diff --git a/.github/workflows/vm-legacy-build.yml b/.github/workflows/vm-legacy-build.yml
new file mode 100644
index 00000000..b1a25e54
--- /dev/null
+++ b/.github/workflows/vm-legacy-build.yml
@@ -0,0 +1,29 @@
+name: vm-legacy-build
+
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - 'src/**'
+      - 'Cargo.toml'
+      - '.github/workflows/vm-legacy-build.yml'
+
+jobs:
+  build-vm-legacy:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache Rust build
+        uses: Swatinem/rust-cache@v2
+        with:
+          cache-targets: true
+
+      - name: Build with vm-legacy + interpreter-legacy (compile check only)
+        run: cargo build --release --features vm-legacy,interpreter-legacy
+
diff --git a/CURRENT_TASK.md b/CURRENT_TASK.md
index 65f0ee19..349cb8cf 100644
--- a/CURRENT_TASK.md
+++ b/CURRENT_TASK.md
@@ -14,29 +14,51 @@ What Changed (recent)
   - 新規サポート: Ternary/Peek の Lowering を実装し、`expr.rs` から `ternary.rs`/`peek.rs` へ委譲（MIR13 PHI‑off=Copy合流／PHI‑on=Phi 合流）。
   - Self‑host 生成器（Stage‑1 JSON v0）に Peek emit を追加: `apps/selfhost-compiler/boxes/parser_box.nyash`。
   - Selfhost/PyVM スモークを通して E2E 確認（peek/ternary）。
-- llvmlite stability for MIR13
-  - Resolver: forbids cross‑block non‑dominating vmap reuse; for multi‑pred and no declared PHI, synthesizes a localization PHI at block head.
-  - Finalize remains function‑local; `block_end_values` snapshots and placeholder wiring still in place.
+- llvmlite stability for MIR13（bring‑up進行中）
+  - Control‑flow 分離: `instructions/controlflow/{branch,jump,while_.py}` を導入し、`llvm_builder.py` の責務を縮小。
+  - プリパス導入（環境変数で有効化）: `NYASH_LLVM_PREPASS_LOOP=1`
+    - ループ検出（単純 while 形）→ 構造化 lower（LoopForm失敗時は regular while）
+    - CFG ユーティリティ: `cfg/utils.py`（preds/succs）
+  - 値解決ポリシー共通化: `utils/values.py`（prefer same‑block SSA → resolver）
+  - vmap の per‑block 化: `lower_block` 内で `vmap_cur` を用意し、ブロック末に `block_end_values` へスナップショット。cross‑block 汚染を抑制。
+  - Resolver 強化: end‑of‑block解決で他ブロックのPHIを安易に採用しない（自己参照/非支配回避）。
 - Parity runner pragmatics
   - `tools/pyvm_vs_llvmlite.sh` compares exit code by default; use `CMP_STRICT=1` for stdout+exit.
   - Stage‑2 smokes更新: `tools/selfhost_stage2_smoke.sh` に "Peek basic" を追加。
 
 Current Status
-- Self‑hosting Bridge → PyVM smokes: PASS (Stage‑2 reps: array/string/logic/if/loop).
-- Curated LLVM (PHI‑off default): PASS.
-- Curated LLVM (PHI‑on experimental): `apps/tests/loop_if_phi.nyash` shows a dominance issue (observed; not blocking, MIR13 recommended).
+- Self‑hosting Bridge → PyVM smokes: PASS（Stage‑2 代表: array/string/logic/if/loop/ternary/peek/dot-chain）
+- PyVM core fixes applied: compare(None,x) の安全化、Copy 命令サポート、最大ステップ上限（NYASH_PYVM_MAX_STEPS）
+- MIR13（PHI‑off）: if/ternary/loop の合流で Copy が正しく JSON に出るよう修正（emit_mir_json + builder no‑phi 合流）
+- Curated LLVM（PHI‑off 既定）: 継続（個別ケースの IR 生成不備は未着手）
+- LLVM ハーネス（llvmlite）:
+  - `loop_if_phi`: プリパスON＋構造化whileで EXE 退出コード 0（緑）。
+  - `ternary_nested`: vmap per‑block で安定度向上。残タスク: merge(ret) の PHI 配線をプリパス/resolve 側で確定・重複排除。
 
 Next (short plan)
+0) Refactor/Structure（継続）
+   - controlflow の切出し完了（branch/jump/while）。binop/compare/copy の前処理を `utils/values.resolve_i64_strict` に集約（完了）。
+   - vmap per‑block 化（完了）。builder の責務縮小と prepass/cfg/util への移譲（進行中）。
+   - if‑merge プリパス実装: ret‑merge の構造化/PHI確定（予定）。
 1) Legacy Interpreter/VM offboarding (phase‑A):
-   - Introduce `vm-legacy` feature (default OFF) to gate old VM execution層。
-   - 抽出: JIT が参照する最小型（例: `VMValue`）を薄い共通モジュールへ切替（`vm_types` 等）。
-   - `interpreter-legacy`/`vm-legacy` を既定ビルドから外し、ビルド警告を縮小。
+   - ✅ Introduced `vm-legacy` feature (default OFF) to gate old VM execution層。
+   - ✅ 抽出: JIT が参照する最小型（例: `VMValue`）を薄い共通モジュールへ切替（`vm_types`）。
+   - ✅ `interpreter-legacy`/`vm-legacy` を既定ビルドから外し、既定は PyVM 経路に（`--backend vm` は PyVM へフォールバック）。
+   - ✅ Runner: vm-legacy OFF のとき `vm`/`interpreter` は PyVM モードで実行。
+   - ✅ HostAPI: VM 依存の GC バリアは vm-legacy ON 時のみ有効。
+   - ✅ PyVM/Bridge Stage‑2 スモークを緑に再整備（短絡/三項/合流 反映）
 2) Legacy Interpreter/VM offboarding (phase‑B):
    - 物理移動: `src/archive/{interpreter_legacy,vm_legacy}/` へ移設（ドキュメント更新）。
-3) PHI‑on lane（任意）: `loop_if_phi` 支配関係を finalize/resolve の順序強化で観察（低優先）。
-4) Runner refactor（小PR）:
+3) LLVM/llvmlite 整備（優先中）:
+   - MIR13 の Copy 合流を LLVM IR に等価反映（pred‑localize or PHI 合成）: per‑block vmap 完了、resolver 強化済。
+   - 代表ケース:
+     - `apps/tests/loop_if_phi.nyash`: プリパスONで緑（退出コード一致）。
+     - `apps/tests/ternary_nested.nyash`: if‑merge プリパスでの構造化/PHI 確定を実装 → IR 検証通過・退出コード一致まで。
+   - `tools/pyvm_vs_llvmlite.sh` で PyVM と EXE の退出コード一致（必要に応じて CMP_STRICT=1）。
+4) PHI‑on lane（任意）: `loop_if_phi` 支配関係を finalize/resolve の順序強化で観察（低優先）。
+5) Runner refactor（小PR）:
    - `selfhost/{child.rs,json.rs}` 分離; `modes/common/{io,resolve,exec}.rs` 分割; `runner/mod.rs`の表面削減。
-5) Optimizer/Verifier thin‑hub cleanup（非機能）: orchestrator最小化とパス境界の明確化。
+6) Optimizer/Verifier thin‑hub cleanup（非機能）: orchestrator最小化とパス境界の明確化。
 
 How to Run
 - PyVM reference smokes: `tools/pyvm_stage2_smoke.sh`
@@ -44,6 +66,27 @@ How to Run
 - LLVM curated (PHI‑off default): `tools/smokes/curated_llvm.sh`
 - LLVM PHI‑on (experimental): `tools/smokes/curated_llvm.sh --phi-on`
 - Parity (AOT vs PyVM): `tools/pyvm_vs_llvmlite.sh <file.nyash>` (`CMP_STRICT=1` to enable stdout check)
+  - 開発時の補助: `NYASH_LLVM_PREPASS_LOOP=1` を併用（loop/if‑merge のプリパス有効化）。
+
+Operational Notes
+- 環境変数
+  - `NYASH_PYVM_MAX_STEPS`: PyVM の最大命令ステップ（既定 200000）。ループ暴走時に安全終了。
+  - `NYASH_VM_USE_PY=1`: `--backend vm` を PyVM ハーネスへ切替。
+  - `NYASH_PIPE_USE_PYVM=1`: `--ny-parser-pipe` / JSON v0 ブリッジも PyVM 実行に切替。
+  - `NYASH_CLI_VERBOSE=1`: ブリッジ/エミットの詳細出力。
+- スモークの実行例
+  - `timeout -s KILL 20s bash tools/pyvm_stage2_smoke.sh`
+  - `timeout -s KILL 30s bash tools/selfhost_stage2_bridge_smoke.sh`
+
+Backend selection (Phase‑A after vm‑legacy off)
+- Default: `vm-legacy` = OFF, `interpreter-legacy` = OFF
+- `--backend vm` → PyVM 実行（python3 と `tools/pyvm_runner.py` が必要）
+- `--backend interpreter` → legacy 警告の上で PyVM 実行
+- `--benchmark` → vm‑legacy が必要（`cargo build --features vm-legacy`）
+
+Enable legacy VM/Interpreter (opt‑in)
+- `cargo build --features vm-legacy,interpreter-legacy`
+- その後 `--backend vm`/`--backend interpreter` が有効
 
 Key Flags
 - `NYASH_MIR_NO_PHI` (default 1): PHI‑off when 1 (MIR13). Set `0` for PHI‑on.
diff --git a/Cargo.toml b/Cargo.toml
index 1251ce03..011ed45e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,8 +11,9 @@ categories = ["development-tools::parsing", "interpreters"]
 
 # Default features - minimal CLI only
 [features]
-default = ["cli", "plugins", "interpreter-legacy"]
+default = ["cli", "plugins"]
 interpreter-legacy = []
+vm-legacy = []
 e2e = []
 cli = []
 plugins-only = []
diff --git a/README.ja.md b/README.ja.md
index 4278864e..1a5aedc2 100644
--- a/README.ja.md
+++ b/README.ja.md
@@ -108,7 +108,15 @@ local py = new PyRuntimeBox()       // Pythonプラグイン
 
 ## 🏗️ **複数の実行モード**
 
-重要: 現在、JIT ランタイム実行はデバッグ容易性のため封印しています。実行は「インタープリター／VM」、配布は「Cranelift AOT(EXE)／LLVM AOT(EXE)」の4体制です。
+重要: 現在、JIT ランタイム実行は封印中です。実行は「PyVM（既定）／VM（任意でレガシー有効）」、配布は「Cranelift AOT(EXE)／LLVM AOT(EXE)」の4体制です。
+
+Phase‑15（自己ホスト期）: VM/インタープリタはフィーチャーで切替
+- 既定ビルド: `--backend vm` は PyVM 実行（python3 + `tools/pyvm_runner.py` が必要）
+- レガシー Rust VM/インタープリターを有効化するには:
+  ```bash
+  cargo build --release --features vm-legacy,interpreter-legacy
+  ```
+  以降、`--backend vm`/`--backend interpreter` が従来経路で動作します。
 
 ### 1. **インタープリターモード** （開発用）
 ```bash
@@ -118,13 +126,17 @@ local py = new PyRuntimeBox()       // Pythonプラグイン
 - 完全なデバッグ情報
 - 開発に最適
 
-### 2. **VMモード** （本番用）
+### 2. **VMモード（既定は PyVM／レガシーは任意）**
 ```bash
+# 既定: PyVM ハーネス（python3 必要）
+./target/release/nyash --backend vm program.nyash
+
+# レガシー Rust VM を使う場合
+cargo build --release --features vm-legacy
 ./target/release/nyash --backend vm program.nyash
 ```
-- インタープリターより13.5倍高速
-- 最適化されたバイトコード実行
-- 本番環境対応のパフォーマンス
+- 既定（vm-legacy OFF）: MIR(JSON) を出力して `tools/pyvm_runner.py` で実行
+- レガシー VM: インタープリター比で 13.5x（歴史的実測）。比較・検証用途で維持
 
 ### 3. **ネイティブバイナリ（Cranelift AOT）** （配布用）
 ```bash
diff --git a/README.md b/README.md
index 16bbe6e5..ccf9b39e 100644
--- a/README.md
+++ b/README.md
@@ -113,7 +113,15 @@ local py = new PyRuntimeBox()       // Python plugin
 
 ## 🏗️ **Multiple Execution Modes**
 
-Important: JIT runtime execution is sealed for now. Use Interpreter/VM for running, and Cranelift AOT/LLVM AOT for native executables.
+Important: JIT runtime execution is sealed for now. Use PyVM/VM for running, and Cranelift AOT/LLVM AOT for native executables.
+
+Phase‑15 (Self‑Hosting): Legacy VM/Interpreter are feature‑gated
+- Default build runs PyVM for `--backend vm` (python3 + `tools/pyvm_runner.py` required)
+- To enable legacy Rust VM/Interpreter, build with:
+  ```bash
+  cargo build --release --features vm-legacy,interpreter-legacy
+  ```
+  Then `--backend vm`/`--backend interpreter` use the legacy paths.
 
 ### 1. **Interpreter Mode** (Development)
 ```bash
@@ -123,13 +131,17 @@ Important: JIT runtime execution is sealed for now. Use Interpreter/VM for runni
 - Full debug information
 - Perfect for development
 
-### 2. **VM Mode** (Production) 
+### 2. **VM Mode (PyVM default / Legacy optional)**
 ```bash
+# Default: PyVM harness (requires python3)
+./target/release/nyash --backend vm program.nyash
+
+# Enable legacy Rust VM if needed
+cargo build --release --features vm-legacy
 ./target/release/nyash --backend vm program.nyash
 ```
-- 13.5x faster than interpreter
-- Optimized bytecode execution
-- Production-ready performance
+- Default (vm-legacy OFF): PyVM executes MIR(JSON) via `tools/pyvm_runner.py`
+- Legacy VM: 13.5x over interpreter (historical); kept for comparison and plugin tests
 
 ### 3. **Native Binary (Cranelift AOT)** (Distribution)
 ```bash
diff --git a/app_loop b/app_loop
new file mode 100644
index 00000000..5d1a5e88
Binary files /dev/null and b/app_loop differ
diff --git a/app_loop2 b/app_loop2
new file mode 100644
index 00000000..5d1a5e88
Binary files /dev/null and b/app_loop2 differ
diff --git a/app_loop_cf b/app_loop_cf
new file mode 100644
index 00000000..5d1a5e88
Binary files /dev/null and b/app_loop_cf differ
diff --git a/app_loop_vmap b/app_loop_vmap
new file mode 100644
index 00000000..5d1a5e88
Binary files /dev/null and b/app_loop_vmap differ
diff --git a/app_pyvm_cmp b/app_pyvm_cmp
index a0f21067..19c17192 100644
Binary files a/app_pyvm_cmp and b/app_pyvm_cmp differ
diff --git a/app_tern4 b/app_tern4
new file mode 100644
index 00000000..6af84438
Binary files /dev/null and b/app_tern4 differ
diff --git a/src/backend/dispatch.rs b/src/backend/dispatch.rs
index 3c40b25f..a224eaf6 100644
--- a/src/backend/dispatch.rs
+++ b/src/backend/dispatch.rs
@@ -295,3 +295,4 @@ impl DispatchTable {
 pub fn execute_entry(_entry: &DispatchEntry) -> Result<(), VMError> {
     Ok(())
 }
+#![cfg(feature = "vm-legacy")]
diff --git a/src/backend/mod.rs b/src/backend/mod.rs
index 0ec60ca2..ed3a2913 100644
--- a/src/backend/mod.rs
+++ b/src/backend/mod.rs
@@ -2,24 +2,48 @@
  * Backend module - Different execution backends for MIR
  */
 
-pub mod vm;
-pub mod vm_boxcall;
-pub mod vm_instructions;
-pub mod vm_phi;
-pub mod vm_stats;
+// VM core types are always available
 pub mod vm_types;
+
+// Legacy VM execution pipeline (feature-gated)
+#[cfg(feature = "vm-legacy")]
+pub mod vm;
+#[cfg(feature = "vm-legacy")]
+pub mod vm_boxcall;
+#[cfg(feature = "vm-legacy")]
+pub mod vm_instructions;
+#[cfg(feature = "vm-legacy")]
+pub mod vm_phi;
+#[cfg(feature = "vm-legacy")]
+pub mod vm_stats;
+#[cfg(feature = "vm-legacy")]
 pub mod vm_values;
+
+// When vm-legacy is disabled, provide a compatibility shim module so
+// crate::backend::vm::VMValue etc. keep resolving to vm_types::*.
+#[cfg(not(feature = "vm-legacy"))]
+pub mod vm {
+    pub use super::vm_types::{VMError, VMValue};
+}
 // Phase 9.78h: VM split scaffolding (control_flow/dispatch/frame)
 pub mod abi_util; // Shared ABI/utility helpers
+#[cfg(feature = "vm-legacy")]
 pub mod control_flow;
+#[cfg(feature = "vm-legacy")]
 pub mod dispatch;
+#[cfg(feature = "vm-legacy")]
 pub mod frame;
 pub mod gc_helpers;
 pub mod mir_interpreter;
+#[cfg(feature = "vm-legacy")]
 pub mod vm_control_flow;
+#[cfg(feature = "vm-legacy")]
 mod vm_exec; // A3: execution loop extracted
+#[cfg(feature = "vm-legacy")]
 mod vm_gc; // A3: GC roots & diagnostics extracted
+#[cfg(feature = "vm-legacy")]
 mod vm_methods; // A3-S1: method dispatch wrappers extracted
+#[cfg(feature = "vm-legacy")]
 mod vm_state; // A3: state & basic helpers extracted // Lightweight MIR interpreter
 
 #[cfg(feature = "wasm-backend")]
@@ -38,7 +62,10 @@ pub mod cranelift;
 pub mod llvm;
 
 pub use mir_interpreter::MirInterpreter;
-pub use vm::{VMError, VMValue, VM};
+// Always re-export VMError/VMValue from vm_types; VM (executor) only when enabled
+pub use vm_types::{VMError, VMValue};
+#[cfg(feature = "vm-legacy")]
+pub use vm::VM;
 
 #[cfg(feature = "wasm-backend")]
 pub use aot::{AotBackend, AotConfig, AotError, AotStats};
diff --git a/src/benchmarks.rs b/src/benchmarks.rs
index 28341d42..8ea95447 100644
--- a/src/benchmarks.rs
+++ b/src/benchmarks.rs
@@ -9,6 +9,7 @@
 
 #[cfg(feature = "wasm-backend")]
 use crate::backend::WasmBackend;
+#[cfg(feature = "vm-legacy")]
 use crate::backend::VM;
 use crate::interpreter::NyashInterpreter;
 use crate::mir::MirCompiler;
@@ -54,6 +55,7 @@ impl BenchmarkSuite {
                     results.push(interpreter_result);
                 }
 
+                #[cfg(feature = "vm-legacy")]
                 if let Ok(vm_result) = self.run_vm_benchmark(name, &source) {
                     results.push(vm_result);
                 }
@@ -104,6 +106,7 @@ impl BenchmarkSuite {
     }
 
     /// Run benchmark on VM backend
+    #[cfg(feature = "vm-legacy")]
     fn run_vm_benchmark(
         &self,
         name: &str,
diff --git a/src/box_factory/mod.rs b/src/box_factory/mod.rs
index 49d55a0b..ec7036f6 100644
--- a/src/box_factory/mod.rs
+++ b/src/box_factory/mod.rs
@@ -230,6 +230,7 @@ impl UnifiedBoxRegistry {
 pub mod builtin;
 pub mod plugin;
 /// Re-export submodules
+#[cfg(feature = "interpreter-legacy")]
 pub mod user_defined;
 
 #[cfg(test)]
diff --git a/src/boxes/mod.rs b/src/boxes/mod.rs
index c6688947..4ea1acff 100644
--- a/src/boxes/mod.rs
+++ b/src/boxes/mod.rs
@@ -155,6 +155,7 @@ pub mod stream;
 
 // P2P通信Box群 (NEW! - Completely rewritten)
 pub mod intent_box;
+#[cfg(feature = "interpreter-legacy")]
 pub mod p2p_box;
 
 // null関数も再エクスポート
@@ -176,4 +177,5 @@ pub use stream::{NyashStreamBox, StreamBox};
 
 // P2P通信Boxの再エクスポート
 pub use intent_box::IntentBox;
+#[cfg(feature = "interpreter-legacy")]
 pub use p2p_box::P2PBox;
diff --git a/src/llvm_py/README.md b/src/llvm_py/README.md
index 8de8f390..ea4b116b 100644
--- a/src/llvm_py/README.md
+++ b/src/llvm_py/README.md
@@ -13,12 +13,35 @@ ChatGPTが設計した`docs/design/LLVM_LAYER_OVERVIEW.md`の設計原則に従
 ## 📂 構造
 ```
 llvm_py/
-├── README.md          # このファイル
-├── mir_reader.py      # MIR JSON読み込み
-├── llvm_builder.py    # メインのLLVM IR生成
-├── resolver.py        # Resolver API（Python版）
-├── types.py          # 型変換ユーティリティ
-└── test_simple.py    # 基本テスト
+├── README.md                  # このファイル
+├── llvm_builder.py            # メインのLLVM IR生成（パスのオーケストレーション）
+├── mir_reader.py              # MIR(JSON) ローダ
+├── resolver.py                # 値解決（SSA/PHIの局所化とキャッシュ）
+├── utils/
+│   └── values.py              # 同一ブロック優先の解決などの共通ポリシー
+├── cfg/
+│   └── utils.py               # CFG ビルド（pred/succ）
+├── prepass/
+│   ├── loops.py               # ループ検出（while 形）
+│   └── if_merge.py            # if-merge（ret-merge）前処理（PHI前宣言プラン）
+├── instructions/
+│   ├── controlflow/
+│   │   ├── branch.py          # 条件分岐
+│   │   ├── jump.py            # 無条件ジャンプ
+│   │   └── while_.py          # 通常の while 降下（LoopForm 失敗時のフォールバック）
+│   ├── binop.py               # 2項演算
+│   ├── compare.py             # 比較演算（i1生成）
+│   ├── const.py               # 定数
+│   ├── copy.py                # Copy（MIR13 PHI-off の合流表現）
+│   ├── call.py                # Ny 関数呼び出し
+│   ├── boxcall.py             # Box メソッド呼び出し
+│   ├── externcall.py          # 外部呼び出し
+│   ├── newbox.py              # Box 生成
+│   ├── ret.py                 # return 降下（if-merge の前宣言PHIを優先）
+│   ├── typeop.py              # 型変換
+│   ├── safepoint.py           # safepoint
+│   └── barrier.py             # メモリバリア
+└── test_simple.py             # 基本テスト
 ```
 
 ## 🚀 使い方
@@ -30,18 +53,40 @@ python src/llvm_py/llvm_builder.py input.mir.json -o output.o
 NYASH_LLVM_USE_HARNESS=1 ./target/release/nyash program.nyash
 ```
 
+## 🔧 開発用フラグ（プリパス/トレース）
+- `NYASH_LLVM_USE_HARNESS=1` … Rust 実行から llvmlite ハーネスへ委譲
+- `NYASH_LLVM_PREPASS_LOOP=1` … ループ検出プリパスON（while 形を構造化）
+- `NYASH_LLVM_PREPASS_IFMERGE=1` … if-merge（ret-merge）プリパスON（ret値 PHI を前宣言）
+- `NYASH_LLVM_TRACE_PHI=1` … PHI 配線と end-of-block 解決の詳細トレース
+- `NYASH_CLI_VERBOSE=1` … 降下やスナップショットの詳細ログ
+- `NYASH_MIR_NO_PHI=1` … MIR13（PHI-off）を明示（既定1）
+- `NYASH_VERIFY_ALLOW_NO_PHI=1` … PHI-less を検証で許容（既定1）
+
 ## 📋 設計原則（LLVM_LAYER_OVERVIEWに準拠）
-1. **Resolver-only reads** - 直接vmapアクセス禁止
-2. **Localize at block start** - BB先頭でPHI生成
-3. **Sealed SSA** - snapshot経由の配線
-4. **BuilderCursor相当** - 挿入位置の厳格管理
+1. Resolver-only reads（原則）: 直接の cross-block vmap 参照は避け、resolver 経由で取得
+2. Localize at block start: ブロック先頭で PHI を作る（if-merge は prepass で前宣言）
+3. Sealed SSA: ブロック末 snapshot を用いた finalize_phis 配線
+4. Builder cursor discipline: 生成位置の厳格化（terminator 後に emit しない）
 
 ## 🎨 実装状況
 - [ ] 基本構造（MIR読み込み）
-- [ ] Core-14命令の実装
-- [ ] Resolver API
-- [ ] LoopForm対応
-- [ ] テストスイート
+- [x] ControlFlow 分離（branch/jump/while_regular）
+- [x] CFG/Prepass 分離（cfg/utils.py, prepass/loops.py, prepass/if_merge.py）
+- [x] if-merge（ret-merge）の PHI 前宣言（ゲート: NYASH_LLVM_PREPASS_IFMERGE=1）
+- [x] ループプリパス（ゲート: NYASH_LLVM_PREPASS_LOOP=1）
+- [ ] 追加命令/Stage-3 の持続的整備
+
+## ✅ テスト・検証
+- パリティ（llvmlite vs PyVM。既定は終了コードのみ比較）
+  - `./tools/pyvm_vs_llvmlite.sh apps/tests/ternary_nested.nyash`
+  - 代表例（プリパス有効）:
+    - `NYASH_LLVM_PREPASS_IFMERGE=1 ./tools/pyvm_vs_llvmlite.sh apps/tests/ternary_nested.nyash`
+    - `NYASH_LLVM_PREPASS_LOOP=1 ./tools/pyvm_vs_llvmlite.sh apps/tests/loop_if_phi.nyash`
+- 厳密比較（標準出力+終了コード）
+  - `CMP_STRICT=1 ./tools/pyvm_vs_llvmlite.sh <file.nyash>`
+- まとまったスモーク（PHI-off 既定）
+  - `tools/smokes/curated_llvm.sh`
+  - PHI-on 検証（実験的）: `tools/smokes/curated_llvm.sh --phi-on`
 
 ## 📊 予想行数
 - 全体: 800-1000行
diff --git a/src/llvm_py/build_ctx.py b/src/llvm_py/build_ctx.py
new file mode 100644
index 00000000..13aed54e
--- /dev/null
+++ b/src/llvm_py/build_ctx.py
@@ -0,0 +1,34 @@
+"""
+Build context for instruction lowering and helpers.
+
+This structure aggregates frequently passed references so call sites can
+remain concise as we gradually refactor instruction signatures.
+"""
+
+from dataclasses import dataclass
+from typing import Any, Dict, List, Optional
+import llvmlite.ir as ir
+
+@dataclass
+class BuildCtx:
+    # Core IR handles
+    module: ir.Module
+    i64: ir.IntType
+    i32: ir.IntType
+    i8: ir.IntType
+    i1: ir.IntType
+    i8p: ir.PointerType
+
+    # SSA maps and CFG
+    vmap: Dict[int, ir.Value]
+    bb_map: Dict[int, ir.Block]
+    preds: Dict[int, List[int]]
+    block_end_values: Dict[int, Dict[int, ir.Value]]
+
+    # Resolver (value queries, casts, string-ish tags)
+    resolver: Any
+
+    # Optional diagnostics toggles (read from env by the builder)
+    trace_phi: bool = False
+    verbose: bool = False
+
diff --git a/src/llvm_py/cfg/utils.py b/src/llvm_py/cfg/utils.py
new file mode 100644
index 00000000..fc757f99
--- /dev/null
+++ b/src/llvm_py/cfg/utils.py
@@ -0,0 +1,36 @@
+"""
+CFG utilities
+Build predecessor/successor maps and simple helpers.
+"""
+
+from typing import Dict, List, Any, Tuple
+
+def build_preds_succs(block_by_id: Dict[int, Dict[str, Any]]) -> Tuple[Dict[int, List[int]], Dict[int, List[int]]]:
+    """Construct predecessor and successor maps from MIR(JSON) blocks."""
+    succs: Dict[int, List[int]] = {}
+    preds: Dict[int, List[int]] = {}
+    for b in block_by_id.values():
+        bid = int(b.get('id', 0))
+        preds.setdefault(bid, [])
+    for b in block_by_id.values():
+        src = int(b.get('id', 0))
+        for inst in b.get('instructions', []) or []:
+            op = inst.get('op')
+            if op == 'jump':
+                t = inst.get('target')
+                if t is not None:
+                    t = int(t)
+                    succs.setdefault(src, []).append(t)
+                    preds.setdefault(t, []).append(src)
+            elif op == 'branch':
+                th = inst.get('then'); el = inst.get('else')
+                if th is not None:
+                    th = int(th)
+                    succs.setdefault(src, []).append(th)
+                    preds.setdefault(th, []).append(src)
+                if el is not None:
+                    el = int(el)
+                    succs.setdefault(src, []).append(el)
+                    preds.setdefault(el, []).append(src)
+    return preds, succs
+
diff --git a/src/llvm_py/instructions/__init__.py b/src/llvm_py/instructions/__init__.py
index cdf561d8..37ac69fd 100644
--- a/src/llvm_py/instructions/__init__.py
+++ b/src/llvm_py/instructions/__init__.py
@@ -7,8 +7,9 @@ Each instruction has its own file, following Rust structure
 from .const import lower_const
 from .binop import lower_binop
 from .compare import lower_compare
-from .jump import lower_jump
-from .branch import lower_branch
+# controlflow
+from .controlflow.jump import lower_jump
+from .controlflow.branch import lower_branch
 from .ret import lower_return
 from .phi import lower_phi
 from .call import lower_call
@@ -29,4 +30,4 @@ __all__ = [
     'lower_externcall', 'lower_typeop', 'lower_safepoint',
     'lower_barrier', 'lower_newbox',
     'LoopFormContext', 'lower_while_loopform'
-]
\ No newline at end of file
+]
diff --git a/src/llvm_py/instructions/binop.py b/src/llvm_py/instructions/binop.py
index 0cc8c865..fdc09b05 100644
--- a/src/llvm_py/instructions/binop.py
+++ b/src/llvm_py/instructions/binop.py
@@ -5,6 +5,7 @@ Handles +, -, *, /, %, &, |, ^, <<, >>
 
 import llvmlite.ir as ir
 from typing import Dict, Optional, Any
+from utils.values import resolve_i64_strict
 from .compare import lower_compare
 import llvmlite.ir as ir
 
@@ -38,12 +39,12 @@ def lower_binop(
     """
     # Resolve operands as i64 (using resolver when available)
     # For now, simple vmap lookup
-    if resolver is not None and preds is not None and block_end_values is not None:
-        lhs_val = resolver.resolve_i64(lhs, current_block, preds, block_end_values, vmap, bb_map)
-        rhs_val = resolver.resolve_i64(rhs, current_block, preds, block_end_values, vmap, bb_map)
-    else:
-        lhs_val = vmap.get(lhs, ir.Constant(ir.IntType(64), 0))
-        rhs_val = vmap.get(rhs, ir.Constant(ir.IntType(64), 0))
+    lhs_val = resolve_i64_strict(resolver, lhs, current_block, preds, block_end_values, vmap, bb_map)
+    rhs_val = resolve_i64_strict(resolver, rhs, current_block, preds, block_end_values, vmap, bb_map)
+    if lhs_val is None:
+        lhs_val = ir.Constant(ir.IntType(64), 0)
+    if rhs_val is None:
+        rhs_val = ir.Constant(ir.IntType(64), 0)
     
     # Relational/equality operators delegate to compare
     if op in ('==','!=','<','>','<=','>='):
@@ -60,6 +61,7 @@ def lower_binop(
             preds=preds,
             block_end_values=block_end_values,
             bb_map=bb_map,
+            ctx=getattr(resolver, 'ctx', None),
         )
         return
 
diff --git a/src/llvm_py/instructions/boxcall.py b/src/llvm_py/instructions/boxcall.py
index f28f5962..c90df67f 100644
--- a/src/llvm_py/instructions/boxcall.py
+++ b/src/llvm_py/instructions/boxcall.py
@@ -4,7 +4,7 @@ Core of Nyash's "Everything is Box" philosophy
 """
 
 import llvmlite.ir as ir
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Any
 
 def _declare(module: ir.Module, name: str, ret, args):
     for f in module.functions:
@@ -47,7 +47,8 @@ def lower_boxcall(
     resolver=None,
     preds=None,
     block_end_values=None,
-    bb_map=None
+    bb_map=None,
+    ctx: Optional[Any] = None,
 ) -> None:
     """
     Lower MIR BoxCall instruction
@@ -68,10 +69,43 @@ def lower_boxcall(
     i8 = ir.IntType(8)
     i8p = i8.as_pointer()
 
+    # Short-hands with ctx (backward-compatible fallback)
+    r = resolver
+    p = preds
+    bev = block_end_values
+    bbm = bb_map
+    if ctx is not None:
+        try:
+            r = getattr(ctx, 'resolver', r)
+            p = getattr(ctx, 'preds', p)
+            bev = getattr(ctx, 'block_end_values', bev)
+            bbm = getattr(ctx, 'bb_map', bbm)
+        except Exception:
+            pass
+    def _res_i64(vid: int):
+        if r is not None and p is not None and bev is not None and bbm is not None:
+            try:
+                return r.resolve_i64(vid, builder.block, p, bev, vmap, bbm)
+            except Exception:
+                return None
+        return vmap.get(vid)
+
+    # If BuildCtx is provided, prefer its maps for consistency.
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
     # Receiver value
-    if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-        recv_val = resolver.resolve_i64(box_vid, builder.block, preds, block_end_values, vmap, bb_map)
-    else:
+    recv_val = _res_i64(box_vid)
+    if recv_val is None:
         recv_val = vmap.get(box_vid, ir.Constant(i64, 0))
 
     # Minimal method bridging for strings and console
@@ -96,11 +130,11 @@ def lower_boxcall(
     if method_name == "substring":
         # substring(start, end)
         # If receiver is a handle (i64), use handle-based helper; else pointer-based API
-        if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-            s = resolver.resolve_i64(args[0], builder.block, preds, block_end_values, vmap, bb_map) if args else ir.Constant(i64, 0)
-            e = resolver.resolve_i64(args[1], builder.block, preds, block_end_values, vmap, bb_map) if len(args) > 1 else ir.Constant(i64, 0)
-        else:
+        s = _res_i64(args[0]) if args else ir.Constant(i64, 0)
+        if s is None:
             s = vmap.get(args[0], ir.Constant(i64, 0)) if args else ir.Constant(i64, 0)
+        e = _res_i64(args[1]) if len(args) > 1 else ir.Constant(i64, 0)
+        if e is None:
             e = vmap.get(args[1], ir.Constant(i64, 0)) if len(args) > 1 else ir.Constant(i64, 0)
         if hasattr(recv_val, 'type') and isinstance(recv_val.type, ir.IntType):
             # handle-based
@@ -191,9 +225,8 @@ def lower_boxcall(
         # ArrayBox.get(index) → nyash.array.get_h(handle, idx)
         # MapBox.get(key) → nyash.map.get_hh(handle, key_any)
         recv_h = _ensure_handle(builder, module, recv_val)
-        if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-            k = resolver.resolve_i64(args[0], builder.block, preds, block_end_values, vmap, bb_map) if args else ir.Constant(i64, 0)
-        else:
+        k = _res_i64(args[0]) if args else ir.Constant(i64, 0)
+        if k is None:
             k = vmap.get(args[0], ir.Constant(i64, 0)) if args else ir.Constant(i64, 0)
         callee_map = _declare(module, "nyash.map.get_hh", i64, [i64, i64])
         res = builder.call(callee_map, [recv_h, k], name="map_get_hh")
@@ -204,9 +237,8 @@ def lower_boxcall(
     if method_name == "push":
         # ArrayBox.push(val) → nyash.array.push_h(handle, val)
         recv_h = _ensure_handle(builder, module, recv_val)
-        if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-            v0 = resolver.resolve_i64(args[0], builder.block, preds, block_end_values, vmap, bb_map) if args else ir.Constant(i64, 0)
-        else:
+        v0 = _res_i64(args[0]) if args else ir.Constant(i64, 0)
+        if v0 is None:
             v0 = vmap.get(args[0], ir.Constant(i64, 0)) if args else ir.Constant(i64, 0)
         callee = _declare(module, "nyash.array.push_h", i64, [i64, i64])
         res = builder.call(callee, [recv_h, v0], name="arr_push_h")
@@ -217,11 +249,11 @@ def lower_boxcall(
     if method_name == "set":
         # MapBox.set(key, val) → nyash.map.set_hh(handle, key_any, val_any)
         recv_h = _ensure_handle(builder, module, recv_val)
-        if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-            k = resolver.resolve_i64(args[0], builder.block, preds, block_end_values, vmap, bb_map) if len(args) > 0 else ir.Constant(i64, 0)
-            v = resolver.resolve_i64(args[1], builder.block, preds, block_end_values, vmap, bb_map) if len(args) > 1 else ir.Constant(i64, 0)
-        else:
+        k = _res_i64(args[0]) if len(args) > 0 else ir.Constant(i64, 0)
+        if k is None:
             k = vmap.get(args[0], ir.Constant(i64, 0)) if len(args) > 0 else ir.Constant(i64, 0)
+        v = _res_i64(args[1]) if len(args) > 1 else ir.Constant(i64, 0)
+        if v is None:
             v = vmap.get(args[1], ir.Constant(i64, 0)) if len(args) > 1 else ir.Constant(i64, 0)
         callee = _declare(module, "nyash.map.set_hh", i64, [i64, i64, i64])
         res = builder.call(callee, [recv_h, k, v], name="map_set_hh")
@@ -232,9 +264,8 @@ def lower_boxcall(
     if method_name == "has":
         # MapBox.has(key) → nyash.map.has_hh(handle, key_any)
         recv_h = _ensure_handle(builder, module, recv_val)
-        if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-            k = resolver.resolve_i64(args[0], builder.block, preds, block_end_values, vmap, bb_map) if args else ir.Constant(i64, 0)
-        else:
+        k = _res_i64(args[0]) if args else ir.Constant(i64, 0)
+        if k is None:
             k = vmap.get(args[0], ir.Constant(i64, 0)) if args else ir.Constant(i64, 0)
         callee = _declare(module, "nyash.map.has_hh", i64, [i64, i64])
         res = builder.call(callee, [recv_h, k], name="map_has_hh")
diff --git a/src/llvm_py/instructions/call.py b/src/llvm_py/instructions/call.py
index d379fa0b..e43dda25 100644
--- a/src/llvm_py/instructions/call.py
+++ b/src/llvm_py/instructions/call.py
@@ -4,7 +4,8 @@ Handles regular function calls (not BoxCall or ExternCall)
 """
 
 import llvmlite.ir as ir
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Any
+from trace import debug as trace_debug
 
 def lower_call(
     builder: ir.IRBuilder,
@@ -16,7 +17,8 @@ def lower_call(
     resolver=None,
     preds=None,
     block_end_values=None,
-    bb_map=None
+    bb_map=None,
+    ctx: Optional[Any] = None,
 ) -> None:
     """
     Lower MIR Call instruction
@@ -30,6 +32,50 @@ def lower_call(
         vmap: Value map
         resolver: Optional resolver for type handling
     """
+    # If BuildCtx is provided, prefer its maps for consistency.
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
+    # Short-hands with ctx (backward-compatible fallback)
+    r = resolver
+    p = preds
+    bev = block_end_values
+    bbm = bb_map
+    if ctx is not None:
+        try:
+            r = getattr(ctx, 'resolver', r)
+            p = getattr(ctx, 'preds', p)
+            bev = getattr(ctx, 'block_end_values', bev)
+            bbm = getattr(ctx, 'bb_map', bbm)
+        except Exception:
+            pass
+
+    # Resolver helpers (prefer resolver when available)
+    def _res_i64(vid: int):
+        if r is not None and p is not None and bev is not None and bbm is not None:
+            try:
+                return r.resolve_i64(vid, builder.block, p, bev, vmap, bbm)
+            except Exception:
+                return None
+        return vmap.get(vid)
+
+    def _res_ptr(vid: int):
+        if r is not None and p is not None and bev is not None:
+            try:
+                return r.resolve_ptr(vid, builder.block, p, bev, vmap)
+            except Exception:
+                return None
+        return vmap.get(vid)
+
     # Resolve function: accepts string name or value-id referencing a string literal
     actual_name = func_name
     if not isinstance(func_name, str):
@@ -58,11 +104,10 @@ def lower_call(
         arg_val = None
         if i < len(func.args):
             expected_type = func.args[i].type
-            if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-                if hasattr(expected_type, 'is_pointer') and expected_type.is_pointer:
-                    arg_val = resolver.resolve_ptr(arg_id, builder.block, preds, block_end_values, vmap)
-                else:
-                    arg_val = resolver.resolve_i64(arg_id, builder.block, preds, block_end_values, vmap, bb_map)
+            if hasattr(expected_type, 'is_pointer') and expected_type.is_pointer:
+                arg_val = _res_ptr(arg_id)
+            else:
+                arg_val = _res_i64(arg_id)
         if arg_val is None:
             arg_val = vmap.get(arg_id)
         if arg_val is None:
@@ -88,13 +133,8 @@ def lower_call(
     # Make the call
     result = builder.call(func, call_args, name=f"call_{func_name}")
     # Optional trace for final debugging
-    try:
-        import os
-        if os.environ.get('NYASH_LLVM_TRACE_FINAL') == '1' and isinstance(actual_name, str):
-            if actual_name in ("Main.node_json/3", "Main.esc_json/1", "main"):
-                print(f"[TRACE] call {actual_name} args={len(call_args)}", flush=True)
-    except Exception:
-        pass
+    if isinstance(actual_name, str) and actual_name in ("Main.node_json/3", "Main.esc_json/1", "main"):
+        trace_debug(f"[TRACE] call {actual_name} args={len(call_args)}")
     
     # Store result if needed
     if dst_vid is not None:
diff --git a/src/llvm_py/instructions/compare.py b/src/llvm_py/instructions/compare.py
index d623f931..7c87ac96 100644
--- a/src/llvm_py/instructions/compare.py
+++ b/src/llvm_py/instructions/compare.py
@@ -5,7 +5,9 @@ Handles comparison operations (<, >, <=, >=, ==, !=)
 
 import llvmlite.ir as ir
 from typing import Dict, Optional, Any
+from utils.values import resolve_i64_strict
 from .externcall import lower_externcall
+from trace import values as trace_values
 
 def lower_compare(
     builder: ir.IRBuilder,
@@ -20,6 +22,7 @@ def lower_compare(
     block_end_values=None,
     bb_map=None,
     meta: Optional[Dict[str, Any]] = None,
+    ctx: Optional[Any] = None,
 ) -> None:
     """
     Lower MIR Compare instruction
@@ -32,15 +35,23 @@ def lower_compare(
         dst: Destination value ID
         vmap: Value map
     """
+    # If BuildCtx is provided, prefer its maps for consistency.
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
     # Get operands
     # Prefer same-block SSA from vmap; fallback to resolver for cross-block dominance
-    lhs_val = vmap.get(lhs)
-    rhs_val = vmap.get(rhs)
-    if (lhs_val is None or rhs_val is None) and resolver is not None and preds is not None and block_end_values is not None and current_block is not None:
-        if lhs_val is None:
-            lhs_val = resolver.resolve_i64(lhs, current_block, preds, block_end_values, vmap, bb_map)
-        if rhs_val is None:
-            rhs_val = resolver.resolve_i64(rhs, current_block, preds, block_end_values, vmap, bb_map)
+    lhs_val = resolve_i64_strict(resolver, lhs, current_block, preds, block_end_values, vmap, bb_map)
+    rhs_val = resolve_i64_strict(resolver, rhs, current_block, preds, block_end_values, vmap, bb_map)
 
     i64 = ir.IntType(64)
     i8p = ir.IntType(8).as_pointer()
@@ -63,12 +74,7 @@ def lower_compare(
         except Exception:
             pass
         if force_string or lhs_tag or rhs_tag:
-            try:
-                import os
-                if os.environ.get('NYASH_LLVM_TRACE_VALUES') == '1':
-                    print(f"[compare] string-eq path: lhs={lhs} rhs={rhs} force={force_string} tagL={lhs_tag} tagR={rhs_tag}", flush=True)
-            except Exception:
-                pass
+            trace_values(f"[compare] string-eq path: lhs={lhs} rhs={rhs} force={force_string} tagL={lhs_tag} tagR={rhs_tag}")
             # Prefer same-block SSA (vmap) since string handles are produced in-place; fallback to resolver
             lh = lhs_val if lhs_val is not None else (
                 resolver.resolve_i64(lhs, current_block, preds, block_end_values, vmap, bb_map)
@@ -78,14 +84,7 @@ def lower_compare(
                 resolver.resolve_i64(rhs, current_block, preds, block_end_values, vmap, bb_map)
                 if (resolver is not None and preds is not None and block_end_values is not None and current_block is not None) else ir.Constant(i64, 0)
             )
-            try:
-                import os
-                if os.environ.get('NYASH_LLVM_TRACE_VALUES') == '1':
-                    lz = isinstance(lh, ir.Constant) and getattr(getattr(lh,'constant',None),'constant',None) == 0
-                    rz = isinstance(rh, ir.Constant) and getattr(getattr(rh,'constant',None),'constant',None) == 0
-                    print(f"[compare] string-eq args: lh_is_const={isinstance(lh, ir.Constant)} rh_is_const={isinstance(rh, ir.Constant)}", flush=True)
-            except Exception:
-                pass
+            trace_values(f"[compare] string-eq args: lh_is_const={isinstance(lh, ir.Constant)} rh_is_const={isinstance(rh, ir.Constant)}")
             eqf = None
             for f in builder.module.functions:
                 if f.name == 'nyash.string.eq_hh':
@@ -117,12 +116,11 @@ def lower_compare(
     # Perform signed comparison using canonical predicates ('<','>','<=','>=','==','!=')
     pred = op if op in ('<','>','<=','>=','==','!=') else '=='
     cmp_result = builder.icmp_signed(pred, lhs_val, rhs_val, name=f"cmp_{dst}")
-    
-    # Convert i1 to i64 (0 or 1)
-    result = builder.zext(cmp_result, i64, name=f"cmp_i64_{dst}")
-    
-    # Store result
-    vmap[dst] = result
+    # Store the canonical i1 compare result. Consumers that require i64
+    # should explicitly cast at their use site (e.g., via resolver or
+    # instruction-specific lowering) to avoid emitting casts after
+    # terminators when used as branch conditions.
+    vmap[dst] = cmp_result
 
 def lower_fcmp(
     builder: ir.IRBuilder,
diff --git a/src/llvm_py/instructions/branch.py b/src/llvm_py/instructions/controlflow/branch.py
similarity index 71%
rename from src/llvm_py/instructions/branch.py
rename to src/llvm_py/instructions/controlflow/branch.py
index 973fafad..481a6abb 100644
--- a/src/llvm_py/instructions/branch.py
+++ b/src/llvm_py/instructions/controlflow/branch.py
@@ -5,6 +5,7 @@ Conditional branch based on condition value
 
 import llvmlite.ir as ir
 from typing import Dict
+from utils.values import resolve_i64_strict
 
 def lower_branch(
     builder: ir.IRBuilder,
@@ -28,22 +29,22 @@ def lower_branch(
         vmap: Value map
         bb_map: Block map
     """
-    # Get condition value
-    if resolver is not None and preds is not None and block_end_values is not None:
-        cond = resolver.resolve_i64(cond_vid, builder.block, preds, block_end_values, vmap, bb_map)
-    else:
-        cond = vmap.get(cond_vid)
-    if not cond:
+    # Get condition value with preference to same-block SSA
+    cond = resolve_i64_strict(resolver, cond_vid, builder.block, preds, block_end_values, vmap, bb_map)
+    if cond is None:
         # Default to false if missing
         cond = ir.Constant(ir.IntType(1), 0)
     
     # Convert to i1 if needed
     if hasattr(cond, 'type'):
-        if cond.type == ir.IntType(64):
+        # If we already have an i1 (canonical compare result), use it directly.
+        if isinstance(cond.type, ir.IntType) and cond.type.width == 1:
+            pass
+        elif isinstance(cond.type, ir.IntType) and cond.type.width == 64:
             # i64 to i1: compare != 0
             zero = ir.Constant(ir.IntType(64), 0)
             cond = builder.icmp_unsigned('!=', cond, zero, name="cond_i1")
-        elif cond.type == ir.IntType(8).as_pointer():
+        elif isinstance(cond.type, ir.PointerType):
             # Pointer to i1: compare != null
             null = ir.Constant(cond.type, None)
             cond = builder.icmp_unsigned('!=', cond, null, name="cond_p1")
diff --git a/src/llvm_py/instructions/jump.py b/src/llvm_py/instructions/controlflow/jump.py
similarity index 93%
rename from src/llvm_py/instructions/jump.py
rename to src/llvm_py/instructions/controlflow/jump.py
index 4f33b589..eaff2f0b 100644
--- a/src/llvm_py/instructions/jump.py
+++ b/src/llvm_py/instructions/controlflow/jump.py
@@ -21,4 +21,5 @@ def lower_jump(
     """
     target_bb = bb_map.get(target_bid)
     if target_bb:
-        builder.branch(target_bb)
\ No newline at end of file
+        builder.branch(target_bb)
+
diff --git a/src/llvm_py/instructions/controlflow/while_.py b/src/llvm_py/instructions/controlflow/while_.py
new file mode 100644
index 00000000..b3071382
--- /dev/null
+++ b/src/llvm_py/instructions/controlflow/while_.py
@@ -0,0 +1,80 @@
+"""
+Lowering helpers for while-control flow (regular structured)
+"""
+
+from typing import List, Dict, Any
+import llvmlite.ir as ir
+
+def lower_while_regular(
+    builder: ir.IRBuilder,
+    func: ir.Function,
+    cond_vid: int,
+    body_insts: List[Dict[str, Any]],
+    loop_id: int,
+    vmap: Dict[int, ir.Value],
+    bb_map: Dict[int, ir.Block],
+    resolver,
+    preds,
+    block_end_values,
+):
+    """Create a minimal while in IR: cond -> body -> cond, with exit.
+    The body instructions are lowered using the caller's dispatcher.
+    """
+    i1 = ir.IntType(1)
+    i64 = ir.IntType(64)
+
+    # Create basic blocks: cond -> body -> cond, and exit
+    cond_bb = func.append_basic_block(name=f"while{loop_id}_cond")
+    body_bb = func.append_basic_block(name=f"while{loop_id}_body")
+    exit_bb = func.append_basic_block(name=f"while{loop_id}_exit")
+
+    # Jump from current to cond
+    builder.branch(cond_bb)
+
+    # Cond block
+    cbuild = ir.IRBuilder(cond_bb)
+    try:
+        # Resolve against the condition block to localize dominance
+        cond_val = resolver.resolve_i64(cond_vid, cond_bb, preds, block_end_values, vmap, bb_map)
+    except Exception:
+        cond_val = vmap.get(cond_vid)
+    if cond_val is None:
+        cond_val = ir.Constant(i1, 0)
+    # Normalize to i1
+    if hasattr(cond_val, 'type'):
+        if isinstance(cond_val.type, ir.IntType) and cond_val.type.width == 64:
+            zero64 = ir.Constant(i64, 0)
+            cond_val = cbuild.icmp_unsigned('!=', cond_val, zero64, name="while_cond_i1")
+        elif isinstance(cond_val.type, ir.PointerType):
+            nullp = ir.Constant(cond_val.type, None)
+            cond_val = cbuild.icmp_unsigned('!=', cond_val, nullp, name="while_cond_p1")
+        elif isinstance(cond_val.type, ir.IntType) and cond_val.type.width == 1:
+            # already i1
+            pass
+        else:
+            # Fallback: treat as false
+            cond_val = ir.Constant(i1, 0)
+    else:
+        cond_val = ir.Constant(i1, 0)
+
+    cbuild.cbranch(cond_val, body_bb, exit_bb)
+
+    # Body block
+    bbuild = ir.IRBuilder(body_bb)
+    # The caller must provide a dispatcher to lower body_insts; do a simple inline here.
+    # We expect the caller to have a method lower_instruction(builder, inst, func).
+    lower_instruction = getattr(resolver, '_owner_lower_instruction', None)
+    if lower_instruction is None:
+        raise RuntimeError('resolver._owner_lower_instruction not set (needs NyashLLVMBuilder.lower_instruction)')
+    for sub in body_insts:
+        if bbuild.block.terminator is not None:
+            cont = func.append_basic_block(name=f"cont_bb_{bbuild.block.name}")
+            bbuild.position_at_end(cont)
+        lower_instruction(bbuild, sub, func)
+    # Ensure terminator: if not terminated, branch back to cond
+    if bbuild.block.terminator is None:
+        bbuild.branch(cond_bb)
+
+    # Continue at exit
+    builder.position_at_end(exit_bb)
+
diff --git a/src/llvm_py/instructions/copy.py b/src/llvm_py/instructions/copy.py
new file mode 100644
index 00000000..82375825
--- /dev/null
+++ b/src/llvm_py/instructions/copy.py
@@ -0,0 +1,46 @@
+"""
+Copy instruction lowering
+MIR13 PHI-off uses explicit copies along edges/blocks to model merges.
+"""
+
+import llvmlite.ir as ir
+from typing import Dict, Optional, Any
+from utils.values import resolve_i64_strict
+
+def lower_copy(
+    builder: ir.IRBuilder,
+    dst: int,
+    src: int,
+    vmap: Dict[int, ir.Value],
+    resolver=None,
+    current_block=None,
+    preds=None,
+    block_end_values=None,
+    bb_map=None,
+    ctx: Optional[Any] = None,
+):
+    """Lower a copy by mapping dst to src value in the current block scope.
+
+    Prefer same-block SSA from vmap; fallback to resolver to preserve
+    dominance and to localize values across predecessors.
+    """
+    # If BuildCtx is provided, prefer its maps for consistency.
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'vmap', None) is not None and vmap is None:
+                vmap = ctx.vmap
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
+    # Prefer local SSA; resolve otherwise to preserve dominance
+    val = resolve_i64_strict(resolver, src, current_block, preds, block_end_values, vmap, bb_map)
+    if val is None:
+        val = ir.Constant(ir.IntType(64), 0)
+    vmap[dst] = val
diff --git a/src/llvm_py/instructions/externcall.py b/src/llvm_py/instructions/externcall.py
index c95c8ca4..7efc0208 100644
--- a/src/llvm_py/instructions/externcall.py
+++ b/src/llvm_py/instructions/externcall.py
@@ -4,7 +4,7 @@ Minimal mapping for NyRT-exported symbols (console/log family等)
 """
 
 import llvmlite.ir as ir
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Any
 
 def lower_externcall(
     builder: ir.IRBuilder,
@@ -16,7 +16,8 @@ def lower_externcall(
     resolver=None,
     preds=None,
     block_end_values=None,
-    bb_map=None
+    bb_map=None,
+    ctx: Optional[Any] = None,
 ) -> None:
     """
     Lower MIR ExternCall instruction
@@ -30,6 +31,19 @@ def lower_externcall(
         vmap: Value map
         resolver: Optional resolver for type handling
     """
+    # If BuildCtx is provided, prefer its maps for consistency.
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
     # Accept full symbol names (e.g., "nyash.console.log", "nyash.string.len_h").
     llvm_name = func_name
 
@@ -83,13 +97,17 @@ def lower_externcall(
     call_args: List[ir.Value] = []
     for i, arg_id in enumerate(args):
         orig_arg_id = arg_id
-        # Prefer resolver
+        # Prefer resolver/ctx
+        aval = None
         if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-            if len(func.args) > i and isinstance(func.args[i].type, ir.PointerType):
-                aval = resolver.resolve_ptr(arg_id, builder.block, preds, block_end_values, vmap)
-            else:
-                aval = resolver.resolve_i64(arg_id, builder.block, preds, block_end_values, vmap, bb_map)
-        else:
+            try:
+                if len(func.args) > i and isinstance(func.args[i].type, ir.PointerType):
+                    aval = resolver.resolve_ptr(arg_id, builder.block, preds, block_end_values, vmap)
+                else:
+                    aval = resolver.resolve_i64(arg_id, builder.block, preds, block_end_values, vmap, bb_map)
+            except Exception:
+                aval = None
+        if aval is None:
             aval = vmap.get(arg_id)
         if aval is None:
             # Default guess
diff --git a/src/llvm_py/instructions/loopform.py b/src/llvm_py/instructions/loopform.py
index 85ad8d12..55526cdd 100644
--- a/src/llvm_py/instructions/loopform.py
+++ b/src/llvm_py/instructions/loopform.py
@@ -123,7 +123,10 @@ def lower_while_loopform(
     lf.tag_phi = tag_phi
     lf.payload_phi = payload_phi
     
-    if os.environ.get('NYASH_CLI_VERBOSE') == '1':
-        print(f"[LoopForm] Created loop structure (id={loop_id})")
+    try:
+        from trace import debug as trace_debug
+        trace_debug(f"[LoopForm] Created loop structure (id={loop_id})")
+    except Exception:
+        pass
     
     return True
diff --git a/src/llvm_py/instructions/newbox.py b/src/llvm_py/instructions/newbox.py
index c86f0ef8..0a045b5f 100644
--- a/src/llvm_py/instructions/newbox.py
+++ b/src/llvm_py/instructions/newbox.py
@@ -4,7 +4,7 @@ Handles box creation (new StringBox(), new IntegerBox(), etc.)
 """
 
 import llvmlite.ir as ir
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Any
 
 def lower_newbox(
     builder: ir.IRBuilder,
@@ -13,7 +13,8 @@ def lower_newbox(
     args: List[int],
     dst_vid: int,
     vmap: Dict[int, ir.Value],
-    resolver=None
+    resolver=None,
+    ctx: Optional[Any] = None
 ) -> None:
     """
     Lower MIR NewBox instruction
diff --git a/src/llvm_py/instructions/phi.py b/src/llvm_py/instructions/phi.py
index 830ff9b3..144c2896 100644
--- a/src/llvm_py/instructions/phi.py
+++ b/src/llvm_py/instructions/phi.py
@@ -134,12 +134,15 @@ def lower_phi(
     import os
     if used_default_zero and os.environ.get('NYASH_LLVM_PHI_STRICT') == '1':
         raise RuntimeError(f"[LLVM_PY] PHI dst={dst_vid} used synthesized zero; check preds/incoming")
-    if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
+    try:
+        from trace import phi as trace_phi
         try:
             blkname = str(current_block.name)
         except Exception:
             blkname = '<blk>'
-        print(f"[PHI] {blkname} v{dst_vid} incoming={len(incoming_pairs)} zero={1 if used_default_zero else 0}")
+        trace_phi(f"[PHI] {blkname} v{dst_vid} incoming={len(incoming_pairs)} zero={1 if used_default_zero else 0}")
+    except Exception:
+        pass
     # Propagate string-ness: if any incoming value-id is tagged string-ish, mark dst as string-ish.
     try:
         if resolver is not None and hasattr(resolver, 'is_stringish') and hasattr(resolver, 'mark_string'):
diff --git a/src/llvm_py/instructions/ret.py b/src/llvm_py/instructions/ret.py
index 842b29fc..8eccbab2 100644
--- a/src/llvm_py/instructions/ret.py
+++ b/src/llvm_py/instructions/ret.py
@@ -4,7 +4,7 @@ Handles void and value returns
 """
 
 import llvmlite.ir as ir
-from typing import Dict, Optional
+from typing import Dict, Optional, Any
 
 def lower_return(
     builder: ir.IRBuilder,
@@ -14,7 +14,8 @@ def lower_return(
     resolver=None,
     preds=None,
     block_end_values=None,
-    bb_map=None
+    bb_map=None,
+    ctx: Optional[Any] = None,
 ) -> None:
     """
     Lower MIR Return instruction
@@ -25,6 +26,19 @@ def lower_return(
         vmap: Value map
         return_type: Expected return type
     """
+    # Prefer BuildCtx maps if provided
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
     if value_id is None:
         # Void return
         builder.ret_void()
@@ -33,6 +47,53 @@ def lower_return(
         ret_val = None
         if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
             try:
+                # If this block has a declared PHI for the return value, force using the
+                # local PHI placeholder to ensure dominance and let finalize_phis wire it.
+                try:
+                    block_name = builder.block.name
+                    cur_bid = int(str(block_name).replace('bb',''))
+                except Exception:
+                    cur_bid = -1
+                try:
+                    bm = getattr(resolver, 'block_phi_incomings', {}) or {}
+                except Exception:
+                    bm = {}
+                if isinstance(value_id, int) and isinstance(bm.get(cur_bid), dict) and value_id in bm.get(cur_bid):
+                    # Reuse predeclared ret-phi when available
+                    cur = None
+                    try:
+                        rp = getattr(resolver, 'ret_phi_map', {}) or {}
+                        key = (int(cur_bid), int(value_id))
+                        if key in rp:
+                            cur = rp[key]
+                    except Exception:
+                        cur = None
+                    if cur is None:
+                        btop = ir.IRBuilder(builder.block)
+                        try:
+                            btop.position_at_start(builder.block)
+                        except Exception:
+                            pass
+                        # Reuse existing local phi if present; otherwise create
+                        cur = vmap.get(value_id)
+                        need_new = True
+                        try:
+                            need_new = not (cur is not None and hasattr(cur, 'add_incoming') and getattr(getattr(cur, 'basic_block', None), 'name', None) == builder.block.name)
+                        except Exception:
+                            need_new = True
+                        if need_new:
+                            cur = btop.phi(ir.IntType(64), name=f"phi_ret_{value_id}")
+                    # Bind to maps
+                    vmap[value_id] = cur
+                    try:
+                        if hasattr(resolver, 'global_vmap') and isinstance(resolver.global_vmap, dict):
+                            resolver.global_vmap[value_id] = cur
+                    except Exception:
+                        pass
+                    ret_val = cur
+                if ret_val is not None:
+                    builder.ret(ret_val)
+                    return
                 if isinstance(return_type, ir.PointerType):
                     ret_val = resolver.resolve_ptr(value_id, builder.block, preds, block_end_values, vmap)
                 else:
diff --git a/src/llvm_py/instructions/safepoint.py b/src/llvm_py/instructions/safepoint.py
index f4fba8e9..f12542d1 100644
--- a/src/llvm_py/instructions/safepoint.py
+++ b/src/llvm_py/instructions/safepoint.py
@@ -4,7 +4,7 @@ GC safepoints where runtime can safely collect garbage
 """
 
 import llvmlite.ir as ir
-from typing import Dict, List, Optional
+from typing import Dict, List, Optional, Any
 
 def lower_safepoint(
     builder: ir.IRBuilder,
@@ -15,7 +15,8 @@ def lower_safepoint(
     resolver=None,
     preds=None,
     block_end_values=None,
-    bb_map=None
+    bb_map=None,
+    ctx: Optional[Any] = None
 ) -> None:
     """
     Lower MIR Safepoint instruction
@@ -53,8 +54,18 @@ def lower_safepoint(
         
         # Store each live value
         for i, vid in enumerate(live_values):
-            if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
-                val = resolver.resolve_i64(vid, builder.block, preds, block_end_values, vmap, bb_map)
+            # Prefer BuildCtx if provided
+            r = resolver; p = preds; bev = block_end_values; bbm = bb_map
+            if ctx is not None:
+                try:
+                    r = getattr(ctx, 'resolver', r)
+                    p = getattr(ctx, 'preds', p)
+                    bev = getattr(ctx, 'block_end_values', bev)
+                    bbm = getattr(ctx, 'bb_map', bbm)
+                except Exception:
+                    pass
+            if r is not None and p is not None and bev is not None and bbm is not None:
+                val = r.resolve_i64(vid, builder.block, p, bev, vmap, bbm)
             else:
                 val = vmap.get(vid, ir.Constant(i64, 0))
             
diff --git a/src/llvm_py/instructions/typeop.py b/src/llvm_py/instructions/typeop.py
index df79333c..986c6d34 100644
--- a/src/llvm_py/instructions/typeop.py
+++ b/src/llvm_py/instructions/typeop.py
@@ -4,7 +4,7 @@ Handles type conversions and type checks
 """
 
 import llvmlite.ir as ir
-from typing import Dict, Optional
+from typing import Dict, Optional, Any
 
 def lower_typeop(
     builder: ir.IRBuilder,
@@ -16,7 +16,8 @@ def lower_typeop(
     resolver=None,
     preds=None,
     block_end_values=None,
-    bb_map=None
+    bb_map=None,
+    ctx: Optional[Any] = None,
 ) -> None:
     """
     Lower MIR TypeOp instruction
@@ -35,6 +36,19 @@ def lower_typeop(
         vmap: Value map
         resolver: Optional resolver for type handling
     """
+    # Prefer BuildCtx maps when provided
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
     if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
         src_val = resolver.resolve_i64(src_vid, builder.block, preds, block_end_values, vmap, bb_map)
     else:
@@ -83,7 +97,8 @@ def lower_convert(
     resolver=None,
     preds=None,
     block_end_values=None,
-    bb_map=None
+    bb_map=None,
+    ctx: Optional[Any] = None,
 ) -> None:
     """
     Lower type conversion between primitive types
@@ -96,6 +111,18 @@ def lower_convert(
         to_type: Target type
         vmap: Value map
     """
+    if ctx is not None:
+        try:
+            if getattr(ctx, 'resolver', None) is not None:
+                resolver = ctx.resolver
+            if getattr(ctx, 'preds', None) is not None and preds is None:
+                preds = ctx.preds
+            if getattr(ctx, 'block_end_values', None) is not None and block_end_values is None:
+                block_end_values = ctx.block_end_values
+            if getattr(ctx, 'bb_map', None) is not None and bb_map is None:
+                bb_map = ctx.bb_map
+        except Exception:
+            pass
     if resolver is not None and preds is not None and block_end_values is not None and bb_map is not None:
         # Choose resolution based on from_type
         if from_type == "ptr":
diff --git a/src/llvm_py/llvm_builder.py b/src/llvm_py/llvm_builder.py
index 5782f1b2..3ae5cc71 100644
--- a/src/llvm_py/llvm_builder.py
+++ b/src/llvm_py/llvm_builder.py
@@ -15,9 +15,10 @@ import llvmlite.binding as llvm
 from instructions.const import lower_const
 from instructions.binop import lower_binop
 from instructions.compare import lower_compare
-from instructions.jump import lower_jump
-from instructions.branch import lower_branch
+from instructions.controlflow.jump import lower_jump
+from instructions.controlflow.branch import lower_branch
 from instructions.ret import lower_return
+from instructions.copy import lower_copy
 # PHI are deferred; finalize_phis wires incoming edges after snapshots
 from instructions.call import lower_call
 from instructions.boxcall import lower_boxcall
@@ -27,6 +28,13 @@ from instructions.newbox import lower_newbox
 from instructions.safepoint import lower_safepoint, insert_automatic_safepoint
 from instructions.barrier import lower_barrier
 from instructions.loopform import lower_while_loopform
+from instructions.controlflow.while_ import lower_while_regular
+from phi_wiring import setup_phi_placeholders as _setup_phi_placeholders, finalize_phis as _finalize_phis
+from trace import debug as trace_debug
+from trace import phi as trace_phi
+from prepass.loops import detect_simple_while
+from prepass.if_merge import plan_ret_phi_predeclare
+from build_ctx import BuildCtx
 
 from resolver import Resolver
 from mir_reader import MIRReader
@@ -71,6 +79,8 @@ class NyashLLVMBuilder:
         # Heuristics for minor gated fixes
         self.current_function_name: Optional[str] = None
         self._last_substring_vid: Optional[int] = None
+        # Map of (block_id, value_id) -> predeclared PHI for ret-merge if-merge prepass
+        self.predeclared_ret_phis: Dict[Tuple[int, int], ir.Instruction] = {}
         
     def build_from_mir(self, mir_json: Dict[str, Any]) -> str:
         """Build LLVM IR from MIR JSON"""
@@ -177,11 +187,12 @@ class NyashLLVMBuilder:
                 os.makedirs(os.path.dirname(dump_path), exist_ok=True)
                 with open(dump_path, 'w') as f:
                     f.write(ir_text)
-            elif os.environ.get('NYASH_CLI_VERBOSE') == '1':
+            else:
                 # Default dump location when verbose and not explicitly set
-                os.makedirs('tmp', exist_ok=True)
-                with open('tmp/nyash_harness.ll', 'w') as f:
-                    f.write(ir_text)
+                if os.environ.get('NYASH_CLI_VERBOSE') == '1':
+                    os.makedirs('tmp', exist_ok=True)
+                    with open('tmp/nyash_harness.ll', 'w') as f:
+                        f.write(ir_text)
         except Exception:
             pass
         return ir_text
@@ -322,13 +333,176 @@ class NyashLLVMBuilder:
         # Prepass: collect producer stringish hints and PHI metadata for all blocks
         # and create placeholders at each block head so that resolver can safely
         # return existing PHIs without creating new ones.
-        self.setup_phi_placeholders(blocks)
-        
+        _setup_phi_placeholders(self, blocks)
+
+        # Optional: if-merge prepass → predeclare PHI for return-merge blocks
+        # Gate with NYASH_LLVM_PREPASS_IFMERGE=1
+        try:
+            if os.environ.get('NYASH_LLVM_PREPASS_IFMERGE') == '1':
+                plan = plan_ret_phi_predeclare(block_by_id)
+                if plan:
+                    # Ensure block_phi_incomings map exists
+                    if not hasattr(self, 'block_phi_incomings') or self.block_phi_incomings is None:
+                        self.block_phi_incomings = {}
+                    for bbid, ret_vid in plan.items():
+                        # Create a placeholder PHI at block head if missing
+                        bb0 = self.bb_map.get(bbid)
+                        if bb0 is not None:
+                            b0 = ir.IRBuilder(bb0)
+                            try:
+                                b0.position_at_start(bb0)
+                            except Exception:
+                                pass
+                            cur = self.vmap.get(ret_vid)
+                            need_new = True
+                            try:
+                                need_new = not (cur is not None and hasattr(cur, 'add_incoming'))
+                            except Exception:
+                                need_new = True
+                            if need_new:
+                                ph = b0.phi(self.i64, name=f"phi_ret_{ret_vid}")
+                                self.vmap[ret_vid] = ph
+                            else:
+                                ph = cur
+                            # Record for later unify
+                            try:
+                                self.predeclared_ret_phis[(int(bbid), int(ret_vid))] = ph
+                            except Exception:
+                                pass
+                        # Record declared incoming metadata using the same value-id
+                        # for each predecessor; finalize_phis will resolve per-pred end values.
+                        try:
+                            preds_raw = [p for p in self.preds.get(bbid, []) if p != bbid]
+                        except Exception:
+                            preds_raw = []
+                        # Dedup while preserving order
+                        seen = set()
+                        preds_list = []
+                        for p in preds_raw:
+                            if p not in seen:
+                                preds_list.append(p)
+                                seen.add(p)
+                        try:
+                            # finalize_phis reads pairs as (decl_b, v_src) and maps to nearest predecessor.
+                            # We provide (bb_pred, ret_vid) for all preds.
+                            self.block_phi_incomings.setdefault(int(bbid), {})[int(ret_vid)] = [
+                                (int(p), int(ret_vid)) for p in preds_list
+                            ]
+                        except Exception:
+                            pass
+                        try:
+                            trace_debug(f"[prepass] if-merge: predeclare PHI at bb{bbid} for v{ret_vid} preds={preds_list}")
+                        except Exception:
+                            pass
+        except Exception:
+            pass
+
+        # Optional: simple loop prepass → synthesize a structured while body
+        loop_plan = None
+        try:
+            if os.environ.get('NYASH_LLVM_PREPASS_LOOP') == '1':
+                loop_plan = detect_simple_while(block_by_id)
+                if loop_plan is not None:
+                    trace_debug(f"[prepass] detect loop header=bb{loop_plan['header']} then=bb{loop_plan['then']} latch=bb{loop_plan['latch']} exit=bb{loop_plan['exit']}")
+        except Exception:
+            loop_plan = None
+
+        # Provide predeclared ret-phi map to resolver for ret lowering to reuse
+        try:
+            self.resolver.ret_phi_map = self.predeclared_ret_phis
+        except Exception:
+            pass
+
         # Now lower blocks
+        skipped: set[int] = set()
+        if loop_plan is not None:
+            try:
+                for bskip in loop_plan.get('skip_blocks', []):
+                    if bskip != loop_plan.get('header'):
+                        skipped.add(int(bskip))
+            except Exception:
+                pass
         for bid in order:
             block_data = block_by_id.get(bid)
             if block_data is None:
                 continue
+            # If loop prepass applies, lower while once at header and skip loop-internal blocks
+            if loop_plan is not None and bid == loop_plan.get('header'):
+                bb = self.bb_map[bid]
+                builder = ir.IRBuilder(bb)
+                try:
+                    self.resolver.builder = builder
+                    self.resolver.module = self.module
+                except Exception:
+                    pass
+                # Lower while via loopform (if enabled) or regular fallback
+                self.loop_count += 1
+                body_insts = loop_plan.get('body_insts', [])
+                cond_vid = loop_plan.get('cond')
+                from instructions.loopform import lower_while_loopform
+                ok = False
+                try:
+                    # Use a clean per-while vmap context seeded from global placeholders
+                    self._current_vmap = dict(self.vmap)
+                    ok = lower_while_loopform(builder, func, cond_vid, body_insts,
+                                              self.loop_count, self.vmap, self.bb_map,
+                                              self.resolver, self.preds, self.block_end_values)
+                except Exception:
+                    ok = False
+                if not ok:
+                    # Prepare resolver backref for instruction dispatcher
+                    try:
+                        self.resolver._owner_lower_instruction = self.lower_instruction
+                    except Exception:
+                        pass
+                    lower_while_regular(builder, func, cond_vid, body_insts,
+                                        self.loop_count, self.vmap, self.bb_map,
+                                        self.resolver, self.preds, self.block_end_values)
+                # Clear while vmap context
+                try:
+                    delattr(self, '_current_vmap')
+                except Exception:
+                    pass
+                # Mark blocks to skip
+                for bskip in loop_plan.get('skip_blocks', []):
+                    skipped.add(bskip)
+                # Ensure skipped original blocks have a valid terminator: branch to while exit
+                try:
+                    exit_name = f"while{self.loop_count}_exit"
+                    exit_bb = None
+                    for bbf in func.blocks:
+                        try:
+                            if str(bbf.name) == exit_name:
+                                exit_bb = bbf
+                                break
+                        except Exception:
+                            pass
+                    if exit_bb is not None:
+                        # Connect while exit to original exit block if available
+                        try:
+                            orig_exit_bb = self.bb_map.get(loop_plan.get('exit'))
+                            if orig_exit_bb is not None and exit_bb.terminator is None:
+                                ibx = ir.IRBuilder(exit_bb)
+                                ibx.branch(orig_exit_bb)
+                        except Exception:
+                            pass
+                        for bskip in loop_plan.get('skip_blocks', []):
+                            if bskip == loop_plan.get('header'):
+                                continue
+                            bb_skip = self.bb_map.get(bskip)
+                            if bb_skip is None:
+                                continue
+                            try:
+                                if bb_skip.terminator is None:
+                                    ib = ir.IRBuilder(bb_skip)
+                                    ib.branch(exit_bb)
+                            except Exception:
+                                pass
+                except Exception:
+                    pass
+                continue
+            if bid in skipped:
+                continue
             bb = self.bb_map[bid]
             self.lower_block(bb, block_data, func)
 
@@ -337,10 +511,32 @@ class NyashLLVMBuilder:
             self.resolver.def_blocks = self.def_blocks
             # Provide phi metadata for this function to resolver
             self.resolver.block_phi_incomings = getattr(self, 'block_phi_incomings', {})
+            # Attach a BuildCtx object for future refactors (non-breaking)
+            try:
+                self.ctx = BuildCtx(
+                    module=self.module,
+                    i64=self.i64,
+                    i32=self.i32,
+                    i8=self.i8,
+                    i1=self.i1,
+                    i8p=self.i8p,
+                    vmap=self.vmap,
+                    bb_map=self.bb_map,
+                    preds=self.preds,
+                    block_end_values=self.block_end_values,
+                    resolver=self.resolver,
+                    trace_phi=os.environ.get('NYASH_LLVM_TRACE_PHI') == '1',
+                    verbose=os.environ.get('NYASH_CLI_VERBOSE') == '1',
+                )
+                # Also expose via resolver for convenience until migration completes
+                self.resolver.ctx = self.ctx
+            except Exception:
+                pass
         except Exception:
             pass
         # Finalize PHIs for this function now that all snapshots for it exist
-        self.finalize_phis()
+        _finalize_phis(self)
+
 
     def setup_phi_placeholders(self, blocks: List[Dict[str, Any]]):
         """Predeclare PHIs and collect incoming metadata for finalize_phis.
@@ -439,8 +635,17 @@ class NyashLLVMBuilder:
             pass
     
     def lower_block(self, bb: ir.Block, block_data: Dict[str, Any], func: ir.Function):
-        """Lower a single basic block"""
+        """Lower a single basic block.
+
+        Emit all non-terminator ops first, then control-flow terminators
+        (branch/jump/ret). This avoids generating IR after a terminator.
+        """
         builder = ir.IRBuilder(bb)
+        try:
+            import os
+            trace_debug(f"[llvm-py] === lower_block bb{block_data.get('id')} ===")
+        except Exception:
+            pass
         # Provide builder/module to resolver for PHI/casts insertion
         try:
             self.resolver.builder = builder
@@ -448,54 +653,187 @@ class NyashLLVMBuilder:
         except Exception:
             pass
         instructions = block_data.get("instructions", [])
-        # Lower non-PHI instructions strictly in original program order.
-        # Reordering here can easily introduce use-before-def within the same
-        # basic block (e.g., string ops that depend on prior me.* calls).
+        # Ensure JSON-declared PHIs are materialized at block start before any terminator
+        try:
+            phi_insts = [inst for inst in (instructions or []) if inst.get('op') == 'phi']
+            if phi_insts:
+                btop = ir.IRBuilder(bb)
+                btop.position_at_start(bb)
+                for pinst in phi_insts:
+                    dstp = pinst.get('dst')
+                    if isinstance(dstp, int):
+                        cur = self.vmap.get(dstp)
+                        need_new = True
+                        try:
+                            need_new = not (cur is not None and hasattr(cur, 'add_incoming'))
+                        except Exception:
+                            need_new = True
+                        if need_new:
+                            phi = btop.phi(self.i64, name=f"phi_{dstp}")
+                            self.vmap[dstp] = phi
+        except Exception:
+            pass
+        # Partition into body ops and terminators
+        body_ops: List[Dict[str, Any]] = []
+        term_ops: List[Dict[str, Any]] = []
+        for inst in (instructions or []):
+            opx = inst.get("op")
+            if opx in ("branch", "jump", "ret"):
+                term_ops.append(inst)
+            elif opx == "phi":
+                continue
+            else:
+                body_ops.append(inst)
+        # Per-block SSA map (avoid cross-block vmap pollution)
+        # Seed with non-PHI globals and PHIs that belong to this block only.
+        vmap_cur: Dict[int, ir.Value] = {}
+        try:
+            for _vid, _val in (self.vmap or {}).items():
+                keep = True
+                try:
+                    if hasattr(_val, 'add_incoming'):
+                        bb_of = getattr(getattr(_val, 'basic_block', None), 'name', None)
+                        keep = (bb_of == bb.name)
+                except Exception:
+                    keep = False
+                if keep:
+                    vmap_cur[_vid] = _val
+        except Exception:
+            vmap_cur = dict(self.vmap)
+        # Expose to lower_instruction users (e.g., while_ regular lowering)
+        self._current_vmap = vmap_cur
         created_ids: List[int] = []
-        non_phi_insts = [inst for inst in instructions if inst.get("op") != "phi"]
-        for inst in non_phi_insts:
-            # Stop if a terminator has already been emitted for this block
+        # Compute ids defined in this block to help with copy/PHI decisions
+        defined_here_all: set = set()
+        for _inst in body_ops:
+            try:
+                d = _inst.get('dst')
+                if isinstance(d, int):
+                    defined_here_all.add(d)
+            except Exception:
+                pass
+        # Keep PHI synthesis on-demand in resolver; avoid predeclaring here to reduce clashes.
+        # Lower body ops first in-order
+        for i_idx, inst in enumerate(body_ops):
+            try:
+                import os
+                trace_debug(f"[llvm-py] body op: {inst.get('op')} dst={inst.get('dst')} cond={inst.get('cond')}")
+            except Exception:
+                pass
             try:
                 if bb.terminator is not None:
                     break
             except Exception:
                 pass
             builder.position_at_end(bb)
-            self.lower_instruction(builder, inst, func)
+            # Special-case copy: avoid forward self-block dependencies only when src is defined later in this block
+            if inst.get('op') == 'copy':
+                src_i = inst.get('src')
+                skip_now = False
+                if isinstance(src_i, int):
+                    try:
+                        # Check if src will be defined in a subsequent instruction
+                        for _rest in body_ops[i_idx+1:]:
+                            try:
+                                if int(_rest.get('dst')) == int(src_i):
+                                    skip_now = True
+                                    break
+                            except Exception:
+                                pass
+                    except Exception:
+                        pass
+                if skip_now:
+                    # Skip now; a later copy will remap after src becomes available
+                    pass
+                else:
+                    self.lower_instruction(builder, inst, func)
+            else:
+                self.lower_instruction(builder, inst, func)
+            # Sync per-block vmap snapshot with any new definitions that were
+            # written into the global vmap by lowering routines (e.g., copy)
             try:
                 dst = inst.get("dst")
-                if isinstance(dst, int) and dst not in created_ids and dst in self.vmap:
-                    created_ids.append(dst)
+                if isinstance(dst, int):
+                    if dst in self.vmap:
+                        _gval = self.vmap[dst]
+                        # Avoid syncing PHIs that belong to other blocks (placeholders)
+                        try:
+                            if hasattr(_gval, 'add_incoming'):
+                                bb_of = getattr(getattr(_gval, 'basic_block', None), 'name', None)
+                                if bb_of == bb.name:
+                                    vmap_cur[dst] = _gval
+                            else:
+                                vmap_cur[dst] = _gval
+                        except Exception:
+                            vmap_cur[dst] = _gval
+                    if dst not in created_ids and dst in vmap_cur:
+                        created_ids.append(dst)
             except Exception:
                 pass
+        # Ret-phi proactive insertion removed; resolver handles ret localization as needed.
+
+        # Lower terminators at end, preserving order
+        for inst in term_ops:
+            try:
+                import os
+            trace_debug(f"[llvm-py] term op: {inst.get('op')} dst={inst.get('dst')} cond={inst.get('cond')}")
+            except Exception:
+                pass
+            try:
+                if bb.terminator is not None:
+                    break
+            except Exception:
+                pass
+            builder.position_at_end(bb)
+            # (if-merge handled by resolver + finalize_phis)
+            self.lower_instruction(builder, inst, func)
+        # Sync back local PHIs created in this block into the global vmap so that
+        # finalize_phis targets the same SSA nodes as terminators just used.
+        try:
+            for vid in created_ids:
+                val = vmap_cur.get(vid)
+                if val is not None and hasattr(val, 'add_incoming'):
+                    try:
+                        if getattr(getattr(val, 'basic_block', None), 'name', None) == bb.name:
+                            self.vmap[vid] = val
+                    except Exception:
+                        self.vmap[vid] = val
+        except Exception:
+            pass
         # Snapshot end-of-block values for sealed PHI wiring
         bid = block_data.get("id", 0)
         # Robust snapshot: clone the entire vmap at block end so that
         # values that were not redefined in this block (but remain live)
         # are available to PHI finalize wiring. This avoids omissions of
         # phi-dst/cyclic and carry-over values.
-        snap: Dict[int, ir.Value] = dict(self.vmap)
+        snap: Dict[int, ir.Value] = dict(vmap_cur)
         try:
             import os
-            if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
-                keys = sorted(list(snap.keys()))
-                print(f"[builder] snapshot bb{bid} keys={keys[:20]}...", flush=True)
+            keys = sorted(list(snap.keys()))
+            trace_phi(f"[builder] snapshot bb{bid} keys={keys[:20]}...")
         except Exception:
             pass
         # Record block-local definitions for lifetime hinting
         for vid in created_ids:
-            if vid in self.vmap:
+            if vid in vmap_cur:
                 self.def_blocks.setdefault(vid, set()).add(block_data.get("id", 0))
         self.block_end_values[bid] = snap
+        # Clear current vmap context
+        try:
+            delattr(self, '_current_vmap')
+        except Exception:
+            pass
     
     def lower_instruction(self, builder: ir.IRBuilder, inst: Dict[str, Any], func: ir.Function):
         """Dispatch instruction to appropriate handler"""
         op = inst.get("op")
+        # Pick current vmap context
+        vmap_ctx = getattr(self, '_current_vmap', self.vmap)
         
         if op == "const":
             dst = inst.get("dst")
             value = inst.get("value")
-            lower_const(builder, self.module, dst, value, self.vmap, self.resolver)
+            lower_const(builder, self.module, dst, value, vmap_ctx, self.resolver)
             
         elif op == "binop":
             operation = inst.get("operation")
@@ -504,23 +842,28 @@ class NyashLLVMBuilder:
             dst = inst.get("dst")
             dst_type = inst.get("dst_type")
             lower_binop(builder, self.resolver, operation, lhs, rhs, dst,
-                        self.vmap, builder.block, self.preds, self.block_end_values, self.bb_map,
+                        vmap_ctx, builder.block, self.preds, self.block_end_values, self.bb_map,
                         dst_type=dst_type)
             
         elif op == "jump":
             target = inst.get("target")
             lower_jump(builder, target, self.bb_map)
             
+        elif op == "copy":
+            dst = inst.get("dst")
+            src = inst.get("src")
+            lower_copy(builder, dst, src, vmap_ctx, self.resolver, builder.block, self.preds, self.block_end_values, self.bb_map, getattr(self, 'ctx', None))
+            
         elif op == "branch":
             cond = inst.get("cond")
             then_bid = inst.get("then")
             else_bid = inst.get("else")
-            lower_branch(builder, cond, then_bid, else_bid, self.vmap, self.bb_map, self.resolver, self.preds, self.block_end_values)
+            lower_branch(builder, cond, then_bid, else_bid, vmap_ctx, self.bb_map, self.resolver, self.preds, self.block_end_values)
             
         elif op == "ret":
             value = inst.get("value")
-            lower_return(builder, value, self.vmap, func.function_type.return_type,
-                         self.resolver, self.preds, self.block_end_values, self.bb_map)
+            lower_return(builder, value, vmap_ctx, func.function_type.return_type,
+                         self.resolver, self.preds, self.block_end_values, self.bb_map, getattr(self, 'ctx', None))
             
         elif op == "phi":
             # No-op here: PHIはメタのみ（resolverがon‑demand生成）
@@ -533,15 +876,16 @@ class NyashLLVMBuilder:
             rhs = inst.get("rhs")
             dst = inst.get("dst")
             cmp_kind = inst.get("cmp_kind")
-            lower_compare(builder, operation, lhs, rhs, dst, self.vmap,
+            lower_compare(builder, operation, lhs, rhs, dst, vmap_ctx,
                           self.resolver, builder.block, self.preds, self.block_end_values, self.bb_map,
-                          meta={"cmp_kind": cmp_kind} if cmp_kind else None)
+                          meta={"cmp_kind": cmp_kind} if cmp_kind else None,
+                          ctx=getattr(self, 'ctx', None))
             
         elif op == "call":
             func_name = inst.get("func")
             args = inst.get("args", [])
             dst = inst.get("dst")
-            lower_call(builder, self.module, func_name, args, dst, self.vmap, self.resolver, self.preds, self.block_end_values, self.bb_map)
+            lower_call(builder, self.module, func_name, args, dst, vmap_ctx, self.resolver, self.preds, self.block_end_values, self.bb_map, getattr(self, 'ctx', None))
             
         elif op == "boxcall":
             box_vid = inst.get("box")
@@ -549,7 +893,7 @@ class NyashLLVMBuilder:
             args = inst.get("args", [])
             dst = inst.get("dst")
             lower_boxcall(builder, self.module, box_vid, method, args, dst,
-                          self.vmap, self.resolver, self.preds, self.block_end_values, self.bb_map)
+                          vmap_ctx, self.resolver, self.preds, self.block_end_values, self.bb_map, getattr(self, 'ctx', None))
             # Optional: honor explicit dst_type for tagging (string handle)
             try:
                 dst_type = inst.get("dst_type")
@@ -571,14 +915,14 @@ class NyashLLVMBuilder:
             args = inst.get("args", [])
             dst = inst.get("dst")
             lower_externcall(builder, self.module, func_name, args, dst,
-                             self.vmap, self.resolver, self.preds, self.block_end_values, self.bb_map)
+                             vmap_ctx, self.resolver, self.preds, self.block_end_values, self.bb_map, getattr(self, 'ctx', None))
             
         elif op == "newbox":
             box_type = inst.get("type")
             args = inst.get("args", [])
             dst = inst.get("dst")
             lower_newbox(builder, self.module, box_type, args, dst, 
-                        self.vmap, self.resolver)
+                        vmap_ctx, self.resolver, getattr(self, 'ctx', None))
             
         elif op == "typeop":
             operation = inst.get("operation")
@@ -586,13 +930,14 @@ class NyashLLVMBuilder:
             dst = inst.get("dst")
             target_type = inst.get("target_type")
             lower_typeop(builder, operation, src, dst, target_type,
-                         self.vmap, self.resolver, self.preds, self.block_end_values, self.bb_map)
+                         vmap_ctx, self.resolver, self.preds, self.block_end_values, self.bb_map, getattr(self, 'ctx', None))
             
         elif op == "safepoint":
             live = inst.get("live", [])
-            lower_safepoint(builder, self.module, live, self.vmap,
+            lower_safepoint(builder, self.module, live, vmap_ctx,
                             resolver=self.resolver, preds=self.preds,
-                            block_end_values=self.block_end_values, bb_map=self.bb_map)
+                            block_end_values=self.block_end_values, bb_map=self.bb_map,
+                            ctx=getattr(self, 'ctx', None))
             
         elif op == "barrier":
             barrier_type = inst.get("type", "memory")
@@ -606,11 +951,16 @@ class NyashLLVMBuilder:
             if not lower_while_loopform(builder, func, cond, body,
                                        self.loop_count, self.vmap, self.bb_map,
                                        self.resolver, self.preds, self.block_end_values):
-                # Fallback to regular while
-                self._lower_while_regular(builder, inst, func)
+                # Fallback to regular while (structured)
+                try:
+                    self.resolver._owner_lower_instruction = self.lower_instruction
+                except Exception:
+                    pass
+                lower_while_regular(builder, func, cond, body,
+                                    self.loop_count, self.vmap, self.bb_map,
+                                    self.resolver, self.preds, self.block_end_values)
         else:
-            if os.environ.get('NYASH_CLI_VERBOSE') == '1':
-                print(f"[Python LLVM] Unknown instruction: {op}")
+            trace_debug(f"[Python LLVM] Unknown instruction: {op}")
         # Record per-inst definition for lifetime hinting as soon as available
         try:
             dst_maybe = inst.get("dst")
@@ -642,7 +992,8 @@ class NyashLLVMBuilder:
         # Cond block
         cbuild = ir.IRBuilder(cond_bb)
         try:
-            cond_val = self.resolver.resolve_i64(cond_vid, builder.block, self.preds, self.block_end_values, self.vmap, self.bb_map)
+            # Resolve against the condition block to localize dominance
+            cond_val = self.resolver.resolve_i64(cond_vid, cbuild.block, self.preds, self.block_end_values, self.vmap, self.bb_map)
         except Exception:
             cond_val = self.vmap.get(cond_vid)
         if cond_val is None:
@@ -697,6 +1048,7 @@ class NyashLLVMBuilder:
             for fr in from_list:
                 succs.setdefault(fr, []).append(to_bid)
         for block_id, dst_map in (getattr(self, 'block_phi_incomings', {}) or {}).items():
+            trace_phi(f"[finalize] bb{block_id} dsts={list(dst_map.keys())}")
             bb = self.bb_map.get(block_id)
             if bb is None:
                 continue
@@ -706,15 +1058,34 @@ class NyashLLVMBuilder:
             except Exception:
                 pass
             for dst_vid, incoming in (dst_map or {}).items():
+                trace_phi(f"[finalize]  dst v{dst_vid} incoming={incoming}")
                 # Ensure placeholder exists at block head
-                phi = self.vmap.get(dst_vid)
-                try:
-                    is_phi = hasattr(phi, 'add_incoming')
-                except Exception:
-                    is_phi = False
-                if not is_phi:
-                    phi = b.phi(self.i64, name=f"phi_{dst_vid}")
+                # Prefer predeclared ret-phi when available and force using it.
+                predecl = getattr(self, 'predeclared_ret_phis', {}) if hasattr(self, 'predeclared_ret_phis') else {}
+                phi = predecl.get((int(block_id), int(dst_vid))) if predecl else None
+                if phi is not None:
+                    # Bind as canonical target
                     self.vmap[dst_vid] = phi
+                else:
+                    phi = self.vmap.get(dst_vid)
+                    # Ensure we target a PHI belonging to the current block; if a
+                    # global mapping points to a PHI in another block (due to
+                    # earlier localization), create/replace with a local PHI.
+                    need_local_phi = False
+                    try:
+                        if not (phi is not None and hasattr(phi, 'add_incoming')):
+                            need_local_phi = True
+                        else:
+                            bb_of_phi = getattr(getattr(phi, 'basic_block', None), 'name', None)
+                            if bb_of_phi != bb.name:
+                                need_local_phi = True
+                    except Exception:
+                        need_local_phi = True
+                    if need_local_phi:
+                        phi = b.phi(self.i64, name=f"phi_{dst_vid}")
+                        self.vmap[dst_vid] = phi
+                n = getattr(phi, 'name', b'').decode() if hasattr(getattr(phi, 'name', None), 'decode') else str(getattr(phi, 'name', ''))
+                trace_phi(f"[finalize]  target phi={n}")
                 # Wire incoming per CFG predecessor; map src_vid when provided
                 preds_raw = [p for p in self.preds.get(block_id, []) if p != block_id]
                 # Deduplicate while preserving order
@@ -820,6 +1191,10 @@ class NyashLLVMBuilder:
                     if pred_bb is None:
                         continue
                     phi.add_incoming(val, pred_bb)
+                    try:
+                        trace_phi(f"[finalize]   add incoming: bb{pred_bid} -> v{dst_vid}")
+                    except Exception:
+                        pass
                 # Tag dst as string-ish if any declared source was string-ish (post-lowering info)
                 try:
                     if hasattr(self.resolver, 'is_stringish') and hasattr(self.resolver, 'mark_string'):
diff --git a/src/llvm_py/phi_wiring.py b/src/llvm_py/phi_wiring.py
new file mode 100644
index 00000000..2413a96e
--- /dev/null
+++ b/src/llvm_py/phi_wiring.py
@@ -0,0 +1,200 @@
+"""
+PHI wiring helpers
+
+- setup_phi_placeholders: Predeclare PHIs and collect incoming metadata
+- finalize_phis: Wire PHI incomings using end-of-block snapshots and resolver
+
+These operate on the NyashLLVMBuilder instance to keep changes minimal.
+"""
+
+from typing import Dict, List, Any
+import llvmlite.ir as ir
+
+def setup_phi_placeholders(builder, blocks: List[Dict[str, Any]]):
+    """Predeclare PHIs and collect incoming metadata for finalize_phis.
+
+    This pass is function-local and must be invoked after basic blocks are
+    created and before lowering individual blocks. It also tags string-ish
+    values eagerly to help downstream resolvers choose correct intrinsics.
+    """
+    try:
+        # Pass A: collect producer stringish hints per value-id
+        produced_str: Dict[int, bool] = {}
+        for block_data in blocks:
+            for inst in block_data.get("instructions", []) or []:
+                try:
+                    opx = inst.get("op")
+                    dstx = inst.get("dst")
+                    if dstx is None:
+                        continue
+                    is_str = False
+                    if opx == "const":
+                        v = inst.get("value", {}) or {}
+                        t = v.get("type")
+                        if t == "string" or (isinstance(t, dict) and t.get("kind") in ("handle","ptr") and t.get("box_type") == "StringBox"):
+                            is_str = True
+                    elif opx in ("binop","boxcall","externcall"):
+                        t = inst.get("dst_type")
+                        if isinstance(t, dict) and t.get("kind") == "handle" and t.get("box_type") == "StringBox":
+                            is_str = True
+                    if is_str:
+                        produced_str[int(dstx)] = True
+                except Exception:
+                    pass
+        # Pass B: materialize PHI placeholders and record incoming metadata
+        builder.block_phi_incomings = {}
+        for block_data in blocks:
+            bid0 = block_data.get("id", 0)
+            bb0 = builder.bb_map.get(bid0)
+            for inst in block_data.get("instructions", []) or []:
+                if inst.get("op") == "phi":
+                    try:
+                        dst0 = int(inst.get("dst"))
+                        incoming0 = inst.get("incoming", []) or []
+                    except Exception:
+                        dst0 = None; incoming0 = []
+                    if dst0 is None:
+                        continue
+                    # Record incoming metadata for finalize_phis
+                    try:
+                        builder.block_phi_incomings.setdefault(bid0, {})[dst0] = [
+                            (int(b), int(v)) for (v, b) in incoming0
+                        ]
+                    except Exception:
+                        pass
+                    # Ensure placeholder exists at block head
+                    if bb0 is not None:
+                        b0 = ir.IRBuilder(bb0)
+                        try:
+                            b0.position_at_start(bb0)
+                        except Exception:
+                            pass
+                        existing = builder.vmap.get(dst0)
+                        is_phi = False
+                        try:
+                            is_phi = hasattr(existing, 'add_incoming')
+                        except Exception:
+                            is_phi = False
+                        if not is_phi:
+                            ph0 = b0.phi(builder.i64, name=f"phi_{dst0}")
+                            builder.vmap[dst0] = ph0
+                        # Tag propagation: if explicit dst_type marks string or any incoming was produced as string-ish, tag dst
+                        try:
+                            dst_type0 = inst.get("dst_type")
+                            mark_str = isinstance(dst_type0, dict) and dst_type0.get("kind") == "handle" and dst_type0.get("box_type") == "StringBox"
+                            if not mark_str:
+                                for (_b_decl_i, v_src_i) in incoming0:
+                                    try:
+                                        if produced_str.get(int(v_src_i)):
+                                            mark_str = True; break
+                                    except Exception:
+                                        pass
+                            if mark_str and hasattr(builder.resolver, 'mark_string'):
+                                builder.resolver.mark_string(int(dst0))
+                        except Exception:
+                            pass
+    except Exception:
+        pass
+
+def finalize_phis(builder):
+    """Finalize PHIs declared in JSON by wiring incoming edges at block heads.
+    Uses resolver._value_at_end_i64 to materialize values at predecessor ends,
+    ensuring casts/boxing are inserted in predecessor blocks (dominance-safe)."""
+    # Build succ map for nearest-predecessor mapping
+    succs: Dict[int, List[int]] = {}
+    for to_bid, from_list in (builder.preds or {}).items():
+        for fr in from_list:
+            succs.setdefault(fr, []).append(to_bid)
+    for block_id, dst_map in (getattr(builder, 'block_phi_incomings', {}) or {}).items():
+        bb = builder.bb_map.get(block_id)
+        if bb is None:
+            continue
+        b = ir.IRBuilder(bb)
+        try:
+            b.position_at_start(bb)
+        except Exception:
+            pass
+        for dst_vid, incoming in (dst_map or {}).items():
+            # Ensure placeholder exists at block head
+            # Prefer predeclared ret-phi when available and force using it.
+            predecl = getattr(builder, 'predeclared_ret_phis', {}) if hasattr(builder, 'predeclared_ret_phis') else {}
+            phi = predecl.get((int(block_id), int(dst_vid))) if predecl else None
+            if phi is not None:
+                builder.vmap[dst_vid] = phi
+            else:
+                phi = builder.vmap.get(dst_vid)
+                need_local_phi = False
+                try:
+                    if not (phi is not None and hasattr(phi, 'add_incoming')):
+                        need_local_phi = True
+                    else:
+                        bb_of_phi = getattr(getattr(phi, 'basic_block', None), 'name', None)
+                        if bb_of_phi != bb.name:
+                            need_local_phi = True
+                except Exception:
+                    need_local_phi = True
+                if need_local_phi:
+                    phi = b.phi(builder.i64, name=f"phi_{dst_vid}")
+                    builder.vmap[dst_vid] = phi
+            # Wire incoming per CFG predecessor; map src_vid when provided
+            preds_raw = [p for p in builder.preds.get(block_id, []) if p != block_id]
+            # Deduplicate while preserving order
+            seen = set()
+            preds_list: List[int] = []
+            for p in preds_raw:
+                if p not in seen:
+                    preds_list.append(p)
+                    seen.add(p)
+            # Helper: find the nearest immediate predecessor on a path decl_b -> ... -> block_id
+            def nearest_pred_on_path(decl_b: int):
+                from collections import deque
+                q = deque([decl_b])
+                visited = set([decl_b])
+                parent: Dict[int, Any] = {decl_b: None}
+                while q:
+                    cur = q.popleft()
+                    if cur == block_id:
+                        par = parent.get(block_id)
+                        return par if par in preds_list else None
+                    for nx in succs.get(cur, []):
+                        if nx not in visited:
+                            visited.add(nx)
+                            parent[nx] = cur
+                            q.append(nx)
+                return None
+            # Precompute a non-self initial source (if present) to use for self-carry cases
+            init_src_vid = None
+            for (b_decl0, v_src0) in incoming:
+                try:
+                    vs0 = int(v_src0)
+                except Exception:
+                    continue
+                if vs0 != int(dst_vid):
+                    init_src_vid = vs0
+                    break
+            # Pre-resolve declared incomings to nearest immediate predecessors
+            chosen: Dict[int, ir.Value] = {}
+            for (b_decl, v_src) in incoming:
+                try:
+                    bd = int(b_decl); vs = int(v_src)
+                except Exception:
+                    continue
+                pred_match = nearest_pred_on_path(bd)
+                if pred_match is None:
+                    continue
+                if vs == int(dst_vid) and init_src_vid is not None:
+                    vs = int(init_src_vid)
+                try:
+                    val = builder.resolver._value_at_end_i64(vs, pred_match, builder.preds, builder.block_end_values, builder.vmap, builder.bb_map)
+                except Exception:
+                    val = None
+                if val is None:
+                    # As a last resort, zero
+                    val = ir.Constant(builder.i64, 0)
+                chosen[pred_match] = val
+            # Finally add incomings
+            for pred_bid, val in chosen.items():
+                pred_bb = builder.bb_map.get(pred_bid)
+                if pred_bb is None:
+                    continue
+                phi.add_incoming(val, pred_bb)
diff --git a/src/llvm_py/prepass/if_merge.py b/src/llvm_py/prepass/if_merge.py
new file mode 100644
index 00000000..932c3e78
--- /dev/null
+++ b/src/llvm_py/prepass/if_merge.py
@@ -0,0 +1,35 @@
+"""
+If-merge prepass utilities
+For blocks that end with return and have multiple predecessors, plan PHI predeclare for return value ids.
+"""
+
+from typing import Dict, Any, Optional
+from cfg.utils import build_preds_succs
+
+def plan_ret_phi_predeclare(block_by_id: Dict[int, Dict[str, Any]]) -> Optional[Dict[int, int]]:
+    """Return a map {block_id: value_id} for blocks that end with ret <value>
+    and have multiple predecessors. The caller can predeclare a PHI for value_id
+    at the block head to ensure dominance for the return.
+    """
+    preds, _ = build_preds_succs(block_by_id)
+    plan: Dict[int, int] = {}
+    for bid, blk in block_by_id.items():
+        term = None
+        if blk.get('instructions'):
+            last = blk.get('instructions')[-1]
+            if last.get('op') in ('jump','branch','ret'):
+                term = last
+        if term is None and 'terminator' in blk:
+            t = blk['terminator']
+            if t and t.get('op') in ('jump','branch','ret'):
+                term = t
+        if not term or term.get('op') != 'ret':
+            continue
+        val = term.get('value')
+        if not isinstance(val, int):
+            continue
+        pred_list = [p for p in preds.get(int(bid), []) if p != int(bid)]
+        if len(pred_list) > 1:
+            plan[int(bid)] = int(val)
+    return plan or None
+
diff --git a/src/llvm_py/prepass/loops.py b/src/llvm_py/prepass/loops.py
new file mode 100644
index 00000000..4ec62306
--- /dev/null
+++ b/src/llvm_py/prepass/loops.py
@@ -0,0 +1,106 @@
+"""
+Loop prepass utilities
+Detect simple while-shaped loops in MIR(JSON) and return a lowering plan.
+"""
+
+from typing import Dict, List, Any, Optional
+from cfg.utils import build_preds_succs
+
+def detect_simple_while(block_by_id: Dict[int, Dict[str, Any]]) -> Optional[Dict[str, Any]]:
+    """Detect a simple loop pattern: header(branch cond → then/else),
+    a latch that jumps back to header reachable from then, and exit on else.
+    Returns a plan dict or None.
+    """
+    # Build succ and pred maps from JSON quickly
+    preds, succs = build_preds_succs(block_by_id)
+    # Find a header with a branch terminator and else leading to a ret (direct)
+    for b in block_by_id.values():
+        bid = int(b.get('id', 0))
+        term = None
+        if b.get('instructions'):
+            last = b.get('instructions')[-1]
+            if last.get('op') in ('jump','branch','ret'):
+                term = last
+        if term is None and 'terminator' in b:
+            t = b['terminator']
+            if t and t.get('op') in ('jump','branch','ret'):
+                term = t
+        if not term or term.get('op') != 'branch':
+            continue
+        then_bid = int(term.get('then'))
+        else_bid = int(term.get('else'))
+        cond_vid = int(term.get('cond')) if term.get('cond') is not None else None
+        if cond_vid is None:
+            continue
+        # Quick check: else block ends with ret
+        else_blk = block_by_id.get(else_bid)
+        has_ret = False
+        if else_blk is not None:
+            insts = else_blk.get('instructions', [])
+            if insts and insts[-1].get('op') == 'ret':
+                has_ret = True
+            elif else_blk.get('terminator', {}).get('op') == 'ret':
+                has_ret = True
+        if not has_ret:
+            continue
+        # Find a latch that jumps back to header reachable from then
+        latch = None
+        visited = set()
+        stack = [then_bid]
+        while stack:
+            cur = stack.pop()
+            if cur in visited:
+                continue
+            visited.add(cur)
+            cur_blk = block_by_id.get(cur)
+            if cur_blk is None:
+                continue
+            for inst in cur_blk.get('instructions', []) or []:
+                if inst.get('op') == 'jump' and int(inst.get('target')) == bid:
+                    latch = cur
+                    break
+            if latch is not None:
+                break
+            for nx in succs.get(cur, []) or []:
+                if nx not in visited and nx != else_bid:
+                    stack.append(nx)
+        if latch is None:
+            continue
+        # Compose body_insts: collect insts along then-branch region up to latch (inclusive),
+        # excluding any final jump back to header to prevent double edges.
+        collect_order: List[int] = []
+        visited2 = set()
+        stack2 = [then_bid]
+        while stack2:
+            cur = stack2.pop()
+            if cur in visited2 or cur == bid or cur == else_bid:
+                continue
+            visited2.add(cur)
+            collect_order.append(cur)
+            if cur == latch:
+                continue
+            for nx in succs.get(cur, []) or []:
+                if nx not in visited2 and nx != else_bid:
+                    stack2.append(nx)
+        body_insts: List[Dict[str, Any]] = []
+        for bbid in collect_order:
+            blk = block_by_id.get(bbid)
+            if blk is None:
+                continue
+            for inst in blk.get('instructions', []) or []:
+                if inst.get('op') == 'jump' and int(inst.get('target', -1)) == bid:
+                    continue
+                body_insts.append(inst)
+        skip_blocks = set(collect_order)
+        skip_blocks.add(bid)
+        return {
+            'header': bid,
+            'then': then_bid,
+            'else': else_bid,
+            'latch': latch,
+            'exit': else_bid,
+            'cond': cond_vid,
+            'body_insts': body_insts,
+            'skip_blocks': list(skip_blocks),
+        }
+    return None
diff --git a/src/llvm_py/pyvm/vm.py b/src/llvm_py/pyvm/vm.py
index 1b5c0270..903dc20d 100644
--- a/src/llvm_py/pyvm/vm.py
+++ b/src/llvm_py/pyvm/vm.py
@@ -112,8 +112,17 @@ class PyVM:
         cur = min(fn.blocks.keys())
         prev: Optional[int] = None
 
-        # Simple block execution loop
+        # Simple block execution loop with step budget to avoid infinite hangs
+        max_steps = 0
+        try:
+            max_steps = int(os.environ.get("NYASH_PYVM_MAX_STEPS", "200000"))
+        except Exception:
+            max_steps = 200000
+        steps = 0
         while True:
+            steps += 1
+            if max_steps and steps > max_steps:
+                raise RuntimeError(f"pyvm: max steps exceeded ({max_steps}) in function {fn.name}")
             block = fn.blocks.get(cur)
             if block is None:
                 raise RuntimeError(f"block not found: {cur}")
@@ -226,18 +235,28 @@ class PyVM:
                     a = self._read(regs, inst.get("lhs"))
                     b = self._read(regs, inst.get("rhs"))
                     res: bool
-                    if operation == "==":
+                    # For ordering comparisons, be robust to None by coercing to ints
+                    if operation in ("<", "<=", ">", ">="):
+                        try:
+                            ai = 0 if a is None else (int(a) if not isinstance(a, str) else 0)
+                        except Exception:
+                            ai = 0
+                        try:
+                            bi = 0 if b is None else (int(b) if not isinstance(b, str) else 0)
+                        except Exception:
+                            bi = 0
+                        if operation == "<":
+                            res = ai < bi
+                        elif operation == "<=":
+                            res = ai <= bi
+                        elif operation == ">":
+                            res = ai > bi
+                        else:
+                            res = ai >= bi
+                    elif operation == "==":
                         res = (a == b)
                     elif operation == "!=":
                         res = (a != b)
-                    elif operation == "<":
-                        res = (a < b)
-                    elif operation == "<=":
-                        res = (a <= b)
-                    elif operation == ">":
-                        res = (a > b)
-                    elif operation == ">=":
-                        res = (a >= b)
                     else:
                         raise RuntimeError(f"unsupported compare: {operation}")
                     # VM convention: booleans are i64 0/1
@@ -287,6 +306,12 @@ class PyVM:
                     i += 1
                     continue
 
+                if op == "copy":
+                    src = self._read(regs, inst.get("src"))
+                    self._set(regs, inst.get("dst"), src)
+                    i += 1
+                    continue
+
                 if op == "boxcall":
                     recv = self._read(regs, inst.get("box"))
                     method = inst.get("method")
diff --git a/src/llvm_py/resolver.py b/src/llvm_py/resolver.py
index 0f132ad2..8e132929 100644
--- a/src/llvm_py/resolver.py
+++ b/src/llvm_py/resolver.py
@@ -5,6 +5,8 @@ Based on src/backend/llvm/compiler/codegen/instructions/resolver.rs
 
 from typing import Dict, Optional, Any, Tuple
 import os
+from trace import phi as trace_phi
+from trace import values as trace_values
 import llvmlite.ir as ir
 
 class Resolver:
@@ -26,6 +28,13 @@ class Resolver:
             # Legacy constructor (vmap, bb_map) — builder/module will be set later when available
             self.builder = None
             self.module = None
+            try:
+                # Keep references to global maps when provided
+                self.global_vmap = a if isinstance(a, dict) else None
+                self.global_bb_map = b if isinstance(b, dict) else None
+            except Exception:
+                self.global_vmap = None
+                self.global_bb_map = None
         
         # Caches: (block_name, value_id) -> llvm value
         self.i64_cache: Dict[Tuple[str, int], ir.Value] = {}
@@ -95,9 +104,35 @@ class Resolver:
                 bmap = self.block_phi_incomings.get(block_id)
                 if isinstance(bmap, dict) and value_id in bmap:
                     existing_cur = vmap.get(value_id)
-                    if existing_cur is not None and hasattr(existing_cur, 'add_incoming'):
+                    # Use placeholder only if it belongs to the current block; otherwise
+                    # create/ensure a local PHI at the current block head to dominate uses.
+                    is_phi_here = False
+                    try:
+                        is_phi_here = (
+                            existing_cur is not None
+                            and hasattr(existing_cur, 'add_incoming')
+                            and getattr(getattr(existing_cur, 'basic_block', None), 'name', None) == current_block.name
+                        )
+                    except Exception:
+                        is_phi_here = False
+                    if is_phi_here:
                         self.i64_cache[cache_key] = existing_cur
                         return existing_cur
+                    # Materialize a local PHI placeholder at block start and bind to vmap
+                    b = ir.IRBuilder(current_block)
+                    try:
+                        b.position_at_start(current_block)
+                    except Exception:
+                        pass
+                    phi_local = b.phi(self.i64, name=f"phi_{value_id}")
+                    vmap[value_id] = phi_local
+                    try:
+                        if isinstance(getattr(self, 'global_vmap', None), dict):
+                            self.global_vmap[value_id] = phi_local
+                    except Exception:
+                        pass
+                    self.i64_cache[cache_key] = phi_local
+                    return phi_local
         except Exception:
             pass
         
@@ -116,8 +151,7 @@ class Resolver:
         if defined_here:
             existing = vmap.get(value_id)
             if existing is not None and hasattr(existing, 'type') and isinstance(existing.type, ir.IntType) and existing.type.width == 64:
-                if os.environ.get('NYASH_LLVM_TRACE_VALUES') == '1':
-                    print(f"[resolve] local reuse: bb{bid} v{value_id}", flush=True)
+                trace_values(f"[resolve] local reuse: bb{bid} v{value_id}")
                 self.i64_cache[cache_key] = existing
                 return existing
         else:
@@ -131,8 +165,7 @@ class Resolver:
             base_val = vmap.get(value_id)
             if base_val is None:
                 result = ir.Constant(self.i64, 0)
-                if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
-                    print(f"[resolve] bb{bid} v{value_id} entry/no-preds → 0", flush=True)
+                trace_phi(f"[resolve] bb{bid} v{value_id} entry/no-preds → 0")
             else:
                 # If pointer string, box to handle in current block (use local builder)
                 if hasattr(base_val, 'type') and isinstance(base_val.type, ir.PointerType) and self.module is not None:
@@ -185,8 +218,7 @@ class Resolver:
                 declared = False
             if declared:
                 # Return existing placeholder if present; do not create a new PHI here.
-                if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
-                    print(f"[resolve] use placeholder PHI: bb{cur_bid} v{value_id}", flush=True)
+                trace_phi(f"[resolve] use placeholder PHI: bb{cur_bid} v{value_id}")
                 placeholder = vmap.get(value_id)
                 result = placeholder if (placeholder is not None and hasattr(placeholder, 'add_incoming')) else ir.Constant(self.i64, 0)
             else:
@@ -258,19 +290,14 @@ class Resolver:
                           bb_map: Optional[Dict[int, ir.Block]] = None,
                           _vis: Optional[set] = None) -> ir.Value:
         """Resolve value as i64 at the end of a given block by traversing predecessors if needed."""
-        if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
-            try:
-                print(f"[resolve] end_i64 enter: bb{block_id} v{value_id}", flush=True)
-            except Exception:
-                pass
+        trace_phi(f"[resolve] end_i64 enter: bb{block_id} v{value_id}")
         key = (block_id, value_id)
         if key in self._end_i64_cache:
             return self._end_i64_cache[key]
         if _vis is None:
             _vis = set()
         if key in _vis:
-            if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
-                print(f"[resolve] cycle detected at end_i64(bb{block_id}, v{value_id}) → 0", flush=True)
+            trace_phi(f"[resolve] cycle detected at end_i64(bb{block_id}, v{value_id}) → 0")
             return ir.Constant(self.i64, 0)
         _vis.add(key)
 
@@ -285,16 +312,21 @@ class Resolver:
                 is_phi_val = hasattr(val, 'add_incoming')
             except Exception:
                 is_phi_val = False
-            if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
-                try:
-                    ty = 'phi' if is_phi_val else ('ptr' if hasattr(val, 'type') and isinstance(val.type, ir.PointerType) else ('i'+str(getattr(val.type,'width','?')) if hasattr(val,'type') and isinstance(val.type, ir.IntType) else 'other'))
-                    print(f"[resolve]  snap hit: bb{block_id} v{value_id} type={ty}", flush=True)
-                except Exception:
-                    pass
+            try:
+                ty = 'phi' if is_phi_val else ('ptr' if hasattr(val, 'type') and isinstance(val.type, ir.PointerType) else ('i'+str(getattr(val.type,'width','?')) if hasattr(val,'type') and isinstance(val.type, ir.IntType) else 'other'))
+                trace_phi(f"[resolve]  snap hit: bb{block_id} v{value_id} type={ty}")
+            except Exception:
+                pass
             if is_phi_val:
-                # Using a dominating PHI placeholder as incoming is valid for finalize_phis
-                self._end_i64_cache[key] = val
-                return val
+                # Accept PHI only when it belongs to the same block (dominates end-of-block).
+                try:
+                    belongs_here = (getattr(getattr(val, 'basic_block', None), 'name', b'').decode() if hasattr(getattr(val, 'basic_block', None), 'name') else str(getattr(getattr(val, 'basic_block', None), 'name', ''))) == f"bb{block_id}"
+                except Exception:
+                    belongs_here = False
+                if belongs_here:
+                    self._end_i64_cache[key] = val
+                    return val
+                # Otherwise ignore and try predecessors to avoid self-carry from foreign PHI
             coerced = self._coerce_in_block_to_i64(val, block_id, bb_map)
             self._end_i64_cache[key] = coerced
             return coerced
@@ -310,9 +342,8 @@ class Resolver:
         # Do not use global vmap here; if not materialized by end of this block
         # (or its preds), bail out with zero to preserve dominance.
 
-        if os.environ.get('NYASH_LLVM_TRACE_PHI') == '1':
-            preds_s = ','.join(str(x) for x in pred_ids)
-            print(f"[resolve] end_i64 miss: bb{block_id} v{value_id} preds=[{preds_s}] → 0", flush=True)
+        preds_s = ','.join(str(x) for x in pred_ids)
+        trace_phi(f"[resolve] end_i64 miss: bb{block_id} v{value_id} preds=[{preds_s}] → 0")
         z = ir.Constant(self.i64, 0)
         self._end_i64_cache[key] = z
         return z
diff --git a/src/llvm_py/test_simple.py b/src/llvm_py/test_simple.py
index e7aa6658..c8bad0b1 100644
--- a/src/llvm_py/test_simple.py
+++ b/src/llvm_py/test_simple.py
@@ -1,51 +1,36 @@
 #!/usr/bin/env python3
 """
-Simple test for Nyash LLVM Python backend
-Tests basic MIR -> LLVM compilation
+Simple smoke for Nyash LLVM Python backend
+Generates a minimal MIR(JSON) in the current schema and compiles it.
 """
 
-import json
 from llvm_builder import NyashLLVMBuilder
 
-# Simple MIR test case: function that returns 42
-test_mir = {
-    "functions": {
-        "main": {
+# Minimal MIR(JSON): main() { ret 42 }
+TEST_MIR = {
+    "functions": [
+        {
             "name": "main",
             "params": [],
-            "return_type": "i64",
-            "entry_block": 0,
-            "blocks": {
-                "0": {
+            "blocks": [
+                {
+                    "id": 0,
                     "instructions": [
-                        {
-                            "kind": "Const",
-                            "dst": 0,
-                            "value": {"type": "i64", "value": 42}
-                        }
-                    ],
-                    "terminator": {
-                        "kind": "Return",
-                        "value": 0
-                    }
+                        {"op": "const", "dst": 0, "value": {"type": "i64", "value": 42}},
+                        {"op": "ret", "value": 0}
+                    ]
                 }
-            }
+            ]
         }
-    }
+    ]
 }
 
 def test_basic():
-    """Test basic MIR -> LLVM compilation"""
     builder = NyashLLVMBuilder()
-    
-    # Generate LLVM IR
-    llvm_ir = builder.build_from_mir(test_mir)
-    print("Generated LLVM IR:")
-    print(llvm_ir)
-    
-    # Compile to object file
+    ir = builder.build_from_mir(TEST_MIR)
+    print("Generated LLVM IR (truncated):\n", ir.splitlines()[0:8])
     builder.compile_to_object("test_simple.o")
-    print("\nCompiled to test_simple.o")
+    print("Compiled to test_simple.o")
 
 if __name__ == "__main__":
-    test_basic()
\ No newline at end of file
+    test_basic()
diff --git a/src/llvm_py/trace.py b/src/llvm_py/trace.py
new file mode 100644
index 00000000..38f9e6ae
--- /dev/null
+++ b/src/llvm_py/trace.py
@@ -0,0 +1,41 @@
+"""
+Lightweight tracing helpers for the LLVM Python backend.
+
+Environment flags (string '1' to enable):
+- NYASH_CLI_VERBOSE: general lowering/debug logs
+- NYASH_LLVM_TRACE_PHI: PHI resolution/snapshot wiring logs
+- NYASH_LLVM_TRACE_VALUES: value resolution logs
+
+Import and use:
+  from trace import debug, phi, values
+  debug("message")
+  phi("phi message")
+  values("values message")
+"""
+
+import os
+
+def _enabled(env_key: str) -> bool:
+    return os.environ.get(env_key) == '1'
+
+def debug(msg: str) -> None:
+    if _enabled('NYASH_CLI_VERBOSE'):
+        try:
+            print(msg, flush=True)
+        except Exception:
+            pass
+
+def phi(msg: str) -> None:
+    if _enabled('NYASH_LLVM_TRACE_PHI'):
+        try:
+            print(msg, flush=True)
+        except Exception:
+            pass
+
+def values(msg: str) -> None:
+    if _enabled('NYASH_LLVM_TRACE_VALUES'):
+        try:
+            print(msg, flush=True)
+        except Exception:
+            pass
+
diff --git a/src/llvm_py/utils/values.py b/src/llvm_py/utils/values.py
new file mode 100644
index 00000000..802d8729
--- /dev/null
+++ b/src/llvm_py/utils/values.py
@@ -0,0 +1,31 @@
+"""
+Value resolution helpers
+Centralize policies like "prefer same-block SSA; otherwise resolve with dominance".
+"""
+
+from typing import Any, Dict, Optional
+import llvmlite.ir as ir
+
+def resolve_i64_strict(
+    resolver,
+    value_id: int,
+    current_block: ir.Block,
+    preds: Dict[int, list],
+    block_end_values: Dict[int, Dict[int, Any]],
+    vmap: Dict[int, Any],
+    bb_map: Optional[Dict[int, ir.Block]] = None,
+    *,
+    prefer_local: bool = True,
+) -> ir.Value:
+    """Resolve i64 under policies:
+    - If prefer_local and vmap has a same-block definition, reuse it.
+    - Otherwise, delegate to resolver to localize with PHI/casts as needed.
+    """
+    # Prefer current vmap SSA first (block-local map is passed in vmap)
+    val = vmap.get(value_id)
+    if prefer_local and val is not None:
+        return val
+    # Fallback to resolver
+    if resolver is None:
+        return ir.Constant(ir.IntType(64), 0)
+    return resolver.resolve_i64(value_id, current_block, preds, block_end_values, vmap, bb_map)
diff --git a/src/main.rs b/src/main.rs
index 55442ddd..2b590bbb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,7 +20,11 @@ pub mod environment;
 pub mod exception_box;
 pub mod finalization;
 pub mod instance_v2; // 🎯 Phase 9.78d: Simplified InstanceBox implementation
+// Legacy interpreter module is not included by default; when disabled, re-export lib's stub
+#[cfg(feature = "interpreter-legacy")]
 pub mod interpreter;
+#[cfg(not(feature = "interpreter-legacy"))]
+pub mod interpreter { pub use nyash_rust::interpreter::*; }
 pub mod messaging; // 🌐 P2P Communication Infrastructure
 pub mod method_box;
 pub mod operator_traits;
@@ -41,8 +45,7 @@ pub mod backend;
 pub mod jit;
 pub mod semantics; // mirror library semantics module for crate path consistency in bin
 
-// 📊 Performance Benchmarks
-pub mod benchmarks;
+// 📊 Performance Benchmarks (lib provides; bin does not re-declare)
 
 // 🚀 Refactored modules for better organization
 pub mod cli;
diff --git a/src/mir/builder/phi.rs b/src/mir/builder/phi.rs
index 51c969ba..a35a3c6a 100644
--- a/src/mir/builder/phi.rs
+++ b/src/mir/builder/phi.rs
@@ -73,6 +73,8 @@ impl MirBuilder {
         &mut self,
         then_block: BasicBlockId,
         else_block: BasicBlockId,
+        then_exit_block_opt: Option<BasicBlockId>,
+        else_exit_block_opt: Option<BasicBlockId>,
         then_value_raw: ValueId,
         else_value_raw: ValueId,
         pre_if_var_map: &HashMap<String, ValueId>,
@@ -91,6 +93,33 @@ impl MirBuilder {
         let result_val = self.value_gen.next();
 
         if self.is_no_phi_mode() {
+            // In PHI-off mode, emit per-predecessor copies into the actual predecessors
+            // of the current (merge) block instead of the entry blocks. This correctly
+            // handles nested conditionals where the then-branch fans out and merges later.
+            let merge_block = self
+                .current_block
+                .ok_or_else(|| "normalize_if_else_phi: no current (merge) block".to_string())?;
+            let preds: Vec<crate::mir::BasicBlockId> = if let Some(ref fun_ro) = self.current_function {
+                if let Some(bb) = fun_ro.get_block(merge_block) {
+                    bb.predecessors.iter().copied().collect()
+                } else {
+                    Vec::new()
+                }
+            } else {
+                Vec::new()
+            };
+            // Prefer explicit exit blocks if provided; fall back to predecessor scan
+            let then_exits: Vec<crate::mir::BasicBlockId> = if let Some(b) = then_exit_block_opt {
+                vec![b]
+            } else {
+                preds.iter().copied().filter(|p| *p != else_block).collect()
+            };
+            let else_exits: Vec<crate::mir::BasicBlockId> = if let Some(b) = else_exit_block_opt {
+                vec![b]
+            } else {
+                preds.iter().copied().filter(|p| *p == else_block).collect()
+            };
+
             if let Some(var_name) = assigned_var_then.clone() {
                 let else_assigns_same = assigned_var_else
                     .as_ref()
@@ -108,13 +137,22 @@ impl MirBuilder {
                 } else {
                     pre_then_var_value.unwrap_or(else_value_raw)
                 };
-                self.insert_edge_copy(then_block, result_val, then_value_for_var)?;
-                self.insert_edge_copy(else_block, result_val, else_value_for_var)?;
+                // Map predecessors: else_block retains else value; others take then value
+                for p in then_exits.iter().copied() {
+                    self.insert_edge_copy(p, result_val, then_value_for_var)?;
+                }
+                for p in else_exits.iter().copied() {
+                    self.insert_edge_copy(p, result_val, else_value_for_var)?;
+                }
                 self.variable_map = pre_if_var_map.clone();
                 self.variable_map.insert(var_name, result_val);
             } else {
-                self.insert_edge_copy(then_block, result_val, then_value_raw)?;
-                self.insert_edge_copy(else_block, result_val, else_value_raw)?;
+                for p in then_exits.iter().copied() {
+                    self.insert_edge_copy(p, result_val, then_value_raw)?;
+                }
+                for p in else_exits.iter().copied() {
+                    self.insert_edge_copy(p, result_val, else_value_raw)?;
+                }
                 self.variable_map = pre_if_var_map.clone();
             }
             return Ok(result_val);
diff --git a/src/mir/builder/stmts.rs b/src/mir/builder/stmts.rs
index af565345..fdd7b3ed 100644
--- a/src/mir/builder/stmts.rs
+++ b/src/mir/builder/stmts.rs
@@ -187,6 +187,7 @@ impl super::MirBuilder {
         // Build then with a clean snapshot of pre-if variables
         self.variable_map = pre_if_var_map.clone();
         let then_value_raw = self.build_expression(then_branch)?;
+        let then_exit_block = Self::current_block(self)?;
         let then_var_map_end = self.variable_map.clone();
         if !self.is_current_block_terminated() {
             self.emit_instruction(MirInstruction::Jump {
@@ -211,6 +212,7 @@ impl super::MirBuilder {
                 })?;
                 (void_val, None, None)
             };
+        let else_exit_block = Self::current_block(self)?;
         if !self.is_current_block_terminated() {
             self.emit_instruction(MirInstruction::Jump {
                 target: merge_block,
@@ -223,6 +225,8 @@ impl super::MirBuilder {
         let result_val = self.normalize_if_else_phi(
             then_block,
             else_block,
+            Some(then_exit_block),
+            Some(else_exit_block),
             then_value_raw,
             else_value_raw,
             &pre_if_var_map,
@@ -489,3 +493,4 @@ impl super::MirBuilder {
         Ok(me_value)
     }
 }
+use crate::mir::loop_api::LoopBuilderApi; // for current_block()
diff --git a/src/runner/dispatch.rs b/src/runner/dispatch.rs
index facbe95f..a4ddf525 100644
--- a/src/runner/dispatch.rs
+++ b/src/runner/dispatch.rs
@@ -115,21 +115,27 @@ pub(crate) fn execute_file_with_backend(runner: &NyashRunner, filename: &str) {
             if std::env::var("NYASH_CLI_VERBOSE").ok().as_deref() == Some("1") {
                 println!("🚀 Nyash VM Backend - Executing file: {} 🚀", filename);
             }
-            runner.execute_vm_mode(filename);
+            #[cfg(feature = "vm-legacy")]
+            {
+                runner.execute_vm_mode(filename);
+            }
+            #[cfg(not(feature = "vm-legacy"))]
+            {
+                // Legacy VM is disabled; use PyVM harness instead.
+                super::modes::pyvm::execute_pyvm_only(runner, filename);
+            }
         }
         "interpreter" => {
             eprintln!("⚠ interpreter backend is legacy and deprecated. Use 'vm' (PyVM/LLVM) instead.");
-            if std::env::var("NYASH_VM_USE_PY").ok().as_deref() == Some("1") {
-                if std::env::var("NYASH_CLI_VERBOSE").ok().as_deref() == Some("1") {
-                    println!("👉 Redirecting to VM backend (PyVM) as requested by NYASH_VM_USE_PY=1");
-                }
-                runner.execute_vm_mode(filename);
-            } else {
-                if std::env::var("NYASH_CLI_VERBOSE").ok().as_deref() == Some("1") {
-                    println!("👉 Redirecting to VM backend");
-                }
+            #[cfg(feature = "vm-legacy")]
+            {
                 runner.execute_vm_mode(filename);
             }
+            #[cfg(not(feature = "vm-legacy"))]
+            {
+                // Legacy VM disabled; route to PyVM-only runner
+                super::modes::pyvm::execute_pyvm_only(runner, filename);
+            }
         }
         #[cfg(feature = "cranelift-jit")]
         "jit-direct" => {
diff --git a/src/runner/mir_json_emit.rs b/src/runner/mir_json_emit.rs
index 5b912000..cb13ae13 100644
--- a/src/runner/mir_json_emit.rs
+++ b/src/runner/mir_json_emit.rs
@@ -18,6 +18,10 @@ pub fn emit_mir_json_for_harness(
                 let mut insts = Vec::new();
                 // PHI first（オプション）
                 for inst in &bb.instructions {
+                    if let I::Copy { dst, src } = inst {
+                        insts.push(json!({"op":"copy","dst": dst.as_u32(), "src": src.as_u32()}));
+                        continue;
+                    }
                     if let I::Phi { dst, inputs } = inst {
                         let incoming: Vec<_> = inputs
                             .iter()
@@ -47,6 +51,13 @@ pub fn emit_mir_json_for_harness(
                 // Non-PHI
                 for inst in &bb.instructions {
                     match inst {
+                        I::Copy { dst, src } => {
+                            insts.push(json!({
+                                "op": "copy",
+                                "dst": dst.as_u32(),
+                                "src": src.as_u32()
+                            }));
+                        }
                         I::UnaryOp { dst, op, operand } => {
                             let kind = match op {
                                 nyash_rust::mir::UnaryOp::Neg => "neg",
@@ -296,6 +307,13 @@ pub fn emit_mir_json_for_harness_bin(
                 }
                 for inst in &bb.instructions {
                     match inst {
+                        I::Copy { dst, src } => {
+                            insts.push(json!({
+                                "op": "copy",
+                                "dst": dst.as_u32(),
+                                "src": src.as_u32()
+                            }));
+                        }
                         I::Const { dst, value } => match value {
                             crate::mir::ConstValue::Integer(i) => {
                                 insts.push(json!({"op":"const","dst": dst.as_u32(), "value": {"type": "i64", "value": i}}));
diff --git a/src/runner/mod.rs b/src/runner/mod.rs
index 9a182ed4..4122e3c0 100644
--- a/src/runner/mod.rs
+++ b/src/runner/mod.rs
@@ -413,8 +413,17 @@ impl NyashRunner {
             println!("====================================");
             println!("Running {} iterations per test...", self.config.iterations);
             println!();
-
-            self.execute_benchmark_mode();
+            #[cfg(feature = "vm-legacy")]
+            {
+                self.execute_benchmark_mode();
+            }
+            #[cfg(not(feature = "vm-legacy"))]
+            {
+                eprintln!(
+                    "❌ Benchmark mode requires VM backend. Rebuild with --features vm-legacy."
+                );
+                std::process::exit(1);
+            }
             return;
         }
 
diff --git a/src/runner/modes/bench.rs b/src/runner/modes/bench.rs
index c0f07a13..3deaba3b 100644
--- a/src/runner/modes/bench.rs
+++ b/src/runner/modes/bench.rs
@@ -236,3 +236,4 @@ impl NyashRunner {
         Ok(())
     }
 }
+#![cfg(feature = "vm-legacy")]
diff --git a/src/runner/modes/mir_interpreter.rs b/src/runner/modes/mir_interpreter.rs
index 15751ee4..57981e1d 100644
--- a/src/runner/modes/mir_interpreter.rs
+++ b/src/runner/modes/mir_interpreter.rs
@@ -101,4 +101,4 @@ impl NyashRunner {
         let _ = runtime; // reserved for future GC/safepoint integration
     }
 }
-
+#![cfg(feature = "interpreter-legacy")]
diff --git a/src/runner/modes/mod.rs b/src/runner/modes/mod.rs
index 1c416642..ecc11d0f 100644
--- a/src/runner/modes/mod.rs
+++ b/src/runner/modes/mod.rs
@@ -1,8 +1,12 @@
+#[cfg(feature = "vm-legacy")]
 pub mod bench;
+#[cfg(feature = "interpreter-legacy")]
 pub mod interpreter;
 pub mod llvm;
 pub mod mir;
+#[cfg(feature = "vm-legacy")]
 pub mod vm;
+pub mod pyvm;
 
 #[cfg(feature = "cranelift-jit")]
 pub mod aot;
diff --git a/src/runner/modes/pyvm.rs b/src/runner/modes/pyvm.rs
new file mode 100644
index 00000000..65c10719
--- /dev/null
+++ b/src/runner/modes/pyvm.rs
@@ -0,0 +1,102 @@
+use super::super::NyashRunner;
+use nyash_rust::{mir::MirCompiler, parser::NyashParser};
+use std::{fs, process};
+
+/// Execute using PyVM only (no Rust VM runtime). Emits MIR(JSON) and invokes tools/pyvm_runner.py.
+pub fn execute_pyvm_only(_runner: &NyashRunner, filename: &str) {
+    // Read the file
+    let code = match fs::read_to_string(filename) {
+        Ok(content) => content,
+        Err(e) => {
+            eprintln!("❌ Error reading file {}: {}", filename, e);
+            process::exit(1);
+        }
+    };
+
+    // Parse to AST
+    let ast = match NyashParser::parse_from_string(&code) {
+        Ok(ast) => ast,
+        Err(e) => {
+            eprintln!("❌ Parse error: {}", e);
+            process::exit(1);
+        }
+    };
+
+    // Compile to MIR (respect default optimizer setting)
+    let mut mir_compiler = MirCompiler::with_options(true);
+    let mut compile_result = match mir_compiler.compile(ast) {
+        Ok(result) => result,
+        Err(e) => {
+            eprintln!("❌ MIR compilation error: {}", e);
+            process::exit(1);
+        }
+    };
+
+    // Optional: VM-only escape analysis elision pass retained for parity with VM path
+    if std::env::var("NYASH_VM_ESCAPE_ANALYSIS").ok().as_deref() == Some("1") {
+        let removed = nyash_rust::mir::passes::escape::escape_elide_barriers_vm(&mut compile_result.module);
+        if removed > 0 && std::env::var("NYASH_CLI_VERBOSE").ok().as_deref() == Some("1") {
+            eprintln!("[PyVM] escape_elide_barriers: removed {} barriers", removed);
+        }
+    }
+
+    // Emit MIR JSON for PyVM harness
+    let tmp_dir = std::path::Path::new("tmp");
+    let _ = std::fs::create_dir_all(tmp_dir);
+    let mir_json_path = tmp_dir.join("nyash_pyvm_mir.json");
+    if let Err(e) = crate::runner::mir_json_emit::emit_mir_json_for_harness(
+        &compile_result.module,
+        &mir_json_path,
+    ) {
+        eprintln!("❌ PyVM MIR JSON emit error: {}", e);
+        process::exit(1);
+    }
+
+    // Pick entry: prefer Main.main or main
+    let entry = if compile_result.module.functions.contains_key("Main.main") {
+        "Main.main"
+    } else if compile_result.module.functions.contains_key("main") {
+        "main"
+    } else {
+        "Main.main"
+    };
+
+    // Locate python3 and run harness
+    let py = which::which("python3").ok();
+    if let Some(py3) = py {
+        let runner = std::path::Path::new("tools/pyvm_runner.py");
+        if !runner.exists() {
+            eprintln!("❌ PyVM runner not found: {}", runner.display());
+            process::exit(1);
+        }
+        if std::env::var("NYASH_CLI_VERBOSE").ok().as_deref() == Some("1") {
+            eprintln!(
+                "[Runner/PyVM] {} (mir={})",
+                filename,
+                mir_json_path.display()
+            );
+        }
+        let status = std::process::Command::new(py3)
+            .args([
+                runner.to_string_lossy().as_ref(),
+                "--in",
+                &mir_json_path.display().to_string(),
+                "--entry",
+                entry,
+            ])
+            .status()
+            .map_err(|e| format!("spawn pyvm: {}", e))
+            .unwrap();
+        let code = status.code().unwrap_or(1);
+        if !status.success() {
+            if std::env::var("NYASH_CLI_VERBOSE").ok().as_deref() == Some("1") {
+                eprintln!("❌ PyVM failed (status={})", code);
+            }
+        }
+        process::exit(code);
+    } else {
+        eprintln!("❌ python3 not found in PATH. Install Python 3 to use PyVM.");
+        process::exit(1);
+    }
+}
+
diff --git a/src/runtime/host_api.rs b/src/runtime/host_api.rs
index 924ab099..75389d08 100644
--- a/src/runtime/host_api.rs
+++ b/src/runtime/host_api.rs
@@ -9,16 +9,20 @@
 use crate::box_trait::NyashBox;
 
 // ===== TLS: current VM pointer during plugin invoke =====
+// When legacy VM is enabled, keep a real pointer for write barriers.
+#[cfg(feature = "vm-legacy")]
 thread_local! {
     static CURRENT_VM: std::cell::Cell<*mut crate::backend::vm::VM> = std::cell::Cell::new(std::ptr::null_mut());
 }
-
+#[cfg(feature = "vm-legacy")]
 pub fn set_current_vm(ptr: *mut crate::backend::vm::VM) {
     CURRENT_VM.with(|c| c.set(ptr));
 }
+#[cfg(feature = "vm-legacy")]
 pub fn clear_current_vm() {
     CURRENT_VM.with(|c| c.set(std::ptr::null_mut()));
 }
+#[cfg(feature = "vm-legacy")]
 fn with_current_vm_mut<F, R>(f: F) -> Option<R>
 where
     F: FnOnce(&mut crate::backend::vm::VM) -> R,
@@ -33,6 +37,19 @@ where
     })
 }
 
+// When legacy VM is disabled, provide stubs (no GC barriers).
+#[cfg(not(feature = "vm-legacy"))]
+pub fn set_current_vm(_ptr: *mut ()) {}
+#[cfg(not(feature = "vm-legacy"))]
+pub fn clear_current_vm() {}
+#[cfg(not(feature = "vm-legacy"))]
+fn with_current_vm_mut<F, R>(_f: F) -> Option<R>
+where
+    F: FnOnce(&mut ()) -> R,
+{
+    None
+}
+
 // ===== Utilities: TLV encode helpers (single-value) =====
 fn tlv_encode_one(val: &crate::backend::vm::VMValue) -> Vec<u8> {
     use crate::runtime::plugin_ffi_common as tlv;
@@ -201,12 +218,15 @@ pub extern "C" fn nyrt_host_call_name(
                     v => v.to_string(),
                 };
                 // Barrier: use current VM runtime if available
-                let _ = with_current_vm_mut(|vm| {
-                    crate::backend::gc_helpers::gc_write_barrier_site(
-                        vm.runtime_ref(),
-                        "HostAPI.setField",
-                    );
-                });
+                #[cfg(feature = "vm-legacy")]
+                {
+                    let _ = with_current_vm_mut(|vm| {
+                        crate::backend::gc_helpers::gc_write_barrier_site(
+                            vm.runtime_ref(),
+                            "HostAPI.setField",
+                        );
+                    });
+                }
                 // Accept primitives only for now
                 let nv_opt = match argv[1].clone() {
                     crate::backend::vm::VMValue::Integer(i) => {
@@ -268,12 +288,15 @@ pub extern "C" fn nyrt_host_call_name(
                     crate::backend::vm::VMValue::BoxRef(b) => b.share_box(),
                     _ => Box::new(crate::box_trait::VoidBox::new()),
                 };
-                let _ = with_current_vm_mut(|vm| {
-                    crate::backend::gc_helpers::gc_write_barrier_site(
-                        vm.runtime_ref(),
-                        "HostAPI.Array.set",
-                    );
-                });
+                #[cfg(feature = "vm-legacy")]
+                {
+                    let _ = with_current_vm_mut(|vm| {
+                        crate::backend::gc_helpers::gc_write_barrier_site(
+                            vm.runtime_ref(),
+                            "HostAPI.Array.set",
+                        );
+                    });
+                }
                 let out = arr.set(Box::new(crate::box_trait::IntegerBox::new(idx)), vb);
                 let vmv = crate::backend::vm::VMValue::from_nyash_box(out);
                 let buf = tlv_encode_one(&vmv);
@@ -402,12 +425,15 @@ pub extern "C" fn nyrt_host_call_slot(
                             crate::backend::vm::VMValue::String(s) => s.clone(),
                             v => v.to_string(),
                         };
-                        let _ = with_current_vm_mut(|vm| {
-                            crate::backend::gc_helpers::gc_write_barrier_site(
-                                vm.runtime_ref(),
-                                "HostAPI.setField",
-                            );
-                        });
+                        #[cfg(feature = "vm-legacy")]
+                        {
+                            let _ = with_current_vm_mut(|vm| {
+                                crate::backend::gc_helpers::gc_write_barrier_site(
+                                    vm.runtime_ref(),
+                                    "HostAPI.setField",
+                                );
+                            });
+                        }
                         let nv_opt = match argv[1].clone() {
                             crate::backend::vm::VMValue::Integer(i) => {
                                 Some(crate::value::NyashValue::Integer(i))
@@ -492,12 +518,15 @@ pub extern "C" fn nyrt_host_call_slot(
                                 crate::backend::vm::VMValue::BoxRef(b) => b.share_box(),
                                 _ => Box::new(crate::box_trait::VoidBox::new()),
                             };
-                            let _ = with_current_vm_mut(|vm| {
-                                crate::backend::gc_helpers::gc_write_barrier_site(
-                                    vm.runtime_ref(),
-                                    "HostAPI.Array.set",
-                                );
-                            });
+                            #[cfg(feature = "vm-legacy")]
+                            {
+                                let _ = with_current_vm_mut(|vm| {
+                                    crate::backend::gc_helpers::gc_write_barrier_site(
+                                        vm.runtime_ref(),
+                                        "HostAPI.Array.set",
+                                    );
+                                });
+                            }
                             let out = arr.set(Box::new(crate::box_trait::IntegerBox::new(idx)), vb);
                             let vmv = crate::backend::vm::VMValue::from_nyash_box(out);
                             let buf = tlv_encode_one(&vmv);
diff --git a/src/tests/mir_no_phi_merge_tests.rs b/src/tests/mir_no_phi_merge_tests.rs
new file mode 100644
index 00000000..f9cd1ef3
--- /dev/null
+++ b/src/tests/mir_no_phi_merge_tests.rs
@@ -0,0 +1,62 @@
+use crate::ast::{ASTNode, LiteralValue, Span, BinaryOperator};
+use crate::mir::{MirCompiler, MirInstruction};
+
+fn lit_i(i: i64) -> ASTNode {
+    ASTNode::Literal { value: LiteralValue::Integer(i), span: Span::unknown() }
+}
+
+fn bool_lt(lhs: ASTNode, rhs: ASTNode) -> ASTNode {
+    ASTNode::BinaryOp { operator: BinaryOperator::LessThan, left: Box::new(lhs), right: Box::new(rhs), span: Span::unknown() }
+}
+
+#[test]
+fn mir13_no_phi_if_merge_inserts_edge_copies_for_return() {
+    // Force PHI-off mode
+    std::env::set_var("NYASH_MIR_NO_PHI", "1");
+
+    // if (1 < 2) { return 40 } else { return 50 }
+    let ast = ASTNode::If {
+        condition: Box::new(bool_lt(lit_i(1), lit_i(2))),
+        then_body: vec![ASTNode::Return { value: Some(Box::new(lit_i(40))), span: Span::unknown() }],
+        else_body: Some(vec![ASTNode::Return { value: Some(Box::new(lit_i(50))), span: Span::unknown() }]),
+        span: Span::unknown(),
+    };
+
+    let mut mc = MirCompiler::with_options(false);
+    let cr = mc.compile(ast).expect("compile");
+    let f = cr.module.functions.get("main").expect("function main");
+
+    // Find the block that returns a value and capture that return value id
+    let mut ret_block_id = None;
+    let mut ret_val = None;
+    for (bid, bb) in &f.blocks {
+        if let Some(MirInstruction::Return { value: Some(v) }) = bb.terminator.clone() {
+            ret_block_id = Some(*bid);
+            ret_val = Some(v);
+            break;
+        }
+    }
+    let ret_block = ret_block_id.expect("ret block");
+    let out_v = ret_val.expect("ret value");
+
+    // In PHI-off mode we expect copies into each predecessor of the merge/ret block
+    let preds: Vec<_> = f
+        .blocks
+        .get(&ret_block)
+        .expect("ret block present")
+        .predecessors
+        .iter()
+        .copied()
+        .collect();
+    assert!(preds.len() >= 2, "expected at least two predecessors at merge");
+
+    for p in preds {
+        let bb = f.blocks.get(&p).expect("pred block present");
+        let has_copy = bb
+            .instructions
+            .iter()
+            .any(|inst| matches!(inst, MirInstruction::Copy { dst, .. } if *dst == out_v));
+        assert!(has_copy, "expected Copy to out_v in predecessor {:?}", p);
+    }
+}
+
diff --git a/tools/llvmlite_harness.py b/tools/llvmlite_harness.py
index 27bcd948..247cb08b 100644
--- a/tools/llvmlite_harness.py
+++ b/tools/llvmlite_harness.py
@@ -50,6 +50,9 @@ def run_dummy(out_path: str) -> None:
 def run_from_json(in_path: str, out_path: str) -> None:
     # Delegate to python builder to keep code unified
     import runpy
+    # Enable safe defaults for prepasses unless explicitly disabled by env
+    os.environ.setdefault('NYASH_LLVM_PREPASS_LOOP', os.environ.get('NYASH_LLVM_PREPASS_LOOP', '0'))
+    os.environ.setdefault('NYASH_LLVM_PREPASS_IFMERGE', os.environ.get('NYASH_LLVM_PREPASS_IFMERGE', '1'))
     # Ensure src/llvm_py is on sys.path for relative imports
     builder_dir = str(PY_BUILDER.parent)
     if builder_dir not in sys.path:
diff --git a/tools/smokes/curated_llvm.sh b/tools/smokes/curated_llvm.sh
index 4a7c041a..b01bcc9d 100644
--- a/tools/smokes/curated_llvm.sh
+++ b/tools/smokes/curated_llvm.sh
@@ -2,7 +2,7 @@
 set -euo pipefail
 
 # Curated LLVM smoke runner (llvmlite harness)
-# Usage: tools/smokes/curated_llvm.sh [--phi-off]
+# Usage: tools/smokes/curated_llvm.sh [--phi-off|--phi-on] [--with-if-merge]
 
 ROOT_DIR=$(cd "$(dirname "$0")/../.." && pwd)
 BIN="$ROOT_DIR/target/release/nyash"
@@ -18,9 +18,15 @@ export NYASH_LLVM_USE_HARNESS=1
 # Default: PHI-off (MIR13). Use --phi-on to test PHI-on path.
 export NYASH_MIR_NO_PHI=${NYASH_MIR_NO_PHI:-1}
 export NYASH_VERIFY_ALLOW_NO_PHI=${NYASH_VERIFY_ALLOW_NO_PHI:-1}
+WITH_IFMERGE=0
 if [[ "${1:-}" == "--phi-on" ]]; then
   export NYASH_MIR_NO_PHI=0
   echo "[curated-llvm] PHI-on (JSON PHI + finalize) enabled" >&2
+elif [[ "${1:-}" == "--with-if-merge" || "${2:-}" == "--with-if-merge" ]]; then
+  WITH_IFMERGE=1
+  echo "[curated-llvm] enabling if-merge prepass for ternary tests" >&2
+  export NYASH_LLVM_PREPASS_IFMERGE=1
+  echo "[curated-llvm] PHI-off (edge-copy) enabled" >&2
 else
   echo "[curated-llvm] PHI-off (edge-copy) enabled" >&2
 fi
@@ -50,4 +56,10 @@ run "$ROOT_DIR/apps/tests/peek_expr_block.nyash"
 # Try/finally control-flow without actual throw
 run "$ROOT_DIR/apps/tests/try_finally_break_inner_loop.nyash"
 
+# Optional: if-merge (ret-merge) tests
+if [[ "$WITH_IFMERGE" == "1" ]]; then
+  run "$ROOT_DIR/apps/tests/ternary_basic.nyash"
+  run "$ROOT_DIR/apps/tests/ternary_nested.nyash"
+fi
+
 echo "[curated-llvm] OK"