Cool_Tools/bemaniutils
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mirror of synced 2024-11-27 23:50:47 +01:00
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Fix a logic error in if statement unwrapping, remove duplicated code in favor of a better true/false detection algorithm.

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This commit is contained in:
Jennifer Taylor 2021-05-04 02:30:37 +00:00
parent 108d7c228d
commit 4790385022
2 changed files with 61 additions and 45 deletions
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102
bemani/format/afp/decompile.py
View File

@ -1061,10 +1061,11 @@ class BitVector:
class ByteCodeDecompiler(VerboseOutput):
def __init__(self, bytecode: ByteCode) -> None:
def __init__(self, bytecode: ByteCode, optimize: bool = False) -> None:
super().__init__()
self.bytecode = bytecode
self.optimize = optimize
self.__statements: Optional[List[Statement]] = None
self.__tmpvar_id: int = 0
self.__goto_body_id: int = -1
@ -1461,17 +1462,14 @@ class ByteCodeDecompiler(VerboseOutput):
if last_action.opcode == AP2Action.IF:
# Calculate true and false jump points.
true_jump_point = offset_map[cast(IfAction, last_action).jump_if_true_offset]
false_jump_points = [n for n in chunk.next_chunks if n != true_jump_point]
if len(false_jump_points) != 1:
raise Exception("Logic error, didn't get exactly one false case jump point!")
false_jump_point = false_jump_points[0]
if true_jump_point == false_jump_point:
# This might be a stubbed-out if statement or debug code. Maybe the right
# thing to do here is to convert it to a goto? Let's see if we ever hit it.
raise Exception("Logic error, true and false jump point are identical!")
true_jump_point, false_jump_point = self.__get_jump_points(chunk, offset_map)
end_offset = offset_map[self.bytecode.end_offset]
# Calculate true and false jump points, see if they are break/continue/goto.
# Its possible for the true and false jump points to be equal if this is an
# if statement which jumps to the next line of code in the true case. The below
# code will still work (it will change both the true and false points to a break,
# continue or return statement).
true_action: Optional[Statement] = None
if true_jump_point == break_point:
self.vprint("Converting jump if true to loop break into break statement.")
@ -1482,7 +1480,7 @@ class ByteCodeDecompiler(VerboseOutput):
true_action = ContinueStatement()
chunk.next_chunks = [n for n in chunk.next_chunks if n != true_jump_point]
elif true_jump_point not in internal_jump_points:
if true_jump_point == offset_map[self.bytecode.end_offset]:
if true_jump_point == end_offset:
self.vprint("Converting jump if true to external point into return statement.")
true_action = NullReturnStatement()
else:
@ -1500,7 +1498,7 @@ class ByteCodeDecompiler(VerboseOutput):
false_action = ContinueStatement()
chunk.next_chunks = [n for n in chunk.next_chunks if n != false_jump_point]
elif false_jump_point not in internal_jump_points:
if false_jump_point == offset_map[self.bytecode.end_offset]:
if false_jump_point == end_offset:
self.vprint("Converting jump if false to external point into return statement.")
false_action = NullReturnStatement()
else:
@ -1686,6 +1684,24 @@ class ByteCodeDecompiler(VerboseOutput):
raise Exception(f"Chunk ID {new_chunk.id} in list of chunks we converted but we expected it to be deleted!")
return updated_chunks
def __get_jump_points(self, chunk: ByteCodeChunk, offset_map: Dict[int, int]) -> Tuple[int, int]:
action = chunk.actions[-1]
if isinstance(action, IfAction):
true_jump_point = offset_map[action.jump_if_true_offset]
false_jump_points = [n for n in chunk.next_chunks if n != true_jump_point]
if len(false_jump_points) != 1:
if chunk.next_chunks[0] != chunk.next_chunks[1]:
raise Exception(f"Logic error, got more than one false jump point for if statement in chunk {chunk.id}")
else:
false_jump_point = true_jump_point
else:
false_jump_point = false_jump_points[0]
return true_jump_point, false_jump_point
else:
raise Exception(f"Logic error, expecting JumpAction but got {action} in chunk {chunk.id}!")
def __break_graph(self, chunks: Sequence[Union[ByteCodeChunk, Loop]], offset_map: Dict[int, int]) -> None:
for chunk in chunks:
if chunk.id == offset_map[self.bytecode.end_offset]:
@ -1716,22 +1732,21 @@ class ByteCodeDecompiler(VerboseOutput):
chunk.actions[-1] = NullReturnStatement()
else:
if last_action.opcode == AP2Action.IF:
raise Exception("Logic error, unexpected if statement with only one successor!")
raise Exception(f"Logic error, unexpected if statement with only one successor in {chunk.id}!")
self.vprint(f"Converting fall-through to end of code in {chunk.id} into a null return.")
chunk.actions.append(NullReturnStatement())
chunk.next_chunks = []
elif len(chunk.next_chunks) == 2:
if last_action.opcode != AP2Action.IF:
raise Exception("Logic error, expected if statement with two successors!")
raise Exception(f"Logic error, expected if statement with two successors in {chunk.id}!")
# This is an if statement, let's see if any of the arms point to a return.
true_jump_point = offset_map[cast(IfAction, last_action).jump_if_true_offset]
false_jump_points = [n for n in chunk.next_chunks if n != true_jump_point]
if len(false_jump_points) != 1:
raise Exception("Logic error, got more than one false jump point for an if statement!")
false_jump_point = false_jump_points[0]
true_jump_point, false_jump_point = self.__get_jump_points(chunk, offset_map)
end_offset = offset_map[self.bytecode.end_offset]
# It's possible for the true and false jump point to be equal, if the code being
# decompiled has not been optimized. The below code will produce the correct
# result for this case (true and false cases both containing the same return).
true_action: Optional[Statement] = None
if true_jump_point == end_offset:
self.vprint(f"Converting jump if true to external point into return statement in {chunk.id}.")
@ -1866,7 +1881,7 @@ class ByteCodeDecompiler(VerboseOutput):
# if-goto patterns.
next_id = chunks_by_id[cur_id].next_chunks[0]
if next_id not in chunks_by_id:
raise Exception(f"Logic error, we can't jump to the next chunk for loop {cur_id} as it is outside of our scope!")
raise Exception(f"Logic error, we can't jump to chunk {next_id} for loop {cur_id} as it is outside of our scope!")
cur_id = next_id
continue
@ -1901,12 +1916,7 @@ class ByteCodeDecompiler(VerboseOutput):
# This should be an if statement. Figure out if it is an if-else or an
# if, and if both branches return.
if_end = self.__find_shallowest_successor(cur_id, chunks_by_id)
true_jump_point = offset_map[last_action.jump_if_true_offset]
false_jump_points = [n for n in cur_chunk.next_chunks if n != true_jump_point]
if len(false_jump_points) != 1:
raise Exception("Logic error, got more than one false jump point for an if statement!")
false_jump_point = false_jump_points[0]
true_jump_point, false_jump_point = self.__get_jump_points(cur_chunk, offset_map)
if true_jump_point == false_jump_point:
# This should never happen.
raise Exception("Logic error, both true and false jumps are to the same location!")
@ -1929,7 +1939,7 @@ class ByteCodeDecompiler(VerboseOutput):
del chunks_by_id[chunk.id]
# Now, recursively attempt to detect if statements within this chunk as well.
true_chunks = self.__separate_ifs(true_jump_point, if_end, true_chunks, offset_map)
true_chunks = self.__separate_ifs(true_jump_point, if_end if if_end is not None else end_id, true_chunks, offset_map)
false_chunks: List[ArbitraryCodeChunk] = []
if false_jump_point not in chunks_by_id and false_jump_point != if_end:
@ -1947,7 +1957,7 @@ class ByteCodeDecompiler(VerboseOutput):
del chunks_by_id[chunk.id]
# Now, recursively attempt to detect if statements within this chunk as well.
false_chunks = self.__separate_ifs(false_jump_point, if_end, false_chunks, offset_map)
false_chunks = self.__separate_ifs(false_jump_point, if_end if if_end is not None else end_id, false_chunks, offset_map)
if (not true_chunks) and (not false_chunks):
# We should have at least one!
@ -2030,12 +2040,7 @@ class ByteCodeDecompiler(VerboseOutput):
# Find the true and false jump points, walk those graphs and assign logical predecessors
# to each of them.
true_jump_point = offset_map[last_action.jump_if_true_offset]
false_jump_points = [n for n in cur_chunk.next_chunks if n != true_jump_point]
if len(false_jump_points) != 1:
raise Exception("Logic error, got more than one false jump point for an if statement!")
false_jump_point = false_jump_points[0]
true_jump_point, false_jump_point = self.__get_jump_points(cur_chunk, offset_map)
if true_jump_point == false_jump_point:
# This should never happen.
raise Exception("Logic error, both true and false jumps are to the same location!")
@ -3179,10 +3184,19 @@ class ByteCodeDecompiler(VerboseOutput):
if unmatched_gotos:
formatted_labels = ", ".join(f"label_{x}" for x in unmatched_gotos)
raise Exception(f"Logic error, gotos found jumping to the following labels which don't exist: {formatted_labels}")
if unmatched_labels:
if unmatched_labels and self.optimize:
formatted_labels = ", ".join(f"label_{x}" for x in unmatched_labels)
raise Exception(f"Logic error, labels found with no gotos pointing at them: {formatted_labels}")
def __verify_no_empty_ifs(self, statements: Sequence[Statement]) -> None:
def check_ifs(statement: Statement) -> Optional[Statement]:
if isinstance(statement, IfStatement):
if (not statement.true_statements) and (not statement.false_statements):
raise Exception(f"If statement {statement} has no true or false statements inside it!")
return statement
self.__walk(statements, check_ifs)
def __pretty_print(self, statements: Sequence[Statement], prefix: str = "") -> str:
output: List[str] = []
@ -3224,18 +3238,20 @@ class ByteCodeDecompiler(VerboseOutput):
statements = self.__eval_chunks(start_id, chunks_loops_and_ifs, offset_map)
# Now, let's do some clean-up passes.
statements = self.__collapse_identical_labels(statements)
statements = self.__eliminate_useless_control_flows(statements)
while True:
statements, changed1 = self.__eliminate_unused_labels(statements)
statements, changed2 = self.__remove_useless_gotos(statements)
if self.optimize:
statements = self.__collapse_identical_labels(statements)
statements = self.__eliminate_useless_control_flows(statements)
while True:
statements, changed1 = self.__eliminate_unused_labels(statements)
statements, changed2 = self.__remove_useless_gotos(statements)
if not changed1 and not changed2:
break
statements = self.__swap_empty_ifs(statements)
if not changed1 and not changed2:
break
statements = self.__swap_empty_ifs(statements)
# Let's sanity check the code for a few things that might trip us up.
self.__verify_balanced_labels(statements)
self.__verify_no_empty_ifs(statements)
# Finally, let's save the code!
self.__statements = statements

4
bemani/tests/test_afp_decompile.py
View File

@ -121,7 +121,7 @@ class TestAFPControlGraph(ExtendedTestCase):
def __call_graph(self, bytecode: ByteCode) -> Tuple[Dict[int, ByteCodeChunk], Dict[int, int]]:
# Just create a dummy compiler so we can access the internal method for testing.
bcd = ByteCodeDecompiler(bytecode)
bcd = ByteCodeDecompiler(bytecode, optimize=True)
# Call it, return the data in an easier to test fashion.
chunks, offset_map = bcd._ByteCodeDecompiler__graph_control_flow(bytecode)
@ -533,7 +533,7 @@ class TestAFPDecompile(ExtendedTestCase):
def __call_decompile(self, bytecode: ByteCode) -> List[Statement]:
# Just create a dummy compiler so we can access the internal method for testing.
bcd = ByteCodeDecompiler(bytecode)
bcd = ByteCodeDecompiler(bytecode, optimize=True)
bcd.decompile(verbose=self.verbose)
return bcd.statements