Files
python-uncompyle6/uncompyle6/parsers/reducecheck/for_block_check.py
rocky ad1fa98870 Detect Python 2.7 weird "for-block" bytecode
It has an unnecessary JUMP_ABSOLUTE to a JUMP_LOOP

Fixes #408
2022-09-27 08:58:35 -04:00

74 lines
2.6 KiB
Python

# Copyright (c) 2022 Rocky Bernstein
from uncompyle6.scanners.tok import Token
def for_block_invalid(self, lhs, n, rule, tree, tokens, first: int, last: int) -> bool:
# print("XXX", first, last)
# for t in range(first, last):
# print(tokens[t])
# print("=" * 30)
if rule == (
"for_block",
("l_stmts_opt", "JUMP_ABSOLUTE", "JUMP_BACK", "JUMP_BACK"),
):
# Check that the two JUMP_BACK's go to the same place.
jump_back1 = tokens[last - 2]
jump_back2 = tokens[last - 1]
if jump_back1.attr != jump_back2.attr:
return True
# Also check that JUMP_ABSOLUTE jumps to the JUMP_BACK.
# In this situation the JUMP_ABSOLUTE and a JUMP_BACK
# is not needed, but it seems to be there anyway.
jump_absolute = tokens[last - 3]
if jump_absolute.attr != jump_back2.offset:
return True
# Right now all of this is known to happen only in Python 2.7.
if self.version[:2] == (2, 7):
return False
if len(rule[1]) <= 1 or not tree:
return False
come_froms = tree[-1]
# This is complicated, but note that the JUMP_IF instruction comes immediately
# *before* _ifstmts_jump so that's what we have to test
# the COME_FROM against. This can be complicated by intervening
# POP_TOP, and pseudo COME_FROM, ELSE instructions
#
pop_jump_index = first - 1
while pop_jump_index > 0 and tokens[pop_jump_index] in (
"ELSE",
"POP_TOP",
"JUMP_FORWARD",
"COME_FROM",
):
pop_jump_index -= 1
# FIXME: something is fishy when and EXTENDED ARG is needed before the
# pop_jump_index instruction to get the argment. In this case, the
# _ifsmtst_jump can jump to a spot beyond the come_froms.
# That is going on in the non-EXTENDED_ARG case is that the POP_JUMP_IF
# jumps to a JUMP_(FORWARD) which is changed into an EXTENDED_ARG POP_JUMP_IF
# to the jumped forwarded address
if tokens[pop_jump_index].attr > 256:
return False
pop_jump_offset = tokens[pop_jump_index].off2int(prefer_last=False)
if isinstance(come_froms, Token):
if tokens[pop_jump_index].attr < pop_jump_offset and tree[0] != "pass":
# This is a jump backwards to a loop. All bets are off here when there the
# unless statement is "pass" which has no instructions associated with it.
return False
return come_froms.attr is not None and pop_jump_offset > come_froms.attr
elif len(come_froms) == 0:
return False
else:
return pop_jump_offset > come_froms[-1].attr