Outline cold opcode handlers from the VM dispatch loop

[samuelcolvin]

Mark ten cold handler methods (unpack_ex, dict_merge, with-statement ops, exception match/unwind, kw method calls, import attr loads) #[inline(never)] so their bodies stay out of VM::run.

This frees enough registers for the hot loop to keep the cached code pointer live instead of reloading it from a spill slot on every opcode.

Claude-Session: https://claude.ai/code/session_01HbZqFxoKRfCeBgU239PMij

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Summary by cubic

Outlined ten cold opcode handlers with #[inline(never)] to move them out of VM::run’s dispatch loop. This lowers register/I-cache pressure, keeps the cached code pointer in a register, shrinks VM::run ~4%, and delivers ~1% geomean speedups with 0.7–3.6% wins on interpreter-heavy benches and ~1% regressions on a few (json_dumps, end_to_end, func_call_kwargs).

• Refactors
  • Handlers outlined: load_attr_import, exec_call_attr_kw; dict_merge, method_dict_merge, unpack_ex; exec_before_with, exec_with_exit, exec_with_except_start, handle_exception_with_value, check_exc_match.

^{Written for commit db30bd3. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files

_{Re-trigger cubic}

[github-actions]

Codecov Results 📊

✅ Patch coverage is 100.00%. Project has 42151 uncovered lines.
✅ Project coverage is 56.7%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    56.70%    56.70%        —%
==========================================
  Files          407       407         —
  Lines        97342     97342         —
  Branches    207204    207204         —
==========================================
+ Hits         55191     55191         —
- Misses       42151     42151         —
- Partials      3969      3969         —

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Generated by Codecov Action

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[macroscopeapp]

Approvability

Verdict: Approved e228128

This PR adds #[inline(never)] attributes to cold VM opcode handlers for I-cache optimization. The changes are purely mechanical compiler hints with no behavioral impact - only inlining decisions are affected. No logic, runtime behavior, or APIs are modified.

No code changes detected at db30bd3. Prior analysis still applies.

^{You can customize Macroscope's approvability policy. Learn more.}

[codspeed-hq]

Merging this PR will not alter performance

✅ 34 untouched benchmarks
⏩ 16 skipped benchmarks¹

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_{Comparing assembly (db30bd3) with main (ca9cca0)}

Footnotes

1. 16 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩