perf(gc): use canonical layout bit in runtime class-field guards

[proggeramlug]

Summary

• use the canonical typed-layout header bit for raw-f64 class-field get/set guards after the exact class, keys, and slot bounds are proven
• retain the independent descriptor-map lookup under PERRY_VERIFY_TYPED_INTACT
• add regression counters proving normal get/set guard paths perform zero descriptor queries

Refs #5094.

Performance

With PERRY_DISABLE_CLASS_FIELD_INLINE=1 to force every access through the runtime guard, 09_method_calls improved from a 649 ms median to 425 ms across 10 interleaved runs on a busy arm64 macOS host (1.53x, 34% faster). Output was identical. Normal inline mode is unchanged.

Validation

• 2,314 release perry-runtime tests passed; 4 ignored
• class-field raw-f64 downgrade matched Node with the runtime guard forced
• forced evacuation stress: 6 copying minors, 15,771 moved objects, output matched Node
• full mark-sweep output matched Node
• PERRY_VERIFY_TYPED_INTACT output matched Node
• cargo fmt check, diff check, and file-size check passed

No version bump.

Summary by CodeRabbit

• Performance
  • Reduced overhead for class-field access by avoiding repeated metadata lookups during normal operation.
• Reliability
  • Strengthened runtime validation for numeric class-field layouts, including safer handling of invalid or downgraded values.
  • Preserved additional verification checks in diagnostic configurations.
• Documentation
  • Added a changelog entry describing the improved runtime safeguards and streamlined class-field access behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: bbbb68bb-34de-42ea-b8f0-6fe6b9501eaf

📥 Commits

Reviewing files that changed from the base of the PR and between 601a02d and b18d497.

📒 Files selected for processing (4)

• changelog.d/8076-class-field-runtime-layout-guard.md
• crates/perry-runtime/src/gc/layout.rs
• crates/perry-runtime/src/typed_feedback/guards.rs
• crates/perry-runtime/src/typed_feedback/tests.rs

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📝 Walkthrough

Walkthrough

The runtime now validates raw-f64 class-field layouts through canonical typed-layout metadata. Normal guards use the per-object typed-intact bit, while verification mode checks the side table. Tests measure descriptor-query activity.

Changes

Raw-f64 class-field layout guards

Layer / File(s)	Summary
Shared layout contract integration crates/perry-runtime/src/typed_feedback/guards.rs	Class-field get, fast-get, and set guards use a shared raw-f64 layout contract. Normal execution uses the typed-intact bit. Verification mode checks the side-table slot and preserves the mismatch abort.
Descriptor-query observability and validation crates/perry-runtime/src/gc/layout.rs, crates/perry-runtime/src/typed_feedback/tests.rs, changelog.d/8076-class-field-runtime-layout-guard.md	Test-only counters track typed raw-f64 descriptor queries. Tests verify zero queries for successful, downgraded, and rejected guard cases. The changelog records the runtime guard changes.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to b18d4

The PR optimizes runtime class-field guards while preserving behavior and adds regression coverage; no actionable merge-blocking risk remains beyond normal checks and review.

Possibly related issues

• PerryTS/perry issue 5094 — Removes per-access TLS descriptor lookups from the typed raw-f64 class-field guard path.

Possibly related PRs

• PerryTS/perry#7423 — Adds sloppy-mode code generation for the related raw-f64 class-field inline store and guard path.
• PerryTS/perry#7686 — Modifies typed class-field layout and slot handling in a related runtime path.
• PerryTS/perry#7698 — Modifies typed class-field layout validation in related runtime and code-generation paths.

Suggested reviewers: thehypnoo

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main runtime optimization for class-field guards.
Description check	✅ Passed	The description covers the change, related issue, performance impact, validation results, and version policy, despite using different section headings.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch perf/5094-canonical-layout-next

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