Update CURRENT_TASK: Phase 3 D1 Complete (GO, +1.06%)

CURRENT_TASK.md

@@ -244,15 +244,68 @@
 - B4 (Wrapper split): +1.47%
 - C3 (Static routing): +2.20%
 - C2 (Metadata cache): -0.45%
-- **Total: ~6.1%** (baseline 37.5M → ~39.8M ops/s)
+- D1 (Free route cache): +1.06%
+- **Total: ~7.2%** (baseline 37.5M → ~40.2M ops/s)
 
-**Commit**: `deecda733`
+**Commit**: `f059c0ec8`
 
-**優先度 C2** - Slab metadata cache optimization:
-- Profile cache-miss hotspots (policy struct, slab metadata)
-- Hot/cold split of metadata
-- Inline first slab descriptor
-- Expected: +5-10%
+#### Phase 3 D1: Free Path Route Cache ✅ GO (+1.06%)
+
+**設計メモ**: `docs/analysis/PHASE3_D1_FREE_ROUTE_CACHE_1_DESIGN.md`
+
+**狙い**: Free path の `tiny_route_for_class()` コストを削減（4.39% self + 24.78% children）
+
+**実装完了** ✅:
+- `core/box/tiny_free_route_cache_env_box.h` (ENV gate + lazy init)
+- `core/front/malloc_tiny_fast.h` (lines 373-385, 780-791) - 2箇所で route cache integration
+  - `free_tiny_fast_cold()` path: direct `g_tiny_route_class[]` lookup
+  - `legacy_fallback` path: direct `g_tiny_route_class[]` lookup
+  - Fallback safety: `g_tiny_route_snapshot_done` check before cache use
+- ENV gate: `HAKMEM_FREE_STATIC_ROUTE=0/1` (default OFF)
+
+**A/B テスト結果** ✅ GO:
+- Mixed (10-run):
+  - Baseline (D1=0): 45,132,610 ops/s (avg), 45,756,040 ops/s (median)
+  - Optimized (D1=1): 45,610,062 ops/s (avg), 45,402,234 ops/s (median)
+  - **Average gain: +1.06%**, **Median gain: -0.77%**
+- **Decision: GO** (average exceeds +1.0% threshold)
+- Action: Keep as ENV-gated optimization (candidate for future default)
+
+**Rationale**:
+- Eliminates `tiny_route_for_class()` call overhead in free path
+- Uses existing `g_tiny_route_class[]` cache from Phase 3 C3 (Static Routing)
+- Safe fallback: checks snapshot initialization before cache use
+- Minimal code footprint: 2 integration points in malloc_tiny_fast.h
+
+**Current Cumulative Gain** (Phase 2-3):
+- B3 (Routing shape): +2.89%
+- B4 (Wrapper split): +1.47%
+- C3 (Static routing): +2.20%
+- D1 (Free route cache): +1.06%
+- **Total: ~7.9%** (cumulative, assuming multiplicative gains)
+
+**Commit**: `f059c0ec8`
+
+#### Phase 3 C4: MIXED MID_V3 Routing Fix ✅ ADOPT
+
+**要点**: `MIXED_TINYV3_C7_SAFE` では `HAKMEM_MID_V3_ENABLED=1` が大きく遅くなるため、**プリセットのデフォルトを OFF に変更**。
+
+**変更**（プリセット）:
+- `core/bench_profile.h`: `MIXED_TINYV3_C7_SAFE` の `HAKMEM_MID_V3_ENABLED=0` / `HAKMEM_MID_V3_CLASSES=0x0`
+- `docs/analysis/ENV_PROFILE_PRESETS.md`: Mixed 本線では MID v3 OFF と明記
+
+**A/B（Mixed, ws=400, 20M iters, 10-run）**:
+- Baseline（MID_V3=1）: **mean ~43.33M ops/s**
+- Optimized（MID_V3=0）: **mean ~48.97M ops/s**
+- **Delta: +13%** ✅（GO）
+
+**理由（観測）**:
+- C6 を MID_V3 にルーティングすると `tiny_alloc_route_cold()`→MID 側が “第2ホット” になり、Mixed では instruction / cache コストが支配的になりやすい
+- Mixed 本線は “全クラス多発” なので、C6 は LEGACY(tiny unified cache) に残した方が速い
+
+**ルール**:
+- Mixed 本線: MID v3 OFF（デフォルト）
+- C6-heavy: MID v3 ON（従来通り）
 
 ### Architectural Insight (Long-term)