Hello, Lua Hackers,
2010年9月19日 Tom N Harris wrote:
- The script code and compiled binary is shorter than
other notation. So
the code will run fast.
Can you give an example of how the bytecode would be shorter?
As far as I can tell, the same instructions should be
generated as using an explicit if-then-else.
I just compiled following code by luac with my patch:
# cat b.lua
x = if a then b else c
y = a and b or c
if a then z = b else z = c end
# src/luac -l b.lua
main <b.lua:0,0> (24 instructions, 96 bytes at 0x10e94c8)
0+ params, 2 slots, 0 upvalues, 0 locals, 6 constants, 0 functions
[snip]
16 [5] GETGLOBAL 0 -2 ; a
17 [5] TEST 0 0 0
18 [5] JMP 3 ; to 22
19 [5] GETGLOBAL 0 -3 ; b
20 [5] SETGLOBAL 0 -6 ; z
21 [5] JMP 2 ; to 24
22 [5] GETGLOBAL 0 -4 ; c
23 [5] SETGLOBAL 0 -6 ; z
24 [5] RETURN 0 1
So, source line 1 was compiled to 7 lines binary, line 3 was 8
lines, line 5 was 9 lines.