feat(llvm): Phase 132 - Pattern 1 exit value parity fix + Box-First refactoring
## Phase 132: Exit PHI Value Parity Fix ### Problem Pattern 1 (Simple While) returned 0 instead of final loop variable value (3) - VM: RC: 3 ✅ (correct) - LLVM: Result: 0 ❌ (wrong) ### Root Cause (Two Layers) 1. **JoinIR/Boundary**: Missing exit_bindings → ExitLineReconnector not firing 2. **LLVM Python**: block_end_values snapshot dropping PHI values ### Fix **JoinIR** (simple_while_minimal.rs): - Jump(k_exit, [i_param]) passes exit value **Boundary** (pattern1_minimal.rs): - Added LoopExitBinding with carrier_name="i", role=LoopState - Enables ExitLineReconnector to update variable_map **LLVM** (block_lower.py): - Use predeclared_ret_phis for reliable PHI filtering - Protect builder.vmap PHIs from overwrites (SSOT principle) ### Result - ✅ VM: RC: 3 - ✅ LLVM: Result: 3 - ✅ VM/LLVM parity achieved ## Phase 132-Post: Box-First Refactoring ### Rust Side **JoinModule::require_function()** (mod.rs): - Encapsulate function search logic - 10 lines → 1 line (90% reduction) - Reusable for Pattern 2-5 ### Python Side **PhiManager Box** (phi_manager.py - new): - Centralized PHI lifecycle management - 47 lines → 8 lines (83% reduction) - SSOT: builder.vmap owns PHIs - Fail-Fast: No silent overwrites **Integration**: - LLVMBuilder: Added phi_manager - block_lower.py: Delegated to PhiManager - tagging.py: Register PHIs with manager ### Documentation **New Files**: - docs/development/architecture/exit-phi-design.md - docs/development/current/main/investigations/phase132-llvm-exit-phi-wrong-result.md - docs/development/current/main/phases/phase-132/ **Updated**: - docs/development/current/main/10-Now.md - docs/development/current/main/phase131-3-llvm-lowering-inventory.md ### Design Principles - Box-First: Logic encapsulated in classes/methods - SSOT: Single Source of Truth (builder.vmap for PHIs) - Fail-Fast: Early explicit failures, no fallbacks - Separation of Concerns: 3-layer architecture 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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# Phase 132: LLVM Exit PHI=0 Bug Investigation & Fix
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**Date**: 2025-12-15
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**Status**: ✅ Fixed
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**Impact**: Critical - Exit PHIs from loops were returning 0 instead of correct values
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## Problem Statement
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LLVM backend was returning 0 for exit PHI values in simple while loops, while VM backend correctly returned the final loop variable value.
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### Test Case
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```nyash
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static box Main {
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main() {
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local i = 0
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loop(i < 3) { i = i + 1 }
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return i // Should return 3, was returning 0 in LLVM
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}
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}
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```
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**Expected**: Result: 3 (matches VM)
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**Actual (before fix)**: Result: 0
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**MIR**: Correct (`bb3: %1 = phi [%3, bb6]; ret %1`)
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**LLVM IR (before fix)**: `ret i64 0` (wrong!)
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**LLVM IR (after fix)**: `ret i64 %"phi_1"` (correct!)
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## Root Cause Analysis
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この不具合は「2層」にまたがっていました:
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1. JoinIR/Boundary 層で exit 値が境界を通っていない（VM でも 0 になり得る）
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2. LLVM Python 層で PHI の SSOT が壊れていて exit PHI が 0 になる（VM は正常でも LLVM が壊れる）
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このページは主に (2) の LLVM Python 層の根治を記録します。
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(1) の修正は Phase 132 の一部として別途コード側で入っています（修正ファイル一覧を参照）。
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### Investigation Path
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1. **PHI filtering issue in vmap_cur initialization**
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- ✅ Confirmed: Filter relied on `phi.basic_block` attribute
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- Issue: llvmlite sets `phi.basic_block = None` until IR finalization
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- Filter at block_lower.py:323-365 was silently dropping ALL PHIs
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2. **builder.vmap overwrite issue**
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- ✅ Confirmed: The real root cause!
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### The Actual Bug
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**Two separate issues** combined to cause the bug:
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#### Issue 1: Unreliable PHI.basic_block Attribute
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- llvmlite's PHI instructions have `basic_block = None` when created
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- Filter logic at block_lower.py:326-340 relied on `phi.basic_block.name` comparison
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- Since `basic_block` was always None, filter excluded ALL PHIs from vmap_cur
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- **Fix**: Use `predeclared_ret_phis` dict instead of `basic_block` attribute
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#### Issue 2: builder.vmap PHI Overwrites (Critical!)
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At block_lower.py:437-448, Pass A syncs created values to builder.vmap:
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```python
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# Phase 131-7: Sync ALL created values to global vmap
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for vid in created_ids:
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val = vmap_cur.get(vid)
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if val is not None:
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builder.vmap[vid] = val # ❌ Unconditional overwrite!
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```
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**The Fatal Sequence**:
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1. Pass A setup: Creates PHI v1 for bb3, stores in `builder.vmap[1]`
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2. Pass A processes bb0:
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- vmap_cur filters out v1 PHI (not from bb0)
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- const v1 instruction writes to vmap_cur[1]
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- **Line 444: Syncs vmap_cur[1] → builder.vmap[1], overwriting PHI!**
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3. Pass A processes bb3:
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- vmap_cur initialized from builder.vmap
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- builder.vmap[1] is now the const (not PHI!)
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- return v1 uses const 0 instead of PHI
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## The Fix
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### Fix 1: PHI Filtering (block_lower.py:320-347)
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**Before** (unreliable basic_block check):
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```python
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if hasattr(_val, 'add_incoming'):
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bb_of = getattr(getattr(_val, 'basic_block', None), 'name', None)
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bb_name = getattr(bb, 'name', None)
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keep = (bb_of == bb_name) # ❌ Always False! bb_of is None
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```
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**After** (use predeclared_ret_phis dict):
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```python
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if hasattr(_val, 'add_incoming'): # Is it a PHI?
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phi_key = (int(bid), int(_vid))
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if phi_key in predecl_phis:
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keep = True # ✅ Reliable tracking
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else:
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keep = False # Avoid namespace collision
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```
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### Fix 2: Protect builder.vmap PHIs (block_lower.py:437-455)
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**Before** (unconditional overwrite):
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```python
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for vid in created_ids:
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val = vmap_cur.get(vid)
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if val is not None:
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builder.vmap[vid] = val # ❌ Overwrites PHIs!
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```
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**After** (PHI protection):
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```python
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for vid in created_ids:
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val = vmap_cur.get(vid)
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if val is not None:
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existing = builder.vmap.get(vid)
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# Don't overwrite existing PHIs - SSOT principle
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if existing is not None and hasattr(existing, 'add_incoming'):
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continue # ✅ Skip sync, preserve PHI
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builder.vmap[vid] = val
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```
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## Verification
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### Test Results
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```bash
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# ✅ LLVM matches VM
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NYASH_LLVM_USE_HARNESS=1 NYASH_LLVM_STRICT=1 ./target/release/hakorune --backend llvm /tmp/p1_return_i.hako
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# Output: Result: 3
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# ✅ VM baseline
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./target/release/hakorune --backend vm /tmp/p1_return_i.hako
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# Output: RC: 3
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```
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### Generated LLVM IR Comparison
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**Before** (wrong):
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```llvm
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bb3:
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%"phi_1" = phi i64 [%"phi_3", %"bb6"]
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ret i64 0 ; ❌ Hardcoded 0!
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```
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**After** (correct):
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```llvm
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bb3:
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%"phi_1" = phi i64 [%"phi_3", %"bb6"]
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ret i64 %"phi_1" ; ✅ Uses PHI value!
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```
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## Design Lessons
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### The SSOT Principle
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**builder.vmap is the Single Source of Truth for PHI nodes**:
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- PHIs are created once in setup_phi_placeholders
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- PHIs must NEVER be overwritten by later instructions
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- vmap_cur is per-block and must filter PHIs correctly
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### PHI Ownership Tracking
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**llvmlite limitation**: PHI.basic_block is None until finalization
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**Solution**: Explicit tracking via `predeclared_ret_phis: Dict[(block_id, value_id), PHI]`
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### Fail-Fast vs Silent Failures
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The original filter silently dropped PHIs via broad exception handling:
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```python
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except Exception:
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keep = False # ❌ Silent failure!
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```
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**Better approach**: Explicit checks with trace logging for debugging.
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## Related Issues
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- Phase 131: Block_end_values SSOT system
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- Phase 131-12: VMap snapshot investigation
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- Phase 131-14-B: Jump-only block resolution
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## Files Modified
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### JoinIR/Boundary 層（exit 値の SSOT を境界で明示）
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- `src/mir/join_ir/lowering/simple_while_minimal.rs`（`Jump(k_exit, [i_param])`）
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- `src/mir/builder/control_flow/joinir/patterns/pattern1_minimal.rs`（`LoopExitBinding` を作って境界へ設定）
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### LLVM Python 層（PHI SSOT の維持）
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- `src/llvm_py/builders/block_lower.py`
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- PHI filtering を `predeclared_ret_phis` ベースへ変更（`phi.basic_block` 依存を排除）
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- `builder.vmap` へ sync する際、既存 PHI を上書きしない（PHI を SSOT として保護）
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## Debug Environment Variables
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```bash
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NYASH_LLVM_STRICT=1 # Fail-fast on errors
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NYASH_LLVM_TRACE_PHI=1 # PHI wiring traces
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NYASH_LLVM_TRACE_VMAP=1 # VMap operation traces
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NYASH_LLVM_DUMP_IR=/tmp/x.ll # Dump generated IR
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```
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## Acceptance Criteria
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✅ `/tmp/p1_return_i.hako` returns 3 in LLVM (was 0)
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✅ STRICT mode enabled, no fallback to 0
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✅ VM and LLVM results match
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✅ No regression on Phase 131 test cases
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✅ Generated LLVM IR uses `ret i64 %phi_1` not `ret i64 0`
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## Next Steps
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- [ ] Add regression test for exit PHI patterns
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- [ ] Document PHI ownership model in the LLVM harness docs (SSOT: `phase131-3-llvm-lowering-inventory.md`)
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