Benchmark of CollectionsMarshal.AsSpan

Program.cs

using System.Runtime.InteropServices;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;
using BenchmarkDotNet.Reports;
using BenchmarkDotNet.Running;

Summary? summary = BenchmarkRunner.Run<AsSpanBenchmark>();

[MemoryDiagnoser]
[SimpleJob(RuntimeMoniker.Net60)]
[SimpleJob(RuntimeMoniker.Net70)]
public class AsSpanBenchmark
{
    private const int NumberToWorkOnSoItIsNotOptimizedAwaySeed = 1337;
    private static readonly Random Random = new(60);

    [Params(0, 1, 2, 3, 4)]
    public ushort ListSize { get; set; }

    private List<int> _list = new();
    [GlobalSetup]
    public void GlobalSetup()
    {
        _list = new List<int>(ListSize);
        for (var i = 0; i < ListSize; i++)
            _list.Add(Random.Next(int.MinValue, int.MaxValue));
    }
    [Benchmark]
    public int ForEach()
    {
        int numberToWorkOnSoItIsNotOptimizedAway = NumberToWorkOnSoItIsNotOptimizedAwaySeed;
        foreach (int number in _list)
            numberToWorkOnSoItIsNotOptimizedAway ^= number;
        return numberToWorkOnSoItIsNotOptimizedAway;
    }

    [Benchmark]
    public int For()
    {
        int numberToWorkOnSoItIsNotOptimizedAway = NumberToWorkOnSoItIsNotOptimizedAwaySeed;
        for (var index = 0; index < _list.Count; index++)
            numberToWorkOnSoItIsNotOptimizedAway ^= _list[index];
        return numberToWorkOnSoItIsNotOptimizedAway;
    }
    [Benchmark]
    public int AsSpanForeach()
    {
        int numberToWorkOnSoItIsNotOptimizedAway = NumberToWorkOnSoItIsNotOptimizedAwaySeed;
        foreach (int number in CollectionsMarshal.AsSpan(_list))
            numberToWorkOnSoItIsNotOptimizedAway ^= number;
        return numberToWorkOnSoItIsNotOptimizedAway;
    }
    [Benchmark]
    public int AsSpanFor()
    {
        int numberToWorkOnSoItIsNotOptimizedAway = NumberToWorkOnSoItIsNotOptimizedAwaySeed;
        Span<int> span = CollectionsMarshal.AsSpan(_list);
        for (var index = 0; index < span.Length; index++)
            numberToWorkOnSoItIsNotOptimizedAway ^= span[index];
        return numberToWorkOnSoItIsNotOptimizedAway;
    }

    [Benchmark]
    public int BenchmarkRiderSuggestedLinq()
    {
        return _list.Aggregate(NumberToWorkOnSoItIsNotOptimizedAwaySeed, (current, t) => current ^ t);
    }
}

Results and conclusions can be found here https://www.linkedin.com/pulse/faster-net-list-loops-collectionsmarshalasspan-henrik-gedionsen/