Benchmark example rewrite + ref locals

Array_ByIndex_vs_CreateLocal.cs

[OrderProvider(SummaryOrderPolicy.FastestToSlowest)]
    [RankColumn]
    [MemoryDiagnoser]
    public class Array_ByIndex_vs_CreateLocal
    {
        [Params(1_000_000)]
        public int LoopCount { get; set; }
        public Arr[] _Array;

        [GlobalSetup]
        public void Init()
        {
            _Array = new Arr[LoopCount];

            for (int i = 0; i < _Array.Length; i++)
            {
                _Array[i] = new Arr(i);
            }
        }

        [Benchmark]
        public object CreateLocal_InLoopVariables()
        {
            var calcs = new(int, int, int, int, int, int, int, int, int)[_Array.Length];
            for (int i = 0; i < _Array.Length; i++)
            {
                var item = _Array[i];

                var x1 = item.x1;
                var x2 = item.x2;
                var x3 = item.x3;
                var x4 = item.x4;
                var x5 = item.x5;
                var x6 = item.x6;
                var x7 = item.x7;
                var x8 = item.x8;
                var x9 = item.x9;

                calcs[i] = (x1, x2, x3, x4, x5, x6, x7, x8, x9);
            }

            return calcs;
        }

        [Benchmark]
        public object CreateLocal_PreDefineVariables()
        {
            var x1 = 0;
            var x2 = 0;
            var x3 = 0;
            var x4 = 0;
            var x5 = 0;
            var x6 = 0;
            var x7 = 0;
            var x8 = 0;
            var x9 = 0;

            for (int i = 0; i < _Array.Length; i++)
            {
                var item = _Array[i];

                x1 = item.x1;
                x2 = item.x2;
                x3 = item.x3;
                x4 = item.x4;
                x5 = item.x5;
                x6 = item.x6;
                x7 = item.x7;
                x8 = item.x8;
                x9 = item.x9;
            }

            return (x1, x2, x3, x4, x5, x6, x7, x8, x9, _Array);
        }

        [Benchmark]
        public object CreateLocalRef_InLoopVariables()
        {
            var calcs = new(int, int, int, int, int, int, int, int, int)[_Array.Length];
            for (int i = 0; i < _Array.Length; i++)
            {
                ref var item = ref _Array[i];

                var x1 = item.x1;
                var x2 = item.x2;
                var x3 = item.x3;
                var x4 = item.x4;
                var x5 = item.x5;
                var x6 = item.x6;
                var x7 = item.x7;
                var x8 = item.x8;
                var x9 = item.x9;

                calcs[i] = (x1, x2, x3, x4, x5, x6, x7, x8, x9);
            }

            return calcs;
        }

        [Benchmark]
        public object CreateLocalRef_PreDefineVariables()
        {
            var x1 = 0;
            var x2 = 0;
            var x3 = 0;
            var x4 = 0;
            var x5 = 0;
            var x6 = 0;
            var x7 = 0;
            var x8 = 0;
            var x9 = 0;

            for (int i = 0; i < _Array.Length; i++)
            {
                ref var item = ref _Array[i];

                x1 = item.x1;
                x2 = item.x2;
                x3 = item.x3;
                x4 = item.x4;
                x5 = item.x5;
                x6 = item.x6;
                x7 = item.x7;
                x8 = item.x8;
                x9 = item.x9;
            }

            return (x1, x2, x3, x4, x5, x6, x7, x8, x9, _Array);
        }

        [Benchmark]
        public object ByIndex_InLoopVariables()
        {
            var calcs = new(int, int, int, int, int, int, int, int, int)[_Array.Length];

            for (int i = 0; i < _Array.Length; i++)
            {
                var x1 = _Array[i].x1;
                var x2 = _Array[i].x2;
                var x3 = _Array[i].x3;
                var x4 = _Array[i].x4;
                var x5 = _Array[i].x5;
                var x6 = _Array[i].x6;
                var x7 = _Array[i].x7;
                var x8 = _Array[i].x8;
                var x9 = _Array[i].x9;

                calcs[i] = (x1, x2, x3, x4, x5, x6, x7, x8, x9);
            }

            return calcs;
        }

        [Benchmark]
        public object ByIndex_PreDefineVariables()
        {
            var x1 = 0;
            var x2 = 0;
            var x3 = 0;
            var x4 = 0;
            var x5 = 0;
            var x6 = 0;
            var x7 = 0;
            var x8 = 0;
            var x9 = 0;

            for (int i = 0; i < _Array.Length; i++)
            {
                x1 = _Array[i].x1;
                x2 = _Array[i].x2;
                x3 = _Array[i].x3;
                x4 = _Array[i].x4;
                x5 = _Array[i].x5;
                x6 = _Array[i].x6;
                x7 = _Array[i].x7;
                x8 = _Array[i].x8;
                x9 = _Array[i].x9;
            }

            return (x1, x2, x3, x4, x5, x6, x7, x8, x9, _Array);
        }
    }

    public struct Arr
    {
        public Arr(int i)
        {
            x1 = i;
            x2 = i + 2;
            x3 = i + 3;
            x4 = i + 4;
            x5 = i + 5;
            x6 = i + 6;
            x7 = i + 7;
            x8 = i + 8;
            x9 = i + 9;
        }

        public int x1 { get; set; }
        public int x2 { get; set; }
        public int x3 { get; set; }
        public int x4 { get; set; }
        public int x5 { get; set; }
        public int x6 { get; set; }
        public int x7 { get; set; }
        public int x8 { get; set; }
        public int x9 { get; set; }
    }