[mono] Array.IndexOf / Span<T>.IndexOf very slow on .net 7  #78008

using System;
using System.Diagnostics;

class Program
{
    private static int[] _testArray = InitAssistArray();

    private static int[] InitAssistArray()
    {
        int[] assistArray = new int[2048];
        Random r = new Random(5);
        for (int i = 0; i < assistArray.Length; i++)
        {
            assistArray[i] = r.Next() % 2048;
        }

        return assistArray;
    }
        
    public static int FindIndex(int n)
    {
        int sum = 0;
        for (int i = 0; i < n; i++)
        {
            sum += _testArray.AsSpan().IndexOf(i % 2048);
        }

        return sum;
    }

    public static void Main()
    {
        FindIndex(100);
        
        Stopwatch sw = Stopwatch.StartNew();
        int sum = FindIndex(100000);
        sw.Stop();
        Console.WriteLine($"time cost: {sw.ElapsedMilliseconds}");
    }
}