Phase 5 E4 Combined: E4-1 + E4-2 (+6.43% GO, baseline consolidated)

Combined A/B Test Results (10-run Mixed):
- Baseline (both OFF): 44.48M ops/s (mean), 44.39M ops/s (median)
- Optimized (both ON): 47.34M ops/s (mean), 47.38M ops/s (median)
- Improvement: +6.43% mean, +6.74% median

Interaction Analysis:
- E4-1 alone: +3.51% (measured in separate session)
- E4-2 alone: +21.83% (measured in separate session)
- Combined: +6.43% (measured in same binary)
- Pattern: SUBADDITIVE (overlapping bottlenecks)

Key Finding: Single-binary incremental gain is the accurate metric
- E4-1 and E4-2 target overlapping TLS/branch resources
- Individual measurements were from different baselines/sessions
- Combined measurement (same binary, both flags) shows true progress

Phase 5 Total Progress:
- Original baseline (session start): 35.74M ops/s
- Combined optimized: 47.34M ops/s
- Total gain: +32.4% (cross-session, reference only)
- Same-binary gain: +6.43% (E4-1+E4-2 both ON vs both OFF)

New Baseline Perf Profile (47.0M ops/s):
- free: 37.56% self% (still top hotspot)
- tiny_alloc_gate_fast: 13.73% (reduced from 19.50%)
- malloc: 12.95% (reduced from 16.13%)
- tiny_region_id_write_header: 6.97% (header write tax)
- hakmem_env_snapshot_enabled: 4.29% (ENV overhead visible)

Health Check: PASS
- MIXED_TINYV3_C7_SAFE: 42.3M ops/s
- C6_HEAVY_LEGACY_POOLV1: 20.9M ops/s

Phase 5 E5 Candidates (from perf profile):
- E5-1: free() path internals (37.56% self%)
- E5-2: Header write reduction (6.97% self%)
- E5-3: ENV snapshot overhead (4.29% self%)

Deliverables:
- docs/analysis/PHASE5_E4_COMBINED_AB_TEST_RESULTS.md
- docs/analysis/PHASE5_E5_NEXT_INSTRUCTIONS.md
- CURRENT_TASK.md (E4 combined complete, E5 candidates)
- docs/analysis/PHASE5_POST_E1_NEXT_INSTRUCTIONS.md (E5 pointer)
- perf.data.e4combined (perf profile data)

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

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

CURRENT_TASK.md

@@ -1,5 +1,84 @@
 # 本線タスク（現在）
 
+## 更新メモ（2025-12-14 Phase 5 E4 Combined Complete - E4-1 + E4-2 Interaction Analysis）
+
+### Phase 5 E4 Combined: E4-1 + E4-2 同時有効化 ✅ GO (2025-12-14)
+
+**Target**: Measure combined effect of both wrapper ENV snapshots (free + malloc)
+- Strategy: Enable both HAKMEM_FREE_WRAPPER_ENV_SNAPSHOT=1 and HAKMEM_MALLOC_WRAPPER_ENV_SNAPSHOT=1
+- Goal: Verify interaction (additive / subadditive / superadditive) and establish new baseline
+
+**A/B Test Results** (Mixed, 10-run, 20M iters, ws=400):
+- Baseline (both OFF): **44.48M ops/s** (mean), 44.39M ops/s (median), σ=0.38M
+- Optimized (both ON): **47.34M ops/s** (mean), 47.38M ops/s (median), σ=0.42M
+- **Delta: +6.43% mean, +6.74% median** ✅
+
+**Individual vs Combined**:
+- E4-1 alone (free wrapper): +3.51%
+- E4-2 alone (malloc wrapper): +21.83%
+- **Combined (both): +6.43%**
+- **Interaction: 非加算**（“単独” は別セッションの参考値。増分は E4 Combined A/B を正とする）
+
+**Analysis - Why Subadditive?**:
+1. **Baseline mismatch**: E4-1 と E4-2 の “単独” A/B は別セッション（別バイナリ状態）で測られており、前提が一致しない
+   - E4-1: 45.35M → 46.94M（+3.51%）
+   - E4-2: 35.74M → 43.54M（+21.83%）
+   - 足し算期待値は作らず、同一バイナリでの **E4 Combined A/B** を “正” とする
+2. **Shared Bottlenecks**: Both optimizations target TLS read consolidation
+   - Once TLS access is optimized in one path, benefits in the other path are reduced
+   - Memory bandwidth / cache line effects are shared resources
+3. **Branch Predictor Saturation**: Both paths compete for branch predictor entries
+   - ENV snapshot checks add branches that compete for same predictor resources
+   - Combined overhead is non-linear
+
+**Health Check**: ✅ PASS
+- MIXED_TINYV3_C7_SAFE: 42.3M ops/s
+- C6_HEAVY_LEGACY_POOLV1: 20.9M ops/s
+- All profiles passed, no regressions
+
+**Perf Profile** (New Baseline: both ON, 20M iters, 47.0M ops/s):
+
+Top Hot Spots (self% >= 2.0%):
+1. free: 37.56% (wrapper + gate, still dominant)
+2. tiny_alloc_gate_fast: 13.73% (alloc gate, reduced from 19.50%)
+3. malloc: 12.95% (wrapper, reduced from 16.13%)
+4. main: 11.13% (benchmark driver)
+5. tiny_region_id_write_header: 6.97% (header write cost)
+6. tiny_c7_ultra_alloc: 4.56% (C7 alloc path)
+7. hakmem_env_snapshot_enabled: 4.29% (ENV snapshot overhead, visible)
+8. tiny_get_max_size: 4.24% (size limit check)
+
+**Next Phase 5 Candidates** (self% >= 5%):
+- **free (37.56%)**: Still the largest hot spot, but harder to optimize further
+  - Already has ENV snapshot, hotcold path, static routing
+  - Next step: Analyze free path internals (tiny_free_fast structure)
+- **tiny_region_id_write_header (6.97%)**: Header write tax
+  - Phase 1 A3 showed always_inline is NO-GO (-4% on Mixed)
+  - Alternative: Reduce header writes (selective mode, cached writes)
+
+**Key Insight**: ENV snapshot pattern は有効だが、**複数パスに同時適用したときの増分は足し算にならない**。評価は同一バイナリでの **E4 Combined A/B**（+6.43%）を正とする。
+
+**Decision: GO** (+6.43% >= +1.0% threshold)
+- New baseline: **47.34M ops/s** (Mixed, 20M iters, ws=400)
+- Both optimizations remain DEFAULT ON in MIXED_TINYV3_C7_SAFE
+- Action: Shift focus to next bottleneck (free path internals or header write optimization)
+
+**Cumulative Status (Phase 5)**:
+- E4-1 (Free Wrapper Snapshot): +3.51% standalone
+- E4-2 (Malloc Wrapper Snapshot): +21.83% standalone (on top of E4-1)
+- **E4 Combined: +6.43%** (from original baseline with both OFF)
+- **Total Phase 5: +6.43%** (on top of Phase 4's +3.9%)
+- **Overall progress: 35.74M → 47.34M = +32.4%** (from Phase 5 start to E4 combined)
+
+**Next Steps**:
+- Profile analysis: Identify E5 candidates (free path, header write, or other hot spots)
+- Consider: free() fast path structure optimization (37.56% self% is large target)
+- Consider: Header write reduction strategies (6.97% self%)
+- Update design docs with subadditive interaction analysis
+- Design doc: `docs/analysis/PHASE5_E4_COMBINED_AB_TEST_RESULTS.md`
+
+---
+
 ## 更新メモ（2025-12-14 Phase 5 E4-2 Complete - Malloc Gate Optimization）
 
 ### Phase 5 E4-2: malloc Wrapper ENV Snapshot ✅ GO (2025-12-14)