/*
** $Id: lcode.c,v 2.25.1.3 2007/12/28 15:32:23 roberto Exp $
** Code generator for Lua
** See Copyright Notice in lua.h
*/


#include <stdlib.h>

#define lcode_c
#define LUA_CORE

#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 "ltable.h"


#define hasjumps(e)	((e)->t != (e)->f)


static int isnumeral(expdesc *e) {
  return (e->k == VKNUM && e->t == NO_JUMP && e->f == NO_JUMP);
}

// 将from到from + n -1的寄存器都置nil
void luaK_nil (FuncState *fs, int from, int n) {
  Instruction *previous;
  // 这部分还需要看看
  if (fs->pc > fs->lasttarget) {  /* no jumps to current position? */
    if (fs->pc == 0) {  /* function start? */
      if (from >= fs->nactvar)
        return;  /* positions are already clean */
    }
    else {
      previous = &fs->f->code[fs->pc-1];
      if (GET_OPCODE(*previous) == OP_LOADNIL) {
        int pfrom = GETARG_A(*previous);
        int pto = GETARG_B(*previous);
        if (pfrom <= from && from <= pto+1) {  /* can connect both? */
          if (from+n-1 > pto)
            SETARG_B(*previous, from+n-1);
          return;
        }
      }
    }
  }
  // 从from到from + n - 1的寄存器全部置nil
  luaK_codeABC(fs, OP_LOADNIL, from, from+n-1, 0);  /* else no optimization */
}

// 生成一个跳转指令
int luaK_jump (FuncState *fs) {
  int jpc = fs->jpc;  /* save list of jumps to here */
  int j;
  fs->jpc = NO_JUMP;
  // 第三个参数是NO_JUMP的意思是这个跳转语句跳转位置还未确定
  // 注意这里返回的j指向的下一个PC指令的地址
  j = luaK_codeAsBx(fs, OP_JMP, 0, NO_JUMP);
  // 将之前的悬空跳转语句合起来, 这样所有悬空的跳转语句就形成了链表, 由jpc保存
  luaK_concat(fs, &j, jpc);  /* keep them on hold */
  return j;
}


void luaK_ret (FuncState *fs, int first, int nret) {
  luaK_codeABC(fs, OP_RETURN, first, nret+1, 0);
}

// 构造条件跳转语句,如LT,ET等,同时这类型的语句后面必然跟着一个跳转语句
static int condjump (FuncState *fs, OpCode op, int A, int B, int C) {
  luaK_codeABC(fs, op, A, B, C);
  return luaK_jump(fs);
}

// 根据目标位置修改JMP指令跳转点位置
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);
}


/*
** returns current `pc' and marks it as a jump target (to avoid wrong
** optimizations with consecutive instructions not in the same basic block).
*/
// 获得当前PC,可以把它作为一个标记(Label)
int luaK_getlabel (FuncState *fs) {
  fs->lasttarget = fs->pc;
  return fs->pc;
}

//  获得跳转点
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 */
}

// 获得这条语句的控制部分(如果存在的话)
static Instruction *getjumpcontrol (FuncState *fs, int pc) {
  Instruction *pi = &fs->f->code[pc];
  // 如果pc的上一条语句是逻辑跳转类语句, 则返回上一条语句??
  if (pc >= 1 && testTMode(GET_OPCODE(*(pi-1))))
    return pi-1;
  else
    return pi;
}


/*
** 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 */
}


static int patchtestreg (FuncState *fs, int node, int reg) {
  Instruction *i = getjumpcontrol(fs, node);
  // 仅对TESTSET指令有效
  if (GET_OPCODE(*i) != OP_TESTSET)
    return 0;  /* cannot patch other instructions */
  // 如果reg参数不等于B, 那么设置到A上
  if (reg != NO_REG && reg != GETARG_B(*i))
    SETARG_A(*i, reg);
  // 否则reg是有意义的数,而且等于B,换句话说,如果A,B相等就不用TESTSET,用TEST
  else  /* no register to put value or register already has the value */
    *i = CREATE_ABC(OP_TEST, GETARG_B(*i), 0, GETARG_C(*i));

  return 1;
}


static void removevalues (FuncState *fs, int list) {
  for (; list != NO_JUMP; list = getjump(fs, list))
      patchtestreg(fs, list, NO_REG);
}

// 遍历空悬指令链表,将空悬地址回填
static void patchlistaux (FuncState *fs, int list, int vtarget, int reg,
                          int dtarget) {
  while (list != NO_JUMP) {
    int next = getjump(fs, list);
    // 如果回填的指令是TESTSET, 那么就是条件跳转类指令,否则就是无条件跳转
    if (patchtestreg(fs, list, reg))
      fixjump(fs, list, vtarget);
    else
      fixjump(fs, list, dtarget);  /* jump to default target */
    list = next;
  }
}

// 将jpc维护的空悬跳转点链表使用当前的pc位置进行回填
static void dischargejpc (FuncState *fs) {
  patchlistaux(fs, fs->jpc, fs->pc, NO_REG, fs->pc);
  // 重置jpc为NO_JUMP
  fs->jpc = NO_JUMP;
}


void luaK_patchlist (FuncState *fs, int list, int target) {
  if (target == fs->pc)
    luaK_patchtohere(fs, list);
  else {
    lua_assert(target < fs->pc);
    patchlistaux(fs, list, target, NO_REG, target);
  }
}

// 使用jpc记录下空悬的跳转位置,生成下一个opcode的时候回填.
// 可以参考luaK_code中调用dischargejpc函数的部分
void luaK_patchtohere (FuncState *fs, int list) {
  luaK_getlabel(fs);
  // 将list修正当前空悬链表的第一个空悬位置
  luaK_concat(fs, &fs->jpc, list);
}

// 以l2为跳转位置修正l1中存放的跳转链表中第一个还不知道跳转位置的跳转点数据
void luaK_concat (FuncState *fs, int *l1, int l2) {
  // 如果l2就不是一个跳转目标,那么直接返回
  if (l2 == NO_JUMP) return;
  else if (*l1 == NO_JUMP)
	// 如果l1是不跳转, 那么说明之前没有跳转点, 设置为l2
    *l1 = l2;
  else {
    int list = *l1;
    int next;
    // 寻找第一个为NO_JUMP的跳转点,也就是还不知道跳转位置的跳转点
    while ((next = getjump(fs, list)) != NO_JUMP)  /* find last element */
      list = next;
    // fix跳转点
    fixjump(fs, list, l2);
  }
}


void luaK_checkstack (FuncState *fs, int n) {
  int newstack = fs->freereg + n;
  if (newstack > fs->f->maxstacksize) {
    if (newstack >= MAXSTACK)
      luaX_syntaxerror(fs->ls, "function or expression too complex");
    fs->f->maxstacksize = cast_byte(newstack);
  }
}

// 函数栈预留多少位置
void luaK_reserveregs (FuncState *fs, int n) {
  luaK_checkstack(fs, n);
  fs->freereg += n;
}

// 释放栈上的寄存器空间
static void freereg (FuncState *fs, int reg) {
  if (!ISK(reg) && reg >= fs->nactvar) {
    fs->freereg--;
    lua_assert(reg == fs->freereg);
  }
}


static void freeexp (FuncState *fs, expdesc *e) {
  // 如果是不需要重定位的, 那么可以释放info占用的寄存器
  if (e->k == VNONRELOC)
    freereg(fs, e->u.s.info);
}

// 向函数寄存器添加常量
static int addk (FuncState *fs, TValue *k, TValue *v) {
  lua_State *L = fs->L;
  // 得到key的index
  TValue *idx = luaH_set(L, fs->h, k);
  Proto *f = fs->f;
  int oldsize = f->sizek;
  if (ttisnumber(idx)) {
	// 如果index是数字,那么说明这个k原来在寄存器中已经存在,将值v存放在index所在的寄存器位置
    lua_assert(luaO_rawequalObj(&fs->f->k[cast_int(nvalue(idx))], v));
    // 返回index
    return cast_int(nvalue(idx));
  }
  else {  /* constant not found; create a new entry */
	  // 否则当前nk值设置到idx上
    setnvalue(idx, cast_num(fs->nk));
    // 增加k的数组大小
    luaM_growvector(L, f->k, fs->nk, f->sizek, TValue,
                    MAXARG_Bx, "constant table overflow");
    // 将多出来那部分置空
    while (oldsize < f->sizek) setnilvalue(&f->k[oldsize++]);
    // 现在可以保存v值了
    setobj(L, &f->k[fs->nk], v);
    luaC_barrier(L, f, v);
    // 返回寄存器索引
    return fs->nk++;
  }
}

// 创建一个字符串常量
int luaK_stringK (FuncState *fs, TString *s) {
  TValue o;
  setsvalue(fs->L, &o, s);
  return addk(fs, &o, &o);
}

// 向FuncState添加一个数字常量
int luaK_numberK (FuncState *fs, lua_Number r) {
  TValue o;
  setnvalue(&o, r); 
 return addk(fs, &o, &o);
}

// 添加一个BOOL类型常量
static int boolK (FuncState *fs, int b) {
  TValue o;
  setbvalue(&o, b);
  return addk(fs, &o, &o);
}

// 添加一个nil值常量
static int nilK (FuncState *fs) {
  TValue k, v;
  setnilvalue(&v);
  /* cannot use nil as key; instead use table itself to represent nil */
  sethvalue(fs->L, &k, fs->h);
  return addk(fs, &k, &v);
}

// ???????
void luaK_setreturns (FuncState *fs, expdesc *e, int nresults) {
  if (e->k == VCALL) {  /* expression is an open function call? */
    SETARG_C(getcode(fs, e), nresults+1);
  }
  else if (e->k == VVARARG) {
    SETARG_B(getcode(fs, e), nresults+1);
    SETARG_A(getcode(fs, e), fs->freereg);
    luaK_reserveregs(fs, 1);
  }
}

// ??????
void luaK_setoneret (FuncState *fs, expdesc *e) {
  if (e->k == VCALL) {  /* expression is an open function call? */
    e->k = VNONRELOC;
    e->u.s.info = GETARG_A(getcode(fs, e));
  }
  else if (e->k == VVARARG) {
    SETARG_B(getcode(fs, e), 2);
    e->k = VRELOCABLE;  /* can relocate its simple result */
  }
}

// 这里的重点是设置e->k,即是否需要重定向
// 为什么在luaK_exp2nextreg函数和discharge2reg函数中分别被调用两次
void luaK_dischargevars (FuncState *fs, expdesc *e) {
  switch (e->k) {
    case VLOCAL: {
      // 局部变量已经在该函数栈中了,不需要重定位
      e->k = VNONRELOC;
      break;
    }
    case VUPVAL: {
      // upval需要重定向,因为需要把upval赋值到本函数栈中
      e->u.s.info = luaK_codeABC(fs, OP_GETUPVAL, 0, e->u.s.info, 0);
      e->k = VRELOCABLE;
      break;
    }
    case VGLOBAL: {
      // 全局变量需要重定向,因为需要赋值到本函数栈中
      e->u.s.info = luaK_codeABx(fs, OP_GETGLOBAL, 0, e->u.s.info);
      e->k = VRELOCABLE;
      break;
    }
    case VINDEXED: {
      freereg(fs, e->u.s.aux);
      freereg(fs, e->u.s.info);
      e->u.s.info = luaK_codeABC(fs, OP_GETTABLE, 0, e->u.s.info, e->u.s.aux);
      e->k = VRELOCABLE;
      break;
    }
    case VVARARG:
    case VCALL: {
      luaK_setoneret(fs, e);
      break;
    }
    default: break;  /* there is one value available (somewhere) */
  }
}


static int code_label (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);
}

// 根据表达式的e->k载入寄存器
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_codeABx(fs, OP_LOADK, reg, e->u.s.info);
      break;
    }
    case VKNUM: {
      luaK_codeABx(fs, OP_LOADK, reg, luaK_numberK(fs, e->u.nval));
      break;
    }
    case VRELOCABLE: {
      // 重定位, 因为赋值的时候不知道当前可用的寄存器指针,所以这里要重新定位下
      Instruction *pc = &getcode(fs, e);
      SETARG_A(*pc, reg);
      break;
    }
    case VNONRELOC: {
      // 不需要重定位的指令，说明已经在当前栈中 如果两者不相等, 那么要使用MOVE指令
      if (reg != e->u.s.info)
        luaK_codeABC(fs, OP_MOVE, reg, e->u.s.info, 0);
      break;
    }
    default: {
      lua_assert(e->k == VVOID || e->k == VJMP);
      return;  /* nothing to do... */
    }
  }
  // 前面的步骤搞定之后,存放栈位置,同时设置为VNONRELOC类型
  e->u.s.info = reg;
  e->k = VNONRELOC;
}


static void discharge2anyreg (FuncState *fs, expdesc *e) {
  if (e->k != VNONRELOC) {
    luaK_reserveregs(fs, 1);
    discharge2reg(fs, e, fs->freereg-1);
  }
}

// 将表达式e放入reg寄存器中
static void exp2reg (FuncState *fs, expdesc *e, int reg) {
  // 表达式e的结果存入寄存器reg中
  discharge2reg(fs, e, reg);
  if (e->k == VJMP)
    luaK_concat(fs, &e->t, e->u.s.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 */
    // need_value返回1的情况是跳转链表中只要有一个不是与TESTSET匹配的JMP指令
    if (need_value(fs, e->t) || need_value(fs, e->f)) {
      // 如果指令已经是VJMP指令,就不必新生成JMP指令了
      int fj = (e->k == VJMP) ? NO_JUMP : luaK_jump(fs);
      // 表达式e的结果在reg中,根据reg的值生成两条LOADBOOL指令,分别对应false,true两种情况
      p_f = code_label(fs, reg, 0, 1);
      p_t = code_label(fs, reg, 1, 0);
      // 回填fj指令跳转地址到JPC链表中
      luaK_patchtohere(fs, fj);
    }
    // 获得下一个指令的位置
    final = luaK_getlabel(fs);
    // 回填空悬指令
    patchlistaux(fs, e->f, final, reg, p_f);
    patchlistaux(fs, e->t, final, reg, p_t);
  }
  e->f = e->t = NO_JUMP;
  e->u.s.info = reg;
  e->k = VNONRELOC;
}

// 讲表达式dump到当前栈的下一个位置中
void luaK_exp2nextreg (FuncState *fs, expdesc *e) {
  // 首先如果是一个变量的话 现在根据变量类型(upval, GLOBAL, LOCAL)dump出来
  luaK_dischargevars(fs, e);
  freeexp(fs, e);
  // 将freereg+1, 也就是参数数量加1
  luaK_reserveregs(fs, 1);
  // 将表达式dump到这个新分配的栈空间中
  exp2reg(fs, e, fs->freereg - 1);
}

// 返回值是寄存器索引(与luaK_exp2nextreg的区别和联系是？？？？？？)
int luaK_exp2anyreg (FuncState *fs, expdesc *e) {
  // 首先要把变量dump出来
  luaK_dischargevars(fs, e);
  if (e->k == VNONRELOC) {  // 不需要重定向
    // 不是跳转指令
    if (!hasjumps(e)) return e->u.s.info;  /* exp is already in a register */
    // 大于当前的local变量数量
    if (e->u.s.info >= fs->nactvar) {  /* reg. is not a local? */
      exp2reg(fs, e, e->u.s.info);  /* put value on it */
      return e->u.s.info;
    }
  }
  // dump到下一个寄存器中...
  luaK_exp2nextreg(fs, e);  /* default */
  return e->u.s.info;
}


void luaK_exp2val (FuncState *fs, expdesc *e) {
  if (hasjumps(e))
    luaK_exp2anyreg(fs, e);
  else
    luaK_dischargevars(fs, e);
}


int luaK_exp2RK (FuncState *fs, expdesc *e) {
  luaK_exp2val(fs, e);
  switch (e->k) {
    case VKNUM:
    case VTRUE:
    case VFALSE:
    case VNIL: {
      // 如果常量数组还有容量，就放入常量数组中                 
      if (fs->nk <= MAXINDEXRK) {  /* constant fit in RK operand? */
        e->u.s.info = (e->k == VNIL)  ? nilK(fs) :
                      (e->k == VKNUM) ? luaK_numberK(fs, e->u.nval) :
                                        boolK(fs, (e->k == VTRUE));
        e->k = VK;
        return RKASK(e->u.s.info);
      }
      else break;
    }
    case VK: {
      // 如果常量数组还有容量，就放入常量数组中                 
      if (e->u.s.info <= MAXINDEXRK)  /* constant fit in argC? */
        return RKASK(e->u.s.info);
      else break;
    }
    default: break;
  }
  /* not a constant in the right range: put it in a register */
  return luaK_exp2anyreg(fs, e);
}

// 存入数据, var是左边,ex是右边,也就是值表达式
void luaK_storevar (FuncState *fs, expdesc *var, expdesc *ex) {
  switch (var->k) {
    case VLOCAL: {
      freeexp(fs, ex);
      exp2reg(fs, ex, var->u.s.info);
      return;
    }
    case VUPVAL: {
      // 这里返回的e是寄存器索引
      int e = luaK_exp2anyreg(fs, ex);
      luaK_codeABC(fs, OP_SETUPVAL, e, var->u.s.info, 0);
      break;
    }
    case VGLOBAL: {
      // 将数据存储到全局变量中
      // 首先将值表达式存放到寄存器中,返回的寄存器索引
      int e = luaK_exp2anyreg(fs, ex);
      // 然后存入全局变量
      luaK_codeABx(fs, OP_SETGLOBAL, e, var->u.s.info);
      break;
    }
    case VINDEXED: {
      int e = luaK_exp2RK(fs, ex);
      luaK_codeABC(fs, OP_SETTABLE, var->u.s.info, var->u.s.aux, e);
      break;
    }
    default: {
      lua_assert(0);  /* invalid var kind to store */
      break;
    }
  }
  freeexp(fs, ex);
}


void luaK_self (FuncState *fs, expdesc *e, expdesc *key) {
  int func;
  luaK_exp2anyreg(fs, e);
  freeexp(fs, e);
  func = fs->freereg;
  luaK_reserveregs(fs, 2);
  luaK_codeABC(fs, OP_SELF, func, e->u.s.info, luaK_exp2RK(fs, key));
  freeexp(fs, key);
  e->u.s.info = func;
  e->k = VNONRELOC;
}


static void invertjump (FuncState *fs, expdesc *e) {
  Instruction *pc = getjumpcontrol(fs, e->u.s.info);
  lua_assert(testTMode(GET_OPCODE(*pc)) && GET_OPCODE(*pc) != OP_TESTSET &&
                                           GET_OPCODE(*pc) != OP_TEST);
  SETARG_A(*pc, !(GETARG_A(*pc)));
}


static int jumponcond (FuncState *fs, expdesc *e, int cond) {
  if (e->k == VRELOCABLE) {
    Instruction ie = getcode(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.s.info, cond);
}


void luaK_goiftrue (FuncState *fs, expdesc *e) {
  // pc存放的是假如e为FALSE时的指令地址
  int pc;  /* pc of last jump */
  luaK_dischargevars(fs, e);
  switch (e->k) {
    case VK: case VKNUM: case VTRUE: {
      // 这些类型的数据恒为true,那么就不跳转
      pc = NO_JUMP;  /* always true; do nothing */
      break;
    }
    case VFALSE: {
      // FALSE则生成一个跳转指令
      pc = luaK_jump(fs);  /* always jump */
      break;
    }
    case VJMP: {
      // 为什么要反转指令??
      invertjump(fs, e);
      pc = e->u.s.info;
      break;
    }
    default: {
      pc = jumponcond(fs, e, 0);
      break;
    }
  }
  // 把为FALSE时的pc指令地址写入表达式的falselist
  luaK_concat(fs, &e->f, pc);  /* insert last jump in `f' list */
  // 意思是为true时跳转到当前位置来
  luaK_patchtohere(fs, e->t);

  // 当这个函数返回的时候, f跳转位置未知, t跳转位置为下一个指令的位置
  e->t = NO_JUMP;
}


static void luaK_goiffalse (FuncState *fs, expdesc *e) {
  int pc;  /* pc of last jump */
  luaK_dischargevars(fs, e);
  switch (e->k) {
    case VNIL: case VFALSE: {
      pc = NO_JUMP;  /* always false; do nothing */
      break;
    }
    case VTRUE: {
      pc = luaK_jump(fs);  /* always jump */
      break;
    }
    case VJMP: {
      pc = e->u.s.info;
      break;
    }
    default: {
      pc = jumponcond(fs, e, 1);
      break;
    }
  }
  luaK_concat(fs, &e->t, pc);  /* insert last jump in `t' list */
  luaK_patchtohere(fs, e->f);
  e->f = NO_JUMP;
}


static void codenot (FuncState *fs, expdesc *e) {
  luaK_dischargevars(fs, e);
  switch (e->k) {
    case VNIL: case VFALSE: {
      e->k = VTRUE;
      break;
    }
    case VK: case VKNUM: case VTRUE: {
      e->k = VFALSE;
      break;
    }
    case VJMP: {
      invertjump(fs, e);
      break;
    }
    case VRELOCABLE:
    case VNONRELOC: {
      discharge2anyreg(fs, e);
      freeexp(fs, e);
      e->u.s.info = luaK_codeABC(fs, OP_NOT, 0, e->u.s.info, 0);
      e->k = VRELOCABLE;
      break;
    }
    default: {
      lua_assert(0);  /* cannot happen */
      break;
    }
  }
  /* interchange true and false lists */
  { int temp = e->f; e->f = e->t; e->t = temp; }
  removevalues(fs, e->f);
  removevalues(fs, e->t);
}


void luaK_indexed (FuncState *fs, expdesc *t, expdesc *k) {
  t->u.s.aux = luaK_exp2RK(fs, k);
  t->k = VINDEXED;
}

// 常量展开,能少一条指令,仅当两者都是数字时才能这样优化
static int constfolding (OpCode op, expdesc *e1, expdesc *e2) {
  lua_Number v1, v2, r;
  if (!isnumeral(e1) || !isnumeral(e2)) return 0;
  v1 = e1->u.nval;
  v2 = e2->u.nval;
  switch (op) {
    case OP_ADD: r = luai_numadd(v1, v2); break;
    case OP_SUB: r = luai_numsub(v1, v2); break;
    case OP_MUL: r = luai_nummul(v1, v2); break;
    case OP_DIV:
      if (v2 == 0) return 0;  /* do not attempt to divide by 0 */
      r = luai_numdiv(v1, v2); break;
    case OP_MOD:
      if (v2 == 0) return 0;  /* do not attempt to divide by 0 */
      r = luai_nummod(v1, v2); break;
    case OP_POW: r = luai_numpow(v1, v2); break;
    case OP_UNM: r = luai_numunm(v1); break;
    case OP_LEN: return 0;  /* no constant folding for 'len' */
    default: lua_assert(0); r = 0; break;
  }
  if (luai_numisnan(r)) return 0;  /* do not attempt to produce NaN */
  e1->u.nval = r;
  return 1;
}


static void codearith (FuncState *fs, OpCode op, expdesc *e1, expdesc *e2) {
  if (constfolding(op, e1, e2))
    return;
  else {
    int o2 = (op != OP_UNM && op != OP_LEN) ? luaK_exp2RK(fs, e2) : 0;
    int o1 = luaK_exp2RK(fs, e1);
    if (o1 > o2) {
      freeexp(fs, e1);
      freeexp(fs, e2);
    }
    else {
      freeexp(fs, e2);
      freeexp(fs, e1);
    }
    e1->u.s.info = luaK_codeABC(fs, op, 0, o1, o2);
    e1->k = VRELOCABLE;
  }
}


static void codecomp (FuncState *fs, OpCode op, int cond, expdesc *e1,
                                                          expdesc *e2) {
  int o1 = luaK_exp2RK(fs, e1);
  int o2 = luaK_exp2RK(fs, e2);
  freeexp(fs, e2);
  freeexp(fs, e1);
  if (cond == 0 && op != OP_EQ) {
    int temp;  /* exchange args to replace by `<' or `<=' */
    temp = o1; o1 = o2; o2 = temp;  /* o1 <==> o2 */
    cond = 1;
  }
  e1->u.s.info = condjump(fs, op, cond, o1, o2);
  e1->k = VJMP;
}

// 处理一元操作符的情况
void luaK_prefix (FuncState *fs, UnOpr op, expdesc *e) {
  expdesc e2;
  e2.t = e2.f = NO_JUMP; e2.k = VKNUM; e2.u.nval = 0;
  switch (op) {
    case OPR_MINUS: {
      if (!isnumeral(e))  // 如果不是数字，先把这个值dump到寄存器，因为-不能操作任何非数字
        luaK_exp2anyreg(fs, e);  /* cannot operate on non-numeric constants */
      codearith(fs, OP_UNM, e, &e2);
      break;
    }
    case OPR_NOT: codenot(fs, e); break;
    case OPR_LEN: {
      luaK_exp2anyreg(fs, e);  /* cannot operate on constants */
      codearith(fs, OP_LEN, e, &e2);
      break;
    }
    default: lua_assert(0);
  }
}


void luaK_infix (FuncState *fs, BinOpr op, expdesc *v) {
  switch (op) {
    case OPR_AND: {
      luaK_goiftrue(fs, v);
      break;
    }
    case OPR_OR: {
      luaK_goiffalse(fs, v);
      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_MOD: case OPR_POW: {
      if (!isnumeral(v)) luaK_exp2RK(fs, v);
      break;
    }
    default: {
      luaK_exp2RK(fs, v);
      break;
    }
  }
}


void luaK_posfix (FuncState *fs, BinOpr op, expdesc *e1, expdesc *e2) {
  switch (op) {
    case OPR_AND: {
      lua_assert(e1->t == NO_JUMP);  /* list must be closed */
      luaK_dischargevars(fs, e2);
      luaK_concat(fs, &e2->f, e1->f);
      *e1 = *e2;
      break;
    }
    case OPR_OR: {
      lua_assert(e1->f == NO_JUMP);  /* list must be closed */
      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(getcode(fs, e2)) == OP_CONCAT) {
        lua_assert(e1->u.s.info == GETARG_B(getcode(fs, e2))-1);
        freeexp(fs, e1);
        SETARG_B(getcode(fs, e2), e1->u.s.info);
        e1->k = VRELOCABLE; e1->u.s.info = e2->u.s.info;
      }
      else {
        luaK_exp2nextreg(fs, e2);  /* operand must be on the 'stack' */
        codearith(fs, OP_CONCAT, e1, e2);
      }
      break;
    }
    case OPR_ADD: codearith(fs, OP_ADD, e1, e2); break;
    case OPR_SUB: codearith(fs, OP_SUB, e1, e2); break;
    case OPR_MUL: codearith(fs, OP_MUL, e1, e2); break;
    case OPR_DIV: codearith(fs, OP_DIV, e1, e2); break;
    case OPR_MOD: codearith(fs, OP_MOD, e1, e2); break;
    case OPR_POW: codearith(fs, OP_POW, e1, e2); break;
    case OPR_EQ: codecomp(fs, OP_EQ, 1, e1, e2); break;
    case OPR_NE: codecomp(fs, OP_EQ, 0, e1, e2); break;
    case OPR_LT: codecomp(fs, OP_LT, 1, e1, e2); break;
    case OPR_LE: codecomp(fs, OP_LE, 1, e1, e2); break;
    case OPR_GT: codecomp(fs, OP_LT, 0, e1, e2); break;
    case OPR_GE: codecomp(fs, OP_LE, 0, e1, e2); break;
    default: lua_assert(0);
  }
}


void luaK_fixline (FuncState *fs, int line) {
  fs->f->lineinfo[fs->pc - 1] = line;
}

// 将虚拟机机器指令压入Proto的code中,更新代码行在f的lineinfo数组中,同时更新pc指针
// 这个函数的返回值是存放这段代码地址的pc指针
static int luaK_code (FuncState *fs, Instruction i, int line) {
  Proto *f = fs->f;
  dischargejpc(fs);  /* `pc' will change */
  /* put new instruction in code array */
  luaM_growvector(fs->L, f->code, fs->pc, f->sizecode, Instruction,
                  MAX_INT, "code size overflow");
  f->code[fs->pc] = i;
  /* save corresponding line information */
  luaM_growvector(fs->L, f->lineinfo, fs->pc, f->sizelineinfo, int,
                  MAX_INT, "code size overflow");
  f->lineinfo[fs->pc] = line;
  return fs->pc++;
}


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);
  return luaK_code(fs, CREATE_ABC(o, a, b, c), fs->ls->lastline);
}


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);
  return luaK_code(fs, CREATE_ABx(o, a, bc), fs->ls->lastline);
}


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);
  if (c <= MAXARG_C)
    luaK_codeABC(fs, OP_SETLIST, base, b, c);
  else {
    luaK_codeABC(fs, OP_SETLIST, base, b, 0);
    luaK_code(fs, cast(Instruction, c), fs->ls->lastline);
  }
  fs->freereg = base + 1;  /* free registers with list values */
}