hakmem/docs/analysis/PHASE4_EXECUTIVE_SUMMARY.md

# Phase 4 Status - Executive Summary

**Date**: 2025-12-14
**Status**: E1 ✅ GO（preset昇格）, E2 🔬 FROZEN, E3-4 ❌ NO-GO
**Baseline**: Mixed 20M/ws=400（E1=1 を前提）

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## Quick Status

### E2 Decision: FREEZE ✅ (NEUTRAL)

**Result**: -0.21% mean, -0.62% median (NEUTRAL)

**Why Freeze?**
- Alloc route optimization saturated by Phase 3 C3 (static routing)
- Free DUALHOT worked (+13%) because it skipped expensive ops
- Alloc DUALHOT doesn't work (-0.21%) because route already cached
- **Lesson**: Per-class specialization only helps when bypassing uncached overhead

**Action**: Keep as research box (default OFF), no further investigation

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## E1/E3-4 Results (Mixed A/B)

### E1: ENV Snapshot Consolidation ✅ GO (opt-in)

**Result**: +3.92% avg, +4.01% median  
**ENV**: `HAKMEM_ENV_SNAPSHOT=1`（`MIXED_TINYV3_C7_SAFE` で default 化、opt-out 可）

### E3-4: ENV Constructor Init ❌ NO-GO (FROZEN)

**Result（re-validation）**: -1.44% mean, -1.03% median（E1=1 前提）  
**ENV**: `HAKMEM_ENV_SNAPSHOT=1 HAKMEM_ENV_SNAPSHOT_CTOR=1`（default OFF / freeze）

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## Phase 4 Cumulative Status

**Active**:
- E1 (ENV Snapshot): +3.92% ✅ GO（opt-in）

**Frozen**:
- D3 (Alloc Gate Shape): +0.56% ⚪
- E2 (Alloc Per-Class FastPath): -0.21% ⚪
- E3-4 (ENV CTOR): ❌ NO-GO

## Next Actions

1. E3-4 を freeze 維持（default OFF）
2. E1 を本線化した状態で perf を取り直し、“self% ≥ 5%” の芯を選ぶ
3. 次の箱は “TLS/分岐” ではなく “実データ構造/ホットループ” を優先（alloc gate / unified_cache / pool など）

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## Key Lessons

1. **Route optimization saturated**: C3 already cached routes, E2 no benefit
2. **Shape optimization plateaued**: D3 +0.56% neutral, branch prediction saturated
3. **ENV consolidation successful**: E1 +3.92%, constructor init is next step
4. **Different optimization vectors needed**: Move beyond route/shape to init/dispatch overhead

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**Full Analysis**: `/mnt/workdisk/public_share/hakmem/docs/analysis/PHASE4_COMPREHENSIVE_STATUS_ANALYSIS.md`