https://github.com/dotnet/roslyn/issues/2773

Benchmark.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.0</TargetFramework>
    <LangVersion>latest</LangVersion>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="BenchmarkDotNet" Version="0.10.11" />
    <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="2.6.1" />
  </ItemGroup>
</Project>

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using BenchmarkDotNet.Diagnosers;
using BenchmarkDotNet.Running;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis.Emit;
using Microsoft.CodeAnalysis.Text;

public class Program
{
    static void Main() => BenchmarkRunner.Run<Program>();
    //static void Main() => new Program().Benchmark();

    const string RoslynDir = "/home/svick/roslyn";
    static readonly string UserDir = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile);

    List<string> files = Directory.GetFiles($"{RoslynDir}/src/Compilers/CSharp/Portable", "*.cs", SearchOption.AllDirectories)
        .Append($"{RoslynDir}/src/Compilers/CSharp/CSharpAnalyzerDriver/CSharpDeclarationComputer.cs")
        .ToList();
        
    List<MetadataReference> references = new[] 
    {
        $"{RoslynDir}/Binaries/Debug/Dlls/CodeAnalysis/ref/Microsoft.CodeAnalysis.dll",
        $"{UserDir}/.nuget/packages/system.collections.concurrent/4.3.0/ref/netstandard1.3/System.Collections.Concurrent.dll",
        $"{UserDir}/.nuget/packages/system.collections/4.3.0/ref/netstandard1.3/System.Collections.dll",
        $"{UserDir}/.nuget/packages/system.collections.immutable/1.3.1/lib/netstandard1.0/System.Collections.Immutable.dll",
        $"{UserDir}/.nuget/packages/system.diagnostics.debug/4.3.0/ref/netstandard1.3/System.Diagnostics.Debug.dll",
        $"{UserDir}/.nuget/packages/system.diagnostics.fileversioninfo/4.3.0/ref/netstandard1.3/System.Diagnostics.FileVersionInfo.dll",
        $"{UserDir}/.nuget/packages/system.diagnostics.tools/4.3.0/ref/netstandard1.0/System.Diagnostics.Tools.dll",
        $"{UserDir}/.nuget/packages/system.globalization/4.3.0/ref/netstandard1.3/System.Globalization.dll",
        $"{UserDir}/.nuget/packages/system.io.compression/4.3.0/ref/netstandard1.3/System.IO.Compression.dll",
        $"{UserDir}/.nuget/packages/system.io/4.3.0/ref/netstandard1.3/System.IO.dll",
        $"{UserDir}/.nuget/packages/system.io.filesystem/4.3.0/ref/netstandard1.3/System.IO.FileSystem.dll",
        $"{UserDir}/.nuget/packages/system.io.filesystem.primitives/4.3.0/ref/netstandard1.3/System.IO.FileSystem.Primitives.dll",
        $"{UserDir}/.nuget/packages/system.linq/4.3.0/ref/netstandard1.0/System.Linq.dll",
        $"{UserDir}/.nuget/packages/system.linq.expressions/4.3.0/ref/netstandard1.3/System.Linq.Expressions.dll",
        $"{UserDir}/.nuget/packages/system.reflection/4.3.0/ref/netstandard1.3/System.Reflection.dll",
        $"{UserDir}/.nuget/packages/system.reflection.extensions/4.3.0/ref/netstandard1.0/System.Reflection.Extensions.dll",
        $"{UserDir}/.nuget/packages/system.reflection.metadata/1.4.2/lib/netstandard1.1/System.Reflection.Metadata.dll",
        $"{UserDir}/.nuget/packages/system.reflection.primitives/4.3.0/ref/netstandard1.0/System.Reflection.Primitives.dll",
        $"{UserDir}/.nuget/packages/system.resources.resourcemanager/4.3.0/ref/netstandard1.0/System.Resources.ResourceManager.dll",
        $"{UserDir}/.nuget/packages/system.runtime/4.3.0/ref/netstandard1.3/System.Runtime.dll",
        $"{UserDir}/.nuget/packages/system.runtime.extensions/4.3.0/ref/netstandard1.3/System.Runtime.Extensions.dll",
        $"{UserDir}/.nuget/packages/system.runtime.handles/4.3.0/ref/netstandard1.3/System.Runtime.Handles.dll",
        $"{UserDir}/.nuget/packages/system.runtime.interopservices/4.3.0/ref/netstandard1.3/System.Runtime.InteropServices.dll",
        $"{UserDir}/.nuget/packages/system.runtime.numerics/4.3.0/ref/netstandard1.1/System.Runtime.Numerics.dll",
        $"{UserDir}/.nuget/packages/system.security.cryptography.algorithms/4.3.0/ref/netstandard1.3/System.Security.Cryptography.Algorithms.dll",
        $"{UserDir}/.nuget/packages/system.security.cryptography.encoding/4.3.0/ref/netstandard1.3/System.Security.Cryptography.Encoding.dll",
        $"{UserDir}/.nuget/packages/system.security.cryptography.primitives/4.3.0/ref/netstandard1.3/System.Security.Cryptography.Primitives.dll",
        $"{UserDir}/.nuget/packages/system.security.cryptography.x509certificates/4.3.0/ref/netstandard1.3/System.Security.Cryptography.X509Certificates.dll",
        $"{UserDir}/.nuget/packages/system.text.encoding.codepages/4.3.0/ref/netstandard1.3/System.Text.Encoding.CodePages.dll",
        $"{UserDir}/.nuget/packages/system.text.encoding/4.3.0/ref/netstandard1.3/System.Text.Encoding.dll",
        $"{UserDir}/.nuget/packages/system.text.encoding.extensions/4.3.0/ref/netstandard1.3/System.Text.Encoding.Extensions.dll",
        $"{UserDir}/.nuget/packages/system.threading/4.3.0/ref/netstandard1.3/System.Threading.dll",
        $"{UserDir}/.nuget/packages/system.threading.tasks/4.3.0/ref/netstandard1.3/System.Threading.Tasks.dll",
        $"{UserDir}/.nuget/packages/system.threading.tasks.parallel/4.3.0/ref/netstandard1.1/System.Threading.Tasks.Parallel.dll",
        $"{UserDir}/.nuget/packages/system.valuetuple/4.3.0/lib/netstandard1.0/System.ValueTuple.dll",
        $"{UserDir}/.nuget/packages/system.xml.readerwriter/4.3.0/ref/netstandard1.3/System.Xml.ReaderWriter.dll",
        $"{UserDir}/.nuget/packages/system.xml.xdocument/4.3.0/ref/netstandard1.3/System.Xml.XDocument.dll",
        $"{UserDir}/.nuget/packages/system.xml.xmldocument/4.3.0/ref/netstandard1.3/System.Xml.XmlDocument.dll",
        $"{UserDir}/.nuget/packages/system.xml.xpath/4.3.0/ref/netstandard1.3/System.Xml.XPath.dll",
        $"{UserDir}/.nuget/packages/system.xml.xpath.xdocument/4.3.0/ref/netstandard1.3/System.Xml.XPath.XDocument.dll"
    }.Select(f => MetadataReference.CreateFromFile(f)).ToList<MetadataReference>();

    CSharpCompilation CreateCompilation(DocumentationMode documentationMode)
    {
        var trees = files.Select(f =>
        {
            using (var stream = File.OpenRead(f))
            {
                return SyntaxFactory.ParseSyntaxTree(SourceText.From(stream), new CSharpParseOptions(LanguageVersion.Latest, documentationMode, preprocessorSymbols: new[] { "NETSTANDARD1_3" }));
            }
        }).ToList();

        return CSharpCompilation.Create(
            "Microsoft.CodeAnalysis.CSharp", trees, references,
            new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary, cryptoKeyFile: $"{RoslynDir}/build/Targets/../Strong Name Keys/35MSSharedLib1024.snk", publicSign: true));
    }

    [Params(EmitMode.None, EmitMode.Null, EmitMode.NullStream)]
    public EmitMode EmitMode { get; set; }

    [Params(DocumentationMode.None, DocumentationMode.Parse, DocumentationMode.Diagnose)]
    public DocumentationMode DocumentationMode { get; set; }

    [Benchmark]
    public void Benchmark()
    {
        var compilation = CreateCompilation(DocumentationMode);

        foreach (var diag in compilation.GetDiagnostics().Where(d => d.Severity >= DiagnosticSeverity.Error).Take(10))
            Console.WriteLine(diag);

        Stream xmlStream;

        switch (EmitMode)
        {
            case EmitMode.None:
                return;
            case EmitMode.Null:
                xmlStream = null;
                break;
            case EmitMode.NullStream:
                xmlStream = Stream.Null;
                break;
            default:
                throw new Exception();
        }

        var result = compilation.Emit(Stream.Null, xmlDocumentationStream: xmlStream);

        if (!result.Success)
            throw new Exception();
    }
}

public enum EmitMode
{
    None,
    Null,
    NullStream
}

results.txt

BenchmarkDotNet=v0.10.11, OS=ubuntu 16.04
Processor=Intel Xeon CPU E5-2673 v3 2.40GHz, ProcessorCount=1
.NET Core SDK=2.1.4
  [Host]     : .NET Core 2.0.5 (Framework 4.6.0.0), 64bit RyuJIT
  DefaultJob : .NET Core 2.0.5 (Framework 4.6.0.0), 64bit RyuJIT


    Method |   EmitMode | DocumentationMode |    Mean |    Error |   StdDev |
---------- |----------- |------------------ |--------:|---------:|---------:|
 Benchmark |       None |          Diagnose | 12.86 s | 0.1969 s | 0.1842 s |
 Benchmark |       None |              None | 12.19 s | 0.1834 s | 0.1716 s |
 Benchmark |       None |             Parse | 12.52 s | 0.1907 s | 0.1784 s |
 Benchmark |       Null |          Diagnose | 26.37 s | 0.3224 s | 0.3016 s |
 Benchmark |       Null |              None | 25.32 s | 0.2050 s | 0.1601 s |
 Benchmark |       Null |             Parse | 24.91 s | 0.3018 s | 0.2823 s |
 Benchmark | NullStream |          Diagnose | 26.02 s | 0.3476 s | 0.3252 s |
 Benchmark | NullStream |              None | 25.36 s | 0.3234 s | 0.3025 s |
 Benchmark | NullStream |             Parse | 25.33 s | 0.2122 s | 0.1985 s |

// * Hints *
Outliers
  Program.Benchmark: Default -> 3 outliers were removed

// * Legends *
  EmitMode          : Value of the 'EmitMode' parameter
  DocumentationMode : Value of the 'DocumentationMode' parameter
  Mean              : Arithmetic mean of all measurements
  Error             : Half of 99.9% confidence interval
  StdDev            : Standard deviation of all measurements
  1 s               : 1 Second (1 sec)