Performance Sensitive simple string concatenation in .NET 8

PerfSensitiveStringConcatenation.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Columns;
using BenchmarkDotNet.Configs;
using BenchmarkDotNet.Jobs;
using BenchmarkDotNet.Order;
using BenchmarkDotNet.Reports;
using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace Benchmarks
{
    [MemoryDiagnoser]
    [Config(typeof(Config))]
    [SimpleJob(RuntimeMoniker.Net80)]
    [HideColumns(Column.Job, Column.RatioSD, Column.AllocRatio)]
    [Orderer(SummaryOrderPolicy.FastestToSlowest)]
    [ReturnValueValidator(failOnError: true)]
    [DisassemblyDiagnoser]
    [GroupBenchmarksBy(BenchmarkLogicalGroupRule.ByCategory)]
    [CategoriesColumn]
    public class PerfSensitiveStringConcatenation
    {
        private class Config : ManualConfig
        {
            public Config()
            {
                SummaryStyle =
                    SummaryStyle.Default.WithRatioStyle(RatioStyle.Percentage);
            }
        }

        private string title = "Mr.", firstName = "David", middleName = "Patrick", lastName = "Callan";

        [BenchmarkCategory("LengthUnknown"), Benchmark]
        public string StringInterpolation() =>
            $"{title} {firstName} {middleName} {lastName}";

        [BenchmarkCategory("LengthUnknown"), Benchmark]
        public string StringJoin() =>
            string.Join(" ", new[] { title, firstName, middleName, lastName });

        [BenchmarkCategory("LengthUnknown"), Benchmark]
        public string StringCreate_TryWrite()
        {
            return string.Create(title.Length + firstName.Length + middleName.Length + lastName.Length + 3,
                (title, firstName, middleName, lastName),
                static (span, state) => span.TryWrite($"{state.title} {state.firstName} {state.middleName} {state.lastName}", out _));
        }

        [BenchmarkCategory("LengthUnknown"), Benchmark]
        public string StringCreate_StringHandler() =>
            string.Create(null, $"{title} {firstName} {middleName} {lastName}");

        [BenchmarkCategory("LengthUnknown"), Benchmark(Baseline = true)]
        public string StringCreate()
        {
            return string.Create(title.Length + firstName.Length + middleName.Length + lastName.Length + 3,
                (title, firstName, middleName, lastName),
                static (span, state) =>
                {
                    state.title.AsSpan().CopyTo(span);
                    span = span.Slice(state.title.Length);
                    span[0] = ' ';
                    span = span.Slice(1);

                    state.firstName.AsSpan().CopyTo(span);
                    span = span.Slice(state.firstName.Length);
                    span[0] = ' ';
                    span = span.Slice(1);

                    state.middleName.AsSpan().CopyTo(span);
                    span = span.Slice(state.middleName.Length);
                    span[0] = ' ';
                    span = span.Slice(1);

                    state.lastName.AsSpan().CopyTo(span);
                }
            );
        }










        [BenchmarkCategory("FinalLengthKnown"), Benchmark]
        public string StringCreate_StringHandler_SpanBuffer() =>
            string.Create(null, stackalloc char[24], $"{title} {firstName} {middleName} {lastName}");

        [BenchmarkCategory("FinalLengthKnown"), Benchmark]
        public string StringCreate_TryWrite_constant()
        {
            return string.Create(24,
                (title, firstName, middleName, lastName),
                static (span, state) => span.TryWrite($"{state.title} {state.firstName} {state.middleName} {state.lastName}", out _));
        }

        [BenchmarkCategory("FinalLengthKnown"), Benchmark(Baseline = true)]
        public string StringCreate_Constant()
        {
            return string.Create(24,
                (title, firstName, middleName, lastName),
                static (span, state) =>
                {
                    state.title.AsSpan().CopyTo(span);
                    span = span.Slice(state.title.Length);
                    span[0] = ' ';
                    span = span.Slice(1);

                    state.firstName.AsSpan().CopyTo(span);
                    span = span.Slice(state.firstName.Length);
                    span[0] = ' ';
                    span = span.Slice(1);

                    state.middleName.AsSpan().CopyTo(span);
                    span = span.Slice(state.middleName.Length);
                    span[0] = ' ';
                    span = span.Slice(1);

                    state.lastName.AsSpan().CopyTo(span);
                }
            );
        }    

        [BenchmarkCategory("FinalLengthKnown"), Benchmark]
        public string RawSpan_Constant()
        {
            Span<char> buffer = stackalloc char[24];
            var span = buffer;
            title.AsSpan().CopyTo(span);
            span = span.Slice(title.Length);
            span[0] = ' ';
            span = span.Slice(1);

            firstName.AsSpan().CopyTo(span);
            span = span.Slice(firstName.Length);
            span[0] = ' ';
            span = span.Slice(1);

            middleName.AsSpan().CopyTo(span);
            span = span.Slice(middleName.Length);
            span[0] = ' ';
            span = span.Slice(1);

            lastName.AsSpan().CopyTo(span);
            return new string(buffer);
        }

        [BenchmarkCategory("FinalLengthKnown"), Benchmark]
        public string FastAllocateString_StringHandler()
        {
            var result = FastAllocateString(null, 24);
            var buffer = MemoryMarshal.CreateSpan(ref GetRawStringData(result), 24);

            Fill(null, buffer, $"{title} {firstName} {middleName} {lastName}");

            return result;
        }




        [BenchmarkCategory("ExactLengthsKnown"), Benchmark]
        public string StringCreate_More_Constant()
        {
            return string.Create(24,
                (title, firstName, middleName, lastName),
                static (span, state) =>
                {
                    state.title.AsSpan().CopyTo(span);
                    span[3] = ' ';
                    span = span.Slice(4);

                    state.firstName.AsSpan().CopyTo(span);
                    span[5] = ' ';
                    span = span.Slice(6);

                    state.middleName.AsSpan().CopyTo(span);
                    span[7] = ' ';
                    span = span.Slice(8);

                    state.lastName.AsSpan().CopyTo(span);
                }
            );
        }

        [BenchmarkCategory("ExactLengthsKnown"), Benchmark]
        public string RawSpan_More_Constant()
        {
            Span<char> buffer = stackalloc char[24];
            var span = buffer;
            title.AsSpan().CopyTo(span);
            span[3] = ' ';
            span = span.Slice(4);

            firstName.AsSpan().CopyTo(span);
            span[5] = ' ';
            span = span.Slice(6);

            middleName.AsSpan().CopyTo(span);
            span[7] = ' ';
            span = span.Slice(8);

            lastName.AsSpan().CopyTo(span);
            return new string(buffer);
        }

        [BenchmarkCategory("ExactLengthsKnown"), Benchmark(Baseline = true)]
        public string FastAllocateString_Raw()
        {
            var result = FastAllocateString(null, 24);
            var span = MemoryMarshal.CreateSpan(ref GetRawStringData(result), 24);

            title.AsSpan().CopyTo(span);
            span[3] = ' ';
            span = span.Slice(4);

            firstName.AsSpan().CopyTo(span);
            span[5] = ' ';
            span = span.Slice(6);

            middleName.AsSpan().CopyTo(span);
            span[7] = ' ';
            span = span.Slice(8);

            lastName.AsSpan().CopyTo(span);
            return result;
        }

        [UnsafeAccessor(UnsafeAccessorKind.StaticMethod, Name = "FastAllocateString")]
        static extern string FastAllocateString(string _, int length);

        [UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_firstChar")]
        static extern ref char GetRawStringData(string _);

        private static void Fill(IFormatProvider provider, Span<char> initialBuffer,
            [InterpolatedStringHandlerArgument(nameof(provider), nameof(initialBuffer))]
        ref DefaultInterpolatedStringHandler handler)
        {
        }
    }
}