hakmem/docs/archive/BRANCH_PREDICTION_OPTIMIZATION_REPORT.md

# Branch Prediction Optimization Investigation Report

**Date:** 2025-11-09
**Author:** Claude Code Analysis
**Context:** HAKMEM Phase 7 + Pool TLS Performance Investigation

---

## Executive Summary

**Problem:** HAKMEM has **10.89% branch-miss rate** vs System malloc's **3.5-3.9%** (3x worse)

**Root Cause Discovery:** The problem is **NOT just misprediction rate**, but **TOTAL BRANCH COUNT**:
- HAKMEM: **17,098,340 branches** (10.84% miss)
- System malloc: **2,006,962 branches** (4.56% miss)
- **HAKMEM executes 8.5x MORE branches than System malloc!**

**Impact:**
- Branch misprediction overhead: ~1.8M misses × 15-20 cycles = **27-36M cycles wasted**
- Total execution: 17M branches vs System's 2M → **8x more branch overhead**
- **Potential gain: 40-60% performance improvement** with recommended optimizations

**Critical Finding:** `HAKMEM_BUILD_RELEASE` is **NOT defined** → All debug code is running in production builds!

---

## 1. Performance Hotspot Analysis

### 1.1 Perf Statistics (256B allocations, 100K iterations)

| Metric | HAKMEM | System malloc | Ratio |
|--------|--------|---------------|-------|
| **Branches** | 17,098,340 | 2,006,962 | **8.5x** |
| **Branch-misses** | 1,854,018 | 91,497 | **20.3x** |
| **Branch-miss rate** | 10.84% | 4.56% | **2.4x** |
| **L1-dcache loads** | 31,307,492 | 4,610,155 | **6.8x** |
| **L1-dcache misses** | 1,063,117 | 44,773 | **23.7x** |
| **L1 miss rate** | 3.40% | 0.97% | **3.5x** |
| **Cycles** | ~83M | ~10M | **8.3x** |
| **Time** | 0.103s | 0.003s | **34x slower** |

**Key insight:** HAKMEM is not just suffering from poor branch prediction, but is executing **8.5x more branches** than System malloc!

### 1.2 Branch Count by Component

**Source file analysis:**

| File | Branch Statements | Critical Issues |
|------|-------------------|-----------------|
| `tiny_alloc_fast.inc.h` | **79** | 8 debug guards, 3 getenv() calls, SFC/SLL dual-layer |
| `hak_free_api.inc.h` | **38** | Pool TLS + Phase 7 dual dispatch, multiple lookups |
| `hakmem_tiny_refill_p0.inc.h` | **~40** | Complex precedence logic, 2 getenv() calls, validation |
| `tiny_refill_opt.h` | **~20** | Corruption checks, guard functions |

**Total: ~177 branch statements in hot path** vs System malloc's **~5 branches**

---

## 2. Branch Count Analysis: Allocation Path

### 2.1 Fast Path: `tiny_alloc_fast()` (lines 454-497)

**Layer 0: SFC (Super Front Cache)** - Lines 177-200
```c
// Branch 1-2: Check if SFC enabled (TLS cache check)
if (!sfc_check_done) { /* getenv() + init */ }  // COLD
if (sfc_is_enabled) {                            // HOT
    // Branch 3: Try SFC
    void* ptr = sfc_alloc(class_idx);            // → 2 branches inside
    if (ptr != NULL) { /* hit */ }               // HOT
}
```
**Branches: 5-6** (3 external + 2-3 in sfc_alloc)

**Layer 1: SLL (TLS Freelist)** - Lines 204-259
```c
// Branch 4: Check if SLL enabled
if (g_tls_sll_enable) {                          // HOT
    // Branch 5: Try SLL pop
    void* head = g_tls_sll_head[class_idx];
    if (head != NULL) {                          // HOT
        // Branch 6-7: Corruption debug (ONLY if failfast ≥ 2)
        if (tiny_refill_failfast_level() >= 2) { // DEBUG
            /* alignment validation (2 branches) */
        }

        // Branch 8-9: Validate next pointer
        void* next = *(void**)head;
        if (tiny_refill_failfast_level() >= 2) { // DEBUG
            /* next pointer validation (2 branches) */
        }

        // Branch 10: Count update
        if (g_tls_sll_count[class_idx] > 0) {   // HOT
            g_tls_sll_count[class_idx]--;
        }

        // Branch 11: Profiling (DEBUG)
        #if !HAKMEM_BUILD_RELEASE
        if (start) { /* rdtsc tracking */ }      // DEBUG
        #endif

        return head;  // SUCCESS
    }
}
```
**Branches: 11-15** (2 unconditional + 5-9 conditional debug)

**Total allocation fast path: 16-21 branches** vs System tcache's **1-2 branches**

### 2.2 Refill Path: `tiny_alloc_fast_refill()` (lines 321-436)

**Phase 2b capacity check:**
```c
// Branch 1: Check available capacity
int available_capacity = get_available_capacity(class_idx);
if (available_capacity <= 0) { return 0; }
```

**Refill count precedence logic (lines 338-363):**
```c
// Branch 2: First-time init check
if (cnt == 0) {  // COLD (once per class per thread)
    // Branch 3-6: Complex precedence logic
    if (g_refill_count_class[class_idx] > 0) { /* ... */ }
    else if (class_idx <= 3 && g_refill_count_hot > 0) { /* ... */ }
    else if (class_idx >= 4 && g_refill_count_mid > 0) { /* ... */ }
    else if (g_refill_count_global > 0) { /* ... */ }

    // Branch 7-8: Clamping
    if (v < 8) v = 8;
    if (v > 256) v = 256;
}
```

**Total refill path: 10-15 branches** (one-time init + runtime checks)

---

## 3. Branch Count Analysis: Free Path

### 3.1 Free Path: `hak_free_at()` (hak_free_api.inc.h)

**Pool TLS dispatch (lines 81-110):**
```c
#ifdef HAKMEM_POOL_TLS_PHASE1
    // Branch 1: Page boundary check
    #if !HAKMEM_TINY_SAFE_FREE
    if (((uintptr_t)header_addr & 0xFFF) == 0) {  // 0.1% frequency
        // Branch 2: Memory readable check (mincore syscall)
        if (!hak_is_memory_readable(header_addr)) { goto skip_pool_tls; }
    }
    #endif

    // Branch 3: Magic check
    if ((header & 0xF0) == POOL_MAGIC) {
        pool_free(ptr);
        goto done;
    }
#endif
```
**Branches: 3** (optimized with hybrid mincore)

**Phase 7 dual-header dispatch (lines 112-167):**
```c
// Branch 4: Try 1-byte Tiny header
if (hak_tiny_free_fast_v2(ptr)) {  // → 3-5 branches inside
    goto done;
}

// Branch 5: Page boundary check for 16-byte header
if (offset_in_page < HEADER_SIZE) {
    // Branch 6: Memory readable check
    if (!hak_is_memory_readable(raw)) { goto slow_path; }
}

// Branch 7: 16-byte header magic check
if (hdr->magic == HAKMEM_MAGIC) {
    // Branch 8: Method dispatch
    if (hdr->method == ALLOC_METHOD_MALLOC) { /* ... */ }
}
```
**Branches: 8-10** (including 3-5 inside hak_tiny_free_fast_v2)

**Mid/L25 lookup (lines 196-206):**
```c
// Branch 9-10: Mid/L25 registry lookups
if (hak_pool_mid_lookup(ptr, &mid_sz)) { /* ... */ }
if (hak_l25_lookup(ptr, &l25_sz)) { /* ... */ }
```
**Branches: 2**

**Total free path: 13-15 branches** vs System tcache's **2-3 branches**

---

## 4. Root Cause Analysis

### 4.1 CRITICAL: Debug Code in Production Builds

**Finding:** `HAKMEM_BUILD_RELEASE` is **NOT defined anywhere** in Makefile

**Impact:** All debug code runs in production:

| Debug Guard | Location | Frequency | Overhead |
|-------------|----------|-----------|----------|
| `!HAKMEM_BUILD_RELEASE` | `tiny_alloc_fast.inc.h:171` | Every allocation | 2-3 branches |
| `!HAKMEM_BUILD_RELEASE` | `tiny_alloc_fast.inc.h:191-196` | Every allocation | 1 branch + rdtsc |
| `!HAKMEM_BUILD_RELEASE` | `tiny_alloc_fast.inc.h:250-256` | Every allocation | 1 branch + rdtsc |
| `!HAKMEM_BUILD_RELEASE` | `tiny_alloc_fast.inc.h:324-326` | Every refill | 1 branch + rdtsc |
| `!HAKMEM_BUILD_RELEASE` | `tiny_alloc_fast.inc.h:427-433` | Every refill | 1 branch + rdtsc |
| `!HAKMEM_BUILD_RELEASE` | `tiny_free_fast_v2.inc.h:99-104` | Every free | 1 branch + capacity check |
| `!HAKMEM_BUILD_RELEASE` | `hak_free_api.inc.h:118-120` | Every free | 1 function call |
| `trc_refill_guard_enabled()` | `tiny_refill_opt.h:61-75` | Every splice | 1 branch + getenv |

**Total overhead: 8-12 branches + 6 rdtsc calls + 2 getenv calls per allocation/free cycle**

**Expected impact of fixing:** **-40-50% total branches**

### 4.2 HIGH: getenv() Calls in Hot Path

**Finding:** 3 lazy-initialized getenv() calls in hot path

| Location | Variable | Call Frequency | Fix |
|----------|----------|----------------|-----|
| `tiny_alloc_fast.inc.h:104` | `HAKMEM_TINY_PROFILE` | Every allocation (if -1) | Cache in global var at init |
| `hakmem_tiny_refill_p0.inc.h:68` | `HAKMEM_TINY_REFILL_COUNT_HOT` | Every refill (class ≤ 3) | Pre-compute at init |
| `hakmem_tiny_refill_p0.inc.h:78` | `HAKMEM_TINY_REFILL_COUNT_MID` | Every refill (class ≥ 4) | Pre-compute at init |

**Impact:**
- getenv() is ~50-100 cycles (string lookup + syscall if not cached)
- Adds 2-3 branches per call (null check, lazy init, result check)
- Total: **6-9 branches + 150-300 cycles** on first access per thread

**Expected impact of fixing:** **-10-15% branches, -5-10% cycles**

### 4.3 MEDIUM: Complex Multi-Layer Cache

**Current architecture:**
```
Allocation: Size check → SFC (Layer 0) → SLL (Layer 1) → SuperSlab → Refill
            1 branch     5-6 branches     11-15 branches   20-30 branches
```

**System malloc tcache:**
```
Allocation: Size check → TLS cache → ptmalloc2
            1 branch     1-2 branches
```

**Problem:** HAKMEM has **3 layers** (SFC → SLL → SuperSlab) vs System's **1 layer** (tcache)

**Why SFC is redundant:**
- SLL already provides TLS freelist (same design as tcache)
- SFC adds 5-6 branches with minimal benefit
- Pre-warming (Phase 7 Task 3) already boosted SLL hit rate to 95%+

**Expected impact of removing SFC:** **-5-10% branches, simpler code**

### 4.4 MEDIUM: Excessive Validation in Hot Path

**Corruption checks (lines 208-235 in tiny_alloc_fast.inc.h):**
```c
if (tiny_refill_failfast_level() >= 2) {  // getenv() call!
    // Alignment validation
    if (((uintptr_t)head % blk) != 0) {
        fprintf(stderr, "[TLS_SLL_CORRUPT] ...");
        abort();
    }

    // Next pointer validation
    if (next != NULL && ((uintptr_t)next % blk) != 0) {
        fprintf(stderr, "[ALLOC_POP_CORRUPT] ...");
        abort();
    }
}
```

**Impact:**
- 1 getenv() call per thread (lazy init) = ~100 cycles
- 5-7 branches per allocation when enabled
- fprintf/abort paths confuse branch predictor

**Solution:** Move to compile-time flag (e.g., `HAKMEM_DEBUG_VALIDATION`) instead of runtime check

**Expected impact:** **-5-10% branches when disabled**

---

## 5. Optimization Recommendations (Ranked by Impact/Risk)

### 5.1 CRITICAL FIX: Enable Release Mode (0 risk, 40-50% impact)

**Action:** Add `-DHAKMEM_BUILD_RELEASE=1` to production build flags

**Implementation:**
```makefile
# Makefile
HAKMEM_RELEASE_FLAGS = -DHAKMEM_BUILD_RELEASE=1 -DNDEBUG -O3 -flto

release: CFLAGS += $(HAKMEM_RELEASE_FLAGS)
release: all
```

**Changes enabled:**
- Removes 8 `!HAKMEM_BUILD_RELEASE` guards → **-8-12 branches**
- Disables rdtsc profiling → **-6 rdtsc calls**
- Disables corruption validation → **-5-10 branches**
- Enables LTO and aggressive optimization

**Expected result:**
- **-40-50% total branches** (17M → 8.5-10M)
- **-20-30% cycles** (better inlining, constant folding)
- **+30-50% performance** (overall)

**A/B test command:**
```bash
# Before
make bench_random_mixed_hakmem
./bench_random_mixed_hakmem 100000 256 42

# After
make HAKMEM_BUILD_RELEASE=1 bench_random_mixed_hakmem
./bench_random_mixed_hakmem 100000 256 42
```

---

### 5.2 HIGH PRIORITY: Pre-compute Env Vars at Init (Low risk, 10-15% impact)

**Action:** Move getenv() calls from hot path to global init

**Current (lazy init in hot path):**
```c
// SLOW: Called on every allocation/refill
if (g_tiny_profile_enabled == -1) {
    const char* env = getenv("HAKMEM_TINY_PROFILE");  // 50-100 cycles!
    g_tiny_profile_enabled = (env && *env && *env != '0') ? 1 : 0;
}
```

**Fixed (pre-compute at init):**
```c
// hakmem_init.c (runs once at startup)
void hakmem_tiny_init_config(void) {
    // Profile mode
    const char* env = getenv("HAKMEM_TINY_PROFILE");
    g_tiny_profile_enabled = (env && *env && *env != '0') ? 1 : 0;

    // Refill counts
    const char* hot_env = getenv("HAKMEM_TINY_REFILL_COUNT_HOT");
    g_refill_count_hot = hot_env ? atoi(hot_env) : HAKMEM_TINY_REFILL_DEFAULT;

    const char* mid_env = getenv("HAKMEM_TINY_REFILL_COUNT_MID");
    g_refill_count_mid = mid_env ? atoi(mid_env) : HAKMEM_TINY_REFILL_DEFAULT;
}
```

**Expected result:**
- **-6-9 branches** (3 getenv lazy-init patterns)
- **-150-300 cycles** on first access per thread
- **+5-10% performance** (cleaner hot path)

**Files to modify:**
- `core/tiny_alloc_fast.inc.h:104` - Remove lazy init
- `core/hakmem_tiny_refill_p0.inc.h:66-84` - Remove lazy init
- `core/hakmem_init.c` - Add global init function

---

### 5.3 MEDIUM PRIORITY: Simplify Cache Layers (Medium risk, 5-10% impact)

**Option A: Remove SFC Layer (Recommended)**

**Rationale:**
- SFC adds 5-6 branches with minimal benefit
- SLL already provides TLS freelist (same as System tcache)
- Phase 7 Task 3 pre-warming gives SLL 95%+ hit rate
- Three cache layers = unnecessary complexity

**Implementation:**
```c
// Remove SFC entirely, use only SLL
static inline void* tiny_alloc_fast(size_t size) {
    int class_idx = hak_tiny_size_to_class(size);

    // Layer 1: TLS freelist (SLL) - DIRECT ACCESS
    void* head = g_tls_sll_head[class_idx];
    if (head != NULL) {
        g_tls_sll_head[class_idx] = *(void**)head;
        g_tls_sll_count[class_idx]--;
        return head;  // 3 instructions, 1-2 branches!
    }

    // Refill from SuperSlab
    if (tiny_alloc_fast_refill(class_idx) > 0) {
        head = g_tls_sll_head[class_idx];
        // ... retry pop
    }

    return hak_tiny_alloc_slow(size, class_idx);
}
```

**Expected result:**
- **-5-10% branches** (remove SFC layer)
- **Simpler code** (easier to debug/maintain)
- **Same or better performance** (fewer layers = less overhead)

**Option B: Unified TLS Cache (Higher risk, 10-20% impact)**

**Design:** Single TLS cache with adaptive sizing (like mimalloc)

```c
// Per-class TLS cache with adaptive capacity
struct TinyTLSCache {
    void* head;
    uint32_t count;
    uint32_t capacity;  // Adaptive: 16-256
};

static __thread TinyTLSCache g_tls_cache[TINY_NUM_CLASSES];
```

**Expected result:**
- **-10-20% branches** (unified design)
- **Better cache utilization** (adaptive sizing)
- **Matches System malloc architecture**

---

### 5.4 LOW PRIORITY: Branch Hint Tuning (Low risk, 2-5% impact)

**Action:** Optimize `__builtin_expect` hints based on profiling

**Current issues:**
- Some hints are incorrect (e.g., SFC disabled in production)
- Missing hints on hot branches

**Recommended changes:**

```c
// Line 184: SFC is DISABLED in most production builds
if (__builtin_expect(sfc_is_enabled, 1)) {  // WRONG!
// Fix:
if (__builtin_expect(sfc_is_enabled, 0)) {  // Expect disabled

// Line 208: Corruption checks are rare in production
if (__builtin_expect(tiny_refill_failfast_level() >= 2, 0)) {  // CORRECT

// Line 457: Size > 1KB is common in mixed workloads
if (__builtin_expect(class_idx < 0, 0)) {  // May be wrong for some workloads
```

**Expected result:**
- **-2-5% branch-misses** (better prediction)
- **+2-5% performance** (reduced pipeline stalls)

---

## 6. Expected Results Summary

### 6.1 Cumulative Impact (All Optimizations)

| Optimization | Branch Reduction | Cycle Reduction | Risk | Effort |
|--------------|------------------|-----------------|------|--------|
| **Enable Release Mode** | -40-50% | -20-30% | None | 1 line |
| **Pre-compute Env Vars** | -10-15% | -5-10% | Low | 1 day |
| **Remove SFC Layer** | -5-10% | -5-10% | Medium | 2 days |
| **Branch Hint Tuning** | -2-5% | -2-5% | Low | 1 day |
| **TOTAL** | **-50-65%** | **-30-45%** | Low | 4-5 days |

**Projected final results:**
- **Branches:** 17M → **6-8.5M** (vs System's 2M)
- **Branch-miss rate:** 10.84% → **6-8%** (vs System's 4.56%)
- **Throughput:** Current → **+40-80% improvement**

**Target:** **70-90% of System malloc performance** (currently ~3% of System)

---

### 6.2 Quick Win: Release Mode Only

**Minimal change, maximum impact:**

```bash
# Add one line to Makefile
CFLAGS += -DHAKMEM_BUILD_RELEASE=1

# Rebuild
make clean && make bench_random_mixed_hakmem

# Test
./bench_random_mixed_hakmem 100000 256 42
```

**Expected:**
- **-40-50% branches** (17M → 8.5-10M)
- **+30-50% performance** (immediate)
- **0 code changes** (just a flag)

---

## 7. A/B Test Plan

### 7.1 Baseline Measurement

```bash
# Measure current performance
perf stat -e branch-misses,branches,cycles,instructions \
  ./bench_random_mixed_hakmem 100000 256 42

# Output:
# branches:       17,098,340
# branch-misses:   1,854,018 (10.84%)
# cycles:         ~83M
```

### 7.2 Test 1: Release Mode

```bash
# Build with release flag
make clean
make CFLAGS="-DHAKMEM_BUILD_RELEASE=1 -O3" bench_random_mixed_hakmem

# Measure
perf stat -e branch-misses,branches,cycles,instructions \
  ./bench_random_mixed_hakmem 100000 256 42

# Expected:
# branches:       ~9M (-47%)
# branch-misses:  ~700K (7.8%)
# cycles:         ~60M (-27%)
```

### 7.3 Test 2: Release + Pre-compute Env

```bash
# Implement env var pre-computation (see 5.2)
make clean
make CFLAGS="-DHAKMEM_BUILD_RELEASE=1 -O3" bench_random_mixed_hakmem

# Expected:
# branches:       ~8M (-53%)
# branch-misses:  ~600K (7.5%)
# cycles:         ~55M (-33%)
```

### 7.4 Test 3: Release + Pre-compute + Remove SFC

```bash
# Remove SFC layer (see 5.3)
make clean
make CFLAGS="-DHAKMEM_BUILD_RELEASE=1 -O3" bench_random_mixed_hakmem

# Expected:
# branches:       ~7M (-59%)
# branch-misses:  ~500K (7.1%)
# cycles:         ~50M (-40%)
```

### 7.5 Success Criteria

| Metric | Current | Target | Stretch Goal |
|--------|---------|--------|--------------|
| **Branches** | 17M | <10M | <8M |
| **Branch-miss rate** | 10.84% | <8% | <7% |
| **vs System malloc** | 8.5x slower | <5x slower | <3x slower |
| **Throughput** | 1.07M ops/s | >2M ops/s | >3M ops/s |

---

## 8. Comparison with System Malloc Strategy

### 8.1 System malloc tcache (glibc 2.27+)

**Design:**
```c
// Allocation (2-3 instructions, 1-2 branches)
void* tcache_get(size_t size) {
    int tc_idx = csize2tidx(size);  // Size to index (no branch)
    tcache_entry* e = tcache->entries[tc_idx];
    if (e != NULL) {  // BRANCH 1
        tcache->entries[tc_idx] = e->next;
        return (void*)e;
    }
    return _int_malloc(av, bytes);  // Slow path
}

// Free (2 instructions, 1 branch)
void tcache_put(void* ptr, size_t size) {
    int tc_idx = csize2tidx(size);  // Size to index (no branch)
    if (tcache->counts[tc_idx] < TCACHE_MAX_BINS) {  // BRANCH 1
        tcache_entry* e = (tcache_entry*)ptr;
        e->next = tcache->entries[tc_idx];
        tcache->entries[tc_idx] = e;
        tcache->counts[tc_idx]++;
    }
    // Else: fall back to _int_free
}
```

**Key insights:**
- **1-2 branches total** (vs HAKMEM's 16-21)
- **No validation** in fast path
- **No debug guards** in production
- **Single TLS cache layer** (vs HAKMEM's 3 layers)
- **No getenv() calls** (all config at compile-time)

### 8.2 mimalloc

**Design:**
```c
// Allocation (3-4 instructions, 1-2 branches)
void* mi_malloc(size_t size) {
    mi_page_t* page = _mi_page_fast();  // TLS page cache
    if (mi_likely(page != NULL)) {  // BRANCH 1
        void* p = page->free;
        if (mi_likely(p != NULL)) {  // BRANCH 2
            page->free = mi_ptr_decode(p);
            return p;
        }
    }
    return mi_malloc_generic(NULL, size);  // Slow path
}
```

**Key insights:**
- **2 branches total** (vs HAKMEM's 16-21)
- **Inline header metadata** (similar to HAKMEM Phase 7)
- **No debug overhead** in release builds
- **Simple TLS structure** (page + free pointer)

---

## 9. Conclusion

**Root Cause:** HAKMEM executes **8.5x more branches** than System malloc due to:
1. Debug code running in production (`HAKMEM_BUILD_RELEASE` not defined)
2. Complex multi-layer cache (SFC → SLL → SuperSlab)
3. Runtime env var checks in hot path
4. Excessive validation and profiling

**Immediate Action (1 line change):**
```makefile
CFLAGS += -DHAKMEM_BUILD_RELEASE=1  # Expected: +30-50% performance
```

**Full Fix (4-5 days work):**
- Enable release mode
- Pre-compute env vars at init
- Remove redundant SFC layer
- Optimize branch hints

**Expected Result:**
- **-50-65% branches** (17M → 6-8.5M)
- **-30-45% cycles**
- **+40-80% throughput**
- **70-90% of System malloc performance** (vs current 3%)

**Next Steps:**
1. ✅ Enable `HAKMEM_BUILD_RELEASE=1` (immediate)
2. Run A/B tests (measure impact)
3. Implement env var pre-computation (1 day)
4. Evaluate SFC removal (2 days)
5. Re-measure and iterate

---

## Appendix A: Detailed Branch Inventory

### Allocation Path (tiny_alloc_fast.inc.h)

| Line | Branch | Frequency | Type | Fix |
|------|--------|-----------|------|-----|
| 177-182 | SFC check done | Cold (once/thread) | Init | Pre-compute |
| 184 | SFC enabled | Hot | Runtime | Remove SFC |
| 186 | SFC ptr != NULL | Hot | Fast path | Keep (necessary) |
| 204 | SLL enabled | Hot | Runtime | Make compile-time |
| 206 | SLL head != NULL | Hot | Fast path | Keep (necessary) |
| 208 | Failfast ≥ 2 | Hot | Debug | Remove in release |
| 211-216 | Alignment check | Hot | Debug | Remove in release |
| 225 | Failfast ≥ 2 | Hot | Debug | Remove in release |
| 227-234 | Next validation | Hot | Debug | Remove in release |
| 241 | Count > 0 | Hot | Unnecessary | Remove |
| 171-173 | Profile enabled | Hot | Debug | Remove in release |
| 250-256 | Profile rdtsc | Hot | Debug | Remove in release |

**Total: 16-21 branches** → **Target: 2-3 branches** (95% reduction)

### Refill Path (hakmem_tiny_refill_p0.inc.h)

| Line | Branch | Frequency | Type | Fix |
|------|--------|-----------|------|-----|
| 33 | !g_use_superslab | Cold | Config | Remove check |
| 41 | !tls->ss | Hot | Refill | Keep (necessary) |
| 46 | !meta | Hot | Refill | Keep (necessary) |
| 56 | room <= 0 | Hot | Capacity | Keep (necessary) |
| 66-73 | Hot override | Cold | Env var | Pre-compute |
| 76-83 | Mid override | Cold | Env var | Pre-compute |
| 116-119 | Remote drain | Hot | Optimization | Keep |
| 138 | Capacity check | Hot | Refill | Keep (necessary) |

**Total: 10-15 branches** → **Target: 5-8 branches** (40-50% reduction)

---

**End of Report**