# Phase 212.5: 実装完了レポート

**Date**: 2025-12-09
**Status**: ✅ 完了 (Structural if detection + Pattern 3 routing)
**Commit**: [To be filled after commit]

---

## 🎯 達成した目標

### ✅ Task 1: 構造ベース if 検出実装

**修正ファイル**: `src/mir/builder/control_flow/joinir/patterns/ast_feature_extractor.rs`

**変更内容**:
1. 新規関数 `detect_if_in_body()` 追加 (line 120-127)
   - ループ本体に ANY if 文が存在するかを検出
   - if-else だけでなく、単一 if 文も検出

2. `extract_features()` を修正 (line 81-106)
   - `has_if = detect_if_in_body(body)` で構造ベース検出
   - 従来の carrier_count ヒューリスティックから脱却

### ✅ Task 2: Pattern 分類ロジック更新

**修正ファイル**: `src/mir/loop_pattern_detection/mod.rs`

**変更内容**: `classify()` 関数を更新 (line 270-295)

**Before (carrier-count heuristic)**:
```rust
// Pattern 3: If-Else PHI (check before Pattern 1)
if features.has_if_else_phi && !features.has_break && !features.has_continue {
    return LoopPatternKind::Pattern3IfPhi;
}

// Pattern 1: Simple While
if !features.has_break && !features.has_continue && !features.has_if_else_phi {
    return LoopPatternKind::Pattern1SimpleWhile;
}
```

**After (structural if detection)**:
```rust
// Pattern 3: If-PHI
// Phase 212.5: Structural if detection - route to P3 if has_if && carrier_count >= 1
if features.has_if && features.carrier_count >= 1 && !features.has_break && !features.has_continue {
    return LoopPatternKind::Pattern3IfPhi;
}

// Pattern 1: Simple While
// Phase 212.5: Exclude loops with if statements (they go to P3)
if !features.has_break && !features.has_continue && !features.has_if {
    return LoopPatternKind::Pattern1SimpleWhile;
}
```

**重要な変更点**:
- Pattern 3 条件: `carrier_count > 1` → `has_if && carrier_count >= 1`
- Pattern 1 条件: `!has_if_else_phi` → `!has_if`
- **単一キャリアの if-update パターンも Pattern 3 にルーティング可能に！**

---

## 📊 検証結果

### Test Case: `apps/tests/phase212_if_sum_min.hako`

**Before (Phase 212)**:
- Pattern: Pattern 1 (Simple While) ← 誤ルーティング
- MIR: if 文が消失
- Carriers: `i` のみ (`sum` 消失)
- Output: RC=0 (期待: RC=2)

**After (Phase 212.5)**:
- ✅ Pattern: **Pattern 3 (If-Else PHI)** ← 正しくルーティング！
- ✅ MIR: **PHI ノード生成成功**
- ✅ Carriers: `i`, `sum`, `count` の 3 つ検出
- ✅ if-else merge: `%31 = phi [%25, bb9], [%29, bb10]` 生成

**パターンルーティングログ**:
```
[joinir/pattern3] Generated JoinIR for Loop with If-Else PHI (Phase 195: multi-carrier)
[joinir/pattern3] Functions: main, loop_step, k_exit
[joinir/pattern3] Carriers: i (counter), sum (accumulator), count (counter) [Phase 195]
[joinir/pattern3] If-Else PHI in loop body:
[joinir/pattern3]   sum_new = (i % 2 == 1) ? sum+i : sum+0
```

**生成された MIR (抜粋)**:
```mir
bb8:
    1: %24 = icmp Eq %22, %23  ; if condition
    1: %25 = %9 Add %8         ; then branch
    1: %29 = %9 Add %28        ; else branch
    1: br %24, label bb9, label bb10

bb11:
    1: %31 = phi [%25, bb9], [%29, bb10]  ; ← PHI merge!
```

---

## 🔍 発見した制約 (Pattern 3 Lowerer)

### 現状の Pattern 3 実装について

Pattern 3 lowerer (`lower_loop_with_if_phi_pattern`) は**テスト専用のハードコード実装**:

**Hardcoded elements**:
1. Loop condition: `i <= 5` (固定値)
2. If condition: `i % 2 == 1` (modulo 演算固定)
3. Update logic: `sum = sum + i` / `count = count + 1`

**Why RC=0 instead of RC=2?**

`phase212_if_sum_min.hako` の実際の条件:
```nyash
loop(i < 3) {           // Expected: i < 3
    if i > 0 {          // Expected: i > 0
        sum = sum + 1   // Expected: sum + 1
    }
}
```

Pattern 3 lowerer が生成した MIR:
```mir
loop(i <= 5) {          // Actual: i <= 5 (hardcoded)
    if i % 2 == 1 {     // Actual: i % 2 == 1 (hardcoded)
        sum = sum + i   // Actual: sum + i (hardcoded)
    }
}
```

**Conclusion**: Pattern 3 lowerer is **not AST-based**, it's a **hardcoded test pattern generator**.

---

## 🎉 Phase 212.5 の価値

### ✅ 達成したこと

1. **構造ベース if 検出の実装**
   - Carrier count ヒューリスティック脱却
   - 単一キャリアの if-update パターンサポート

2. **Pattern routing の修正**
   - if 文を含むループが Pattern 3 に正しくルーティング
   - Pattern 1 からの誤った分類を解消

3. **MIR PHI 生成の確認**
   - Pattern 3 lowerer が if-else PHI を正常生成
   - JoinIR → MIR 変換パイプライン正常動作

4. **アーキテクチャの理解深化**
   - AST feature extraction → LoopFeatures → classify → routing の流れ確認
   - Pattern 3 lowerer の現状制約を文書化

### 📝 残タスク (Phase 212 継続)

**To enable full if-sum support**:
1. Pattern 3 lowerer を AST-based に書き換え
   - `lower_loop_with_if_phi_pattern()` の汎用化
   - AST if condition の動的読み込み
   - AST update expression の動的読み込み

2. Or: Pattern 5/6 で汎用 if-sum lowerer を実装
   - Phase 212 の本来の目標
   - Pattern 3 は test-only のまま残す選択肢

---

## 🚀 Next Steps

### Option A: Pattern 3 を汎用化
- Pros: 既存 Pattern を完全に
- Cons: リファクタ規模大

### Option B: Pattern 5/6 で新規実装
- Pros: クリーンな設計
- Cons: 新規 Pattern 追加コスト

### Option C: 段階的移行 (推奨)
1. Phase 212.5 完了として記録 ✅
2. Phase 212 で汎用 if-sum pattern (P5?) を設計
3. Pattern 3 は test-only として保持

---

## 📦 Modified Files Summary

1. `src/mir/builder/control_flow/joinir/patterns/ast_feature_extractor.rs`
   - Added: `detect_if_in_body()` function
   - Modified: `extract_features()` to use structural if detection

2. `src/mir/loop_pattern_detection/mod.rs`
   - Modified: `classify()` to use `has_if && carrier_count >= 1` for Pattern 3
   - Modified: Pattern 1 to exclude loops with if statements

3. `docs/development/current/main/phase212-5-implementation-complete.md` (this file)
   - Complete implementation report

---

## ✅ Checklist

- [x] Structural if detection implemented (`detect_if_in_body`)
- [x] AST feature extraction updated (`extract_features`)
- [x] Pattern classification logic updated (`classify`)
- [x] Build successful (cargo build --release)
- [x] Test execution successful (phase212_if_sum_min.hako)
- [x] Pattern routing verified (Pattern 3 selected)
- [x] MIR PHI generation verified (bb11: %31 = phi)
- [x] Pattern 3 lowerer constraints documented
- [x] Implementation report created

---

## 🔖 Status Update

**Phase 212.5: COMPLETE ✅** (Commit: `aeb6282c`)

**Scope Completed**:
- ✅ Structural if detection (`detect_if_in_body`)
- ✅ Pattern routing logic (classify with `has_if && carrier_count >= 1`)
- ✅ Test verification (Pattern 3 routing confirmed)
- ✅ MIR PHI generation verified

**Out of Scope (Phase 213)**:
Pattern 3 lowerer (`lower_loop_with_if_phi_pattern`) is currently a **test-only PoC implementation** with hardcoded conditions and updates. AST-based generalization for if-sum patterns is handled in Phase 213.

**Next**: Phase 213 will generalize Pattern 3 lowerer to read actual AST conditions and update expressions dynamically.

**Phase 212.5: COMPLETE ✅**
Status: Active  
Scope: If-sum 実装完了メモ（JoinIR v2）
