[Code Generator] Simplify Expressions

decompiler/pipeline/controlflowanalysis/__init__.py

@@ -1,4 +1,4 @@
-from .expression_simplification import ExpressionSimplification
+from .expression_simplification.stages import ExpressionSimplificationAst, ExpressionSimplificationCfg
 from .instruction_length_handler import InstructionLengthHandler
 from .readability_based_refinement import ReadabilityBasedRefinement
 from .variable_name_generation import VariableNameGeneration

decompiler/pipeline/controlflowanalysis/expression_simplification/constant_folding.py

@@ -0,0 +1,145 @@
+import operator
+from functools import partial
+from typing import Callable, Optional
+
+from decompiler.structures.pseudo import Constant, Integer, OperationType
+
+
+def constant_fold(operation: OperationType, constants: list[Constant]) -> Constant:
+    """
+    Fold operation with constants as operands.
+
+    :param operation: The operation.
+    :param constants: All constant operands of the operation.
+    :return: A constant representing the result of the operation.
+    """
+
+    if operation not in _OPERATION_TO_FOLD_FUNCTION:
+        raise ValueError(f"Constant folding not implemented for operation '{operation}'.")
+
+    return _OPERATION_TO_FOLD_FUNCTION[operation](constants)
+
+
+def _constant_fold_arithmetic_binary(
+        constants: list[Constant],
+        fun: Callable[[int, int], int],
+        norm_sign: Optional[bool] = None
+) -> Constant:
+    """
+    Fold an arithmetic binary operation with constants as operands.
+
+    :param constants: A list of exactly 2 constant operands.
+    :param fun: The binary function to perform on the constants.
+    :param norm_sign: Optional boolean flag to indicate if/how to normalize the input constants to 'fun':
+        - None (default): no normalization
+        - True:  normalize inputs, interpreted as signed values
+        - False: normalize inputs, interpreted as unsigned values
+    :return: A constant representing the result of the operation.
+    """
+
+    if len(constants) != 2:
+        raise ValueError(f"Expected exactly 2 constants to fold, got {len(constants)}.")
+    if not all(constant.type == constants[0].type for constant in constants):
+        raise ValueError(f"Can not fold constants with different types: {(constant.type for constant in constants)}")
+    if not all(isinstance(constant.type, Integer) for constant in constants):
+        raise ValueError(f"All constants must be integers, got {list(constant.type for constant in constants)}.")
+
+    left, right = constants
+
+    left_value = left.value
+    right_value = right.value
+    if norm_sign is not None:
+        left_value = normalize_int(left_value, left.type.size, norm_sign)
+        right_value = normalize_int(right_value, right.type.size, norm_sign)
+
+    return Constant(
+        normalize_int(fun(left_value, right_value), left.type.size, left.type.signed),
+        left.type
+    )
+
+
+def _constant_fold_arithmetic_unary(constants: list[Constant], fun: Callable[[int], int]) -> Constant:
+    """
+    Fold an arithmetic unary operation with a constant operand.
+
+    :param constants: A list containing a single constant operand.
+    :param fun: The unary function to perform on the constant.
+    :return: A constant representing the result of the operation.
+    """
+
+    if len(constants) != 1:
+        raise ValueError("Expected exactly 1 constant to fold")
+    if not isinstance(constants[0].type, Integer):
+        raise ValueError(f"Constant must be of type integer: {constants[0].type}")
+
+    return Constant(normalize_int(fun(constants[0].value), constants[0].type.size, constants[0].type.signed), constants[0].type)
+
+
+def _constant_fold_shift(constants: list[Constant], fun: Callable[[int, int], int], signed: bool) -> Constant:
+    """
+    Fold a shift operation with constants as operands.
+
+    :param constants: A list of exactly 2 constant operands.
+    :param fun: The shift function to perform on the constants.
+    :param signed: Boolean flag indicating whether the shift is signed.
+    This is used to normalize the sign of the input constant to simulate unsigned shifts.
+    :return: A constant representing the result of the operation.
+    """
+
+    if len(constants) != 2:
+        raise ValueError("Expected exactly 2 constants to fold")
+    if not all(isinstance(constant.type, Integer) for constant in constants):
+        raise ValueError("All constants must be integers")
+
+    left, right = constants
+
+    shifted_value = fun(
+        normalize_int(left.value, left.type.size, left.type.signed and signed),
+        right.value
+    )
+    return Constant(
+        normalize_int(shifted_value, left.type.size, left.type.signed),
+        left.type
+    )
+
+
+def normalize_int(v: int, size: int, signed: bool) -> int:
+    """
+    Normalizes an integer value to a specific size and signedness.
+
+    This function takes an integer value 'v' and normalizes it to fit within
+    the specified 'size' in bits by discarding overflowing bits. If 'signed' is
+    true, the value is treated as a signed integer, i.e. interpreted as a two's complement.
+    Therefore the return value will be negative iff 'signed' is true and the most-significant bit is set.
+
+    :param v: The value to be normalized.
+    :param size: The desired bit size for the normalized integer.
+    :param signed: True if the integer should be treated as signed.
+    :return: The normalized integer value.
+    """
+    value = v & ((1 << size) - 1)
+    if signed and value & (1 << (size - 1)):
+        return value - (1 << size)
+    else:
+        return value
+
+
+_OPERATION_TO_FOLD_FUNCTION: dict[OperationType, Callable[[list[Constant]], Constant]] = {
+    OperationType.minus: partial(_constant_fold_arithmetic_binary, fun=operator.sub),
+    OperationType.plus: partial(_constant_fold_arithmetic_binary, fun=operator.add),
+    OperationType.multiply: partial(_constant_fold_arithmetic_binary, fun=operator.mul, norm_sign=True),
+    OperationType.multiply_us: partial(_constant_fold_arithmetic_binary, fun=operator.mul, norm_sign=False),
+    OperationType.divide: partial(_constant_fold_arithmetic_binary, fun=operator.floordiv, norm_sign=True),
+    OperationType.divide_us: partial(_constant_fold_arithmetic_binary, fun=operator.floordiv, norm_sign=False),
+    OperationType.negate: partial(_constant_fold_arithmetic_unary, fun=operator.neg),
+    OperationType.left_shift: partial(_constant_fold_shift, fun=operator.lshift, signed=True),
+    OperationType.right_shift: partial(_constant_fold_shift, fun=operator.rshift, signed=True),
+    OperationType.right_shift_us: partial(_constant_fold_shift, fun=operator.rshift, signed=False),
+    OperationType.bitwise_or: partial(_constant_fold_arithmetic_binary, fun=operator.or_),
+    OperationType.bitwise_and: partial(_constant_fold_arithmetic_binary, fun=operator.and_),
+    OperationType.bitwise_xor: partial(_constant_fold_arithmetic_binary, fun=operator.xor),
+    OperationType.bitwise_not: partial(_constant_fold_arithmetic_unary, fun=operator.inv),
+}
+
+
+FOLDABLE_OPERATIONS = _OPERATION_TO_FOLD_FUNCTION.keys()

decompiler/pipeline/controlflowanalysis/expression_simplification/rules/collapse_add_neg.py

@@ -0,0 +1,30 @@
+from decompiler.pipeline.controlflowanalysis.expression_simplification.rules.rule import SimplificationRule
+from decompiler.structures.pseudo import BinaryOperation, Expression, Operation, OperationType, UnaryOperation
+
+
+class CollapseAddNeg(SimplificationRule):
+    """
+    Simplifies additions/subtraction with negated expression.
+
+    - `e0 + -(e1) -> e0 - e1`
+    - `e0 - -(e1) -> e0 + e1`
+    """
+
+    def apply(self, operation: Operation) -> list[tuple[Expression, Expression]]:
+        if operation.operation not in [OperationType.plus, OperationType.minus]:
+            return []
+        if not isinstance(operation, BinaryOperation):
+            raise TypeError(f"Expected BinaryOperation, got {type(operation)}")
+
+        right = operation.right
+        if not isinstance(right, UnaryOperation) or right.operation != OperationType.negate:
+            return []
+
+        return [(
+            operation,
+            BinaryOperation(
+                OperationType.minus if operation.operation == OperationType.plus else OperationType.plus,
+                [operation.left, right.operand],
+                operation.type
+            )
+        )]

decompiler/pipeline/controlflowanalysis/expression_simplification/rules/collapse_constants.py

@@ -0,0 +1,20 @@
+from decompiler.pipeline.controlflowanalysis.expression_simplification.constant_folding import FOLDABLE_OPERATIONS, constant_fold
+from decompiler.pipeline.controlflowanalysis.expression_simplification.rules.rule import SimplificationRule
+from decompiler.structures.pseudo import Constant, Expression, Operation
+
+
+class CollapseConstants(SimplificationRule):
+    """
+    Fold operations with only constants as operands:
+    """
+
+    def apply(self, operation: Operation) -> list[tuple[Expression, Expression]]:
+        if not all(isinstance(o, Constant) for o in operation.operands):
+            return []
+        if operation.operation not in FOLDABLE_OPERATIONS:
+            return []
+
+        return [(
+            operation,
+            constant_fold(operation.operation, operation.operands)
+        )]