Update CURRENT_TASK: Phase 19-6C Complete (+1.98% GO)

CURRENT_TASK.md

@@ -80,6 +80,40 @@
 **Ref**:
 - `docs/analysis/PHASE19_FASTLANE_INSTRUCTION_REDUCTION_6B_FREE_STATIC_ROUTE_FOR_FREE_AB_TEST_RESULTS.md`
 
+### Phase 19-6C Duplicate tiny_route_for_class() Consolidation — ✅ GO (+1.98%)
+
+**Goal**: Eliminate 2-3x redundant route computations in free path
+- `free_tiny_fast_hot()` line 654-661: Computed route_kind_free (SmallRouteKind)
+- `free_tiny_fast_cold()` line 389-402: **RECOMPUTED** route (tiny_route_kind_t) — REDUNDANT
+- `free_tiny_fast()` legacy_fallback line 894-905: **RECOMPUTED** same as cold — REDUNDANT
+
+**Solution**: Pass-down pattern (no function split)
+- Create helper: `free_tiny_fast_compute_route_and_heap()`
+- Compute route once in caller context, pass as 2 parameters
+- Remove redundant computation from cold path body
+- Update call sites to use helper instead of recomputing
+
+**A/B Test Results** (Mixed 10-run):
+- Baseline (Phase 19-6B state): mean **53.49M** ops/s
+- Optimized (Phase 19-6C): mean **54.55M** ops/s
+- Delta: **+1.98% mean** → ✅ GO (exceeds +0.5-1.0% target)
+
+**Changes**:
+- File: `core/front/malloc_tiny_fast.h`
+  - Add helper function `free_tiny_fast_compute_route_and_heap()` (lines 382-403)
+  - Modify `free_tiny_fast_cold()` signature to accept pre-computed route + use_tiny_heap (lines 411-412)
+  - Remove route computation from cold path body (was lines 416-429)
+  - Update call site in `free_tiny_fast_hot()` cold_path label (lines 720-722)
+  - Replace duplicate computation in `legacy_fallback` with helper call (line 901)
+
+**Key insight**:
+- Instruction delta: -15-25 instructions per cold-path free (~20% of cold path overhead)
+- Route computation eliminated: 1x (was computed 2-3x before)
+- Parameter passing overhead: negligible (2 ints on stack)
+
+**Ref**:
+- `docs/analysis/PHASE19_FASTLANE_INSTRUCTION_REDUCTION_6C_DUPLICATE_ROUTE_DEDUP_DESIGN.md`
+
 ---
 
 ## 更新メモ（2025-12-15 Phase 19-3b ENV-SNAPSHOT-PASSDOWN）