Compilers & JIT
V8 JIT Benchmarks: Monomorphic vs Megamorphic Inline Caches
Analyze JavaScript execution speed variations in the V8 engine based on monomorphic versus megamorphic object shapes.
Test Environment
CPUIntel Core i9-13900K
RAM32GB
OSWindows 11
ToolNode.js Benchmark
Metrics Comparison
Property Access
Unit: Ops/sec (Millions)Monomorphic
800★
Megamorphic
45
Detailed Analysis
Functions dealing with a single object shape (monomorphic) execute drastically faster than those dealing with varying shapes (megamorphic).
V8 uses Inline Caching. If an object shape changes too many times, it falls back to a slow dictionary hash lookup.
Property Lookup
Finding memory offset of a property
Bottleneck: Megamorphic state forces slow hash table lookups.
Architectural Recommendations
- Keep object shapes consistent
- Initialize properties in constructors
Frequently Asked Questions
What is a Hidden Class?
V8 assigns a hidden class (map) to objects based on their properties and order of initialization.