ArrayAccessPerformance

ArrayAccessPerformance.cs

using System.Runtime.CompilerServices;
 using BenchmarkDotNet.Attributes;
 
 namespace Jint.Benchmark
 {
     public class ArrayAccessBenchmark
     {
         private class PropertyDescriptor
         {
         }
 
         private PropertyDescriptor[] _dense;
 
         [GlobalSetup]
         public void Setup()
         {
             _dense = new PropertyDescriptor[1000];
         }
                                                     
         [Benchmark]
         public bool Access()
         {
             bool ok = false;
             for (uint i = 0; i < 1000; ++i)
             {
                 ok |= TryGetValue(i, out _);
             }
 
             return ok;
         }
 
         public bool TryGetValue(uint index, out JsValue value)
         {
             value = JsValue.Undefined;
             return TryGetDescriptor(index, out var desc);
         }
 
         public class JsValue
         {
             public static readonly JsValue Undefined = new JsValue();
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private bool TryGetDescriptor(uint index, out PropertyDescriptor descriptor)
         {
             if (_dense != null)
             {
                 if (index >= _dense.Length)
                 {
                     descriptor = null;
                     return false;
                 }
 
                 descriptor = _dense[index];
                 return descriptor != null;
             }
 
             descriptor = null;
             return false;
         }
     }
 }
 

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-6820HQ CPU 2.70GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.300
  [Host]     : .NET Core 2.0.7 (CoreCLR 4.6.26328.01, CoreFX 4.6.26403.03), 64bit RyuJIT
  DefaultJob : .NET Core 2.0.7 (CoreCLR 4.6.26328.01, CoreFX 4.6.26403.03), 64bit RyuJIT

Method	Mean	Error	StdDev
Access	1.489 us	0.0067 us	0.0056 us

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.17134
Intel Core i7-6820HQ CPU 2.70GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=2.1.300
 [Host]     : .NET Core 2.1.0 (CoreCLR 4.6.26515.07, CoreFX 4.6.26515.06), 64bit RyuJIT
 DefaultJob : .NET Core 2.1.0 (CoreCLR 4.6.26515.07, CoreFX 4.6.26515.06), 64bit RyuJIT

Method	Mean	Error	StdDev	Allocated
Access	1.931 us	0.0072 us	0.0052 us	0 B

The problem goes away by changing the array index validation to check that is less than length instead of not more or equal to lenght:

    private bool TryGetDescriptor(uint index, out PropertyDescriptor descriptor)
    {
        descriptor = null;
        if (_dense != null)
        {
            if (index < _dense.Length)
            {
                descriptor = _dense[index];
            }

            return descriptor != null;
        }

        return false;
    }

@lahma thanks for the update!