Re: Lua code generation and optimisation
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- Subject: Re: Lua code generation and optimisation
- From: Michal Kolodziejczyk <miko@...>
- Date: 2012年10月03日 09:30:00 +0200
On 02.10.2012 18:36, David Collier wrote:
> I'm thinking about code size.
>
> If I write
>
> if CheckCarefully and fred > 3
> then
> print("help fred is >3 which is a very bad idea in our case")
> return
> else
> <whatever using fred>
> end
>
> Can I set up the value of CheckCarefully so that the compiler can omit
> the print and omit storing the error string.
What compiler are you writing about? Lua has an interpreter and no
compiler. LuaJIT has just-in-time compiler, but it "compiles" code as it
runs (so it still needs the full original source/bytecode).
> Or will it always create the strings in the bytecode?
Yes. Check for yourself:
$ luac -l example.lua
main <example.lua:0,0> (15 instructions, 60 bytes at 0x985bd18)
0+ params, 2 slots, 0 upvalues, 0 locals, 6 constants, 0 functions
1 [2] GETGLOBAL 0 -1 ; CheckCarefully
2 [2] TEST 0 0 0
3 [2] JMP 8 ; to 12
4 [2] GETGLOBAL 0 -2 ; fred
5 [2] LT 0 -3 0 ; 3 -
6 [2] JMP 5 ; to 12
7 [3] GETGLOBAL 0 -4 ; print
8 [3] LOADK 1 -5 ; "help fred is >3 which is a very bad idea in our
case"
9 [3] CALL 0 2 1
10 [4] RETURN 0 1
11 [4] JMP 3 ; to 15
12 [6] GETGLOBAL 0 -4 ; print
13 [6] LOADK 1 -6 ; "<whatever using fred>"
14 [6] CALL 0 2 1
15 [7] RETURN 0 1
> If this won't work, anyone got a good way to have code and strings in
> during testing phase and omitted in deployed code?
You are looking for any kind of preprocessor, echeck out metalua:
http://metalua.luaforge.net/
Regards,
miko