"""
Transforms are simple Instruction modifiers that can be called on each
Instruction by the :func:`~jawa.attributes.code.CodeAttribute.disassemble`
function.
"""
from jawa.util.bytecode import Instruction, Operand, OperandTypes, opcode_table
[docs]def expand_constants(ins: Instruction, *, cf) -> Instruction:
"""Replace CONSTANT_INDEX operands with the literal Constant object from
the constant pool.
:param ins: Instruction to potentially modify.
:param cf: The ClassFile instance used to resolve Constants.
:return: Potentially modified instruction.
"""
for i, operand in enumerate(ins.operands):
if not isinstance(operand, Operand):
continue
if operand.op_type == OperandTypes.CONSTANT_INDEX:
ins.operands[i] = cf.constants[operand.value]
return ins
[docs]def simple_swap(ins: Instruction) -> Instruction:
"""Replaces one instruction with another based on the transform rules in
the bytecode definitions. This can help simplify your code as it reduces
the overall number of instructions. For example, `aload_0` will become
`aload 0`.
:param ins: Instruction to potentially modify.
:return: Potentially modified instruction.
"""
try:
rule = ins.details['transform']['simple_swap']
except KeyError:
return ins
replacement_ins = opcode_table[rule['op']]
return Instruction(
replacement_ins['mnemonic'],
replacement_ins['op'],
[Operand(
replacement_ins['operands'][i][1],
r
) for i, r in enumerate(rule['operands'])],
ins.pos
)