Summary
A large share of the remaining bytecode drift comes from control-flow graph normalization, jump threading, and
cleanup-tail layout differences. This affects multiple files, including Lib/test/test_buffer.py, Lib/test/ test_dis.py, Lib/test/test_math.py, Lib/test/test_tarfile.py, and Lib/dataclasses.py.
Evidence
Representative mismatches include:
POP_JUMP_IF_TRUE vs POP_JUMP_IF_FALSE polarity flipsFOR_ITER target driftJUMP_FORWARD vs duplicated inline tail blocks- CPython
NOP anchors vs RustPython LOAD_CONST None
- shared exit blocks being duplicated or threaded differently from CPython
Top affected tracked files include:
Lib/test/test_buffer.py: 5131 diffsLib/test/test_dis.py: 3194 diffsLib/test/test_math.py: 2368 diffsLib/test/test_tarfile.py: 2149 diffsLib/dataclasses.py: 1577 diffs
Expected direction
Late CFG passes should be aligned with CPython’s codegen.c and flowgraph.c behavior, especially for:
- conditional-chain normalization
- jump threading
- empty-block cleanup
- exit duplication
- synthetic
NOP / no-location anchor handling
Likely implementation areas
crates/codegen/src/ir.rscrates/codegen/src/compile.rs
Done when
Representative functions such as jumpy, dataclasses._asdict_inner, dataclasses._replace, tarfile
context-manager tests, and the larger test_buffer.py helpers converge to CPython bytecode structure instead
of only matching outcome.
Summary
A large share of the remaining bytecode drift comes from control-flow graph normalization, jump threading, and
cleanup-tail layout differences. This affects multiple files, including
Lib/test/test_buffer.py,Lib/test/ test_dis.py,Lib/test/test_math.py,Lib/test/test_tarfile.py, andLib/dataclasses.py.Evidence
Representative mismatches include:
POP_JUMP_IF_TRUEvsPOP_JUMP_IF_FALSEpolarity flipsFOR_ITERtarget driftJUMP_FORWARDvs duplicated inline tail blocksNOPanchors vs RustPythonLOAD_CONST NoneTop affected tracked files include:
Lib/test/test_buffer.py: 5131 diffsLib/test/test_dis.py: 3194 diffsLib/test/test_math.py: 2368 diffsLib/test/test_tarfile.py: 2149 diffsLib/dataclasses.py: 1577 diffsExpected direction
Late CFG passes should be aligned with CPython’s
codegen.candflowgraph.cbehavior, especially for:NOP/ no-location anchor handlingLikely implementation areas
crates/codegen/src/ir.rscrates/codegen/src/compile.rsDone when
Representative functions such as
jumpy,dataclasses._asdict_inner,dataclasses._replace, tarfilecontext-manager tests, and the larger
test_buffer.pyhelpers converge to CPython bytecode structure insteadof only matching outcome.