Lua 5.2 Changes

• string subtypes different in versions
  5.2.0 does not have LUA_TSHRSTR and LUA_TLNGSTR
  but 5.2.1 and newer version of 5.2 all have defined these.

/* Variant tags for strings */
#define LUA_TSHRSTR (LUA_TSTRING | (0 << 4))  /* short strings */
#define LUA_TLNGSTR (LUA_TSTRING | (1 << 4))  /* long strings */

• upval _ENV instead of _G
  _ENV is a upval, the top level function has only one upval _ENV, other function's _ENV links to top one by one.
  _ENV 是 upval ，顶层函数有且只有一个 upval _ENV ，其他函数的 _ENV 逐层向上指到顶层。

OP_GETGLOBAL --> OP_GETTABUP
OP_SETGLOBAL --> OP_SETTABUP
a --> _ENV.a

• new operators

OP_LOADKX,/*	A 	R(A) := Kst(extra arg)				*/
OP_EXTRAARG/*	Ax	extra (larger) argument for previous opcode	*/

• changed operators

- OP_CLOSE,/*	A	close all upvalues >= R(A)	*/
* OP_JMP,/*	A sBx	pc+=sBx; if (A) close all upvalues >= R(A-1)	*/

- OP_LOADNIL,/*	A B	R(A) := ... := R(B) := nil			*/
+ OP_LOADNIL,/*	A B	R(A), R(A+1), ..., R(A+B) := nil		*/

- OP_TFORLOOP,/*	A C	R(A+3), ... ,R(A+2+C) := R(A)(R(A+1), R(A+2)); 
                        if R(A+3) ~= nil then R(A+2)=R(A+3) else pc++	*/
+ OP_TFORCALL,/*	A C	R(A+3), ... ,R(A+2+C) := R(A)(R(A+1), R(A+2));	*/
+ OP_TFORLOOP,/*	A sBx	if R(A+1) ~= nil then { R(A)=R(A+1); pc += sBx }*/

• Proto.upvalues

- Proto.nups
TString** Proto.upvalues --> Upvaldesc* Proto.upvalues

OP_CLOSURE will not be followed by OP_MOVE or OP_GETUPVALUE, use Proto.upvalues.instack and Proto.upvalues.idx
OP_CLOSURE 后面不会再有设置 upval 的 OP_MOVE or OP_GETUPVALUE 了，现在用 Proto.upvalues.instack 和 Proto.upvalues.idx 来取代。

#if LUA_VERSION_NUM == 501
	#define luadec_freearray(L, b, n, t) luaM_freearray(L, b, n, t)

	#define UPVAL_TYPE TString*
	#define NUPS(f) (f->nups)
	#define UPVAL_NAME(f, r) (f->upvalues[r])
#endif
#if LUA_VERSION_NUM == 502
	#define lua_open()	luaL_newstate()
	#define luadec_freearray(L, b, n, t) luaM_freearray(L, b, n)

	#define UPVAL_TYPE Upvaldesc
	#define NUPS(f) (f->sizeupvalues)
	#define UPVAL_NAME(f, r) (f->upvalues[r].name)
#endif

• no nil optimizations for locals defined at start of a function

5.1 with nil optimizations
>local a,b,c; local d=3;
[1] loadk      3   0        ; R3 := 3
[2] return     0   1        ; return

5.2 and 5.3 without nil optimizations
>local a,b,c; local d=3;
[1] loadnil   0   2        ; R0 to R2 := nil
[2] loadk     3   0        ; R3 := K0(=3)
[3] return    0   1        ; return