Propagate native-root decisions to codegen-unit workers

[proggeramlug]

Summary

• carry the producer-selected native-root backend explicitly into text and native codegen-unit workers
• use one explicit value for RS4GC rewriting, assembly/compact-map planning, and finishing
• make the split precise-root witness non-vacuous and add a shadow-stack negative worker arm

Local proof

Exact main base f9475fb, LLVM 22.1.4:

• before: PERRY_CODEGEN_UNIT_JOBS=1 focused split native-root test fails; native object has no map while text has one
• after: focused native_emit tests 4/4 pass with one codegen job
• after: in-process RS4GC tests 2/2 pass; compile-plan tests 5/5 pass; focused perry-codegen cargo check passes
• cargo fmt --all --check and git diff --check pass

No broad workspace test was used.

Closes #8070.
Refs #7966.

Summary by CodeRabbit

• Bug Fixes
  • Fixed native root handling during split compilation so all workers consistently use the selected root backend.
  • Improved statepoint rewriting and compact GC-map generation for native-root builds.
  • Ensured native and shadow-stack compilation modes remain consistent across direct, split, and differential builds.
• Tests
  • Expanded coverage for root-backend propagation, GC-map output, concurrent compilation, and native emission scenarios.

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Configuration used: defaults

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Run ID: 7ad3c528-fb77-4a8a-9de5-72597ad5ef97

📥 Commits

Reviewing files that changed from the base of the PR and between f9475fb and 11b61e5.

📒 Files selected for processing (7)

• changelog.d/8071-split-native-root-workers.md
• crates/perry-codegen/src/inprocess.rs
• crates/perry-codegen/src/linker.rs
• crates/perry-codegen/src/linker_temp_lifecycle_tests.rs
• crates/perry-codegen/src/linker_tests.rs
• crates/perry-codegen/src/native_emit.rs
• crates/perry-codegen/src/native_root_coverage/mod.rs

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📝 Walkthrough

Walkthrough

The codegen pipeline now captures the producer-selected native-roots backend and passes it through compile planning, LLVM emission, split workers, and fallback paths. Tests validate statepoint rewriting, compact GC-map output, shadow-stack behavior, and updated APIs.

Changes

Native-roots codegen propagation

Layer / File(s)	Summary
Explicit compilation selection crates/perry-codegen/src/inprocess.rs, crates/perry-codegen/src/linker.rs	Compilation and emission APIs now accept explicit native_roots and compact_gc_map values. Statepoint rewriting uses the propagated root mode.
Worker root-mode propagation crates/perry-codegen/src/linker.rs, crates/perry-codegen/src/native_emit.rs	The producer thread captures the native-roots decision and passes it through sequential, parallel, direct-native, and differential codegen paths.
Root-mode regression coverage crates/perry-codegen/src/native_emit.rs, crates/perry-codegen/src/linker_temp_lifecycle_tests.rs, crates/perry-codegen/src/linker_tests.rs, crates/perry-codegen/src/native_root_coverage/mod.rs, changelog.d/8071-split-native-root-workers.md	Tests cover compact GC-map detection, native and shadow-stack output, byte equality, lifecycle calls, compile-plan calls, and native assembly emission. The changelog records the fix.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 11b61

The change explicitly propagates native-root decisions to codegen-unit workers and is supported by passing focused validation; no actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant Producer
  participant compile_units_to_object
  participant Worker
  participant optimize_and_emit_module
  Producer->>compile_units_to_object: select native_roots
  compile_units_to_object->>Worker: pass native_roots
  Worker->>optimize_and_emit_module: pass native_roots
  optimize_and_emit_module->>Worker: rewrite statepoints and emit GC map

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Possibly related issues

• PerryTS/perry issue 8065: Both changes modify the LLVM RS4GC pipeline, including statepoint processing.

Possibly related PRs

• PerryTS/perry#8062: Both modify native LLVM codegen and split-worker paths for precise roots.
• PerryTS/perry#7370: Both address explicit propagation of the native-roots decision through LLVM compilation.
• PerryTS/perry#7653: Both modify native-root coverage and compact GC-map emission.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes satisfy issue #8070 by propagating native-root decisions, validating GC-map output, preserving a negative case, and testing with LLVM 22.1.4.
Out of Scope Changes check	✅ Passed	The code, tests, and changelog entry directly support the linked issue objectives, with no unrelated changes identified.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Title check	✅ Passed	The title clearly and concisely describes the main change: propagating native-root decisions to codegen-unit workers.
Description check	✅ Passed	The description explains the change, related issues, and focused validation, but omits several template headings and checklist details.

✨ 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 fix/8070-split-native-roots

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[proggeramlug]

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[proggeramlug]

Independent exact-head audit: APPROVE 11b61e5. The producer-selected native-root decision is carried coherently through text and native unit workers, RS4GC, compile planning, compact-map finishing, and non-split paths. The positive split arm requires a real platform map section plus PGCM payload on both objects before byte equality; the shadow negative proves the producer emits shadow binds and no addrspace(1) root, then requires both text and worker-native artifacts to have no map/payload and to match exactly. Local focused evidence is 4/4 native_emit tests, 2/2 in-process RS4GC tests, 5/5 compile-plan tests, cargo check, fmt, and diff check. CI was not used as correctness evidence. Changelog/closure scope are correct, no version bump, and CodeRabbit completed with zero review threads.