fix(joinir): Phase 177-3 ValueId collision fix for multi-carrier loops

Root cause: JoinIR ValueId collision between function parameters and condition bindings
- Same ValueId used for both `result_init` (carrier param) and `limit` (condition var)
- Phase 33-21 was overwriting condition bindings when remapping carrier PHIs

Fix implemented (Option B - immediate protection):
1. Phase 177-3: Protect condition-only variables from Phase 33-21 override
   - Collect condition_bindings that are NOT carriers (by checking exit_bindings)
   - Skip remapping for these protected ValueIds
2. Phase 177-3-B: Handle body-only carriers explicitly
   - Carriers that appear in condition_bindings (added by Phase 176-5)
   - Map them to correct PHI dsts by name lookup

Investigation tools added:
- [DEBUG-177] trace logs for remapper state tracking
- Phase 177-3 protection logging
- BoundaryInjector PHI collision detection

Test results:
- ✅ Integer multi-carrier test: Output 3 (expected)
- ⚠️ String test: RC=0 but empty output (separate issue - string concat emit)

Design docs created:
- phase177-parse-string-design.md: _parse_string loop analysis
- phase177-carrier-evolution.md: Carrier progression Phase 174-179

Next: Investigate string concatenation emit for full _parse_string support

docs/development/current/main/phase177-carrier-evolution.md

@@ -0,0 +1,165 @@
+# Phase 177: Carrier Evolution - min から Production へ
+
+## 視覚的比較: ループ構造の進化
+
+### Phase 174: min（1-carrier）
+```
+Input:  "hello world""
+         ^start      ^target
+
+loop(pos < len) {
+    ch = s[pos]
+    if ch == '"' → break ✓
+    else         → pos++
+}
+
+Carriers: 1
+- pos (ループ変数)
+
+Pattern: 4 (Loop + If PHI)
+Exit:    pos = 11
+```
+
+### Phase 175/176: min2（2-carrier）
+```
+Input:  "hello world""
+         ^start      ^target
+
+loop(pos < len) {
+    ch = s[pos]
+    if ch == '"' → break ✓
+    else         → result += ch
+                   pos++
+}
+
+Carriers: 2
+- pos    (ループ変数)
+- result (バッファ)
+
+Pattern: 4 (Loop + If PHI)
+Exit:    pos = 11, result = "hello world"
+```
+
+### Phase 177-A: Simple Case（2-carrier, Production-like）
+```
+Input:  "hello world""
+         ^start      ^target
+
+loop(p < len) {
+    ch = s[p]
+    if ch == '"' → break ✓
+    else         → str += ch
+                   p++
+}
+
+Carriers: 2
+- p   (ループ変数)
+- str (バッファ)
+
+Pattern: 4 (Loop + If PHI)
+Exit:    p = 11, str = "hello world"
+```
+
+### Phase 178: Escape Handling（2-carrier + continue）
+```
+Input:  "hello \"world\"""
+         ^start ^escape  ^target
+
+loop(p < len) {
+    ch = s[p]
+    if ch == '"'  → break ✓
+    if ch == '\\' → str += ch
+                    p++
+                    str += s[p]
+                    p++
+                    continue ←← 新要素
+    else          → str += ch
+                    p++
+}
+
+Carriers: 2 (変わらず)
+- p   (ループ変数)
+- str (バッファ)
+
+Pattern: 4? (continue 対応は未検証)
+Exit:    p = 15, str = "hello \"world\""
+```
+
+### Phase 179: Full Production（2-carrier + early return）
+```
+Input:  "hello \"world\"""
+         ^start ^escape  ^target
+
+loop(p < len) {
+    ch = s[p]
+    if ch == '"'  → return MapBox {...} ✓ ←← early return
+    if ch == '\\' → if p+1 >= len → return null ←← error
+                    str += ch
+                    p++
+                    str += s[p]
+                    p++
+                    continue
+    else          → str += ch
+                    p++
+}
+return null  ←← ループ終端エラー
+
+Carriers: 2 (変わらず)
+- p   (ループ変数)
+- str (バッファ)
+
+Pattern: 4? (early return 対応は未検証)
+Exit:    正常: MapBox, 異常: null
+```
+
+## Carrier 安定性分析
+
+### 重要な発見
+**Phase 174 → 179 を通じて Carrier 数は安定（1 → 2）**
+
+| Phase | Carriers | 新要素 | P5昇格候補 |
+|-------|----------|--------|-----------|
+| 174 | 1 (pos) | - | なし |
+| 175/176 | 2 (pos + result) | バッファ追加 | なし |
+| 177-A | 2 (p + str) | - | なし |
+| 178 | 2 (p + str) | continue | なし（確認中） |
+| 179 | 2 (p + str) | early return | なし（確認中） |
+
+### P5昇格候補の不在
+**Trim と異なり、`is_ch_match` 相当は不要**
+
+理由:
+- Trim: `is_ch_match` が「次も空白か？」を決定（**次の判断に影響**）
+- _parse_string: `ch == '"'` は「今終了か？」のみ（**次に影響しない**）
+
+```
+Trim の制御フロー:
+  is_ch_match = (ch == ' ')
+  if is_ch_match → pos++ → 次も is_ch_match を評価 ←← 連鎖
+
+_parse_string の制御フロー:
+  if ch == '"' → break → 終了
+  else         → str += ch, p++ → 次は独立判断 ←← 連鎖なし
+```
+
+## JoinIR Pattern 対応予測
+
+| Phase | Pattern 候補 | 理由 |
+|-------|-------------|------|
+| 177-A | Pattern4 | Loop + If PHI + break（実装済み） |
+| 178 | Pattern4? | continue は Pattern4-with-continue（要実装確認） |
+| 179 | Pattern5? | early return は新パターン候補（要設計） |
+
+## まとめ
+
+### 段階的検証戦略
+1. **Phase 177-A**: min2 と同型 → P5 安定性確認
+2. **Phase 178**: continue 追加 → JoinIR 拡張必要性評価
+3. **Phase 179**: early return 追加 → Pattern5 設計判断
+
+### Carrier 設計の教訓
+- **最小構成で開始**: 1-carrier (Phase 174)
+- **段階的拡張**: 2-carrier (Phase 175/176)
+- **Production 適用**: 構造は変えず、制御フローのみ追加（Phase 177+）
+
+→ **「Carrier 数を固定して制御フローを段階的に複雑化」が正解**

docs/development/current/main/phase177-parse-string-design.md

@@ -0,0 +1,178 @@
+# Phase 177: _parse_string 本体 JoinIR 適用設計
+
+## 目的
+Production `JsonParserBox._parse_string` メソッドに JoinIR P5 パイプラインを適用する。
+Phase 174/175/176 で確立した「1-carrier → 2-carrier」検証の成果を、実際の JSON パーサーに展開する。
+
+## 本番ループ構造（lines 144-181）
+
+### 前提条件
+- 開始位置 `pos` は `"` を指している（line 145 でチェック）
+- ループ開始時 `p = pos + 1`（引用符の次の文字から開始）
+
+### ループ本体（lines 150-178）
+```hako
+loop(p < s.length()) {
+    local ch = s.substring(p, p+1)
+
+    if ch == '"' {
+        // End of string (lines 153-160)
+        local result = new MapBox()
+        result.set("value", me._unescape_string(str))
+        result.set("pos", p + 1)
+        result.set("type", "string")
+        return result  // ← Early return (通常の exit)
+    }
+
+    if ch == "\\" {
+        // Escape sequence (lines 162-174)
+        local has_next = 0
+        if p + 1 < s.length() { has_next = 1 }
+
+        if has_next == 0 { return null }  // ← Early return (エラー)
+
+        str = str + ch
+        p = p + 1
+        str = str + s.substring(p, p+1)
+        p = p + 1
+        continue  // ← ループ継続
+    }
+
+    str = str + ch  // 通常文字の追加
+    p = p + 1
+}
+
+return null  // ← ループ終端に到達（エラー）
+```
+
+### 制御フロー分岐
+1. **終端クォート検出** (`ch == '"'`): 成功 return
+2. **エスケープ検出** (`ch == "\\"`) + continue: 2文字消費してループ継続
+3. **通常文字**: バッファ蓄積 + 位置進行
+4. **ループ終端**: 引用符が閉じていない（エラー）
+
+## Carriers 分析
+
+| 変数 | 初期値 | 役割 | 更新式 | P5 昇格対象？ | 備考 |
+|------|--------|------|--------|---------------|------|
+| `p` | `pos + 1` | カウンタ（位置） | `p = p + 1` | **N（ループ変数）** | 条件式に使用 |
+| `str` | `""` | バッファ（蓄積） | `str = str + ch` | **N（通常キャリア）** | エスケープ時2回更新 |
+| `has_next` | - | 一時変数（フラグ） | - | - | ループ内のみ有効 |
+| `is_escape` | - | （潜在的フラグ） | - | - | 明示的変数なし |
+
+### 重要な発見
+- **エスケープ処理は continue 経由**: `p` と `str` を 2 回更新してから continue
+- **Early return が 2 箇所**: 成功 return (line 159) とエラー return (line 167)
+- **通常キャリアのみ**: P5 昇格対象（`is_ch_match` 相当）は**不要**
+
+## min ケースとの差分
+
+### 共通点
+| 項目 | min (Phase 174) | min2 (Phase 175) | 本番 (Phase 177) |
+|------|-----------------|------------------|------------------|
+| ループ変数 | `pos` | `pos` | `p` |
+| バッファ | なし | `result` | `str` |
+| 終端条件 | `ch == '"'` → break | `ch == '"'` → break | `ch == '"'` → return |
+| 通常処理 | `pos++` | `result += ch; pos++` | `str += ch; p++` |
+
+### 差分
+| 項目 | min/min2 | 本番 |
+|------|----------|------|
+| 終端処理 | `break` のみ | Early `return` (MapBox 返却) |
+| エスケープ処理 | なし | `continue` を使った複雑な分岐 |
+| エラー処理 | なし | ループ内・外に `return null` |
+
+## 方針決定: 段階的アプローチ
+
+### Phase 177-A: Simple Case（今回）
+**対象**: エスケープ**なし**・終端クォート検出のみ
+- **ループ構造**: min2 と完全同型（`p` + `str` の 2-carrier）
+- **終端処理**: `break` → 直後に MapBox 構築（return 代替）
+- **目的**: P5 パイプラインが「2-carrier + break」で動作することを確認
+
+```hako
+// Simplified for Phase 177-A
+loop(p < s.length()) {
+    local ch = s.substring(p, p+1)
+    if ch == '"' {
+        break  // P5: Pattern4 対応（Loop+If PHI merge）
+    } else {
+        str = str + ch
+        p = p + 1
+    }
+}
+// break 後: MapBox 構築
+```
+
+### Phase 178: Escape Handling（次回）
+**追加要素**:
+- `continue` 分岐（エスケープ処理）
+- Early return（エラーハンドリング）
+- P5 昇格キャリア候補の検討（`is_escape` フラグ？）
+
+### Phase 179: Full Production（最終）
+**統合**:
+- `_unescape_string()` 呼び出し
+- 完全なエラーハンドリング
+- 本番同等の MapBox 返却
+
+## Phase 177-A 実装計画
+
+### Test Case: `test_jsonparser_parse_string_simple.hako`
+```hako
+// Phase 177-A: Production-like simple case
+static box JsonParserStringTest3 {
+    parse_string_simple() {
+        local s = "hello world\""
+        local p = 0  // pos + 1 相当（簡略化のため 0 から開始）
+        local str = ""
+        local len = s.length()
+
+        // 2-carrier loop (min2 と同型)
+        loop(p < len) {
+            local ch = s.substring(p, p+1)
+            if ch == "\"" {
+                break
+            } else {
+                str = str + ch
+                p = p + 1
+            }
+        }
+
+        // Post-loop: 結果出力（MapBox 構築の代替）
+        print("Parsed string: ")
+        print(str)
+        print(", final pos: ")
+        print(p)
+    }
+
+    main() {
+        me.parse_string_simple()
+        return "OK"
+    }
+}
+```
+
+### 期待される MIR 構造
+- **Pattern4 検出**: Loop + If PHI merge（Phase 170 実装済み）
+- **2 carriers**: `p` (ループ変数) + `str` (バッファ)
+- **Exit PHI**: ループ後の `p` と `str` が正しく伝播
+
+### 検証項目
+1. ✅ P5 パイプライン通過（JoinIR → MIR）
+2. ✅ 2-carrier の正しい伝播（`p` と `str`）
+3. ✅ `break` 後の変数値が正しく使用可能
+
+## 成功基準
+- [ ] `test_jsonparser_parse_string_simple.hako` が実行成功
+- [ ] MIR ダンプで Pattern4 検出確認
+- [ ] 出力: `Parsed string: hello world, final pos: 11`
+
+## 次のステップ（Phase 178）
+- `continue` 分岐の追加（エスケープ処理）
+- P5 昇格キャリア候補の検討（必要性を再評価）
+- Early return 対応（JoinIR での処理検討）
+
+## まとめ
+**Phase 177-A では、min2 と同型の Simple Case を Production 環境に適用する。**
+エスケープ処理は Phase 178 以降に回し、まず「2-carrier + break」の動作確認を優先する。

src/mir/builder/control_flow/joinir/merge/block_allocator.rs

@@ -12,15 +12,20 @@ use super::super::trace;
 /// Phase 1: Allocate new block IDs for ALL functions (Phase 189)
 ///
 /// DETERMINISM: Sort functions and blocks by name/ID to ensure consistent iteration order
+///
+/// Returns: (JoinIrIdRemapper, exit_block_id)
 pub(super) fn allocate_blocks(
     builder: &mut crate::mir::builder::MirBuilder,
     mir_module: &MirModule,
     debug: bool,
-) -> Result<JoinIrIdRemapper, String> {
+) -> Result<(JoinIrIdRemapper, crate::mir::BasicBlockId), String> {
     let mut remapper = JoinIrIdRemapper::new();
 
-    // Create exit block for Return conversion (single for all functions)
-    let _exit_block_id = builder.block_gen.next();
+    // Phase 177-3: Allocate exit block FIRST to ensure it doesn't conflict with JoinIR blocks
+    // This exit_block_id will be returned and used by instruction_rewriter and exit_phi_builder
+    let exit_block_id = builder.block_gen.next();
+
+    eprintln!("[cf_loop/joinir/block_allocator] Phase 177-3: Allocated exit_block_id = {:?}", exit_block_id);
 
     // Phase 195: Use unified trace
     trace::trace().blocks("allocator", "Phase 189: Allocating block IDs for all functions");
@@ -61,5 +66,6 @@ pub(super) fn allocate_blocks(
         );
     }
 
-    Ok(remapper)
+    // Phase 177-3: Return both remapper and exit_block_id
+    Ok((remapper, exit_block_id))
 }

src/mir/builder/control_flow/joinir/merge/instruction_rewriter.rs

@@ -30,6 +30,11 @@ use std::collections::HashMap;
 /// Uses extracted modules:
 /// - tail_call_classifier: TailCallKind classification
 /// - merge_result: MergeResult data structure
+///
+/// # Phase 177-3
+///
+/// `exit_block_id` is now passed in from block_allocator to ensure it doesn't
+/// conflict with JoinIR function blocks.
 pub(super) fn merge_and_rewrite(
     builder: &mut crate::mir::builder::MirBuilder,
     mir_module: &MirModule,
@@ -38,13 +43,11 @@ pub(super) fn merge_and_rewrite(
     function_params: &HashMap<String, Vec<ValueId>>,
     boundary: Option<&JoinInlineBoundary>,
     loop_header_phi_info: &mut LoopHeaderPhiInfo,
+    exit_block_id: BasicBlockId,
     debug: bool,
-) -> Result<MergeResult, String> {
-    // Create exit block for Return conversion (single for all functions)
-    let exit_block_id = builder.block_gen.next();
-    if debug {
-        eprintln!("[cf_loop/joinir]   Exit block: {:?}", exit_block_id);
-    }
+)-> Result<MergeResult, String> {
+    // Phase 177-3: exit_block_id is now passed in from block_allocator
+    eprintln!("[cf_loop/joinir/instruction_rewriter] Phase 177-3: Using exit_block_id = {:?}", exit_block_id);
 
     // Phase 189 FIX: Build set of boundary join_inputs to skip their Const initializers
     let boundary_input_set: std::collections::HashSet<ValueId> = boundary
@@ -172,8 +175,58 @@ pub(super) fn merge_and_rewrite(
             let mut found_tail_call = false;
             let mut tail_call_target: Option<(BasicBlockId, Vec<ValueId>)> = None;
 
+            // Phase 177-3: Check if this block is the loop header with PHI nodes
+            let is_loop_header_with_phi = is_loop_entry_point && !loop_header_phi_info.carrier_phis.is_empty();
+
+            if is_loop_entry_point {
+                eprintln!(
+                    "[cf_loop/joinir] Phase 177-3 DEBUG: is_loop_entry_point={}, carrier_phis.len()={}, is_loop_header_with_phi={}",
+                    is_loop_entry_point,
+                    loop_header_phi_info.carrier_phis.len(),
+                    is_loop_header_with_phi
+                );
+            }
+
+            // Phase 177-3: Collect PHI dst IDs that will be created for this block
+            // (if this is the loop header)
+            let phi_dst_ids_for_block: std::collections::HashSet<ValueId> = if is_loop_header_with_phi {
+                loop_header_phi_info.carrier_phis.values()
+                    .map(|entry| entry.phi_dst)
+                    .collect()
+            } else {
+                std::collections::HashSet::new()
+            };
+
+            if is_loop_header_with_phi && !phi_dst_ids_for_block.is_empty() {
+                eprintln!(
+                    "[cf_loop/joinir] Phase 177-3: Loop header with {} PHI dsts to protect: {:?}",
+                    phi_dst_ids_for_block.len(),
+                    phi_dst_ids_for_block
+                );
+            }
+
             // First pass: Process all instructions, identify tail calls
             for inst in &old_block.instructions {
+                // Phase 177-3: Skip Copy instructions that would overwrite PHI dsts
+                // The loop header PHIs will provide these values, so copies are redundant/harmful
+                if is_loop_header_with_phi {
+                    if let MirInstruction::Copy { dst, src } = inst {
+                        // Check if this copy's dst is a PHI dst (after remapping)
+                        let dst_remapped = remapper.get_value(*dst).unwrap_or(*dst);
+                        eprintln!(
+                            "[cf_loop/joinir]   Phase 177-3 DEBUG: Copy {:?} = {:?}, dst_remapped = {:?}, in phi_dsts = {}",
+                            dst, src, dst_remapped, phi_dst_ids_for_block.contains(&dst_remapped)
+                        );
+                        if phi_dst_ids_for_block.contains(&dst_remapped) {
+                            eprintln!(
+                                "[cf_loop/joinir]   Phase 177-3: ✅ Skipping loop header Copy to PHI dst {:?} (original {:?})",
+                                dst_remapped, dst
+                            );
+                            continue; // Skip - would overwrite PHI
+                        }
+                    }
+                }
+
                 // Phase 189: Skip Const String instructions that define function names
                 if let MirInstruction::Const { dst, value } = inst {
                     if let crate::mir::types::ConstValue::String(_) = value {
@@ -653,15 +706,30 @@ pub(super) fn merge_and_rewrite(
             }
         }
 
+        // Phase 177-3: Collect PHI dst IDs from loop_header_phi_info
+        let phi_dst_ids: std::collections::HashSet<ValueId> = loop_header_phi_info
+            .carrier_phis
+            .values()
+            .map(|entry| entry.phi_dst)
+            .collect();
+
         // Use BoundaryInjector to inject Copy instructions
+        // Phase 177-3 Option B: Returns reallocations map for condition_bindings with PHI collisions
         if let Some(ref mut current_func) = builder.current_function {
-            BoundaryInjector::inject_boundary_copies(
+            let _reallocations = BoundaryInjector::inject_boundary_copies(
                 current_func,
                 entry_block_remapped,
                 boundary,
                 &value_map_for_injector,
+                &phi_dst_ids,
                 debug,
             )?;
+
+            // Note: reallocations map is returned but not currently used.
+            // If condition variables need to be referenced after this point,
+            // the reallocations map would need to be applied to update references.
+            // For now, condition_bindings are read-only variables used only in
+            // the loop condition, so no further updates are needed.
         }
     }
 

src/mir/builder/control_flow/joinir/merge/mod.rs

@@ -80,7 +80,8 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
     }
 
     // Phase 1: Allocate block IDs for all functions
-    let mut remapper = block_allocator::allocate_blocks(builder, mir_module, debug)?;
+    // Phase 177-3: block_allocator now returns exit_block_id to avoid conflicts
+    let (mut remapper, exit_block_id) = block_allocator::allocate_blocks(builder, mir_module, debug)?;
 
     // Phase 2: Collect values from all functions
     let (mut used_values, value_to_func_name, function_params) =
@@ -113,6 +114,30 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
     // Phase 3: Remap ValueIds
     remap_values(builder, &used_values, &mut remapper, debug)?;
 
+    // Phase 177-3 DEBUG: Verify remapper state after Phase 3
+    eprintln!("[DEBUG-177] === Remapper state after Phase 3 ===");
+    eprintln!("[DEBUG-177] used_values count: {}", used_values.len());
+    for value_id in &used_values {
+        if let Some(remapped) = remapper.get_value(*value_id) {
+            eprintln!("[DEBUG-177]   JoinIR {:?} → Host {:?}", value_id, remapped);
+        } else {
+            eprintln!("[DEBUG-177]   JoinIR {:?} → NOT FOUND ❌", value_id);
+        }
+    }
+
+    // Check condition_bindings specifically
+    if let Some(boundary) = boundary {
+        eprintln!("[DEBUG-177] === Condition bindings check ===");
+        for binding in &boundary.condition_bindings {
+            let lookup_result = remapper.get_value(binding.join_value);
+            eprintln!(
+                "[DEBUG-177]   '{}': JoinIR {:?} → {:?}",
+                binding.name, binding.join_value, lookup_result
+            );
+        }
+    }
+    eprintln!("[DEBUG-177] ==============================");
+
     // Phase 3.5: Build loop header PHIs (if loop pattern with loop_var_name)
     //
     // We need to know PHI dsts before instruction_rewriter runs, so that:
@@ -215,9 +240,47 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
             // 2. loop body uses PHI result
             // 3. tail call args are correctly routed
 
-            // Map main's parameters
-            // MIR function keys use join_func_N format from join_func_name()
+            // Phase 177-3 fix: Protect condition-ONLY bindings from being overridden to PHI dsts
+            //
+            // Problem: condition_bindings may contain:
+            // 1. True condition-only variables (e.g., 'limit' in loop(i < limit)) - NOT carriers
+            // 2. Body-only carriers added by Phase 176-5 (e.g., 'result') - ARE carriers
+            //
+            // We must ONLY protect (1), not (2), because:
+            // - Condition-only vars should keep their HOST mapping (e.g., limit = %8)
+            // - Body-only carriers MUST be remapped to PHI dsts (e.g., result = %24)
+            //
+            // Solution: Protect condition_bindings that are NOT in exit_bindings (i.e., not carriers)
+            let carrier_names: std::collections::HashSet<&str> = boundary
+                .exit_bindings
+                .iter()
+                .map(|eb| eb.carrier_name.as_str())
+                .collect();
+
+            let condition_binding_ids: std::collections::HashSet<ValueId> = boundary
+                .condition_bindings
+                .iter()
+                .filter(|cb| !carrier_names.contains(cb.name.as_str()))
+                .map(|cb| cb.join_value)
+                .collect();
+
+            if !condition_binding_ids.is_empty() {
+                eprintln!(
+                    "[cf_loop/joinir] Phase 177-3: Protected ValueIds (condition-only, not carriers): {:?}",
+                    condition_binding_ids
+                );
+                for cb in &boundary.condition_bindings {
+                    let is_carrier = carrier_names.contains(cb.name.as_str());
+                    eprintln!(
+                        "[cf_loop/joinir] Phase 177-3:   '{}': JoinIR {:?} (carrier={})",
+                        cb.name, cb.join_value, is_carrier
+                    );
+                }
+            }
+
             let main_func_name = "join_func_0";
+            let loop_step_func_name = "join_func_1";
+
             if function_params.get(main_func_name).is_none() {
                 eprintln!(
                     "[cf_loop/joinir] WARNING: function_params.get('{}') returned None. Available keys: {:?}",
@@ -226,30 +289,57 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
                 );
             }
             if let Some(main_params) = function_params.get(main_func_name) {
-                if debug {
                 eprintln!(
-                        "[cf_loop/joinir] Phase 33-21: main ({}) params: {:?}",
+                    "[DEBUG-177] Phase 33-21: main ({}) params: {:?}",
                     main_func_name, main_params
                 );
-                }
+                eprintln!(
+                    "[DEBUG-177] Phase 33-21: carrier_phis count: {}, names: {:?}",
+                    phi_info.carrier_phis.len(),
+                    phi_info.carrier_phis.iter().map(|(n, _)| n.as_str()).collect::<Vec<_>>()
+                );
                 // Map main's parameters to header PHI dsts
                 // main params: [i_init, carrier1_init, ...]
                 // carrier_phis: [("i", entry), ("sum", entry), ...]
                 for (idx, (carrier_name, entry)) in phi_info.carrier_phis.iter().enumerate() {
                     if let Some(&main_param) = main_params.get(idx) {
-                        if debug {
+                        // Phase 177-3: Don't override condition_bindings
+                        if condition_binding_ids.contains(&main_param) {
                             eprintln!(
-                                "[cf_loop/joinir] Phase 33-21: REMAP main param {:?} → {:?} ('{}')",
-                                main_param, entry.phi_dst, carrier_name
+                                "[cf_loop/joinir] Phase 177-3: Skipping override for condition_binding {:?} ('{}')",
+                                main_param, carrier_name
                             );
+                            continue;
                         }
+                        eprintln!(
+                            "[DEBUG-177] Phase 33-21: REMAP main param[{}] {:?} → {:?} ('{}')",
+                            idx, main_param, entry.phi_dst, carrier_name
+                        );
                         remapper.set_value(main_param, entry.phi_dst);
                     }
                 }
             }
 
+            // Phase 177-3-B: Handle body-only carriers
+            // These are carriers in carrier_phis that are NOT in main function params.
+            // They appear in condition_bindings (added by Phase 176-5) but need PHI remapping.
+            for (carrier_name, entry) in &phi_info.carrier_phis {
+                // Check if this carrier has a condition_binding
+                if let Some(binding) = boundary.condition_bindings.iter().find(|cb| cb.name == *carrier_name) {
+                    // Skip if it's a true condition-only variable (already protected above)
+                    if condition_binding_ids.contains(&binding.join_value) {
+                        continue;
+                    }
+                    // This is a body-only carrier - remap it to PHI dst
+                    eprintln!(
+                        "[cf_loop/joinir] Phase 177-3-B: Body-only carrier '{}': JoinIR {:?} → PHI {:?}",
+                        carrier_name, binding.join_value, entry.phi_dst
+                    );
+                    remapper.set_value(binding.join_value, entry.phi_dst);
+                }
+            }
+
             // Map loop_step's parameters
-            let loop_step_func_name = "join_func_1";
             if debug {
                 eprintln!(
                     "[cf_loop/joinir] Phase 33-21: function_params keys: {:?}",
@@ -275,6 +365,14 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
                 // carrier_phis: [("i", entry), ("sum", entry), ...]
                 for (idx, (carrier_name, entry)) in phi_info.carrier_phis.iter().enumerate() {
                     if let Some(&loop_step_param) = loop_step_params.get(idx) {
+                        // Phase 177-3: Don't override condition_bindings
+                        if condition_binding_ids.contains(&loop_step_param) {
+                            eprintln!(
+                                "[cf_loop/joinir] Phase 177-3: Skipping override for condition_binding {:?} ('{}')",
+                                loop_step_param, carrier_name
+                            );
+                            continue;
+                        }
                         if debug {
                             eprintln!(
                                 "[cf_loop/joinir] Phase 33-21: REMAP loop_step param {:?} → {:?} ('{}')",
@@ -290,6 +388,8 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
                 // Fallback: Use old behavior (ValueId(0), ValueId(1), ...)
                 // This handles patterns that don't have loop_step function
                 if let Some(phi_dst) = phi_info.get_carrier_phi(loop_var_name) {
+                    // Phase 177-3: Don't override condition_bindings
+                    if !condition_binding_ids.contains(&ValueId(0)) {
                         remapper.set_value(ValueId(0), phi_dst);
                         if debug {
                             eprintln!(
@@ -297,12 +397,19 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
                                 phi_dst
                             );
                         }
+                    } else {
+                        eprintln!(
+                            "[cf_loop/joinir] Phase 177-3 fallback: Skipping override for condition_binding ValueId(0)"
+                        );
+                    }
                 }
                 for (idx, (carrier_name, entry)) in phi_info.carrier_phis.iter().enumerate() {
                     if carrier_name == loop_var_name {
                         continue;
                     }
                     let join_value_id = ValueId(idx as u32);
+                    // Phase 177-3: Don't override condition_bindings
+                    if !condition_binding_ids.contains(&join_value_id) {
                         remapper.set_value(join_value_id, entry.phi_dst);
                         if debug {
                             eprintln!(
@@ -310,8 +417,24 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
                                 join_value_id, entry.phi_dst, carrier_name
                             );
                         }
+                    } else {
+                        eprintln!(
+                            "[cf_loop/joinir] Phase 177-3 fallback: Skipping override for condition_binding {:?} ('{}')",
+                            join_value_id, carrier_name
+                        );
                     }
                 }
+            }
+
+            // Phase 177-3 DEBUG: Check remapper after Phase 33-21 overrides
+            eprintln!("[DEBUG-177] === Remapper state after Phase 33-21 ===");
+            for binding in &boundary.condition_bindings {
+                let lookup_result = remapper.get_value(binding.join_value);
+                eprintln!(
+                    "[DEBUG-177]   '{}': JoinIR {:?} → {:?} (after 33-21)",
+                    binding.name, binding.join_value, lookup_result
+                );
+            }
 
             phi_info
         } else {
@@ -323,6 +446,7 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
 
     // Phase 4: Merge blocks and rewrite instructions
     // Phase 33-16: Pass mutable loop_header_phi_info for latch_incoming tracking
+    // Phase 177-3: Pass exit_block_id from allocator to avoid conflicts
     let merge_result = instruction_rewriter::merge_and_rewrite(
         builder,
         mir_module,
@@ -331,6 +455,7 @@ pub(in crate::mir::builder) fn merge_joinir_mir_blocks(
         &function_params,
         boundary,
         &mut loop_header_phi_info,
+        exit_block_id,
         debug,
     )?;
 

src/mir/builder/joinir_inline_boundary_injector.rs

@@ -39,13 +39,26 @@ impl BoundaryInjector {
     /// When `boundary.loop_var_name` is set, ALL carriers (loop var + other carriers
     /// from exit_bindings) are handled by header PHIs. We skip ALL join_inputs
     /// Copy instructions to avoid overwriting the PHI results.
+    ///
+    /// # Phase 177-3: PHI Collision Avoidance (Option B)
+    ///
+    /// When `phi_dst_ids` contains ValueIds of existing PHI dsts in the header block,
+    /// we allocate a NEW ValueId for condition_bindings instead of skipping the copy.
+    /// This ensures the condition variable is available even when its remapped ValueId
+    /// collides with a PHI dst.
+    ///
+    /// # Returns
+    ///
+    /// Returns a HashMap mapping original ValueIds to their reallocated ValueIds
+    /// (only for condition_bindings that had collisions).
     pub fn inject_boundary_copies(
         func: &mut MirFunction,
         entry_block_id: BasicBlockId,
         boundary: &JoinInlineBoundary,
         value_map: &HashMap<ValueId, ValueId>,
+        phi_dst_ids: &std::collections::HashSet<ValueId>,
         debug: bool,
-    ) -> Result<(), String> {
+    ) -> Result<HashMap<ValueId, ValueId>, String> {
         // Phase 33-20: When loop_var_name is set, ALL join_inputs are handled by header PHIs
         // This includes the loop variable AND all other carriers from exit_bindings.
         // We skip ALL join_inputs Copy instructions, only condition_bindings remain.
@@ -59,7 +72,8 @@ impl BoundaryInjector {
         };
         let total_inputs = effective_join_inputs + boundary.condition_bindings.len();
         if total_inputs == 0 {
-            return Ok(());
+            // No inputs to process, return empty reallocations map
+            return Ok(HashMap::new());
         }
 
         if debug {
@@ -73,7 +87,38 @@ impl BoundaryInjector {
             );
         }
 
-        // Entry block を取得
+        // Phase 177-3: Use PHI dst IDs passed from caller
+        if debug && !phi_dst_ids.is_empty() {
+            eprintln!(
+                "[BoundaryInjector] Phase 177-3: Received {} PHI dst IDs to avoid: {:?}",
+                phi_dst_ids.len(),
+                phi_dst_ids
+            );
+        }
+
+        // Phase 177-3 Option B: First pass - allocate all new ValueIds for PHI collisions
+        // We need to do this BEFORE acquiring the entry_block reference to avoid borrow conflicts
+        let mut reallocations = HashMap::new();
+
+        for binding in &boundary.condition_bindings {
+            let remapped_join = value_map.get(&binding.join_value).copied().unwrap_or(binding.join_value);
+
+            if phi_dst_ids.contains(&remapped_join) {
+                // Collision detected! Allocate a fresh ValueId
+                let fresh_dst = func.next_value_id();
+
+                if debug {
+                    eprintln!(
+                        "[BoundaryInjector] Phase 177-3 Option B: PHI collision for condition binding '{}': {:?} → reallocated to {:?}",
+                        binding.name, remapped_join, fresh_dst
+                    );
+                }
+
+                reallocations.insert(binding.join_value, fresh_dst);
+            }
+        }
+
+        // Now get entry block reference (after all ValueId allocations are done)
         let entry_block = func
             .get_block_mut(entry_block_id)
             .ok_or(format!("Entry block {:?} not found", entry_block_id))?;
@@ -110,17 +155,34 @@ impl BoundaryInjector {
             }
         }
 
+        // Phase 177-3 DEBUG: Check value_map in BoundaryInjector
+        if debug {
+            eprintln!("[DEBUG-177] === BoundaryInjector value_map ===");
+            for binding in &boundary.condition_bindings {
+                let lookup = value_map.get(&binding.join_value);
+                eprintln!(
+                    "[DEBUG-177]   '{}': JoinIR {:?} → {:?}",
+                    binding.name, binding.join_value, lookup
+                );
+            }
+        }
+
         // Phase 171-fix: Inject Copy instructions for condition_bindings (condition-only variables)
         // These variables are read-only and used ONLY in the loop condition.
         // Each binding explicitly specifies HOST ValueId → JoinIR ValueId mapping.
         // We inject Copy: remapped_join_value = Copy host_value
+        //
+        // Phase 177-3 Option B: Use pre-allocated reallocations for PHI collision cases
         for binding in &boundary.condition_bindings {
             // Look up the remapped JoinIR ValueId from value_map
             let remapped_join = value_map.get(&binding.join_value).copied().unwrap_or(binding.join_value);
 
-            // Copy instruction: remapped_join_value = Copy host_value
+            // Phase 177-3 Option B: Check if this binding was reallocated (PHI collision case)
+            let final_dst = reallocations.get(&binding.join_value).copied().unwrap_or(remapped_join);
+
+            // Copy instruction: final_dst = Copy host_value
             let copy_inst = MirInstruction::Copy {
-                dst: remapped_join,
+                dst: final_dst,
                 src: binding.host_value,
             };
 
@@ -128,8 +190,9 @@ impl BoundaryInjector {
 
             if debug {
                 eprintln!(
-                    "[BoundaryInjector]   Condition binding '{}': Copy {:?} = Copy {:?} (JoinIR {:?} → remapped {:?})",
-                    binding.name, remapped_join, binding.host_value, binding.join_value, remapped_join
+                    "[BoundaryInjector]   Condition binding '{}': Copy {:?} = Copy {:?} (JoinIR {:?} → remapped {:?}{})",
+                    binding.name, final_dst, binding.host_value, binding.join_value, remapped_join,
+                    if final_dst != remapped_join { format!(" → reallocated {:?}", final_dst) } else { String::new() }
                 );
             }
         }
@@ -145,7 +208,8 @@ impl BoundaryInjector {
             entry_block.instruction_spans.insert(0, default_span);
         }
 
-        Ok(())
+        // Return reallocations map for condition_bindings that had PHI collisions
+        Ok(reallocations)
     }
 }