Phase 4 D3 Design: Alloc Gate Shape

docs/analysis/PHASE3_BASELINE_AND_CANDIDATES.md

@@ -303,18 +303,20 @@ static inline void* tiny_alloc_gate_fast(size_t size)
 ---
 
 ### Phase 3 D3: Alloc Gate Specialization (MEDIUM PRIORITY)
-**Target**: `tiny_alloc_gate_fast()` for LEGACY-only route
+**Target**: `tiny_alloc_gate_fast()` の分岐形を最短化（MIXED 向け）
 **Expected Gain**: +1-2%
 **Risk**: LOW
 **Effort**: 2-3 hours
 
 **Implementation**:
-1. Create `tiny_alloc_gate_fast_legacy()` specialized variant
-2. Eliminate ROUTE_POOL_ONLY and ROUTE_TINY_FIRST branches
-3. Use in MIXED profile where all classes are LEGACY
+1. New ENV gate: `HAKMEM_ALLOC_GATE_SHAPE=0/1`
+2. `tiny_route_get()` を避け、`g_tiny_route[]` の直接参照に置換（release logging branch を回避）
+3. `ROUTE_POOL_ONLY` は必ず尊重（`HAKMEM_TINY_PROFILE=hot/off` を壊さない）
 4. A/B test: BASELINE vs D3
 
-**ENV Gate**: `HAKMEM_ALLOC_GATE_LEGACY_ONLY=1` (default: 0)
+**Design**: `docs/analysis/PHASE4_D3_ALLOC_GATE_SPECIALIZATION_1_DESIGN.md`
+
+**ENV Gate**: `HAKMEM_ALLOC_GATE_SHAPE=0/1` (default: 0)
 
 ---
 
@@ -376,7 +378,7 @@ static inline void* tiny_alloc_gate_fast(size_t size)
 
 2. **Optional**: Phase 3 D3 (Alloc gate specialization) - pending perf validation
    - Only proceed if perf shows ≥5% self% in alloc gate
-   - ENV: `HAKMEM_ALLOC_GATE_LEGACY_ONLY=0/1`
+   - ENV: `HAKMEM_ALLOC_GATE_SHAPE=0/1`
 
 3. **Phase 4 Planning**: If no more 5%+ targets, prepare Phase 4 roadmap