lcode.c

/*
** $Id: lcode.c,v 2.160 2018/03/16 14:22:09 roberto Exp roberto $
** 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 k) {
 luaK_codeABCk(fs, op, A, B, 0, 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);
}


/*
** Correct a jump list to jump to 'target'. If 'hasclose' is true,
** 'target' contains an OP_CLOSE instruction (see first assert).
** Only the jumps with ('m' == true) need that close; other jumps
** avoid it jumping to the next instruction.
*/
void luaK_patchgoto (FuncState *fs, int list, int target, int hasclose) {
 lua_assert(!hasclose || GET_OPCODE(fs->f->code[target]) == OP_CLOSE);
 while (list != NO_JUMP) {
 int next = getjump(fs, list);
 lua_assert(!GETARG_m(fs->f->code[list]) || hasclose);
 patchtestreg(fs, list, NO_REG); /* do not generate values */
 if (!hasclose || GETARG_m(fs->f->code[list]))
 fixjump(fs, list, target);
 else /* there is a CLOSE instruction but jump does not need it */
 fixjump(fs, list, target + 1); /* avoid CLOSE instruction */
 list = next;
 }
}


/*
** Mark (using the 'm' arg) all jumps in 'list' to close upvalues. Mark
** will instruct 'luaK_patchgoto' to make these jumps go to OP_CLOSE
** instructions.
*/
void luaK_patchclose (FuncState *fs, int list) {
 for (; list != NO_JUMP; list = getjump(fs, list)) {
 lua_assert(GET_OPCODE(fs->f->code[list]) == OP_JMP);
 SETARG_m(fs->f->code[list], 1);
 }
}


#if !defined(MAXIWTHABS)
#define MAXIWTHABS	120
#endif

/*
** 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 pc, int line) {
 int linedif = line - fs->previousline;
 if (abs(linedif) >= 0x80 || 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 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 */
}


/*
** 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->pc, fs->ls->lastline);
 return fs->pc++;
}


/*
** 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));
}


#define codeABsC(fs,o,a,b,c,k)	luaK_codeABCk(fs,o,a,b,((c) + OFFSET_sC),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->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 = 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);
 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 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);
}


/*
** 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 if expression is K, 0 otherwise.
*/
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 1;
 else break;
 default: break;
 }
 /* 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.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 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) {
 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 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 register sC
*/
static int isSCnumber (expdesc *e, lua_Integer *i) {
 if (e->k == VKINT)
 *i = e->u.ival;
 else if (!(e->k == VKFLT && floatI(e->u.nval, i)))
 return 0; /* not a number */
 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) && (vkisinreg(t->k) || t->k == VUPVAL));
 if (t->k == VUPVAL && !isKstr(fs, k)) /* upvalue indexed by non string? */
 luaK_exp2anyreg(fs, t); /* put it in a register */
 t->u.ind.t = t->u.info; /* register or upvalue index */
 if (t->k == VUPVAL) {
 t->u.ind.idx = k->u.info; /* literal string */
 t->k = VINDEXUP;
 }
 else 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); /* integer 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);
}


static void finishbinexpval (FuncState *fs, expdesc *e1, expdesc *e2,
 int pc, int line) {
 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"
** (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 codebinexpval (FuncState *fs, OpCode op,
 expdesc *e1, expdesc *e2, int line) {
 int v2 = luaK_exp2anyreg(fs, e2); /* both operands are in registers */
 int v1 = luaK_exp2anyreg(fs, e1);
 int pc = luaK_codeABC(fs, op, 0, v1, v2); /* generate opcode */
 finishbinexpval(fs, e1, e2, pc, 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); /* immediate operand */
 int v1 = luaK_exp2anyreg(fs, e1);
 int pc = codeABsC(fs, op, 0, v1, v2, k); /* generate opcode */
 finishbinexpval(fs, e1, e2, pc, line);
}


/*
** Code arithmetic operators ('+', '-', ...). If second operand is a
** constant in the proper range, use variant opcodes with immediate
** operands.
*/
static void codearith (FuncState *fs, OpCode op,
 expdesc *e1, expdesc *e2, int flip, int line) {
 if (!isSCint(e2))
 codebinexpval(fs, op, e1, e2, line); /* use standard operators */
 else /* use immediate operators */
 codebini(fs, cast(OpCode, op - OP_ADD + OP_ADDI), e1, e2, flip, line);
}


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


/*
** Code commutative operators ('+', '*'). If first operand is a
** constant, change order of operands to use immediate operator.
*/
static void codecommutative (FuncState *fs, OpCode op,
 expdesc *e1, expdesc *e2, int line) {
 int flip = 0;
 if (isSCint(e1)) {
 swapexps(e1, e2);
 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 v1, v2, pc;
 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;
 }
 v1 = luaK_exp2anyreg(fs, e1);
 v2 = e2->u.info; /* index in K array */
 op = cast(OpCode, opr - OPR_BAND + OP_BANDK);
 lua_assert(ttisinteger(&fs->f->k[v2]));
 pc = luaK_codeABCk(fs, op, 0, v1, v2, inv);
 finishbinexpval(fs, e1, e2, pc, 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 the first operand A is an integral value in the proper range,
** change (A < B) to (B > A) and (A <= B) to (B >= A) so that
** it can use an immediate operand.
*/
static void codeorder (FuncState *fs, OpCode op, expdesc *e1, expdesc *e2) {
 int r1, r2;
 lua_Integer im;
 if (isSCnumber(e2, &im)) {
 /* 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)) {
 /* 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, 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;
 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)) {
 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, (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;
 if (!isSCnumber(v, &dummy))
 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. If that
** information is absolute, just change it and correct 'previousline'.
** Otherwise, restore 'previousline' to its value before saving the
** current position and than saves the line information again, with the
** new line.
*/
void luaK_fixline (FuncState *fs, int line) {
 Proto *f = fs->f;
 if (f->lineinfo[fs->pc - 1] == ABSLINEINFO) {
 lua_assert(f->abslineinfo[fs->nabslineinfo - 1].pc == fs->pc - 1);
 f->abslineinfo[fs->nabslineinfo - 1].line = line;
 fs->previousline = line;
 }
 else {
 fs->previousline -= f->lineinfo[fs->pc - 1]; /* undo previous info. */
 savelineinfo(fs, f, fs->pc - 1, line); /* redo it */
 }
}


/*
** 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 (p->sizep == 0 && !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 (p->sizep > 0 || 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;
 }
 }
}