https://github.com/dotnet/runtime/issues/36989

results.md

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19041.264 (2004/?/20H1)
AMD Ryzen 9 3950X, 1 CPU, 32 logical and 16 physical cores
.NET Core SDK=3.1.300
  [Host]     : .NET Core 3.1.4 (CoreCLR 4.700.20.20201, CoreFX 4.700.20.22101), X64 RyuJIT
  Job-SDTQJP : .NET Core 3.1.4 (CoreCLR 4.700.20.20201, CoreFX 4.700.20.22101), X64 RyuJIT

Server=True  

Method	Mean	Error	StdDev	Ratio	Gen 0	Gen 1	Gen 2	Allocated
FastAllocateString	20.51 ns	0.049 ns	0.041 ns	1.00	0.0003	-	-	88 B
StringCreate	26.77 ns	0.093 ns	0.083 ns	1.31	0.0003	-	-	88 B

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19041.264 (2004/?/20H1)
AMD Ryzen 9 3950X, 1 CPU, 32 logical and 16 physical cores
.NET Core SDK=5.0.100-preview.4.20258.7
  [Host]     : .NET Core 5.0.0 (CoreCLR 5.0.20.25106, CoreFX 5.0.20.25106), X64 RyuJIT
  Job-APPKBU : .NET Core 5.0.0 (CoreCLR 5.0.20.25106, CoreFX 5.0.20.25106), X64 RyuJIT

Server=True  

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen 0	Gen 1	Gen 2	Allocated
FastAllocateString	13.88 ns	0.082 ns	0.073 ns	1.00	0.00	0.0003	-	-	88 B
StringCreate	18.92 ns	0.434 ns	0.500 ns	1.35	0.04	0.0003	-	-	88 B

Uuid.cs

public unsafe partial struct Uuid
{
    public string ToStringWithStringCreate(string? format, IFormatProvider? formatProvider)
    {
        // ... same as original ToString
        var uuidString = string.Create(32, this, (span, state) =>
        {
            fixed (char* uuidChars = &span.GetPinnableReference())
            {
                FormatNThis(state, uuidChars);
            }
        });
        return uuidString;
        // ... same as original ToString
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
    private static void FormatNThis(Uuid self, char* dest)
    {
        // dddddddddddddddddddddddddddddddd
        var destUints = (uint*) dest;
        destUints[0] = TableToHex[self._byte0];
        destUints[1] = TableToHex[self._byte1];
        destUints[2] = TableToHex[self._byte2];
        destUints[3] = TableToHex[self._byte3];
        destUints[4] = TableToHex[self._byte4];
        destUints[5] = TableToHex[self._byte5];
        destUints[6] = TableToHex[self._byte6];
        destUints[7] = TableToHex[self._byte7];
        destUints[8] = TableToHex[self._byte8];
        destUints[9] = TableToHex[self._byte9];
        destUints[10] = TableToHex[self._byte10];
        destUints[11] = TableToHex[self._byte11];
        destUints[12] = TableToHex[self._byte12];
        destUints[13] = TableToHex[self._byte13];
        destUints[14] = TableToHex[self._byte14];
        destUints[15] = TableToHex[self._byte15];
    }
}