Implement compile-time configuration system for dead code elimination in Tiny
allocation hot paths. The Config Box provides dual-mode configuration:
- Normal mode: Runtime ENV checks (backward compatible, flexible)
- PGO mode: Compile-time constants (dead code elimination, performance)
PERFORMANCE:
- Baseline (runtime config): 50.32 M ops/s (avg of 5 runs)
- Config Box (PGO mode): 52.77 M ops/s (avg of 5 runs)
- Improvement: +2.45 M ops/s (+4.87% with outlier, +2.72% without)
- Target: +5-8% (partially achieved)
IMPLEMENTATION:
1. core/box/tiny_front_config_box.h (NEW):
- Defines TINY_FRONT_*_ENABLED macros for all config checks
- PGO mode (#if HAKMEM_TINY_FRONT_PGO): Macros expand to constants (0/1)
- Normal mode (#else): Macros expand to function calls
- Functions remain in their original locations (no code duplication)
2. core/hakmem_build_flags.h:
- Added HAKMEM_TINY_FRONT_PGO build flag (default: 0, off)
- Documentation: Usage with make EXTRA_CFLAGS="-DHAKMEM_TINY_FRONT_PGO=1"
3. core/box/hak_wrappers.inc.h:
- Replaced front_gate_unified_enabled() with TINY_FRONT_UNIFIED_GATE_ENABLED
- 2 call sites updated (malloc and free fast paths)
- Added config box include
EXPECTED DEAD CODE ELIMINATION (PGO mode):
if (TINY_FRONT_UNIFIED_GATE_ENABLED) { ... }
→ if (1) { ... } // Constant, always true
→ Compiler optimizes away the branch, keeps body
SCOPE:
Currently only front_gate_unified_enabled() is replaced (2 call sites).
To achieve full +5-8% target, expand to other config checks:
- ultra_slim_mode_enabled()
- tiny_heap_v2_enabled()
- sfc_cascade_enabled()
- tiny_fastcache_enabled()
- tiny_metrics_enabled()
- tiny_diag_enabled()
BUILD USAGE:
Normal mode (runtime config, default):
make bench_random_mixed_hakmem
PGO mode (compile-time config, dead code elimination):
make EXTRA_CFLAGS="-DHAKMEM_TINY_FRONT_PGO=1" bench_random_mixed_hakmem
BOX PATTERN COMPLIANCE:
✅ Single Responsibility: Configuration management ONLY
✅ Clear Contract: Dual-mode (PGO = constants, Normal = runtime)
✅ Observable: Config report function (debug builds)
✅ Safe: Backward compatible (default is normal mode)
✅ Testable: Easy A/B comparison (PGO vs normal builds)
WHY +2.7-4.9% (below +5-8% target)?
- Limited scope: Only 2 call sites for 1 config function replaced
- Lazy init overhead: front_gate_unified_enabled() cached after first call
- Need to expand to more config checks for full benefit
NEXT STEPS:
- Expand config macro usage to other functions (optional)
- OR proceed with PGO re-enablement (Final polish)
🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>
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