extra argument" instruction (format 'iAx')
  */
  static int codeextraarg (FuncState *fs, int a) {
    lua_assert(a <= MAXARG_Ax);
    return luaK_code(fs, CREATE_Ax(OP_EXTRAARG, a));
  }
  
  
  /*
  ** Emit a "load constant" instruction, using either 'OP_LOADK'
  ** (if constant index 'k' fits in 18 bits) or an 'OP_LOADKX'
  ** instruction with "extra argument".
  */
  int luaK_codek (FuncState *fs, int reg, int k) {
    if (k <= MAXARG_Bx)
      return luaK_codeABx(fs, OP_LOADK, reg, k);
    else {
      int p = luaK_codeABx(fs, OP_LOADKX, reg, 0);
      codeextraarg(fs, k);
      return p;
    }
  }
  
  
  /*
  ** Check register-stack level, keeping track of its maximum size
  ** in field 'maxstacksize'
  */
  void luaK_checkstack (FuncState *fs, int n) {
    int newstack = fs->freereg + n;
    if (newstack > fs->f->maxstacksize) {
      if (newstack >= MAXREGS)
        luaX_syntaxerror(fs->ls,
          "function or expression needs too many registers");
      fs->f->maxstacksize = cast_byte(newstack);
    }
  }
  
  
  /*
  ** Reserve 'n' registers in register stack
  */
  void luaK_reserveregs (FuncState *fs, int n) {
    luaK_checkstack(fs, n);
    fs->freereg += n;
  }
  
  
  /*
  ** Free register 'reg', if it is neither a constant index nor
  ** a local variable.
  )
  */
  static void freereg (FuncState *fs, int reg) {
    if (!ISK(reg) && reg >= fs->nactvar) {
      fs->freereg--;
      lua_assert(reg == fs->freereg);
    }
  }
  
  
  /*
  ** Free register used by expression 'e' (if any)
  */
  static void freeexp (FuncState *fs, expdesc *e) {
    if (e->k == VNONRELOC)
      freereg(fs, e->u.info);
  }
  
  
  /*
  ** Free registers used by expressions 'e1' and 'e2' (if any) in proper
  ** order.
  */
  static void freeexps (FuncState *fs, expdesc *e1, expdesc *e2) {
    int r1 = (e1->k == VNONRELOC) ? e1->u.info : -1;
    int r2 = (e2->k == VNONRELOC) ? e2->u.info : -1;
    if (r1 > r2) {
      freereg(fs, r1);
      freereg(fs, r2);
    }
    else {
      freereg(fs, r2);
      freereg(fs, r1);
    }
  }
  
  
  /*
  ** Add constant 'v' to prototype's list of constants (field 'k').
  ** Use scanner's table to cache position of constants in constant list
  ** and try to reuse constants. Because some values should not be used
  ** as keys (nil cannot be a key, integer keys can collapse with float
  ** keys), the caller must provide a useful 'key' for indexing the cache.
  */
  static int addk (FuncState *fs, TValue *key, TValue *v) {
    lua_State *L = fs->ls->L;
    Proto *f = fs->f;
    TValue *idx = luaH_set(L, fs->ls->h, key);  /* index scanner table */
    int k, oldsize;
    if (ttisinteger(idx)) {  /* is there an index there? */
      k = cast_int(ivalue(idx));
      /* correct value? (warning: must distinguish floats from integers!) */
      if (k < fs->nk && ttype(&f->k[k]) == ttype(v) &&
                        luaV_rawequalobj(&f->k[k], v))
        return k;  /* reuse index */
    }
    /* constant not found; create a new entry */
    oldsize = f->sizek;
    k = fs->nk;
    /* numerical value does not need GC barrier;
       table has no metatable, so it does not need to invalidate cache */
    setivalue(idx, k);
    luaM_growvector(L, f->k, k, f->sizek, TValue, MAXARG_Ax, "constants");
    while (oldsize < f->sizek) setnilvalue(&f->k[oldsize++]);
    setobj(L, &f->k[k], v);
    fs->nk++;
    luaC_barrier(L, f, v);
    return k;
  }
  
  
  /*
  ** Add a string to list of constants and return its index.
  */
  int luaK_stringK (FuncState *fs, TString *s) {
    TValue o;
    setsvalue(fs->ls->L, &o, s);
    return addk(fs, &o, &o);  /* use string itself as key */
  }
  
  
  /*
  ** Add an integer to list of constants and return its index.
  ** Integers use userdata as keys to avoid collision with floats with
  ** same value; conversion to 'void*' is used only for hashing, so there
  ** are no "precision" problems.
  */
  int luaK_intK (FuncState *fs, lua_Integer n) {
    TValue k, o;
    setpvalue(&k, cast(void*, cast(size_t, n)));
    setivalue(&o, n);
    return addk(fs, &k, &o);
  }
  
  /*
  ** Add a float to list of constants and return its index.
  */
  static int luaK_numberK (FuncState *fs, lua_Number r) {
    TValue o;
    setfltvalue(&o, r);
    return addk(fs, &o, &o);  /* use number itself as key */
  }
  
  
  /*
  ** Add a boolean to list of constants and return its index.
  */
  static int boolK (FuncState *fs, int b) {
    TValue o;
    setbvalue(&o, b);
    return addk(fs, &o, &o);  /* use boolean itself as key */
  }
  
  
  /*
  ** Add nil to list of constants and return its index.
  */
  static int nilK (FuncState *fs) {
    TValue k, v;
    setnilvalue(&v);
    /* cannot use nil as key; instead use table itself to represent nil */
    sethvalue(fs->ls->L, &k, fs->ls->h);
    return addk(fs, &k, &v);
  }
  
  
  /*
  ** Fix an expression to return the number of results 'nresults'.
  ** Either 'e' is a multi-ret expression (function call or vararg)
  ** or 'nresults' is LUA_MULTRET (as any expression can satisfy that).
  */
  void luaK_setreturns (FuncState *fs, expdesc *e, int nresults) {
    if (e->k == VCALL) {  /* expression is an open function call? */
      SETARG_C(getinstruction(fs, e), nresults + 1);
    }
    else if (e->k == VVARARG) {
      Instruction *pc = &getinstruction(fs, e);
      SETARG_B(*pc, nresults + 1);
      SETARG_A(*pc, fs->freereg);
      luaK_reserveregs(fs, 1);
    }
    else lua_assert(nresults == LUA_MULTRET);
  }
  
  
  /*
  ** Fix an expression to return one result.
  ** If expression is not a multi-ret expression (function call or
  ** vararg), it already returns one result, so nothing needs to be done.
  ** Function calls become VNONRELOC expressions (as its result comes
  ** fixed in the base register of the call), while vararg expressions
  ** become VRELOCABLE (as OP_VARARG puts its results where it wants).
  ** (Calls are created returning one result, so that does not need
  ** to be fixed.)
  */
  void luaK_setoneret (FuncState *fs, expdesc *e) {
    if (e->k == VCALL) {  /* expression is an open function call? */
      /* already returns 1 value */
      lua_assert(GETARG_C(getinstruction(fs, e)) == 2);
      e->k = VNONRELOC;  /* result has fixed position */
      e->u.info = GETARG_A(getinstruction(fs, e));
    }
    else if (e->k == VVARARG) {
      SETARG_B(getinstruction(fs, e), 2);
      e->k = VRELOCABLE;  /* can relocate its simple result */
    }
  }
  
  
  /*
  ** Ensure that expression 'e' is not a variable.
  */
  void luaK_dischargevars (FuncState *fs, expdesc *e) {
    switch (e->k) {
      case VLOCAL: {  /* already in a register */
        e->k = VNONRELOC;  /* becomes a non-relocatable value */
        break;
      }
      case VUPVAL: {  /* move value to some (pending) register */
        e->u.info = luaK_codeABC(fs, OP_GETUPVAL, 0, e->u.info, 0);
        e->k = VRELOCABLE;
        break;
      }
      case VINDEXED: {
        OpCode op;
        freereg(fs, e->u.ind.idx);
        if (e->u.ind.vt == VLOCAL) {  /* is 't' in a register? */
          freereg(fs, e->u.ind.t);
          op = OP_GETTABLE;
        }
        else {
          lua_assert(e->u.ind.vt == VUPVAL);
          op = OP_GETTABUP;  /* 't' is in an upvalue */
        }
        e->u.info = luaK_codeABC(fs, op, 0, e->u.ind.t, e->u.ind.idx);
        e->k = VRELOCABLE;
        break;
      }
      case VVARARG: case VCALL: {
        luaK_setoneret(fs, e);
        break;
      }
      default: break;  /* there is one value available (somewhere) */
    }
  }
  
  
  /*
  ** Ensures expression value is in register 'reg' (and therefore
  ** 'e' will become a non-relocatable expression).
  */
  static void discharge2reg (FuncState *fs, expdesc *e, int reg) {
    luaK_dischargevars(fs, e);
    switch (e->k) {
      case VNIL: {
        luaK_nil(fs, reg, 1);
        break;
      }
      case VFALSE: case VTRUE: {
        luaK_codeABC(fs, OP_LOADBOOL, reg, e->k == VTRUE, 0);
        break;
      }
      case VK: {
        luaK_codek(fs, reg, e->u.info);
        break;
      }
      case VKFLT: {
        luaK_codek(fs, reg, luaK_numberK(fs, e->u.nval));
        break;
      }
      case VKINT: {
        luaK_codek(fs, reg, luaK_intK(fs, e->u.ival));
        break;
      }
      case VRELOCABLE: {
        Instruction *pc = &getinstruction(fs, e);
        SETARG_A(*pc, reg);  /* instruction will put result in 'reg' */
        break;
      }
      case VNONRELOC: {
        if (reg != e->u.info)
          luaK_codeABC(fs, OP_MOVE, reg, e->u.info, 0);
        break;
      }
      default: {
        lua_assert(e->k == VJMP);
        return;  /* nothing to do... */
      }
    }
    e->u.info = reg;
    e->k = VNONRELOC;
  }
  
  
  /*
  ** Ensures expression value is in any register.
  */
  static void discharge2anyreg (FuncState *fs, expdesc *e) {
    if (e->k != VNONRELOC) {  /* no fixed register yet? */
      luaK_reserveregs(fs, 1);  /* get a register */
      discharge2reg(fs, e, fs->freereg-1);  /* put value there */
    }
  }
  
  
  static int code_loadbool (FuncState *fs, int A, int b, int jump) {
    luaK_getlabel(fs);  /* those instructions may be jump targets */
    return luaK_codeABC(fs, OP_LOADBOOL, A, b, jump);
  }
  
  
  /*
  ** check whether list has any jump that do not produce a value
  ** or produce an inverted value
  */
  static int need_value (FuncState *fs, int list) {
    for (; list != NO_JUMP; list = getjump(fs, list)) {
      Instruction i = *getjumpcontrol(fs, list);
      if (GET_OPCODE(i) != OP_TESTSET) return 1;
    }
    return 0;  /* not found */
  }
  
  
  /*
  ** Ensures final expression result (including results from its jump
  ** lists) is in register 'reg'.
  ** If expression has jumps, need to patch these jumps either to
  ** its final position or to "load" instructions (for those tests
  ** that do not produce values).
  */
  static void exp2reg (FuncState *fs, expdesc *e, int reg) {
    discharge2reg(fs, e, reg);
    if (e->k == VJMP)  /* expression itself is a test? */
      luaK_concat(fs, &e->t, e->u.info);  /* put this jump in 't' list */
    if (hasjumps(e)) {
      int final;  /* position after whole expression */
      int p_f = NO_JUMP;  /* position of an eventual LOAD false */
      int p_t = NO_JUMP;  /* position of an eventual LOAD true */
      if (need_value(fs, e->t) || need_value(fs, e->f)) {
        int fj = (e->k == VJMP) ? NO_JUMP : luaK_jump(fs);
        p_f = code_loadbool(fs, reg, 0, 1);
        p_t = code_loadbool(fs, reg, 1, 0);
        luaK_patchtohere(fs, fj);
      }
      final = luaK_getlabel(fs);
      patchlistaux(fs, e->f, final, reg, p_f);
      patchlistaux(fs, e->t, final, reg, p_t);
    }
    e->f = e->t = NO_JUMP;
    e->u.info = reg;
    e->k = VNONRELOC;
  }
  
  
  /*
  ** Ensures final expression result (including results from its jump
  ** lists) is in next available register.
  */
  void luaK_exp2nextreg (FuncState *fs, expdesc *e) {
    luaK_dischargevars(fs, e);
    freeexp(fs, e);
    luaK_reserveregs(fs, 1);
    exp2reg(fs, e, fs->freereg - 1);
  }
  
  
  /*
  ** Ensures final expression result (including results from its jump
  ** lists) is in some (any) register and return that register.
  */
  int luaK_exp2anyreg (FuncState *fs, expdesc *e) {
    luaK_dischargevars(fs, e);
    if (e->k == VNONRELOC) {  /* expression already has a register? */
      if (!hasjumps(e))  /* no jumps? */
        return e->u.info;  /* result is already in a register */
      if (e->u.info >= fs->nactvar) {  /* reg. is not a local? */
        exp2reg(fs, e, e->u.info);  /* put final result in it */
        return e->u.info;
      }
    }
    luaK_exp2nextreg(fs, e);  /* otherwise, use next available register */
    return e->u.info;
  }
  
  
  /*
  ** Ensures final expression result is either in a register or in an
  ** upvalue.
  */
  void luaK_exp2anyregup (FuncState *fs, expdesc *e) {
    if (e->k != VUPVAL || hasjumps(e))
      luaK_exp2anyreg(fs, e);
  }
  
  
  /*
  ** Ensures final expression result is either in a register or it is
  ** a constant.
  */
  void luaK_exp2val (FuncState *fs, expdesc *e) {
    if (hasjumps(e))
      luaK_exp2anyreg(fs, e);
    else
      luaK_dischargevars(fs, e);
  }
  
  
  /*
  ** Ensures final expression result is in a valid R/K index
  ** (that is, it is either in a register or in 'k' with an index
  ** in the range of R/K indices).
  ** Returns R/K index.
  */
  int luaK_exp2RK (FuncState *fs, expdesc *e) {
    luaK_exp2val(fs, e);
    switch (e->k) {  /* move constants to 'k' */
      case VTRUE: e->u.info = boolK(fs, 1); goto vk;
      case VFALSE: e->u.info = boolK(fs, 0); goto vk;
      case VNIL: e->u.info = nilK(fs); goto vk;
      case VKINT: e->u.info = luaK_intK(fs, e->u.ival); goto vk;
      case VKFLT: e->u.info = luaK_numberK(fs, e->u.nval); goto vk;
      case VK:
       vk:
        e->k = VK;
        if (e->u.info <= MAXINDEXRK)  /* constant fits in 'argC'? */
          return RKASK(e->u.info);
        else break;
      default: break;
    }
    /* not a constant in the right range: put it in a register */
    return luaK_exp2anyreg(fs, e);
  }
  
  
  /*
  ** Generate code to store result of expression 'ex' into variable 'var'.
  */
  void luaK_storevar (FuncState *fs, expdesc *var, expdesc *ex) {
    switch (var->k) {
      case VLOCAL: {
        freeexp(fs, ex);
        exp2reg(fs, ex, var->u.info);  /* compute 'ex' into proper place */
        return;
      }
      case VUPVAL: {
        int e = luaK_exp2anyreg(fs, ex);
        luaK_codeABC(fs, OP_SETUPVAL, e, var->u.info, 0);
        break;
      }
      case VINDEXED: {
        OpCode op = (var->u.ind.vt == VLOCAL) ? OP_SETTABLE : OP_SETTABUP;
        int e = luaK_exp2RK(fs, ex);
        luaK_codeABC(fs, op, var->u.ind.t, var->u.ind.idx, e);
        break;
      }
      default: lua_assert(0);  /* invalid var kind to store */
    }
    freeexp(fs, ex);
  }
  
  
  /*
  ** Emit SELF instruction (convert expression 'e' into 'e:key(e,').
  */
  void luaK_self (FuncState *fs, expdesc *e, expdesc *key) {
    int ereg;
    luaK_exp2anyreg(fs, e);
    ereg = e->u.info;  /* register where 'e' was placed */
    freeexp(fs, e);
    e->u.info = fs->freereg;  /* base register for op_self */
    e->k = VNONRELOC;  /* self expression has a fixed register */
    luaK_reserveregs(fs, 2);  /* function and 'self' produced by op_self */
    luaK_codeABC(fs, OP_SELF, e->u.info, ereg, luaK_exp2RK(fs, key));
    freeexp(fs, key);
  }
  
  
  /*
  ** Negate condition 'e' (where 'e' is a comparison).
  */
  static void negatecondition (FuncState *fs, expdesc *e) {
    Instruction *pc = getjumpcontrol(fs, e->u.info);
    lua_assert(testTMode(GET_OPCODE(*pc)) && GET_OPCODE(*pc) != OP_TESTSET &&
                                             GET_OPCODE(*pc) != OP_TEST);
    SETARG_A(*pc, !(GETARG_A(*pc)));
  }
  
  
  /*
  ** Emit instruction to jump if 'e' is 'cond' (that is, if 'cond'
  ** is true, code will jump if 'e' is true.) Return jump position.
  ** Optimize when 'e' is 'not' something, inverting the condition
  ** and removing the 'not'.
  */
  static int jumponcond (FuncState *fs, expdesc *e, int cond) {
    if (e->k == VRELOCABLE) {
      Instruction ie = getinstruction(fs, e);
      if (GET_OPCODE(ie) == OP_NOT) {
        fs->pc--;  /* remove previous OP_NOT */
        return condjump(fs, OP_TEST, GETARG_B(ie), 0, !cond);
      }
      /* else go through */
    }
    discharge2anyreg(fs, e);
    freeexp(fs, e);
    return condjump(fs, OP_TESTSET, NO_REG, e->u.info, cond);
  }
  
  
  /*
  ** Emit code to go through if 'e' is true, jump otherwise.
  */
  void luaK_goiftrue (FuncState *fs, expdesc *e) {
    int pc;  /* pc of new jump */
    luaK_dischargevars(fs, e);
    switch (e->k) {
      case VJMP: {  /* condition? */
        negatecondition(fs, e);  /* jump when it is false */
        pc = e->u.info;  /* save jump position */
        break;
      }
      case VK: case VKFLT: case VKINT: case VTRUE: {
        pc = NO_JUMP;  /* always true; do nothing */
        break;
      }
      default: {
        pc = jumponcond(fs, e, 0);  /* jump when false */
        break;
      }
    }
    luaK_concat(fs, &e->f, pc);  /* insert new jump in false list */
    luaK_patchtohere(fs, e->t);  /* true list jumps to here (to go through) */
    e->t = NO_JUMP;
  }
  
  
  /*
  ** Emit code to go through if 'e' is false, jump otherwise.
  */
  void luaK_goiffalse (FuncState *fs, expdesc *e) {
    int pc;  /* pc of new jump */
    luaK_dischargevars(fs, e);
    switch (e->k) {
      case VJMP: {
        pc = e->u.info;  /* already jump if true */
        break;
      }
      case VNIL: case VFALSE: {
        pc = NO_JUMP;  /* always false; do nothing */
        break;
      }
      default: {
        pc = jumponcond(fs, e, 1);  /* jump if true */
        break;
      }
    }
    luaK_concat(fs, &e->t, pc);  /* insert new jump in 't' list */
    luaK_patchtohere(fs, e->f);  /* false list jumps to here (to go through) */
    e->f = NO_JUMP;
  }
  
  
  /*
  ** Code 'not e', doing constant folding.
  */
  static void codenot (FuncState *fs, expdesc *e) {
    luaK_dischargevars(fs, e);
    switch (e->k) {
      case VNIL: case VFALSE: {
        e->k = VTRUE;  /* true == not nil == not false */
        break;
      }
      case VK: case VKFLT: case VKINT: case VTRUE: {
        e->k = VFALSE;  /* false == not "x" == not 0.5 == not 1 == not true */
        break;
      }
      case VJMP: {
        negatecondition(fs, e);
        break;
      }
      case VRELOCABLE:
      case VNONRELOC: {
        discharge2anyreg(fs, e);
        freeexp(fs, e);
        e->u.info = luaK_codeABC(fs, OP_NOT, 0, e->u.info, 0);
        e->k = VRELOCABLE;
        break;
      }
      default: lua_assert(0);  /* cannot happen */
    }
    /* interchange true and false lists */
    { int temp = e->f; e->f = e->t; e->t = temp; }
    removevalues(fs, e->f);  /* values are useless when negated */
    removevalues(fs, e->t);
  }
  
  
  /*
  ** Create expression 't[k]'. 't' must have its final result already in a
  ** register or upvalue.
  */
  void luaK_indexed (FuncState *fs, expdesc *t, expdesc *k) {
    lua_assert(!hasjumps(t) && (vkisinreg(t->k) || t->k == VUPVAL));
    t->u.ind.t = t->u.info;  /* register or upvalue index */
    t->u.ind.idx = luaK_exp2RK(fs, k);  /* R/K index for key */
    t->u.ind.vt = (t->k == VUPVAL) ? VUPVAL : VLOCAL;
    t->k = VINDEXED;
  }
  
  
  /*
  ** Return false if folding can raise an error.
  ** Bitwise operations need operands convertible to integers; division
  ** operations cannot have 0 as divisor.
  */
  static int validop (int op, TValue *v1, TValue *v2) {
    switch (op) {
      case LUA_OPBAND: case LUA_OPBOR: case LUA_OPBXOR:
      case LUA_OPSHL: case LUA_OPSHR: case LUA_OPBNOT: {  /* conversion errors */
        lua_Integer i;
        return (tointeger(v1, &i) && tointeger(v2, &i));
      }
      case LUA_OPDIV: case LUA_OPIDIV: case LUA_OPMOD:  /* division by 0 */
        return (nvalue(v2) != 0);
      default: return 1;  /* everything else is valid */
    }
  }
  
  
  /*
  ** Try to "constant-fold" an operation; return 1 iff successful.
  ** (In this case, 'e1' has the final result.)
  */
  static int constfolding (FuncState *fs, int op, expdesc *e1,
                                                  const expdesc *e2) {
    TValue v1, v2, res;
    if (!tonumeral(e1, &v1) || !tonumeral(e2, &v2) || !validop(op, &v1, &v2))
      return 0;  /* non-numeric operands or not safe to fold */
    luaO_arith(fs->ls->L, op, &v1, &v2, &res);  /* does operation */
    if (ttisinteger(&res)) {
      e1->k = VKINT;
      e1->u.ival = ivalue(&res);
    }
    else {  /* folds neither NaN nor 0.0 (to avoid problems with -0.0) */
      lua_Number n = fltvalue(&res);
      if (luai_numisnan(n) || n == 0)
        return 0;
      e1->k = VKFLT;
      e1->u.nval = n;
    }
    return 1;
  }
  
  
  /*
  ** Emit code for unary expressions that "produce values"
  ** (everything but 'not').
  ** Expression to produce final result will be encoded in 'e'.
  */
  static void codeunexpval (FuncState *fs, OpCode op, expdesc *e, int line) {
    int r = luaK_exp2anyreg(fs, e);  /* opcodes operate only on registers */
    freeexp(fs, e);
    e->u.info = luaK_codeABC(fs, op, 0, r, 0);  /* generate opcode */
    e->k = VRELOCABLE;  /* all those operations are relocatable */
    luaK_fixline(fs, line);
  }
  
  
  /*
  ** Emit code for binary expressions that "produce values"
  ** (everything but logical operators 'and'/'or' and comparison
  ** operators).
  ** Expression to produce final result will be encoded in 'e1'.
  ** Because 'luaK_exp2RK' can free registers, its calls must be
  ** in "stack order" (that is, first on 'e2', which may have more
  ** recent registers to be released).
  */
  static void codebinexpval (FuncState *fs, OpCode op,
                             expdesc *e1, expdesc *e2, int line) {
    int rk2 = luaK_exp2RK(fs, e2);  /* both operands are "RK" */
    int rk1 = luaK_exp2RK(fs, e1);
    freeexps(fs, e1, e2);
    e1->u.info = luaK_codeABC(fs, op, 0, rk1, rk2);  /* generate opcode */
    e1->k = VRELOCABLE;  /* all those operations are relocatable */
    luaK_fixline(fs, line);
  }
  
  
  /*
  ** Emit code for comparisons.
  ** 'e1' was already put in R/K form by 'luaK_infix'.
  */
  static void codecomp (FuncState *fs, BinOpr opr, expdesc *e1, expdesc *e2) {
    int rk1 = (e1->k == VK) ? RKASK(e1->u.info)
                            : check_exp(e1->k == VNONRELOC, e1->u.info);
    int rk2 = luaK_exp2RK(fs, e2);
    freeexps(fs, e1, e2);
    switch (opr) {
      case OPR_NE: {  /* '(a ~= b)' ==> 'not (a == b)' */
        e1->u.info = condjump(fs, OP_EQ, 0, rk1, rk2);
        break;
      }
      case OPR_GT: case OPR_GE: {
        /* '(a > b)' ==> '(b < a)';  '(a >= b)' ==> '(b <= a)' */
        OpCode op = cast(OpCode, (opr - OPR_NE) + OP_EQ);
        e1->u.info = condjump(fs, op, 1, rk2, rk1);  /* invert operands */
        break;
      }
      default: {  /* '==', '<', '<=' use their own opcodes */
        OpCode op = cast(OpCode, (opr - OPR_EQ) + OP_EQ);
        e1->u.info = condjump(fs, op, 1, rk1, rk2);
        break;
      }
    }
    e1->k = VJMP;
  }
  
  
  /*
  ** Aplly prefix operation 'op' to expression 'e'.
  */
  void luaK_prefix (FuncState *fs, UnOpr op, expdesc *e, int line) {
    static const expdesc ef = {VKINT, {0}, NO_JUMP, NO_JUMP};
    switch (op) {
      case OPR_MINUS: case OPR_BNOT:  /* use 'ef' as fake 2nd operand */
        if (constfolding(fs, op + LUA_OPUNM, e, &ef))
          break;
        /* FALLTHROUGH */
      case OPR_LEN:
        codeunexpval(fs, cast(OpCode, op + OP_UNM), e, line);
        break;
      case OPR_NOT: codenot(fs, e); break;
      default: lua_assert(0);
    }
  }
  
  
  /*
  ** Process 1st operand 'v' of binary operation 'op' before reading
  ** 2nd operand.
  */
  void luaK_infix (FuncState *fs, BinOpr op, expdesc *v) {
    switch (op) {
      case OPR_AND: {
        luaK_goiftrue(fs, v);  /* go ahead only if 'v' is true */
        break;
      }
      case OPR_OR: {
        luaK_goiffalse(fs, v);  /* go ahead only if 'v' is false */
        break;
      }
      case OPR_CONCAT: {
        luaK_exp2nextreg(fs, v);  /* operand must be on the 'stack' */
        break;
      }
      case OPR_ADD: case OPR_SUB:
      case OPR_MUL: case OPR_DIV: case OPR_IDIV:
      case OPR_MOD: case OPR_POW:
      case OPR_BAND: case OPR_BOR: case OPR_BXOR:
      case OPR_SHL: case OPR_SHR: {
        if (!tonumeral(v, NULL))
          luaK_exp2RK(fs, v);
        /* else keep numeral, which may be folded with 2nd operand */
        break;
      }
      default: {
        luaK_exp2RK(fs, v);
        break;
      }
    }
  }
  
  
  /*
  ** Finalize code for binary operation, after reading 2nd operand.
  ** For '(a .. b .. c)' (which is '(a .. (b .. c))', because
  ** concatenation is right associative), merge second CONCAT into first
  ** one.
  */
  void luaK_posfix (FuncState *fs, BinOpr op,
                    expdesc *e1, expdesc *e2, int line) {
    switch (op) {
      case OPR_AND: {
        lua_assert(e1->t == NO_JUMP);  /* list closed by 'luK_infix' */
        luaK_dischargevars(fs, e2);
        luaK_concat(fs, &e2->f, e1->f);
        *e1 = *e2;
        break;
      }
      case OPR_OR: {
        lua_assert(e1->f == NO_JUMP);  /* list closed by 'luK_infix' */
        luaK_dischargevars(fs, e2);
        luaK_concat(fs, &e2->t, e1->t);
        *e1 = *e2;
        break;
      }
      case OPR_CONCAT: {
        luaK_exp2val(fs, e2);
        if (e2->k == VRELOCABLE &&
            GET_OPCODE(getinstruction(fs, e2)) == OP_CONCAT) {
          lua_assert(e1->u.info == GETARG_B(getinstruction(fs, e2))-1);
          freeexp(fs, e1);
          SETARG_B(getinstruction(fs, e2), e1->u.info);
          e1->k = VRELOCABLE; e1->u.info = e2->u.info;
        }
        else {
          luaK_exp2nextreg(fs, e2);  /* operand must be on the 'stack' */
          codebinexpval(fs, OP_CONCAT, e1, e2, line);
        }
        break;
      }
      case OPR_ADD: case OPR_SUB: case OPR_MUL: case OPR_DIV:
      case OPR_IDIV: case OPR_MOD: case OPR_POW:
      case OPR_BAND: case OPR_BOR: case OPR_BXOR:
      case OPR_SHL: case OPR_SHR: {
        if (!constfolding(fs, op + LUA_OPADD, e1, e2))
          codebinexpval(fs, cast(OpCode, op + OP_ADD), e1, e2, line);
        break;
      }
      case OPR_EQ: case OPR_LT: case OPR_LE:
      case OPR_NE: case OPR_GT: case OPR_GE: {
        codecomp(fs, op, e1, e2);
        break;
      }
      default: lua_assert(0);
    }
  }
  
  
  /*
  ** Change line information associated with current position.
  */
  void luaK_fixline (FuncState *fs, int line) {
    fs->f->lineinfo[fs->pc - 1] = line;
  }
  
  
  /*
  ** Emit a SETLIST instruction.
  ** 'base' is register that keeps table;
  ** 'nelems' is #table plus those to be stored now;
  ** 'tostore' is number of values (in registers 'base + 1',...) to add to
  ** table (or LUA_MULTRET to add up to stack top).
  */
  void luaK_setlist (FuncState *fs, int base, int nelems, int tostore) {
    int c =  (nelems - 1)/LFIELDS_PER_FLUSH + 1;
    int b = (tostore == LUA_MULTRET) ? 0 : tostore;
    lua_assert(tostore != 0 && tostore <= LFIELDS_PER_FLUSH);
    if (c <= MAXARG_C)
      luaK_codeABC(fs, OP_SETLIST, base, b, c);
    else if (c <= MAXARG_Ax) {
      luaK_codeABC(fs, OP_SETLIST, base, b, 0);
      codeextraarg(fs, c);
    }
    else
      luaX_syntaxerror(fs->ls, "constructor too long");
    fs->freereg = base + 1;  /* free registers with list values */
  }
  
  