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Add configuration option for allowing for-loops #351

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merged 3 commits into from
Oct 16, 2023
Merged

Add configuration option for allowing for-loops #351

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4edea6b
add config option for allowing for-loops
ebehner Oct 16, 2023
42563be
Update decompiler/util/default.json
ebehner Oct 16, 2023
9a8e94e
Update decompiler/util/default.json
ebehner Oct 16, 2023
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71 changes: 41 additions & 30 deletions decompiler/pipeline/controlflowanalysis/readability_based_refinement.py
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Original file line number Diff line number Diff line change
Expand Up @@ -26,11 +26,11 @@ def _get_potential_guarded_do_while_loops(ast: AbstractSyntaxTree) -> tuple(Unio


def remove_guarded_do_while(ast: AbstractSyntaxTree):
""" Removes a if statement which guards a do-while loop/while loop when:
-> there is nothing in between the if-node and the do-while-node/while-node
-> the if-node has only one branch (true branch)
-> the condition of the branch is the same as the condition of the do-while-node
Replacement is a WhileLoop, otherwise the control flow would not be correct
"""Removes a if statement which guards a do-while loop/while loop when:
-> there is nothing in between the if-node and the do-while-node/while-node
-> the if-node has only one branch (true branch)
-> the condition of the branch is the same as the condition of the do-while-node
Replacement is a WhileLoop, otherwise the control flow would not be correct
"""
for do_while_node, condition_node in _get_potential_guarded_do_while_loops(ast):
if condition_node.false_branch:
Expand All @@ -43,40 +43,51 @@ def remove_guarded_do_while(ast: AbstractSyntaxTree):

class WhileLoopReplacer:
"""Convert WhileLoopNodes to ForLoopNodes depending on the configuration.
-> keep_empty_for_loops will keep empty for-loops in the code
-> force_for_loops will transform every while-loop into a for-loop, worst case with empty declaration/modification statement
-> forbidden_condition_types_in_simple_for_loops will not transform trivial for-loop candidates (with only one condition) into for-loops
if the operator matches one of the forbidden operator list
-> max_condition_complexity_for_loop_recovery will transform for-loop candidates only into for-loops if the condition complexity is
less/equal then the threshold
-> max_modification_complexity_for_loop_recovery will transform for-loop candidates only into for-loops if the modification complexity is
less/equal then the threshold
-> keep_empty_for_loops will keep empty for-loops in the code
-> force_for_loops will transform every while-loop into a for-loop, worst case with empty declaration/modification statement
-> forbidden_condition_types_in_simple_for_loops will not transform trivial for-loop candidates (with only one condition) into for-loops
if the operator matches one of the forbidden operator list
-> max_condition_complexity_for_loop_recovery will transform for-loop candidates only into for-loops if the condition complexity is
less/equal then the threshold
-> max_modification_complexity_for_loop_recovery will transform for-loop candidates only into for-loops if the modification complexity is
less/equal then the threshold
"""

def __init__(self, ast: AbstractSyntaxTree, options: Options):
self._ast = ast
self._restructure_for_loops = options.getboolean("readability-based-refinement.restructure_for_loops", fallback=True)
self._keep_empty_for_loops = options.getboolean("readability-based-refinement.keep_empty_for_loops", fallback=False)
self._hide_non_init_decl = options.getboolean("readability-based-refinement.hide_non_initializing_declaration", fallback=False)
self._force_for_loops = options.getboolean("readability-based-refinement.force_for_loops", fallback=False)
self._forbidden_condition_types = options.getlist("readability-based-refinement.forbidden_condition_types_in_simple_for_loops", fallback=[])
self._condition_max_complexity = options.getint("readability-based-refinement.max_condition_complexity_for_loop_recovery", fallback=100)
self._modification_max_complexity = options.getint("readability-based-refinement.max_modification_complexity_for_loop_recovery", fallback=100)
self._forbidden_condition_types = options.getlist(
"readability-based-refinement.forbidden_condition_types_in_simple_for_loops", fallback=[]
)
self._condition_max_complexity = options.getint(
"readability-based-refinement.max_condition_complexity_for_loop_recovery", fallback=100
)
self._modification_max_complexity = options.getint(
"readability-based-refinement.max_modification_complexity_for_loop_recovery", fallback=100
)

def run(self):
"""For each WhileLoop in AST check the following conditions:
-> any variable in loop condition has a valid continuation instruction in loop body
-> variable is initialized
-> loop condition complexity < condition complexity
-> loop condition complexity < condition complexity
-> possible modification complexity < modification complexity
-> if condition is only a symbol: check condition type for allowed one

If 'force_for_loops' is enabled, the complexity options are ignored and every while loop after the
initial transformation will be forced into a for loop with an empty declaration/modification
"""

If 'force_for_loops' is enabled, the complexity options are ignored and every while loop after the
initial transformation will be forced into a for loop with an empty declaration/modification
"""
if not self._restructure_for_loops:
return
for loop_node in list(self._ast.get_while_loop_nodes_topological_order()):
if loop_node.is_endless_loop or (not self._keep_empty_for_loops and _is_single_instruction_loop_node(loop_node)) \
or self._invalid_simple_for_loop_condition_type(loop_node.condition):
if (
loop_node.is_endless_loop
or (not self._keep_empty_for_loops and _is_single_instruction_loop_node(loop_node))
or self._invalid_simple_for_loop_condition_type(loop_node.condition)
):
continue

if any(node.does_end_with_continue for node in loop_node.body.get_descendant_code_nodes_interrupting_ancestor_loop()):
Expand All @@ -100,11 +111,11 @@ def run(self):
self._ast.substitute_loop_node(
loop_node,
ForLoopNode(
declaration=None,
condition=loop_node.condition,
modification=None,
reaching_condition=loop_node.reaching_condition,
)
declaration=None,
condition=loop_node.condition,
modification=None,
reaching_condition=loop_node.reaching_condition,
),
)

def _replace_with_for_loop(self, loop_node: WhileLoopNode, continuation: AstInstruction, init: AstInstruction):
Expand Down Expand Up @@ -139,9 +150,9 @@ def _replace_with_for_loop(self, loop_node: WhileLoopNode, continuation: AstInst
)
continuation.node.instructions.remove(continuation.instruction)
self._ast.clean_up()

def _invalid_simple_for_loop_condition_type(self, logic_condition) -> bool:
""" Checks if a logic condition is only a symbol, if true checks condition type of symbol for forbidden ones"""
"""Checks if a logic condition is only a symbol, if true checks condition type of symbol for forbidden ones"""
if not logic_condition.is_symbol or not self._forbidden_condition_types:
return False

Expand Down
10 changes: 10 additions & 0 deletions decompiler/util/default.json
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Original file line number Diff line number Diff line change
Expand Up @@ -275,6 +275,16 @@
"is_hidden_from_cli": false,
"argument_name": "--return-complexity-threshold"
},
{
"dest": "readability-based-refinement.restructure_for_loops",
"default": true,
"type": "boolean",
"title": "Enable for-loop recovery",
"description": "If enabled, certain while-loops will be transformed to for-loops. If set to false, no for-loops will be emitted at all.",,
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"is_hidden_from_gui": false,
"is_hidden_from_cli": false,
"argument_name": "--restructure-for-loops"
},
{
"dest": "readability-based-refinement.keep_empty_for_loops",
"default": false,
Expand Down
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