Design Notes – Phase 11.7 JIT Complete (Meeting Summary)

Date: 2025-09-01

Key Decisions

Single Semantics Source: Introduce a MIR semantics layer (trait) as the single source of truth. All backends (VM/Cranelift/LLVM/WASM) implement this interface.
No Runtime Fallback: Remove VM→JIT fallback complexity. VM becomes the reference executor; codegen backends handle execution/AOT. JIT is compile-only/AOT‑assist when needed.
Handle‑First ABI: Unify handle/i64/ptr conversions, tag classification, concat/extern/boxcall via shared helpers; call into NyRT shims from backends.
GC Hooks: Insert sync barriers and async safepoints as MIR‑level hooks that each backend lowers appropriately.
Backends Roadmap: LLVM AOT は一旦アーカイブ。Cranelift を主線（JIT/軽量AOT）とし、WASM は同一セマンティクスで後段。Windows DX を軽く保つ。

Architecture Sketch

MIR → Semantics
- VmSem: executes values (reference)
- ClifSem: builds Cranelift IR (JIT/AOT)
- LlvmSem: builds LLVM IR (AOT)
- WasmSem: builds Wasm (future)
Shared ABI utilities: handle↔i64/ptr, to_bool, compare, tags, invoke variants, NyRT shims.

Implementation Plan (Progressive)

Phase 1: Skeleton + minimal lowering (Const/Return/Add) → echo-lite returns 0 via Cranelift JIT skeleton.
Phase 2: Control (Jump/Branch/Phi), Load/Store, Compare, String concat via NyRT, Box/Extern by-id (fixed/vector).
Phase 3: GC barriers/safepoints; parity with VM（CountingGc での観測を含む）。
Phase 4: Stability, logs, strict/legacy guards; optional AOT via cranelift-object + link scripts.

Notes from Review

Using Semantics trait enables zero‑cost abstractions with static dispatch.
Add optional debug hooks (location/value) and optimization hints (likely_branch, pure_function_hint) later.
Testing: MockSemantics for unit tests; parity tests VM vs CLIF.

Action Items

Land Semantics trait + minimal MirInterpreter (skeleton added).
Implement ClifSem minimal lowering; wire Runner --backend cranelift.
Centralize ABI helpers; migrate existing scattered logic to shared module.
Emit nyash.rt.checkpoint and nyash.gc.barrier_write from LowerCore at appropriate sites; wire Await (PoC: blocking get).
Add build_cl scripts for AOT when ready.

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