feat(llvm): Phase 131-4 P1 完了 - PHI ordering 修正（multi-pass architecture）

Phase 131-4 P1: PHI After Terminator Bug 修正

問題:
- LLVM IR で PHI が terminator の後に出現（LLVM invariant 違反）
- Case B (loop_min_while.hako) が TAG-EMIT で失敗

修正:
- Multi-pass block lowering architecture 実装:
  - Pass A: non-terminator instructions のみ emit
  - Pass B: PHI finalization（block head に確実に配置）
  - Pass C: deferred terminators を最後に emit

変更ファイル:
- src/llvm_py/builders/block_lower.py (~40行):
  - lower_blocks() で terminator を defer
  - lower_terminators() 新設（Pass C）
  - _deferred_terminators dict で管理
- src/llvm_py/builders/function_lower.py (3行):
  - Pass 順序更新: A→B→C
- src/llvm_py/instructions/ret.py (5行):
  - _disable_phi_synthesis flag で Pass C 中の PHI 生成を抑制

テスト結果:
- Case B EMIT: ❌→✅ (修正成功)
- Case B LINK: ❌ (新 TAG-LINK: undefined nyash_console_log)
- Case A/B2: ✅ (退行なし)

箱化モジュール化:
- ✅ Multi-pass で責務分離
- ✅ Flag mechanism で構造的制御
- ✅ ハードコード禁止原則遵守

Next: Phase 131-5 (TAG-LINK 修正)

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/development/current/main/phase131-3-llvm-lowering-inventory.md

@@ -8,7 +8,7 @@
 | Case | File | Emit | Link | Run | Notes |
 |------|------|------|------|-----|-------|
 | A | `apps/tests/phase87_llvm_exe_min.hako` | ✅ | ✅ | ✅ | **PASS** - Simple return 42, no BoxCall, exit code verified |
-| B | `apps/tests/loop_min_while.hako` | ❌ | - | - | **TAG-EMIT** - Loop generates invalid LLVM IR (observed: PHI placement/order issue; also mentions empty block) |
+| B | `apps/tests/loop_min_while.hako` | ✅ | ❌ | - | **TAG-LINK** - EMIT fixed (Phase 131-4), LINK fails (undefined nyash_console_log) |
 | B2 | `/tmp/case_b_simple.hako` | ✅ | ✅ | ✅ | **PASS** - Simple print(42) without loop works |
 | C | `apps/tests/llvm_stage3_loop_only.hako` | ❌ | - | - | **TAG-EMIT** - Complex loop (break/continue) fails JoinIR pattern matching |
 
@@ -72,9 +72,51 @@ This strongly suggests an **emission ordering / insertion-position** problem in
 - PHI insertion rules + debug: `src/llvm_py/phi_wiring/wiring.py` (`NYASH_PHI_ORDERING_DEBUG=1`)
 - “Empty block” safety pass (separate concern): `src/llvm_py/builders/function_lower.py:_enforce_terminators`
 
+**✅ FIXED (Phase 131-4)**: Multi-pass block lowering architecture
+
+**Solution implemented**:
+- **Pass A**: Lower non-terminator instructions (body ops only)
+- **Pass B**: Finalize PHIs (wire incoming edges) - happens in `function_lower.py`
+- **Pass C**: Lower deferred terminators (after PHIs are placed)
+
+**Key changes**:
+1. `src/llvm_py/builders/block_lower.py`:
+   - Split `lower_blocks()` to defer terminators
+   - Added `lower_terminators()` function for Pass C
+   - Deferred terminators stored in `builder._deferred_terminators`
+
+2. `src/llvm_py/builders/function_lower.py`:
+   - Updated pass ordering: Pass A → Pass B → Pass C
+   - Added call to `_lower_terminators()` after `_finalize_phis()`
+
+3. `src/llvm_py/instructions/ret.py`:
+   - Added `_disable_phi_synthesis` flag check
+   - Prevents PHI creation during Pass C (terminators should only use existing values)
+
+**Result**:
+- Case B EMIT now succeeds ✅
+- Generated LLVM IR is valid (PHIs before terminators)
+- No regression in Cases A and B2
+
 ---
 
-### 2. TAG-EMIT: JoinIR Pattern Mismatch (Case C)
+### 2. TAG-LINK: Missing runtime symbols (Case B)
+
+**File**: `apps/tests/loop_min_while.hako`
+
+**Link Error**:
+```
+/usr/bin/ld: /home/tomoaki/git/hakorune-selfhost/target/aot_objects/loop_min_while.o: in function `condition_fn':
+<string>:(.text+0x99): undefined reference to `nyash_console_log'
+```
+
+**Root Cause**: ExternCall lowering emits calls to runtime functions (e.g., `nyash_console_log`) but these symbols are not provided by NyKernel (`libnyash_kernel.a`).
+
+**Next Steps**: Map ExternCall names to actual NyKernel symbols or add missing runtime functions.
+
+---
+
+### 3. TAG-EMIT: JoinIR Pattern Mismatch (Case C)
 
 **File**: `apps/tests/llvm_stage3_loop_only.hako`
 
@@ -127,24 +169,33 @@ Hint: This loop pattern is not supported. All loops must use JoinIR lowering.
 
 ## Next Steps
 
-### Priority 1: Fix TAG-EMIT (PHI After Terminator Bug) ⚠️ CRITICAL
+### ✅ Priority 1: COMPLETED - Fix TAG-EMIT (PHI After Terminator Bug)
 **Target**: Case B (`loop_min_while.hako`)
 
-**Goal**: Ensure PHIs are always emitted/inserted before any terminator in the same basic block.
+**Status**: ✅ FIXED in Phase 131-4 (see Root Cause #1 above)
 
-**Candidate approach** (docs-only; implementation to be decided):
-- Split lowering into multi-pass so that PHI placeholders exist before terminators are emitted, or delay terminator emission until after PHI finalization:
-  - (A) Predeclare PHIs at block creation time (placeholders), then emit body ops, then wire incomings, then emit terminators.
-  - (B) Keep current finalize order, but guarantee `ensure_phi()` always inserts at head even when a terminator exists (verify llvmlite positioning behavior).
-
-**Primary files to look at for the fix**:
-- `src/llvm_py/builders/function_lower.py` (pass ordering)
-- `src/llvm_py/builders/block_lower.py` (terminator emission split point)
-- `src/llvm_py/phi_wiring/wiring.py` (PHI insertion positioning)
+**Result**: Case B EMIT now succeeds. LINK still fails (TAG-LINK), but that's a separate issue (Priority 2).
 
 ---
 
-### Priority 2: Fix TAG-EMIT (JoinIR Pattern Coverage)
+### Priority 2: Fix TAG-LINK (Missing Runtime Symbols)
+**Target**: Case B (`loop_min_while.hako`)
+
+**Approach**:
+1. Identify all ExternCall lowering paths in Python harness
+2. Map to actual NyKernel symbols (e.g., `nyash_console_log` → `ny_console_log` or similar)
+3. Update ExternCall lowering to use correct symbol names
+4. OR: Add wrapper functions in NyKernel to provide missing symbols
+
+**Files**:
+- `src/llvm_py/instructions/externcall.py` - ExternCall lowering
+- `crates/nyash_kernel/src/lib.rs` - NyKernel runtime symbols
+
+**Expected**: Case B should LINK ✅ RUN ✅ after fix
+
+---
+
+### Priority 3: Fix TAG-EMIT (JoinIR Pattern Coverage)
 **Target**: Case C (`llvm_stage3_loop_only.hako`)
 
 **Approach**: