Phase 19-3a: remove backwards UNLIKELY env-snapshot hints

CURRENT_TASK.md

@@ -1,6 +1,41 @@
 # 本線タスク（現在）
 
-## 更新メモ（2025-12-15 Phase 19-1b FASTLANE-DIRECT-1B）
+## 更新メモ（2025-12-15 Phase 19-3a UNLIKELY-HINT-REMOVAL）
+
+### Phase 19-3a UNLIKELY-HINT-REMOVAL: ENV Snapshot UNLIKELY Hint Removal — ✅ GO (+4.42%)
+
+**Result**: UNLIKELY hint (`__builtin_expect(..., 0)`) 削除により throughput **+4.42%** 達成。期待値（+0-2%）を大幅超過。
+
+**A/B Test Results** (HAKMEM_PROFILE=MIXED_TINYV3_C7_SAFE, 20M ops, 3-run average):
+- Baseline (Phase 19-1b): 52.06M ops/s
+- Optimized (Phase 19-3a): 54.36M ops/s (53.99, 54.44, 54.66)
+- Delta: **+4.42%** (GO判定、期待値 +0-2% を大幅超過)
+
+**修正内容**:
+- File: `/mnt/workdisk/public_share/hakmem/core/front/malloc_tiny_fast.h`
+- 修正箇所: 5箇所
+  - Line 237: malloc_tiny_fast_for_class (C7 ULTRA alloc)
+  - Line 405: free_tiny_fast_cold (Front V3 free hotcold)
+  - Line 627: free_tiny_fast_hot (C7 ULTRA free)
+  - Line 834: free_tiny_fast (C7 ULTRA free larson)
+  - Line 915: free_tiny_fast (Front V3 free larson)
+- 変更: `__builtin_expect(hakmem_env_snapshot_enabled(), 0)` → `hakmem_env_snapshot_enabled()`
+- 理由: ENV snapshot は ON by default (MIXED_TINYV3_C7_SAFE preset) → UNLIKELY hint が逆効果
+
+**Why it works**:
+- Phase 19-1b で学んだ教訓: `__builtin_expect(..., 0)` は branch misprediction を誘発
+- ENV snapshot は MIXED_TINYV3_C7_SAFE で ON → "UNLIKELY" hint が backwards
+- Hint 削除により compiler が正しい branch prediction を生成 → misprediction penalty 削減
+
+**Impact**:
+- Throughput: 52.06M → 54.36M ops/s (+4.42%)
+- Expected future gains (from design doc Phase 19-3b/c): Additional +3-5% from ENV consolidation
+
+**Next**: Phase 19-3b (ENV Snapshot Consolidation) — Pass env snapshot down from wrapper entry to eliminate 8 additional TLS reads/op.
+
+---
+
+## 前回タスク（2025-12-15 Phase 19-1b FASTLANE-DIRECT-1B）
 
 ### Phase 19-1b FASTLANE-DIRECT-1B: FastLane Direct (Revised) — ✅ GO (+5.88%)