Re: upvals in Lua bytecode

[Xingzhi Pan <vengeance.storm@...>]

Oh mine, it is a bit unintuitive to leave "global" as default.  Thank
you people!

Harry

On Wed, Jun 1, 2011 at 11:49 PM, François Perrad
<francois.perrad@gadz.org> wrote:
>
>
> 2011/6/2 Xingzhi Pan <vengeance.storm@gmail.com>
>>
>> Hi,
>>
>> I'm using luac -l to observe the bytecode of the following Lua source:
>>
>>  1 function fo (i)
>>  2     uv = 0
>>  3     function fi1 ()
>>  4         print(uv)
>>  5         uv = 1
>>  6         print(uv)
>>  7     end
>>  8     function fi2 ()
>>  9         print(uv)
>> 10         uv = 2
>> 11         print(uv)
>> 12     end
>> 13     if i == 1 then return fi1 end
>> 14     if i == 2 then return fi2 end
>> 15 end
>> 16
>>
>> And this is what I get:
>>
>> main <../upval.lua:0,0> (3 instructions, 12 bytes at 0x100101050)
>> 0+ params, 2 slots, 0 upvalues, 0 locals, 1 constant, 1 function
>>        1       [15]    CLOSURE         0 0     ; 0x1001011f0
>>        2       [1]     SETGLOBAL       0 -1    ; fo
>>        3       [15]    RETURN          0 1
>>
>> function <../upval.lua:1,15> (15 instructions, 60 bytes at 0x1001011f0)
>> 1 param, 2 slots, 0 upvalues, 1 local, 6 constants, 2 functions
>>        1       [2]     LOADK           1 -2    ; 0
>>        2       [2]     SETGLOBAL       1 -1    ; uv
>>        3       [7]     CLOSURE         1 0     ; 0x1001015c0
>>        4       [3]     SETGLOBAL       1 -3    ; fi1
>>        5       [12]    CLOSURE         1 1     ; 0x1001017c0
>>        6       [8]     SETGLOBAL       1 -4    ; fi2
>>        7       [13]    EQ              0 0 -5  ; - 1
>>        8       [13]    JMP             2       ; to 11
>>        9       [13]    GETGLOBAL       1 -3    ; fi1
>>        10      [13]    RETURN          1 2
>>        11      [14]    EQ              0 0 -6  ; - 2
>>        12      [14]    JMP             2       ; to 15
>>        13      [14]    GETGLOBAL       1 -4    ; fi2
>>        14      [14]    RETURN          1 2
>>        15      [15]    RETURN          0 1
>>
>> function <../upval.lua:3,7> (9 instructions, 36 bytes at 0x1001015c0)
>> 0 params, 2 slots, 0 upvalues, 0 locals, 3 constants, 0 functions
>>        1       [4]     GETGLOBAL       0 -1    ; print
>>        2       [4]     GETGLOBAL       1 -2    ; uv
>>        3       [4]     CALL            0 2 1
>>        4       [5]     LOADK           0 -3    ; 1
>>        5       [5]     SETGLOBAL       0 -2    ; uv
>>        6       [6]     GETGLOBAL       0 -1    ; print
>>        7       [6]     GETGLOBAL       1 -2    ; uv
>>        8       [6]     CALL            0 2 1
>>        9       [7]     RETURN          0 1
>>
>> function <../upval.lua:8,12> (9 instructions, 36 bytes at 0x1001017c0)
>> 0 params, 2 slots, 0 upvalues, 0 locals, 3 constants, 0 functions
>>        1       [9]     GETGLOBAL       0 -1    ; print
>>        2       [9]     GETGLOBAL       1 -2    ; uv
>>        3       [9]     CALL            0 2 1
>>        4       [10]    LOADK           0 -3    ; 2
>>        5       [10]    SETGLOBAL       0 -2    ; uv
>>        6       [11]    GETGLOBAL       0 -1    ; print
>>        7       [11]    GETGLOBAL       1 -2    ; uv
>>        8       [11]    CALL            0 2 1
>>        9       [12]    RETURN          0 1
>>
>> So my question is that for inner functions fi1 and fi2, why GETGLOBAL
>> and SETGLOBAL, rather than GETUPVAL and SETUPVAL, are used?  Isn't uv
>> an upvalue?
>
> Currently, uv is a global variable.
> If you want an upvalue, you must use 'local uv = 0' line 2.
>
> François
>
>>
>> Also, it shows "0 upvalues" for these 2 functions, where I thought
>> should be one.
>>
>> Thanks,
>> Xingzhi 'Harry' Pan
>>
>
>



-- 
Pan, Xingzhi
http://www.panxingzhi.net