Jumps out of more than 4 nested blocks are not allowed
Closed this issue · 3 comments
I understand the reason for the limitation - you don't want to have to recompute jumps.
However, there is a simple method of overcoming this that should work: If you don't have enough space, you emit as many POP_BLOCKs as possible and a jump to the end of the buffer (+ 1), append the remaining POP_BLOCKs to the end of the buffer, and then append a jump back to the goto target.
Hopefully that makes sense. Perhaps an example:
def test():
if a:
if b:
if c:
if d:
if e:
goto .end
label .end
This becomes:
4 0 LOAD_GLOBAL 0 (a)
3 POP_JUMP_IF_FALSE 52
5 6 LOAD_GLOBAL 1 (b)
9 POP_JUMP_IF_FALSE 52
6 12 LOAD_GLOBAL 2 (c)
15 POP_JUMP_IF_FALSE 49
7 18 LOAD_GLOBAL 3 (d)
21 POP_JUMP_IF_FALSE 46
8 24 LOAD_GLOBAL 4 (e)
27 POP_JUMP_IF_FALSE 43
9 30 LOAD_GLOBAL 5 (goto)
33 LOAD_ATTR 6 (end)
36 POP_TOP
37 JUMP_ABSOLUTE 43
40 JUMP_ABSOLUTE 46
>> 43 JUMP_ABSOLUTE 49
>> 46 JUMP_ABSOLUTE 52
>> 49 JUMP_FORWARD 0 (to 52)
10 >> 52 LOAD_GLOBAL 7 (label)
55 LOAD_ATTR 6 (end)
58 POP_TOP
59 LOAD_CONST 0 (None)
62 RETURN_VALUE
Which you then transform into:
4 0 LOAD_GLOBAL 0 (a)
3 POP_JUMP_IF_FALSE 52
5 6 LOAD_GLOBAL 1 (b)
9 POP_JUMP_IF_FALSE 52
6 12 LOAD_GLOBAL 2 (c)
15 POP_JUMP_IF_FALSE 49
7 18 LOAD_GLOBAL 3 (d)
21 POP_JUMP_IF_FALSE 46
8 24 LOAD_GLOBAL 4 (e)
27 POP_JUMP_IF_FALSE 43
9 30 POP_BLOCK
31 POP_BLOCK
32 POP_BLOCK
33 POP_BLOCK
34 JUMP_ABSOLUTE 63
37 JUMP_ABSOLUTE 43
40 JUMP_ABSOLUTE 46
>> 43 JUMP_ABSOLUTE 49
>> 46 JUMP_ABSOLUTE 52
>> 49 JUMP_FORWARD 0 (to 52)
10 >> 52 NOP
53 NOP
54 NOP
55 NOP
56 NOP
57 NOP
58 NOP
59 LOAD_CONST 0 (None)
62 RETURN_VALUE
63 POP_BLOCK
64 JUMP_ABSOLUTE 34
Note: I haven't actually tried this, just tossing this out there.
(On an unrelated note: wow Python's bytecode compiler is naive.)
Note that you don't need any POP_BLOCK instructions in your example above, as if-statements don't create blocks. Only loops, try-except, try-finally and with statements do. And I cannot remember having seen any Python code that uses 5 or more nested loops. So I don't think this limitation will be a problem. And therefore I'd rather not make things more complicated as they already are.
Ok.
I am running into this problem too. The reason why I am using this package is because I am writing fairly complex procedure flows for a reinforcement learning project. Two loop + two with statements resulted in this error:
SyntaxError: Jump out of too many nested blocks