Refactor (structure): add vm_stats module; move BoxCall debug logger into vm_boxcall; add quick-reference/code-map.md for AI-friendly repo navigation. Keep behavior unchanged.

docs/quick-reference/code-map.md

@@ -0,0 +1,25 @@
+# Code Map (Backend VM) — Quick Guide
+
+Purpose: Make it obvious where to look without reading everything.
+
+## Backend Modules (VM)
+- `src/backend/vm.rs`: Core VM struct, execute loop, storage, control-flow.
+- `src/backend/vm_instructions.rs`: Instruction handlers called from `execute_instruction`.
+- `src/backend/vm_values.rs`: Value-level ops (binary/unary/compare), boolean coercions.
+- `src/backend/vm_boxcall.rs`: Box method dispatch (`call_box_method_impl`), BoxCall debug logger。
+- `src/backend/vm_phi.rs`: Loop/phi utilities (LoopExecutor)。
+- `src/backend/vm_stats.rs`: Stats/diagnostics printing（JSON/Text, envで制御）。
+
+## MIR Pipeline (where to check next)
+- `src/mir/printer.rs`: `--mir-verbose(--effects)`の出力。
+- `src/mir/verification.rs`: SSA/支配/CFG/merge-phi + WeakRef/Barrier 最小検証＋Strict Barrier診断。
+- `src/mir/optimizer.rs`: DCE/CSE/順序調整 + 未lowering検知（is/as 系）。
+
+## Useful env flags
+- `NYASH_VM_DEBUG_BOXCALL=1`: BoxCallの受け手/引数/結果型をstderrに出力。
+- `NYASH_VM_STATS=1` (`NYASH_VM_STATS_JSON=1`): 実行統計を表示（JSON可）。
+- `NYASH_VERIFY_BARRIER_STRICT=1`: Barrierの軽い文脈診断を有効化。
+- `NYASH_OPT_DIAG_FAIL=1`: Optimizerの未lowering検知でエラー終了（CI向け）。
+
+Last updated: 2025-08-25
+