2025-08-28 09:26:58 +09:00
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JIT Phase 10_7 — Known Issues and Future Refinements (2025-08-27)
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2025-12-04 14:19:48 +09:00
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Status: Legacy snapshot（フェーズ固有の既知問題メモ）
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2025-08-28 09:26:58 +09:00
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Scope: LowerCore(Core-1), Branch/PHI wiring, ABI(min), Stats/CFG dump
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1) b1 PHI tagging heuristics
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- Symptom: (b1) tag may not appear for some PHI nodes when inputs are routed via variables (Load/Store) or multi-step copies.
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- Current mitigation:
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- Pre-scan: mark Compare/Const Bool as boolean producers.
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- Propagate through Copy; close over PHI if all inputs are boolean-like.
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- CFG dump heuristic: mark (b1) if pre-analysis true OR all inputs look boolean OR the PHI output is used as branch condition.
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- Residual risk: Complex IR (loads/stores, deep copies, optimizer rewrites) can hide provenance; tag may still be missed.
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- Future: Track boolean type via MIR type system or a dedicated lattice in analysis pass; extend provenance across Load/Store when safe.
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2) f64 arithmetic/compare on VM backend
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- Symptom: VM path errors on f64 BinOp/Compare (e.g., Add/>, mixed types).
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- Cause: VM does not yet implement floating-point arithmetic/compare ops.
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- Current mitigation: Examples using f64 are marked for Cranelift-enabled JIT environments; VM returns type errors as expected.
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- Future: Implement f64 BinOp/Compare in VM or add auto-promotion layer consistent with JIT behavior.
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3) JIT execution stub semantics
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- Symptom: Previously, enabling NYASH_JIT_EXEC could alter results via stub returns when Cranelift was not enabled.
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- Fix: Stub disabled; compilation skipped without Cranelift, full VM fallback retains semantics.
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- Future: None (resolved). Keep behavior documented.
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4) ret_bool_hint_count visibility
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- Symptom: Counter can remain 0 when MIR signatures don’t mark Bool return even if code returns boolean values via VM-level boxes.
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- Cause: Counter increments on MIR signature Bool return detection; not on dynamic boolean returns.
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- Future: Consider counting dynamic sites or adding per-function attributes post-inference.
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5) PHI dump dependency on phi_min
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- Symptom: Detailed PHI dump (with (b1) tags) only shows when NYASH_JIT_PHI_MIN=1.
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- Current stance: Intended; PHI path is opt-in while stabilizing.
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- Future: Always-on summary rows possible; keep detail behind flag to reduce noise.
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6) Stats scope and sources
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- Symptom: JitStatsBox and unified stats currently reflect process-local counters; function-level detail via top5 only.
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- Future: Add per-function structured stats via Box API; expose compilation state/timings when available.
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7) Toolchain capability gating (b1 ABI)
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- Symptom: Native boolean (b1) return in signatures remains disabled (cap false).
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- Current stance: Switch point centralized; flips on when toolchain supports b1 in signatures.
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- Future: Periodically probe toolchain; add CI check to toggle automatically.
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8) Warning noise (unexpected cfg: llvm)
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- Symptom: Warnings about unknown `llvm` feature in conditional cfg.
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- Cause: Feature not declared in Cargo.toml; code guards are placeholders.
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- Future: Add feature or silence warnings for non-supported builds.
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9) Documentation sync
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- Symptom: Some flags visible via CLI and boxes; ensure README/CURRENT_TASK stay aligned.
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- Future: Add short “JIT quick flags” section with examples in docs.
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