Phase 35-39: FAST build optimization complete (+7.13% cumulative)

Phase 35-A: BENCH_MINIMAL gate function elimination (GO +4.39%)
- tiny_front_v3_enabled() → constant true
- tiny_metadata_cache_enabled() → constant 0
- learner_v7_enabled() → constant false
- small_learner_v2_enabled() → constant false

Phase 36: Policy snapshot init-once (GO +0.71%)
- small_policy_v7_snapshot() version check skip in BENCH_MINIMAL
- TLS cache for policy snapshot

Phase 37: Standard TLS cache (NO-GO -0.07%)
- TLS cache for Standard build attempted
- Runtime gate overhead negates benefit

Phase 38: FAST/OBSERVE/Standard workflow established
- make perf_fast, make perf_observe targets
- Scorecard and documentation updates

Phase 39: Hot path gate constantization (GO +1.98%)
- front_gate_unified_enabled() → constant 1
- alloc_dualhot_enabled() → constant 0
- g_bench_fast_front, g_v3_enabled blocks → compile-out
- free_dispatch_stats_enabled() → constant false

Results:
- FAST v3: 56.04M ops/s (47.4% of mimalloc)
- Standard: 53.50M ops/s (45.3% of mimalloc)
- M1 target (50%): 5.5% remaining

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/analysis/PHASE39_FAST_V3_GATE_CONSTANTIZATION_RESULTS.md

@@ -0,0 +1,60 @@
+# Phase 39: FAST v3 Gate Function Constantization — Results
+
+## Summary
+
+**Result: GO (+1.98%)**
+
+Phase 39 の gate function 定数化により、FAST build は **+1.98%** の性能改善を達成。
+
+## A/B Test Results（10-run 正式計測）
+
+### Baseline (FAST v2 without Phase 39)
+```
+Mean: 54.95M ops/s
+```
+
+### Treatment (FAST v3 with Phase 39)
+```
+Mean: 56.04M ops/s
+```
+
+### Delta
+- **+1.98%**（GO 閾値 +0.5% を大幅に上回る）
+
+計測条件:
+- `make perf_fast`（10-run clean env）
+- `ITERS=20000000 WS=400`
+
+## Changes Made
+
+### A) malloc hot path (core/front/malloc_tiny_fast.h)
+1. `front_gate_unified_enabled()` → BENCH_MINIMAL で固定 `1`
+2. `alloc_dualhot_enabled()` → BENCH_MINIMAL で固定 `0`
+
+### B) free dispatcher (core/box/hak_free_api.inc.h)
+1. `g_bench_fast_front` block → BENCH_MINIMAL で compile-out
+2. `g_v3_enabled` block → BENCH_MINIMAL で compile-out
+3. `g_free_dispatch_ssot` → **保留** (lazy-init 維持)
+
+### C) stats gate (core/box/free_dispatch_stats_box.h)
+1. `free_dispatch_stats_enabled()` → BENCH_MINIMAL で固定 `false`
+
+## Analysis
+
+10-run 正式計測により、lazy-init gate function の compile-out が **+1.98%** の性能改善を達成することが確認された。
+
+改善の要因:
+1. **Branch elimination**: `__builtin_expect` による予測は効率的だが、branch 自体の除去はそれ以上に効果的
+2. **I-cache pressure**: lazy-init コードパスの除去により I-cache footprint が縮小
+3. **Compiler optimization**: 定数化により、呼び出し元での追加最適化が可能に
+
+## Recommendation
+
+**判定: GO (+1.98% > +0.5%)**
+
+Phase 39 の変更は全て採用。FAST v3 として確定。
+
+## Files Modified
+- `core/front/malloc_tiny_fast.h`
+- `core/box/hak_free_api.inc.h`
+- `core/box/free_dispatch_stats_box.h`