mudgangster

lcode.cc (34308B)

---

 /*
 ** $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 */
 }