Phase 5 E5-3: Candidate Analysis (All DEFERRED) + E5-4 Instructions

E5-3 Analysis Results:
- free_tiny_fast_cold (7.14%): DEFER - cold path, low ROI
- unified_cache_push (3.39%): DEFER - already optimized
- hakmem_env_snapshot_enabled (2.97%): DEFER - low headroom

Key Insight: perf self% is time-weighted, not frequency-weighted.
Cold paths appear hot but have low total impact.

Next: E5-4 (Malloc Tiny Direct Path)
- Apply E5-1 winning pattern to malloc side
- Target: tiny_alloc_gate_fast() gate tax elimination
- ENV gate: HAKMEM_MALLOC_TINY_DIRECT=0/1

Files added:
- docs/analysis/PHASE5_E5_3_ANALYSIS_AND_RECOMMENDATIONS.md
- docs/analysis/PHASE5_E5_4_MALLOC_TINY_DIRECT_NEXT_INSTRUCTIONS.md
- core/box/free_cold_shape_env_box.{h,c} (research box, not tested)
- core/box/free_cold_shape_stats_box.{h,c} (research box, not tested)

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

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

CURRENT_TASK.md

@@ -1,5 +1,68 @@
 # 本線タスク（現在）
 
+## 更新メモ（2025-12-14 Phase 5 E5-3 Analysis - Strategic Pivot）
+
+### Phase 5 E5-3: Candidate Analysis & Strategic Recommendations ⚠️ DEFER (2025-12-14)
+
+**Decision**: **DEFER all E5-3 candidates** (E5-3a/b/c). Pivot to E5-4 (Malloc Direct Path, E5-1 pattern replication).
+
+**Analysis**:
+- **E5-3a (free_tiny_fast_cold 7.14%)**: NO-GO (cold path, low frequency despite high self%)
+- **E5-3b (unified_cache_push 3.39%)**: MAYBE (already optimized, marginal ROI ~+1.0%)
+- **E5-3c (hakmem_env_snapshot_enabled 2.97%)**: NO-GO (E3-4 precedent shows -1.44% regression)
+
+**Key Insight**: **Profiler self% ≠ optimization opportunity**
+- Self% is time-weighted (samples during execution), not frequency-weighted
+- Cold paths appear hot due to expensive operations when hit, not total cost
+- E5-2 lesson: 3.35% self% → +0.45% NEUTRAL (branch overhead ≈ savings)
+
+**ROI Assessment**:
+| Candidate | Self% | Frequency | Expected Gain | Risk | Decision |
+|-----------|-------|-----------|---------------|------|----------|
+| E5-3a (cold path) | 7.14% | LOW | +0.5% | HIGH | NO-GO |
+| E5-3b (push) | 3.39% | HIGH | +1.0% | MEDIUM | DEFER |
+| E5-3c (env snapshot) | 2.97% | HIGH | -1.0% | HIGH | NO-GO |
+
+**Strategic Pivot**: Focus on **E5-1 Success Pattern** (wrapper-level deduplication)
+- E5-1 (Free Tiny Direct): +3.35% (GO) ✅
+- **Next**: E5-4 (Malloc Tiny Direct) - Apply E5-1 pattern to alloc side
+- **Expected**: +2-4% (similar to E5-1, based on malloc wrapper overhead)
+
+**Cumulative Status (Phase 5)**:
+- E4-1 (Free Wrapper Snapshot): +3.51% standalone
+- E4-2 (Malloc Wrapper Snapshot): +21.83% standalone
+- E4 Combined: +6.43% (from baseline with both OFF)
+- E5-1 (Free Tiny Direct): +3.35% (from E4 baseline)
+- E5-2 (Header Write-Once): +0.45% NEUTRAL (frozen)
+- **E5-3**: **DEFER** (analysis complete, no implementation/test)
+- **Total Phase 5**: ~+9-10% cumulative (E4+E5-1 promoted, E5-2 frozen, E5-3 deferred)
+
+**Implementation** (E5-3a research box, NOT TESTED):
+- Files created:
+  - `core/box/free_cold_shape_env_box.{h,c}` (ENV gate, default OFF)
+  - `core/box/free_cold_shape_stats_box.{h,c}` (stats counters)
+  - `docs/analysis/PHASE5_E5_3_ANALYSIS_AND_RECOMMENDATIONS.md` (analysis)
+- Files modified:
+  - `core/front/malloc_tiny_fast.h` (lines 418-437, cold path shape optimization)
+- Pattern: Early exit for LEGACY path (skip LARSON check when !use_tiny_heap)
+- **Status**: FROZEN (default OFF, pre-analysis shows NO-GO, not worth A/B testing)
+
+**Key Lessons**:
+1. **Profiler self% misleads** when frequency is low (cold path)
+2. **Micro-optimizations plateau** in already-optimized code (E5-2, E5-3b)
+3. **Branch hints are profile-dependent** (E3-4 failure, E5-3c risk)
+4. **Wrapper-level deduplication wins** (E4-1, E4-2, E5-1 pattern)
+
+**Next Steps**:
+- **E5-4 Design**: Malloc Tiny Direct Path (E5-1 pattern for alloc)
+  - Target: malloc() wrapper overhead (~12.95% self% in E4 profile)
+  - Method: Single size check → direct call to malloc_tiny_fast_for_class()
+  - Expected: +2-4% (based on E5-1 precedent +3.35%)
+- Design doc: `docs/analysis/PHASE5_E5_4_MALLOC_TINY_DIRECT_DESIGN.md`
+- Next instructions: `docs/analysis/PHASE5_E5_4_MALLOC_TINY_DIRECT_NEXT_INSTRUCTIONS.md`
+
+---
+
 ## 更新メモ（2025-12-14 Phase 5 E5-2 Complete - Header Write-Once）
 
 ### Phase 5 E5-2: Header Write-Once Optimization ⚪ NEUTRAL (2025-12-14)
@@ -120,12 +183,15 @@
 
 **Next Steps**:
 - ✅ Promote: `HAKMEM_FREE_TINY_DIRECT=1` to `MIXED_TINYV3_C7_SAFE` preset
-- Next: E5-2 (Header Prefill at Refill, 2.59% target) or E5-3 (ENV Snapshot Shape, 2.57% target)
+- ✅ E5-2: NEUTRAL → FREEZE
+- ✅ E5-3: DEFER（ROI 低）
+- Next: **E5-4 (Malloc Tiny Direct)**（E5-1 パターンの alloc 側複製）
 - Design docs:
   - `docs/analysis/PHASE5_E5_1_FREE_TINY_DIRECT_1_DESIGN.md`
   - `docs/analysis/PHASE5_E5_1_FREE_TINY_DIRECT_1_AB_TEST_RESULTS.md`
   - `docs/analysis/PHASE5_E5_1_FREE_TINY_DIRECT_NEXT_INSTRUCTIONS.md`
   - `docs/analysis/PHASE5_E5_COMPREHENSIVE_ANALYSIS.md`
+  - `docs/analysis/PHASE5_E5_4_MALLOC_TINY_DIRECT_NEXT_INSTRUCTIONS.md`
 
 ---