35db1f8d78
Phase 131-6 根治調査: SSA Dominance 診断完了 確定結果: - ✅ MIR は正しい（SSA 形式完璧、use-before-def なし） - ✅ Rust VM は正常（0,1,2 を出力して停止） - ❌ LLVM backend が壊れている（0 を無限に出力） 根本原因特定: - 場所: src/llvm_py/llvm_builder.py の finalize_phis() (lines 601-735) - 問題: PHI incoming value wiring が壊れている - 疑わしいコード: lines 679-681 の self-carry logic - 結果: PHI %3 が常に初期値 0 を返す → ループカウンタ増えない テスト結果: - Simple Add: VM ✅ 1, LLVM ✅ 1 (PASS) - Loop Min While: VM ✅ 0,1,2, LLVM ❌ 0 forever (BUG) - Phase 87 Min: VM ✅ 42, LLVM ✅ 42 (PASS) 新規ドキュメント: - phase131-6-ssa-dominance-diagnosis.md: 完全な診断結果 - phase131-6-next-steps.md: 修正戦略と実装チェックリスト - phase131-3-llvm-lowering-inventory.md: 更新済み Next: Phase 131-7 (finalize_phis 修正) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
126 lines
4.2 KiB
Markdown
126 lines
4.2 KiB
Markdown
# Phase 131-6: Next Steps - PHI Bug Fix
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## Summary
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**Problem**: LLVM backend generates infinite loop for `loop_min_while.hako`
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**Root Cause**: PHI node incoming values not properly wired in `finalize_phis()`
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**Impact**: P0 - Breaks basic loop functionality
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## Recommended Fix Strategy
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### Option A: Structural Fix (Recommended)
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**Approach**: Fix the PHI wiring logic in `finalize_phis()` to properly connect incoming values.
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**Location**: `/home/tomoaki/git/hakorune-selfhost/src/llvm_py/llvm_builder.py:601-735`
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**Suspected Issue**:
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```python
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# Lines 679-681: Self-carry logic
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if vs == int(dst_vid) and init_src_vid is not None:
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vs = int(init_src_vid) # ← May incorrectly replace %12 with %2
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```
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**Fix Hypothesis**:
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The self-carry logic is meant to handle PHI nodes that reference themselves, but it may be incorrectly triggering for normal loop-carried dependencies. We need to:
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1. Add trace logging to see what values are being resolved
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2. Check if `vs == int(dst_vid)` is incorrectly matching %12 (the updated value) as a self-reference
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3. Verify that `_value_at_end_i64()` is correctly retrieving the value of %12 from bb7
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**Debug Commands**:
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```bash
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# Enable verbose logging (if available)
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export NYASH_CLI_VERBOSE=1
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export NYASH_LLVM_DEBUG=1
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# Generate LLVM IR to inspect
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tools/build_llvm.sh apps/tests/loop_min_while.hako -o /tmp/loop_test
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# Check generated LLVM IR
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llvm-dis /tmp/loop_test.o # If object contains IR
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# Or add --emit-llvm-ir flag if available
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```
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**Steps**:
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1. Add debug prints in `finalize_phis()` to log:
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- Which incoming values are being wired: `(block_id, dst_vid, [(pred_id, value_id)])`
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- What `nearest_pred_on_path()` returns for each incoming edge
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- What `_value_at_end_i64()` returns for each value
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2. Compare debug output between working (VM) and broken (LLVM) paths
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3. Fix the logic that's causing %12 to be ignored or replaced
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4. Verify fix doesn't break Case A or B2
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### Option B: Workaround (Not Recommended)
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Disable loop optimization or use VM backend for loops. This doesn't solve the root cause.
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## Acceptance Tests
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### Must Pass
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1. **Simple Add** (already passing):
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```bash
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./target/release/hakorune /tmp/simple_add.hako # Should print 1
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```
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2. **Loop Min While** (currently failing):
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```bash
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tools/build_llvm.sh apps/tests/loop_min_while.hako -o /tmp/loop_test
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timeout 2 /tmp/loop_test # Should print 0\n1\n2 and exit
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```
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3. **Phase 87 LLVM Min** (regression check):
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```bash
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tools/build_llvm.sh apps/tests/phase87_llvm_exe_min.hako -o /tmp/phase87_test
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/tmp/phase87_test
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echo $? # Should be 42
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```
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### Should Not Regress
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- Case A: `phase87_llvm_exe_min.hako` ✅
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- Case B2: Simple print without loop ✅
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- VM backend: All existing VM tests ✅
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## Implementation Checklist
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- [ ] Add debug logging to `finalize_phis()`
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- [ ] Identify which incoming value is being incorrectly wired
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- [ ] Fix the wiring logic
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- [ ] Test Case B (loop_min_while) - must output `0\n1\n2`
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- [ ] Test Case A regression - must exit with 42
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- [ ] Test Case B2 regression - must print 42
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- [ ] Document the fix in this file and phase131-3-llvm-lowering-inventory.md
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- [ ] Consider adding MIR→LLVM IR validation pass
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## Timeline
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- **Phase 131-6 Diagnosis**: 2025-12-14 ✅ Complete
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- **Phase 131-7 Fix**: TBD
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- **Phase 131-8 Verification**: TBD
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## Related Documents
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- [Phase 131-6 Diagnosis](phase131-6-ssa-dominance-diagnosis.md) - Full diagnostic report
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- [Phase 131-3 Inventory](phase131-3-llvm-lowering-inventory.md) - Test case matrix
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- [LLVM Builder Code](../../src/llvm_py/llvm_builder.py) - Implementation
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## Notes for Future Self
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**Why MIR is correct but LLVM is wrong**:
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- MIR SSA form verified ✅
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- VM execution verified ✅
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- LLVM emission succeeds ✅
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- LLVM linking succeeds ✅
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- **LLVM runtime fails** ❌ → Bug is in IR generation, not MIR
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**Key Insight**:
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The bug is NOT in the MIR builder or JoinIR merger. The bug is specifically in how the Python LLVM builder (`llvm_builder.py`) translates MIR PHI nodes into LLVM IR PHI nodes. This is a **translation bug**, not a **semantic bug**.
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**Architecture Note**:
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This confirms the value of the 2-pillar strategy (VM + LLVM). The VM serves as a reference implementation to verify MIR correctness before blaming the frontend.
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