clang/lua | Gitverse

lcode.c
1 692 строки47 KB
Roberto Ierusalimschy
First implementation for 'const' variables
17 май 2019, 17:11
17 май 2019, 17:11d9f40e3
/*
** $Id: lcode.c $
** Code generator for Lua
** See Copyright Notice in lua.h
*/

#define lcode_c
#define LUA_CORE

#include "lprefix.h"


#include <limits.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)


static int codesJ (FuncState *fs, OpCode o, int sj, int k);



/* semantic error */
l_noret luaK_semerror (LexState *ls, const char *msg) {
  ls->t.token = 0;  /* remove "near <token>" from final message */
  luaX_syntaxerror(ls, msg);
}


/*
** 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;
  }
}


/*
** Return the previous instruction of the current code. If there
** may be a jump target between the current instruction and the
** previous one, return an invalid instruction (to avoid wrong
** optimizations).
*/
static Instruction *previousinstruction (FuncState *fs) {
  static const Instruction invalidinstruction = -1;
  if (fs->pc > fs->lasttarget)
    return &fs->f->code[fs->pc - 1];  /* previous instruction */
  else
    return cast(Instruction*, &invalidinstruction);
}


/*
** 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) {
  int l = from + n - 1;  /* last register to set nil */
  Instruction *previous = previousinstruction(fs);
  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_sJ(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 (!(-OFFSET_sJ <= offset && offset <= MAXARG_sJ - OFFSET_sJ))
    luaX_syntaxerror(fs->ls, "control structure too long");
  lua_assert(GET_OPCODE(*jmp) == OP_JMP);
  SETARG_sJ(*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').
*/
int luaK_jump (FuncState *fs) {
  return codesJ(fs, OP_JMP, NO_JUMP, 0);
}


/*
** Code a 'return' instruction
*/
void luaK_ret (FuncState *fs, int first, int nret) {
  OpCode op;
  switch (nret) {
    case 0: op = OP_RETURN0; break;
    case 1: op = OP_RETURN1; break;
    default: op = OP_RETURN; break;
  }
  luaK_codeABC(fs, op, 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, int k) {
  luaK_codeABCk(fs, op, A, B, C, k);
  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_ABCk(OP_TEST, GETARG_B(*i), 0, 0, GETARG_k(*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;
  }
}


/*
** 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) {
  lua_assert(target <= fs->pc);
  patchlistaux(fs, list, target, NO_REG, target);
}


void luaK_patchtohere (FuncState *fs, int list) {
  int hr = luaK_getlabel(fs);  /* mark "here" as a jump target */
  luaK_patchlist(fs, list, hr);
}


/*
** MAXimum number of successive Instructions WiTHout ABSolute line
** information.
*/
#if !defined(MAXIWTHABS)
#define MAXIWTHABS	120
#endif


/* limit for difference between lines in relative line info. */
#define LIMLINEDIFF	0x80


/*
** Save line info for a new instruction. If difference from last line
** does not fit in a byte, of after that many instructions, save a new
** absolute line info; (in that case, the special value 'ABSLINEINFO'
** in 'lineinfo' signals the existence of this absolute information.)
** Otherwise, store the difference from last line in 'lineinfo'.
*/
static void savelineinfo (FuncState *fs, Proto *f, int line) {
  int linedif = line - fs->previousline;
  int pc = fs->pc - 1;  /* last instruction coded */
  if (abs(linedif) >= LIMLINEDIFF || fs->iwthabs++ > MAXIWTHABS) {
    luaM_growvector(fs->ls->L, f->abslineinfo, fs->nabslineinfo,
                    f->sizeabslineinfo, AbsLineInfo, MAX_INT, "lines");
    f->abslineinfo[fs->nabslineinfo].pc = pc;
    f->abslineinfo[fs->nabslineinfo++].line = line;
    linedif = ABSLINEINFO;  /* signal that there is absolute information */
    fs->iwthabs = 0;  /* restart counter */
  }
  luaM_growvector(fs->ls->L, f->lineinfo, pc, f->sizelineinfo, ls_byte,
                  MAX_INT, "opcodes");
  f->lineinfo[pc] = linedif;
  fs->previousline = line;  /* last line saved */
}


/*
** Remove line information from the last instruction.
** If line information for that instruction is absolute, set 'iwthabs'
** above its max to force the new (replacing) instruction to have
** absolute line info, too.
*/
static void removelastlineinfo (FuncState *fs) {
  Proto *f = fs->f;
  int pc = fs->pc - 1;  /* last instruction coded */
  if (f->lineinfo[pc] != ABSLINEINFO) {  /* relative line info? */
    fs->previousline -= f->lineinfo[pc];  /* last line saved */
    fs->iwthabs--;
  }
  else {  /* absolute line information */
    fs->nabslineinfo--;  /* remove it */
    lua_assert(f->abslineinfo[fs->nabslineinfo].pc = pc);
    fs->iwthabs = MAXIWTHABS + 1;  /* force next line info to be absolute */
  }
}


/*
** Remove the last instruction created, correcting line information
** accordingly.
*/
static void removelastinstruction (FuncState *fs) {
  removelastlineinfo(fs);
  fs->pc--;
}


/*
** 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;
  /* 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;
  savelineinfo(fs, f, fs->ls->lastline);
  return fs->pc - 1;  /* index of new instruction */
}


/*
** Format and emit an 'iABC' instruction. (Assertions check consistency
** of parameters versus opcode.)
*/
int luaK_codeABCk (FuncState *fs, OpCode o, int a, int b, int c, int k) {
  lua_assert(getOpMode(o) == iABC);
  lua_assert(a <= MAXARG_A && b <= MAXARG_B &&
             c <= MAXARG_C && (k & ~1) == 0);
  return luaK_code(fs, CREATE_ABCk(o, a, b, c, k));
}


/*
** Format and emit an 'iABx' instruction.
*/
int luaK_codeABx (FuncState *fs, OpCode o, int a, unsigned int bc) {
  lua_assert(getOpMode(o) == iABx);
  lua_assert(a <= MAXARG_A && bc <= MAXARG_Bx);
  return luaK_code(fs, CREATE_ABx(o, a, bc));
}


/*
** Format and emit an 'iAsBx' instruction.
*/
int luaK_codeAsBx (FuncState *fs, OpCode o, int a, int bc) {
  unsigned int b = bc + OFFSET_sBx;
  lua_assert(getOpMode(o) == iAsBx);
  lua_assert(a <= MAXARG_A && b <= MAXARG_Bx);
  return luaK_code(fs, CREATE_ABx(o, a, b));
}


/*
** Format and emit an 'isJ' instruction.
*/
static int codesJ (FuncState *fs, OpCode o, int sj, int k) {
  unsigned int j = sj + OFFSET_sJ;
  lua_assert(getOpMode(o) == isJ);
  lua_assert(j <= MAXARG_sJ && (k & ~1) == 0);
  return luaK_code(fs, CREATE_sJ(o, j, k));
}


/*
** 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".
*/
static 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 (reg >= fs->nactvar) {
    fs->freereg--;
    lua_assert(reg == fs->freereg);
  }
}


/*
** Free two registers in proper order
*/
static void freeregs (FuncState *fs, int r1, int r2) {
  if (r1 > r2) {
    freereg(fs, r1);
    freereg(fs, r2);
  }
  else {
    freereg(fs, r2);
    freereg(fs, r1);
  }
}


/*
** 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;
  freeregs(fs, r1, r2);
}


/*
** 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 && ttypetag(&f->k[k]) == ttypetag(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.
*/
static int luaK_intK (FuncState *fs, lua_Integer n) {
  TValue k, o;
  setpvalue(&k, cast_voidp(cast_sizet(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);
}


/*
** Check whether 'i' can be stored in an 'sC' operand.
** Equivalent to (0 <= i + OFFSET_sC && i + OFFSET_sC <= MAXARG_C)
** but without risk of overflows in the addition.
*/
static int fitsC (lua_Integer i) {
  return (-OFFSET_sC <= i && i <= MAXARG_C - OFFSET_sC);
}


/*
** Check whether 'i' can be stored in an 'sBx' operand.
*/
static int fitsBx (lua_Integer i) {
  return (-OFFSET_sBx <= i && i <= MAXARG_Bx - OFFSET_sBx);
}


void luaK_int (FuncState *fs, int reg, lua_Integer i) {
  if (fitsBx(i))
    luaK_codeAsBx(fs, OP_LOADI, reg, cast_int(i));
  else
    luaK_codek(fs, reg, luaK_intK(fs, i));
}


static int floatI (lua_Number f, lua_Integer *fi) {
  return (luaV_flttointeger(f, fi, 0) && fitsBx(*fi));
}


static void luaK_float (FuncState *fs, int reg, lua_Number f) {
  lua_Integer fi;
  if (floatI(f, &fi))
    luaK_codeAsBx(fs, OP_LOADF, reg, cast_int(fi));
  else
    luaK_codek(fs, reg, luaK_numberK(fs, f));
}


/*
** 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) {
  Instruction *pc = &getinstruction(fs, e);
  if (e->k == VCALL)  /* expression is an open function call? */
    SETARG_C(*pc, nresults + 1);
  else if (e->k == VVARARG) {
    SETARG_C(*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 VRELOC (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_C(getinstruction(fs, e), 2);
    e->k = VRELOC;  /* can relocate its simple result */
  }
}


/*
** Ensure that expression 'e' is not a variable.
** (Expression still may have jump lists.)
*/
void luaK_dischargevars (FuncState *fs, expdesc *e) {
  switch (e->k) {
    case VLOCAL: {  /* already in a register */
      e->u.info = e->u.var.idx;
      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.var.idx, 0);
      e->k = VRELOC;
      break;
    }
    case VINDEXUP: {
      e->u.info = luaK_codeABC(fs, OP_GETTABUP, 0, e->u.ind.t, e->u.ind.idx);
      e->k = VRELOC;
      break;
    }
    case VINDEXI: {
      freereg(fs, e->u.ind.t);
      e->u.info = luaK_codeABC(fs, OP_GETI, 0, e->u.ind.t, e->u.ind.idx);
      e->k = VRELOC;
      break;
    }
    case VINDEXSTR: {
      freereg(fs, e->u.ind.t);
      e->u.info = luaK_codeABC(fs, OP_GETFIELD, 0, e->u.ind.t, e->u.ind.idx);
      e->k = VRELOC;
      break;
    }
    case VINDEXED: {
      freeregs(fs, e->u.ind.t, e->u.ind.idx);
      e->u.info = luaK_codeABC(fs, OP_GETTABLE, 0, e->u.ind.t, e->u.ind.idx);
      e->k = VRELOC;
      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).
** (Expression still may have jump lists.)
*/
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_float(fs, reg, e->u.nval);
      break;
    }
    case VKINT: {
      luaK_int(fs, reg, e->u.ival);
      break;
    }
    case VRELOC: {
      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.
** (Expression still may have jump lists.)
*/
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 (which includes 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);  /* load false and skip next i. */
      p_t = code_loadbool(fs, reg, 1, 0);  /* load true */
      /* jump around these booleans if 'e' is not a test */
      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 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 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);
}


/*
** Try to make 'e' a K expression with an index in the range of R/K
** indices. Return true iff succeeded.
*/
static int luaK_exp2K (FuncState *fs, expdesc *e) {
  if (!hasjumps(e)) {
    int info;
    switch (e->k) {  /* move constants to 'k' */
      case VTRUE: info = boolK(fs, 1); break;
      case VFALSE: info = boolK(fs, 0); break;
      case VNIL: info = nilK(fs); break;
      case VKINT: info = luaK_intK(fs, e->u.ival); break;
      case VKFLT: info = luaK_numberK(fs, e->u.nval); break;
      case VK: info = e->u.info; break;
      default: return 0;  /* not a constant */
    }
    if (info <= MAXINDEXRK) {  /* does constant fit in 'argC'? */
      e->k = VK;  /* make expression a 'K' expression */
      e->u.info = info;
      return 1;
    }
  }
  /* else, expression doesn't fit; leave it unchanged */
  return 0;
}


/*
** 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 1 iff expression is K.
*/
int luaK_exp2RK (FuncState *fs, expdesc *e) {
  if (luaK_exp2K(fs, e))
    return 1;
  else {  /* not a constant in the right range: put it in a register */
    luaK_exp2anyreg(fs, e);
    return 0;
  }
}


static void codeABRK (FuncState *fs, OpCode o, int a, int b,
                      expdesc *ec) {
  int k = luaK_exp2RK(fs, ec);
  luaK_codeABCk(fs, o, a, b, ec->u.info, k);
}


/*
** 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.var.idx);  /* compute 'ex' into proper place */
      return;
    }
    case VUPVAL: {
      int e = luaK_exp2anyreg(fs, ex);
      luaK_codeABC(fs, OP_SETUPVAL, e, var->u.var.idx, 0);
      break;
    }
    case VINDEXUP: {
      codeABRK(fs, OP_SETTABUP, var->u.ind.t, var->u.ind.idx, ex);
      break;
    }
    case VINDEXI: {
      codeABRK(fs, OP_SETI, var->u.ind.t, var->u.ind.idx, ex);
      break;
    }
    case VINDEXSTR: {
      codeABRK(fs, OP_SETFIELD, var->u.ind.t, var->u.ind.idx, ex);
      break;
    }
    case VINDEXED: {
      codeABRK(fs, OP_SETTABLE, var->u.ind.t, var->u.ind.idx, ex);
      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 */
  codeABRK(fs, OP_SELF, e->u.info, ereg, 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_k(*pc, (GETARG_k(*pc) ^ 1));
}


/*
** 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 == VRELOC) {
    Instruction ie = getinstruction(fs, e);
    if (GET_OPCODE(ie) == OP_NOT) {
      removelastinstruction(fs);  /* remove previous OP_NOT */
      return condjump(fs, OP_TEST, GETARG_B(ie), 0, 0, !cond);
    }
    /* else go through */
  }
  discharge2anyreg(fs, e);
  freeexp(fs, e);
  return condjump(fs, OP_TESTSET, NO_REG, e->u.info, 0, 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 VRELOC:
    case VNONRELOC: {
      discharge2anyreg(fs, e);
      freeexp(fs, e);
      e->u.info = luaK_codeABC(fs, OP_NOT, 0, e->u.info, 0);
      e->k = VRELOC;
      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);
}


/*
** Check whether expression 'e' is a small literal string
*/
static int isKstr (FuncState *fs, expdesc *e) {
  return (e->k == VK && !hasjumps(e) && e->u.info <= MAXARG_B &&
          ttisshrstring(&fs->f->k[e->u.info]));
}

/*
** Check whether expression 'e' is a literal integer.
*/
int luaK_isKint (expdesc *e) {
  return (e->k == VKINT && !hasjumps(e));
}


/*
** Check whether expression 'e' is a literal integer in
** proper range to fit in register C
*/
static int isCint (expdesc *e) {
  return luaK_isKint(e) && (l_castS2U(e->u.ival) <= l_castS2U(MAXARG_C));
}


/*
** Check whether expression 'e' is a literal integer in
** proper range to fit in register sC
*/
static int isSCint (expdesc *e) {
  return luaK_isKint(e) && fitsC(e->u.ival);
}


/*
** Check whether expression 'e' is a literal integer or float in
** proper range to fit in a register (sB or sC).
*/
static int isSCnumber (expdesc *e, lua_Integer *i, int *isfloat) {
  if (e->k == VKINT)
    *i = e->u.ival;
  else if (!(e->k == VKFLT && floatI(e->u.nval, i)))
    return 0;  /* not a number */
  else
    *isfloat = 1;
  if (!hasjumps(e) && fitsC(*i)) {
    *i += OFFSET_sC;
    return 1;
  }
  else
    return 0;
}


/*
** Create expression 't[k]'. 't' must have its final result already in a
** register or upvalue. Upvalues can only be indexed by literal strings.
** Keys can be literal strings in the constant table or arbitrary
** values in registers.
*/
void luaK_indexed (FuncState *fs, expdesc *t, expdesc *k) {
  lua_assert(!hasjumps(t) &&
             (t->k == VLOCAL || t->k == VNONRELOC || t->k == VUPVAL));
  if (t->k == VUPVAL && !isKstr(fs, k))  /* upvalue indexed by non string? */
    luaK_exp2anyreg(fs, t);  /* put it in a register */
  if (t->k == VUPVAL) {
    t->u.ind.t = t->u.var.idx;  /* upvalue index */
    t->u.ind.idx = k->u.info;  /* literal string */
    t->k = VINDEXUP;
  }
  else {
    /* register index of the table */
    t->u.ind.t = (t->k == VLOCAL) ? t->u.var.idx: t->u.info;
    if (isKstr(fs, k)) {
      t->u.ind.idx = k->u.info;  /* literal string */
      t->k = VINDEXSTR;
    }
    else if (isCint(k)) {
      t->u.ind.idx = cast_int(k->u.ival);  /* int. constant in proper range */
      t->k = VINDEXI;
    }
    else {
      t->u.ind.idx = luaK_exp2anyreg(fs, k);  /* register */
      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 (tointegerns(v1, &i) && tointegerns(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_rawarith(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 = VRELOC;  /* 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_exp2anyreg' 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 finishbinexpval (FuncState *fs, expdesc *e1, expdesc *e2,
                             OpCode op, int v2, int k, int line) {
  int v1 = luaK_exp2anyreg(fs, e1);
  int pc = luaK_codeABCk(fs, op, 0, v1, v2, k);
  freeexps(fs, e1, e2);
  e1->u.info = pc;
  e1->k = VRELOC;  /* all those operations are relocatable */
  luaK_fixline(fs, line);
}


/*
** Emit code for binary expressions that "produce values" over
** two registers.
*/
static void codebinexpval (FuncState *fs, OpCode op,
                           expdesc *e1, expdesc *e2, int line) {
  int v2 = luaK_exp2anyreg(fs, e2);  /* both operands are in registers */
  finishbinexpval(fs, e1, e2, op, v2, 0, line);
}


/*
** Code binary operators ('+', '-', ...) with immediate operands.
*/
static void codebini (FuncState *fs, OpCode op,
                       expdesc *e1, expdesc *e2, int k, int line) {
  int v2 = cast_int(e2->u.ival) + OFFSET_sC;  /* immediate operand */
  finishbinexpval(fs, e1, e2, op, v2, k, line);
}


static void swapexps (expdesc *e1, expdesc *e2) {
  expdesc temp = *e1; *e1 = *e2; *e2 = temp;  /* swap 'e1' and 'e2' */
}


/*
** Code arithmetic operators ('+', '-', ...). If second operand is a
** constant in the proper range, use variant opcodes with immediate
** operands or K operands.
*/
static void codearith (FuncState *fs, OpCode op,
                       expdesc *e1, expdesc *e2, int flip, int line) {
  if (isSCint(e2))  /* immediate operand? */
    codebini(fs, cast(OpCode, op - OP_ADD + OP_ADDI), e1, e2, flip, line);
  else if (tonumeral(e2, NULL) && luaK_exp2K(fs, e2)) {  /* K operand? */
    int v2 = e2->u.info;  /* K index */
    op = cast(OpCode, op - OP_ADD + OP_ADDK);
    finishbinexpval(fs, e1, e2, op, v2, flip, line);
  }
  else {  /* 'e2' is neither an immediate nor a K operand */
    if (flip)
      swapexps(e1, e2);  /* back to original order */
    codebinexpval(fs, op, e1, e2, line);  /* use standard operators */
  }
}


/*
** Code commutative operators ('+', '*'). If first operand is a
** numeric constant, change order of operands to try to use an
** immediate or K operator.
*/
static void codecommutative (FuncState *fs, OpCode op,
                             expdesc *e1, expdesc *e2, int line) {
  int flip = 0;
  if (tonumeral(e1, NULL)) {  /* is first operand a numeric constant? */
    swapexps(e1, e2);  /* change order */
    flip = 1;
  }
  codearith(fs, op, e1, e2, flip, line);
}


/*
** Code bitwise operations; they are all associative, so the function
** tries to put an integer constant as the 2nd operand (a K operand).
*/
static void codebitwise (FuncState *fs, BinOpr opr,
                         expdesc *e1, expdesc *e2, int line) {
  int inv = 0;
  int v2;
  OpCode op;
  if (e1->k == VKINT && luaK_exp2RK(fs, e1)) {
    swapexps(e1, e2);  /* 'e2' will be the constant operand */
    inv = 1;
  }
  else if (!(e2->k == VKINT && luaK_exp2RK(fs, e2))) {  /* no constants? */
    op = cast(OpCode, opr - OPR_BAND + OP_BAND);
    codebinexpval(fs, op, e1, e2, line);  /* all-register opcodes */
    return;
  }
  v2 = e2->u.info;  /* index in K array */
  op = cast(OpCode, opr - OPR_BAND + OP_BANDK);
  lua_assert(ttisinteger(&fs->f->k[v2]));
  finishbinexpval(fs, e1, e2, op, v2, inv, line);
}


/*
** Code shift operators. If second operand is constant, use immediate
** operand (negating it if shift is in the other direction).
*/
static void codeshift (FuncState *fs, OpCode op,
                       expdesc *e1, expdesc *e2, int line) {
  if (isSCint(e2)) {
    int changedir = 0;
    if (op == OP_SHL) {
      changedir = 1;
      e2->u.ival = -(e2->u.ival);
    }
    codebini(fs, OP_SHRI, e1, e2, changedir, line);
  }
  else
    codebinexpval(fs, op, e1, e2, line);
}


/*
** Emit code for order comparisons. When using an immediate operand,
** 'isfloat' tells whether the original value was a float.
*/
static void codeorder (FuncState *fs, OpCode op, expdesc *e1, expdesc *e2) {
  int r1, r2;
  lua_Integer im;
  int isfloat = 0;
  if (isSCnumber(e2, &im, &isfloat)) {
    /* use immediate operand */
    r1 = luaK_exp2anyreg(fs, e1);
    r2 = cast_int(im);
    op = cast(OpCode, (op - OP_LT) + OP_LTI);
  }
  else if (isSCnumber(e1, &im, &isfloat)) {
    /* transform (A < B) to (B > A) and (A <= B) to (B >= A) */
    r1 = luaK_exp2anyreg(fs, e2);
    r2 = cast_int(im);
    op = (op == OP_LT) ? OP_GTI : OP_GEI;
  }
  else {  /* regular case, compare two registers */
    r1 = luaK_exp2anyreg(fs, e1);
    r2 = luaK_exp2anyreg(fs, e2);
  }
  freeexps(fs, e1, e2);
  e1->u.info = condjump(fs, op, r1, r2, isfloat, 1);
  e1->k = VJMP;
}


/*
** Emit code for equality comparisons ('==', '~=').
** 'e1' was already put as RK by 'luaK_infix'.
*/
static void codeeq (FuncState *fs, BinOpr opr, expdesc *e1, expdesc *e2) {
  int r1, r2;
  lua_Integer im;
  int isfloat = 0;  /* not needed here, but kept for symmetry */
  OpCode op;
  if (e1->k != VNONRELOC) {
    lua_assert(e1->k == VK || e1->k == VKINT || e1->k == VKFLT);
    swapexps(e1, e2);
  }
  r1 = luaK_exp2anyreg(fs, e1);  /* 1nd expression must be in register */
  if (isSCnumber(e2, &im, &isfloat)) {
    op = OP_EQI;
    r2 = cast_int(im);  /* immediate operand */
  }
  else if (luaK_exp2RK(fs, e2)) {  /* 1st expression is constant? */
    op = OP_EQK;
    r2 = e2->u.info;  /* constant index */
  }
  else {
    op = OP_EQ;  /* will compare two registers */
    r2 = luaK_exp2anyreg(fs, e2);
  }
  freeexps(fs, e1, e2);
  e1->u.info = condjump(fs, op, r1, r2, isfloat, (opr == OPR_EQ));
  e1->k = VJMP;
}


/*
** Apply 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_exp2anyreg(fs, v);
      /* else keep numeral, which may be folded with 2nd operand */
      break;
    }
    case OPR_EQ: case OPR_NE: {
      if (!tonumeral(v, NULL))
        luaK_exp2RK(fs, v);
      /* else keep numeral, which may be an immediate operand */
      break;
    }
    case OPR_LT: case OPR_LE:
    case OPR_GT: case OPR_GE: {
      lua_Integer dummy;
      int dummy2;
      if (!isSCnumber(v, &dummy, &dummy2))
        luaK_exp2anyreg(fs, v);
      /* else keep numeral, which may be an immediate operand */
      break;
    }
    default: lua_assert(0);
  }
}

/*
** Create code for '(e1 .. e2)'.
** For '(e1 .. e2.1 .. e2.2)' (which is '(e1 .. (e2.1 .. e2.2))',
** because concatenation is right associative), merge both CONCATs.
*/
static void codeconcat (FuncState *fs, expdesc *e1, expdesc *e2, int line) {
  Instruction *ie2 = previousinstruction(fs);
  if (GET_OPCODE(*ie2) == OP_CONCAT) {  /* is 'e2' a concatenation? */
    int n = GETARG_B(*ie2);  /* # of elements concatenated in 'e2' */
    lua_assert(e1->u.info + 1 == GETARG_A(*ie2));
    freeexp(fs, e2);
    SETARG_A(*ie2, e1->u.info);  /* correct first element ('e1') */
    SETARG_B(*ie2, n + 1);  /* will concatenate one more element */
  }
  else {  /* 'e2' is not a concatenation */
    luaK_codeABC(fs, OP_CONCAT, e1->u.info, 2, 0);  /* new concat opcode */
    freeexp(fs, e2);
    luaK_fixline(fs, line);
  }
}


/*
** Finalize code for binary operation, after reading 2nd operand.
*/
void luaK_posfix (FuncState *fs, BinOpr opr,
                  expdesc *e1, expdesc *e2, int line) {
  switch (opr) {
    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: {  /* e1 .. e2 */
      luaK_exp2nextreg(fs, e2);
      codeconcat(fs, e1, e2, line);
      break;
    }
    case OPR_ADD: case OPR_MUL: {
      if (!constfolding(fs, opr + LUA_OPADD, e1, e2))
        codecommutative(fs, cast(OpCode, opr + OP_ADD), e1, e2, line);
      break;
    }
    case OPR_SUB: case OPR_DIV:
    case OPR_IDIV: case OPR_MOD: case OPR_POW: {
      if (!constfolding(fs, opr + LUA_OPADD, e1, e2))
        codearith(fs, cast(OpCode, opr + OP_ADD), e1, e2, 0, line);
      break;
    }
    case OPR_BAND: case OPR_BOR: case OPR_BXOR: {
      if (!constfolding(fs, opr + LUA_OPADD, e1, e2))
        codebitwise(fs, opr, e1, e2, line);
      break;
    }
    case OPR_SHL: {
      if (!constfolding(fs, LUA_OPSHL, e1, e2)) {
        if (isSCint(e1)) {
          swapexps(e1, e2);
          codebini(fs, OP_SHLI, e1, e2, 1, line);
        }
        else
          codeshift(fs, OP_SHL, e1, e2, line);
      }
      break;
    }
    case OPR_SHR: {
      if (!constfolding(fs, LUA_OPSHR, e1, e2))
        codeshift(fs, OP_SHR, e1, e2, line);
      break;
    }
    case OPR_EQ: case OPR_NE: {
      codeeq(fs, opr, e1, e2);
      break;
    }
    case OPR_LT: case OPR_LE: {
      OpCode op = cast(OpCode, (opr - OPR_EQ) + OP_EQ);
      codeorder(fs, op, e1, e2);
      break;
    }
    case OPR_GT: case OPR_GE: {
      /* '(a > b)' <=> '(b < a)';  '(a >= b)' <=> '(b <= a)' */
      OpCode op = cast(OpCode, (opr - OPR_NE) + OP_EQ);
      swapexps(e1, e2);
      codeorder(fs, op, e1, e2);
      break;
    }
    default: lua_assert(0);
  }
}


/*
** Change line information associated with current position, by removing
** previous info and adding it again with new line.
*/
void luaK_fixline (FuncState *fs, int line) {
  removelastlineinfo(fs);
  savelineinfo(fs, fs->f, 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 */
}


/*
** return the final target of a jump (skipping jumps to jumps)
*/
static int finaltarget (Instruction *code, int i) {
  int count;
  for (count = 0; count < 100; count++) {  /* avoid infinite loops */
    Instruction pc = code[i];
    if (GET_OPCODE(pc) != OP_JMP)
      break;
     else
       i += GETARG_sJ(pc) + 1;
  }
  return i;
}


/*
** Do a final pass over the code of a function, doing small peephole
** optimizations and adjustments.
*/
void luaK_finish (FuncState *fs) {
  int i;
  Proto *p = fs->f;
  for (i = 0; i < fs->pc; i++) {
    Instruction *pc = &p->code[i];
    lua_assert(i == 0 || isOT(*(pc - 1)) == isIT(*pc));
    switch (GET_OPCODE(*pc)) {
      case OP_RETURN0: case OP_RETURN1: {
        if (!(fs->needclose || p->is_vararg))
          break;  /* no extra work */
        /* else use OP_RETURN to do the extra work */
        SET_OPCODE(*pc, OP_RETURN);
      }  /* FALLTHROUGH */
      case OP_RETURN: case OP_TAILCALL: {
        if (fs->needclose || p->is_vararg) {
          SETARG_C(*pc, p->is_vararg ? p->numparams + 1 : 0);
          SETARG_k(*pc, 1);  /* signal that there is extra work */
        }
        break;
      }
      case OP_JMP: {
        int target = finaltarget(p->code, i);
        fixjump(fs, i, target);
        break;
      }
      default: break;
    }
  }
}