Peephole optimizer: optimize Python code objects. It is implemented with the
It is based on the peephole optimizer of CPython 3.6 which is written in C.
Content of the
- class PeepholeOptimizer¶
- optimize(code: types.CodeType) types.CodeType ¶
Optimize a Python code object.
Return a new optimized Python code object.
Note: This method will disassemble code to a ConcreteBytecode, then a Bytecode, then a ControlFlowGraph. Then the CFG is optimized. And then the optimized CFG is converted back to a Bytecode, ConcreteBytecode, and then code. Depending on what you are doing you may get better performance by calling
import dis from bytecode.peephole_opt import PeepholeOptimizer code = compile('print(5+5)', '<string>', 'exec') print("Non-optimized:") dis.dis(code) print() code = PeepholeOptimizer().optimize(code) print("Optimized:") dis.dis(code)
Output of Python 3.6 patched with the PEP 511 with
python -o noopt (to
disable the builtin peephole optimizer):
Non-optimized: 1 0 LOAD_NAME 0 (print) 3 LOAD_CONST 0 (5) 6 LOAD_CONST 0 (5) 9 BINARY_ADD 10 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 13 POP_TOP 14 LOAD_CONST 1 (None) 17 RETURN_VALUE Optimized: 1 0 LOAD_NAME 0 (print) 3 LOAD_CONST 0 (10) 6 CALL_FUNCTION 1 (1 positional, 0 keyword pair) 9 POP_TOP 10 LOAD_CONST 1 (None) 13 RETURN_VALUE
Optimizations implemented in the peephole optimizer:
unary operations: +a, -a, ~a
a + b, a - b, a * b, a / b, a // b, a % b, a ** b
a << b, a >> b, a & b, a | b, a ^ b
BUILD_TUPLE: convert to a constant
Replace BUILD_TUPLE <n> + UNPACK_SEQUENCE <n> and BUILD_LIST <n> + UNPACK_SEQUENCE <n> with ROT_TWO (2 arguments) or ROT_THREE+ROT_TWO (3 arguments). For BUILD_LIST, if inputs are LOAD_CONST, rewrite LOAD_CONST in the reverse order.
BUILD_LIST + COMPARE_OP(in/not in): convert list to tuple
BUILD_SET + COMPARE_OP(in/not in): convert set to frozenset
not(a is b)with
a is not b
not(a is not b)with
a is b
not(a in b)with
a not in b
not(a not in b)with
a in b
Remove NOP instructions
Dead code elimination
Remove unreachable code after a final operation (
Remove unreachable blocks (
Replace UNARY_NOT+POP_JUMP_IF_FALSE with POP_JUMP_IF_TRUE
Replace unconditional jumps to RETURN_VALUE with RETURN_VALUE
Replace jumps to unconditional jumps with jumps to the final target
Remove unconditional jumps to the following block
For tuples, constant folding is only run if the result has 20 items or less.
By design, only basic optimizations can be implemented. A peephole optimizer has a narrow view on the bytecode (a few instructions) and only a very limited knownledge of the code.
3 < 5 or
(1, 2, 3) are not optimized.