Comment by buybackoff

I use an extension for arrays, something like:

    internal static class ArrayExtensions
    {
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static ref T RefAtUnsafe<T>(this T[] array, nint index)
        {
    #if DEBUG
            return ref array[index];
    #else
            Debug.Assert((uint)index < array.Length, "RefAtUnsafe: (uint)index < array.Length");
            return ref Unsafe.Add(ref MemoryMarshal.GetArrayDataReference(array), (nuint)index);
    #endif
        }
    }

then your example turns into:

    public static void AddBatch(int[] a, int[] b, int count)
    {
        // Storing a reference is often more expensive that re-taking it in a loop, requires benchmarking
        for (nint i = 0; i < (uint)count; i++)
            a.RefAtUnsafe(i) += b.RefAtUnsafe(i);
    }

The JITted assembly: https://sharplab.io/#v2:EYLgxg9gTgpgtADwGwBYA0AXEBDAzgWwB8AB...

I'm convinced C# is so much better for high perf code, because yes it can do everything (including easy-to-use x-arch SIMD), but it lets one not bother about things that do not matter and use safe code. It's so pragmatic.

See also the top comments from a recent thread, I totally agree. https://news.ycombinator.com/item?id=45253012

BTW, do not use [MethodImpl(MethodImplOptions.AggressiveOptimization)], it disables TieredPGO, which is a huge thing for latest .NET versions.