From 79b9d2b32c69add43a30c5b69970d9f6840f861c Mon Sep 17 00:00:00 2001
From: nyash-codex <codex@nyash.local>
Date: Sat, 1 Nov 2025 14:37:54 +0900
Subject: [PATCH] fix(mir): edge-copy insertion before terminator - resolve
 ValueId undefined errors
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【問題】
Stage-B（JSON v0 Bridge）で「use of undefined value ValueId(...)」エラー発生
- 原因: merge.rs:38-42でedge-copyを終端命令**後**に追加していた
- 結果: Copy命令が到達不能となり、ValueIdが未定義のまま参照される

【根本原因分析】
1. if_else.rs:34で`set_terminator(Jump)`を設定
2. if_else.rs:62で`merge_var_maps()`呼び出し
3. merge.rs:39で`add_instruction(Copy)` ← **ここで終端後に追加！**
4. BasicBlock構造上、terminator設定後のadd_instruction()は到達不能

【修正内容】
1. BasicBlock::add_instruction_before_terminator()メソッド追加
   - 終端命令の有無に関わらず、instructions vecに追加
   - terminator自体の追加は許可しない（panic）

2. merge_values()でedge-copy挿入方法を変更
   - add_instruction() → add_instruction_before_terminator()
   - これによりCopyが終端の**前**に配置される

【修正箇所】
- src/mir/basic_block.rs: add_instruction_before_terminator()追加（12行）
- src/runner/json_v0_bridge/lowering/merge.rs: 呼び出し変更（2行）

【テスト結果】
✅ if文PHIテスト: /tmp/phi_simple_if2.nyash → 出力 1
✅ loop文PHIテスト: /tmp/phi_loop_test.nyash → 出力 10
✅ userbox_*スモークテスト: 全6テストPASS
⚠️ Stage-B: namespace conflict未解決のため未確認
   （apps/selfhost.vm.* と lang/hakorune.vm.* の競合）

【影響範囲】
- JSON v0 Bridge経路のif/else合流処理
- edge-copy（PHI-off mode）の正しい配置保証
- Builder経路は元々正常動作（影響なし）

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
---
 src/mir/basic_block.rs                      | 14 ++++++++++++++
 src/runner/json_v0_bridge/lowering/merge.rs |  5 +++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/mir/basic_block.rs b/src/mir/basic_block.rs
index 37d5040e..88953c72 100644
--- a/src/mir/basic_block.rs
+++ b/src/mir/basic_block.rs
@@ -102,6 +102,20 @@ impl BasicBlock {
         }
     }
 
+    /// Add instruction before terminator (for edge-copy in PHI-off mode)
+    /// If no terminator exists, behaves like add_instruction()
+    pub fn add_instruction_before_terminator(&mut self, instruction: MirInstruction) {
+        // Update effect mask
+        self.effects = self.effects | instruction.effects();
+
+        // Non-terminator instructions always go into instructions vec
+        if !self.is_terminator(&instruction) {
+            self.instructions.push(instruction);
+        } else {
+            panic!("Cannot add terminator via add_instruction_before_terminator");
+        }
+    }
+
     /// Check if an instruction is a terminator
     fn is_terminator(&self, instruction: &MirInstruction) -> bool {
         matches!(
diff --git a/src/runner/json_v0_bridge/lowering/merge.rs b/src/runner/json_v0_bridge/lowering/merge.rs
index 3a20a312..9628dae0 100644
--- a/src/runner/json_v0_bridge/lowering/merge.rs
+++ b/src/runner/json_v0_bridge/lowering/merge.rs
@@ -35,11 +35,12 @@ pub(super) fn merge_values(
     }
     let dst = f.next_value_id();
     if no_phi {
+        // Insert edge-copy BEFORE terminator (critical fix for ValueId undefined errors)
         if let Some(bb) = f.get_block_mut(pred_a) {
-            bb.add_instruction(MirInstruction::Copy { dst, src: val_a });
+            bb.add_instruction_before_terminator(MirInstruction::Copy { dst, src: val_a });
         }
         if let Some(bb) = f.get_block_mut(pred_b) {
-            bb.add_instruction(MirInstruction::Copy { dst, src: val_b });
+            bb.add_instruction_before_terminator(MirInstruction::Copy { dst, src: val_b });
         }
     } else if let Some(bb) = f.get_block_mut(merge_bb) {
         bb.insert_instruction_after_phis(MirInstruction::Phi {