Bytecode compatibility - Exception-Handling Bytecode Stack Sequence Mismatch #19

Summary

Background:
compare_bytecode.report shows high-frequency mismatches in exception control flow,
especially around COPY/POP_EXCEPT/RERAISE/RETURN_VALUE transitions. This indicates
instability in CPython 3.14-compatible exception-frame sequencing.

Task:

• Align RustPython bytecode emission for exception-sensitive paths (try/except/finally,
  with, raise/re-raise).
• Verify sequencing for instruction pairs:
  • COPY -> POP_EXCEPT
  • POP_EXCEPT -> RERAISE
  • RETURN_VALUE / RERAISE / COPY interaction in exception epilogues.
• Compare outputs against CPython at parser/codegen level and adjust stack effect
  handling if needed.

Acceptance criteria:

• Top bytecode diff pair counts for exception-related instructions drop significantly.
• test_traceback, traceback, inspect, pydoc no longer show broad control-flow
  mismatch in repeated patterns.
• No new CPython/RustPython crashes in basic exception-heavy test cases.

Details