Phase 11.7 – JIT Complete Plan (Cranelift)

Goal

Ship a complete JIT backend (Cranelift) for MIR Core‑15 with Semantics layer as the single source of truth, GC sync/async support, and full Box/Extern integration. Keep DX simple and cross‑platform.

Milestones

Add backend module: src/backend/cranelift/{mod.rs,context.rs,lower.rs,jit.rs,object.rs}
Context: host ISA, FunctionBuilder, Module (JIT/Object) setup helpers
Runner: --backend cranelift execution path; feature flag reuse (cranelift-jit)
Minimal ops: Const i64/f64/bool/null/string → CLIF values; Return; straight‑line add/sub
Smoke: apps/tests/ny-echo-lite returns 0 via JIT

Control: Jump/Branch/Phi, Load/Store (alloca on entry; i1↔i64 widen/narrow)
Unary/Binary/Compare: int/float/ptr eq/ne; logical and/or via to_bool
TypeOp (when needed) + pointer/int casts (handle→i64/i8* via ABI helpers)
Strings: concat via NyRT shims (nyash.string.concat_*)
BoxCall (by‑id): fixed/tagged args (<=4) + vector path; handle‑first returns (i64/ptr)
ExternCall: env.console.*, env.debug.trace, console.readLine via NyRT shims
Smokes: array/map/vinvoke(size/ret), echo; compare outputs with VM

Sync barriers: insert read/write barriers at Load/Store & NewBox as per VM semantics
Async safepoints: at call sites/loop backedges; NyRT entry glue to yield if required
Tests: targeted barrier smoke (array/map mutations) + perf sanity (no excessive barriers)

UnsupportedLegacyInstruction: maintain strict mode; allow env override for debug
Error reporting: source op pretty‑print, MIR value ids in error messages
Logging: NYASH_CLI_VERBOSE=1 shows JIT compile stages + object sizes (optional)
Doc/Doctor script: tools/doctor.ps1/.sh for quick env checks (optional nice‑to‑have)

cranelift-object emit: .o for main; link with NyRT → exe (tools/build_cl.*)
Windows: clang/lld link; Linux: cc link; parity with LLVM’s scripts

Instruction Coverage (MIR Core‑15)

ABI & Shims

Handle‑first: receiver/values normalized to i64; ptr/int casts via helpers
NyRT shims used: nyash.console.*, nyash.debug.trace, nyash.console.readline, nyash_string_new, nyash.string.concat_*, nyash_array_*_h, nyash.instance.*_h, plugin invoke (by‑id tagged, vector variants)

Semantics Integration (new in 11.7)

Add Semantics trait as unified MIR semantics API.
Provide SemanticsVM (exec) and SemanticsClif (lower) so the same MIR walks yield identical behavior across VM and JIT.
Use semantics::MirInterpreter for parity tests; prefer zero‑cost abstractions with static dispatch.

Status Notes (2025‑09‑01)

LLVM AOT: closed for now due to Windows dependency weight; Cranelift is the mainline.
VM: safepoint/barrier/scheduler wired and observable (CountingGc).
JIT: nyash.rt.checkpoint/nyash.gc.barrier_write symbols are available via NyRT; LowerCore needs to emit safepoints and barriers; Await lowering pending.

Deliverables

Risks & Mitigations

Pointer/int mismatch → normalize via i64/ptr helpers in one place; add asserts
Barrier placement overhead → start with conservative placement; measure; trim if safe
Windows toolchain variance → Cranelift avoids external LLVM; keep MSVC only

Timeline (indicative)