Decompiling the differences
I have created about the simplest test I can, the “SimpleLoop” programmes. AS3 version HaXe version The difference in performace is dramatic - 10 to 20 fold. But all is not as bad as it seems…
I have been looking at the very interesting tool, abcdump.exe, as described here.
You can really get a feel for the differences between the outputs. And there is a simple explaination for the differences in file size - haXe includes a small library in the SWF. Fair enough.
I will concentrate on the “Run2″ test - both using “while” loops, rather than “for” loops. HaXe’s iterator-style for loops are slower than its while style loops - I’m hoping that this will not always be the case [Edit: actually the timings both vary and seem about the same]. (Although as a side note, I hope haXe will support both styles of for loops, since it makes porting easier amongst other reasons).
A quick look at the decompile of the Run2 function (two nested while… loops) shows the use of the command “iflt”, presumably “if less than”, which seems ideal for these loops. HaXe uses 3 statements here: coerce_a, lessthan, iffalse. I believe that haXe could easily use this optimisation, especially considering the for(i in 1…1000) style syntax. Also the increment operation. AS3 uses “inclocal_i”, where haXe uses 4 statements: getlocal, increment, coerce_a, setlocal. Again some low-hanging fruit for haXe to pick up.
Another trick is “pushshort” rather than “pushint” where size will allow, and it seems haXe integer constants are followed by “coerce_a”, whereas AS3 ones are not. AS3 used “convert_i” whereas haXe uses “coerce_a”. I’m not sure of the performace implications of this.
So, after some initial doubts, now I think haXe could get about a 10 fold increase in speed (in these very tight loops) pretty easily. HaXe (especially for flash 9) is very new, and I’m condifent these optimisation will come soon enough.
| AS3 | haXe |
function Run2():int /* disp_id 0*/
{
// local_count=4 max_scope=1
// max_stack=2 code_len=60
0 getlocal0
1 pushscope
2 pushbyte 0
4 setlocal1
5 pushbyte 0
7 setlocal2
8 pushbyte 0
10 setlocal3
11 pushbyte 0
13 setlocal1
14 pushbyte 0
16 setlocal2
17 jump L1
L2:
21 label
22 pushbyte 0
24 setlocal1
25 pushbyte 0
27 setlocal3
28 jump L3
L4:
32 label
33 getlocal1
34 getlocal3
35 add
36 convert_i
37 setlocal1
38 inclocal_i 3
L3:
40 getlocal3
41 pushshort 10000
44 iflt L4
48 inclocal_i 2
L1:
50 getlocal2
51 pushshort 1000
54 iflt L2
58 getlocal1
59 returnvalue
}
|
function Run2():* /* disp_id 0*/
{
// local_count=4 max_scope=1
// max_stack=2 code_len=70
0 getlocal0
1 pushscope
2 pushbyte 0
4 coerce_a
5 setlocal1
6 pushbyte 0
8 coerce_a
9 setlocal2
10 jump L1
L2:
14 label
L1:
15 getlocal2
16 pushint 1000 // 0x3e8
18 coerce_a
19 lessthan
20 iffalse L3
24 pushbyte 0
26 coerce_a
27 setlocal1
28 pushbyte 0
30 coerce_a
31 setlocal3
32 jump L4
L5:
36 label
L4:
37 getlocal3
38 pushint 10000 // 0x2710
40 coerce_a
41 lessthan
42 iffalse L6
46 getlocal1
47 getlocal3
48 add
49 coerce_a
50 setlocal1
51 getlocal3
52 increment
53 coerce_a
54 setlocal3
55 jump L5
L6:
59 getlocal2
60 increment
61 coerce_a
62 setlocal2
63 jump L2
L3:
67 getlocal1
68 returnvalue
69 returnvoid
}
|
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