Phase 4: E1 docs + E2 next instructions

CURRENT_TASK.md

@@ -1,6 +1,36 @@
 # 本線タスク（現在）
 
-## 更新メモ（2025-12-14 Phase 4 E1 Next - ENV Snapshot Consolidation）
+## 更新メモ（2025-12-14 Phase 4 E1 Complete - ENV Snapshot Consolidation）
+
+### Phase 4 E1: ENV Snapshot Consolidation ✅ COMPLETE (2025-12-14)
+
+**Target**: Consolidate 3 ENV gate TLS reads → 1 TLS read
+- `tiny_c7_ultra_enabled_env()`: 1.28% self
+- `tiny_front_v3_enabled()`: 1.01% self
+- `tiny_metadata_cache_enabled()`: 0.97% self
+- **Total ENV overhead: 3.26% self** (from perf profile)
+
+**Implementation**:
+- Created `core/box/hakmem_env_snapshot_box.{h,c}` (new ENV snapshot box)
+- Migrated 8 call sites across 3 hot path files to use snapshot
+- ENV gate: `HAKMEM_ENV_SNAPSHOT=0/1` (default: 0, research box)
+- Pattern: Similar to `tiny_front_v3_snapshot` (proven approach)
+
+**A/B Test Results** (Mixed, 10-run, 20M iters):
+- Baseline (E1=0): **43.62M ops/s** (avg), 43.56M ops/s (median)
+- Optimized (E1=1): **45.33M ops/s** (avg), 45.31M ops/s (median)
+- **Improvement: +3.92% avg, +4.01% median**
+
+**Decision: GO** (+3.92% >= +2.5% threshold)
+- Exceeded conservative expectation (+1-3%) → Achieved +3.92%
+- Action: Keep as research box for now (default OFF)
+- Commit: `88717a873`
+
+**Key Insight**: Shifting from shape optimizations (plateaued) to TLS/memory overhead yields strong returns. ENV snapshot consolidation represents new optimization frontier beyond branch prediction tuning.
+
+### Next: Phase 4 E2 - Alloc Per-Class Fast Path
+- 指示書（SSOT）: `docs/analysis/PHASE4_E2_ALLOC_PER_CLASS_FASTPATH_NEXT_INSTRUCTIONS.md`
+- 設計メモ: `docs/analysis/PHASE4_E2_ALLOC_PER_CLASS_FASTPATH_1_DESIGN.md`
 
 ### Phase 4 Perf Profiling Complete ✅ (2025-12-14)
 
@@ -9,30 +39,10 @@
 - Samples: 922 samples @ 999Hz, 3.1B cycles
 - Analysis doc: `docs/analysis/PHASE4_PERF_PROFILE_ANALYSIS.md`
 
-**Key Findings**:
-1. **ENV Gate Overhead (3.26% combined)**:
-   - `tiny_c7_ultra_enabled_env()` (1.28%)
-   - `tiny_front_v3_enabled()` (1.01%)
-   - `tiny_metadata_cache_enabled()` (0.97%)
-   - Root cause: 3 separate TLS reads + lazy init checks on every hot path call
-
-2. **Shape Optimization Plateau**:
-   - B3 (Routing Shape): +2.89% (initial win)
-   - D3 (Alloc Gate Shape): +0.56% (NEUTRAL, diminishing returns)
-   - Lesson: Branch prediction saturation → Next approach should target memory/TLS overhead
-
-3. **tiny_alloc_gate_fast (15.37% self%)**:
-   - Route determination: 15.74% (local)
-   - C7 logging: 17.04% (local, rare in Mixed)
-   - Opportunity: Per-class fast path specialization (defer to E2)
-
-**Next Target**: **Phase 4 E1 - ENV Snapshot Consolidation**
-- Expected gain: **+3.0-3.5%** (eliminate 3.26% ENV overhead)
-- Approach: Consolidate all ENV gates into single TLS snapshot struct
-- Precedent: `tiny_front_v3_snapshot` pattern (already proven)
-- Cross-cutting: Improves both alloc and free paths
-- Next instructions (SSOT): `docs/analysis/PHASE4_E1_ENV_SNAPSHOT_CONSOLIDATION_NEXT_INSTRUCTIONS.md`
-- Design memo: `docs/analysis/PHASE4_E1_ENV_SNAPSHOT_CONSOLIDATION_1_DESIGN.md`
+**Key Findings Leading to E1**:
+1. ENV Gate Overhead (3.26% combined) → **E1 target**
+2. Shape Optimization Plateau (B3 +2.89%, D3 +0.56% NEUTRAL)
+3. tiny_alloc_gate_fast (15.37% self%) → defer to E2
 
 ### Phase 4 D3: Alloc Gate Shape（HAKMEM_ALLOC_GATE_SHAPE）
 - ✅ 実装完了（ENV gate + alloc gate 分岐形）