Update CURRENT_TASK.md: Phase 7-Step4 complete (+55.5% total improvement!)

**Updated**:
- Status: Phase 7 Step 1-3 → Step 1-4 (complete)
- Achievement: +54.2% → +55.5% total (+1.1% from Step 4)
- Performance: 52.3M → 81.5M ops/s (+29.2M ops/s total)

**Phase 7-Step4 Summary**:
- Replace 3 runtime checks with config macros in hot path
- Dead code elimination in PGO mode (bench builds)
- Performance: 80.6M → 81.5M ops/s (+1.1%, +0.9M ops/s)

**Macro Replacements**:
1. `g_fastcache_enable` → `TINY_FRONT_FASTCACHE_ENABLED` (line 421)
2. `tiny_heap_v2_enabled()` → `TINY_FRONT_HEAP_V2_ENABLED` (line 809)
3. `ultra_slim_mode_enabled()` → `TINY_FRONT_ULTRA_SLIM_ENABLED` (line 757)

**Dead Code Eliminated** (PGO mode):
- FastCache path: fastcache_pop() + hit/miss tracking
- Heap V2 path: tiny_heap_v2_alloc_by_class() + metrics
- Ultra SLIM path: ultra_slim_alloc_with_refill() early return

**Cumulative Phase 7 Results**:
- Step 1: Branch hint reversal (+54.2%)
- Step 2: PGO mode infrastructure (neutral)
- Step 3: Config box integration (neutral)
- Step 4: Macro replacement (+1.1%)
- **Total: +55.5% improvement (52.3M → 81.5M ops/s)**

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

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

CURRENT_TASK.md

@@ -1,21 +1,22 @@
 # Current Task: Phase 7 Complete - Next Steps
 
 **Date**: 2025-11-29
-**Status**: Phase 7 ✅ COMPLETE (Step 1-3)
-**Achievement**: Tiny Front Hot Path Unification (+54.2% improvement!)
+**Status**: Phase 7 ✅ COMPLETE (Step 1-4)
+**Achievement**: Tiny Front Hot Path Unification + Dead Code Elimination (+55.5% total!)
 
 ---
 
 ## Phase 7 Complete! ✅
 
-**Result**: Tiny Front Hot Path Unification **COMPLETE** (Step 1-3)
-**Performance**: 52.3M → 80.6M ops/s (+54.2% improvement, +28.3M ops/s)
+**Result**: Tiny Front Hot Path Unification **COMPLETE** (Step 1-4)
+**Performance**: 52.3M → 81.5M ops/s (+55.5% improvement, +29.2M ops/s)
 **Duration**: <1 day (extremely quick win!)
 
 **Completed Steps**:
 - ✅ Step 1: Branch hint reversal (0→1) - **+54.2% improvement**
 - ✅ Step 2: Compile-time unified gate (PGO mode) - Code quality improvement
 - ✅ Step 3: Config box integration - Dead code elimination infrastructure
+- ✅ Step 4: Macro replacement in hot path - **+1.1% additional improvement**
 
 **Key Discovery** (from ChatGPT + Task agent analysis):
 - Unified fast path existed but was marked UNLIKELY (`__builtin_expect(..., 0)`)
@@ -34,9 +35,10 @@ Phase 3 (mincore removal):     56.8 M ops/s
 Phase 4 (Hot/Cold Box):         57.2 M ops/s (+0.7%)
 Phase 5 (Mid MT fix):           52.3 M ops/s (-8.6% regression)
 Phase 6 (Lock-free Mid MT):     42.1 M ops/s (Mid MT: +2.65%)
-Phase 7 (Unified front):        80.6 M ops/s (+54.2%!) ⭐
+Phase 7-Step1 (Unified front):  80.6 M ops/s (+54.2%!) ⭐
+Phase 7-Step4 (Dead code):      81.5 M ops/s (+1.1%) ⭐⭐
 
-Total improvement: +41.9% (56.8M → 80.6M) from Phase 3
+Total improvement: +43.5% (56.8M → 81.5M) from Phase 3
 ```
 
 ### Benchmark Results Summary
@@ -46,6 +48,7 @@ Total improvement: +41.9% (56.8M → 80.6M) from Phase 3
 Phase 7-Step1 (branch hint):    80.6 M ops/s (+54.2%)
 Phase 7-Step2 (PGO mode):       80.3 M ops/s (-0.37%, noise)
 Phase 7-Step3 (config box):     80.6 M ops/s (+0.37%, noise)
+Phase 7-Step4 (macros):         81.5 M ops/s (+1.1%, dead code elimination!)
 ```
 
 **bench_mid_mt_gap (1KB-8KB, Mid MT workload, ws=256)**:
@@ -136,6 +139,53 @@ bench_random_mixed_hakmem.o: bench_random_mixed.c hakmem.h
 #define TINY_FRONT_ULTRA_SLIM_ENABLED    ultra_slim_mode_enabled() // Runtime check
 ```
 
+### Phase 7-Step4 (Macro Replacement)
+
+**File**: `core/tiny_alloc_fast.inc.h`
+**Lines**: 421, 757, 809 (3 hot path checks)
+
+**Changes**:
+Replace runtime checks with config macros for dead code elimination:
+
+```c
+// Line 421: FastCache check
+// Before:
+if (__builtin_expect(g_fastcache_enable && class_idx <= 3, 1)) {
+// After:
+if (__builtin_expect(TINY_FRONT_FASTCACHE_ENABLED && class_idx <= 3, 1)) {
+
+// Line 809: Heap V2 check
+// Before:
+if (__builtin_expect(tiny_heap_v2_enabled() && front_prune_heapv2_enabled() && class_idx <= 3, 0)) {
+// After:
+if (__builtin_expect(TINY_FRONT_HEAP_V2_ENABLED && front_prune_heapv2_enabled() && class_idx <= 3, 0)) {
+
+// Line 757: Ultra SLIM check
+// Before:
+if (__builtin_expect(ultra_slim_mode_enabled(), 0)) {
+// After:
+if (__builtin_expect(TINY_FRONT_ULTRA_SLIM_ENABLED, 0)) {
+```
+
+**Effect**: Dead code elimination in PGO mode
+- PGO mode (`-DHAKMEM_TINY_FRONT_PGO=1`):
+  - `if (0 && ...) { ... }` → entire block removed by compiler
+  - Smaller code size, better instruction cache locality
+  - Fewer branches in hot path
+- Normal mode (default):
+  - `if (g_fastcache_enable && ...) { ... }` → runtime check preserved
+  - Full backward compatibility with ENV variables
+
+**Performance Impact**:
+- Before: 80.6 M ops/s (Phase 7-Step3)
+- After: 81.0 / 81.0 / 82.4 M ops/s (3 runs)
+- Average: 81.5 M ops/s (+1.1%, +0.9 M ops/s)
+
+**Dead Code Eliminated**:
+1. FastCache path (C0-C3): `fastcache_pop()` call + hit/miss tracking
+2. Heap V2 path: `tiny_heap_v2_alloc_by_class()` + metrics
+3. Ultra SLIM path: `ultra_slim_alloc_with_refill()` early return
+
 ---
 
 ## Next Phase Options (from Task Agent Plan)