title: Self-compiled Roslyn build performance: Not as fast as originally shipped Roslyn version
body: <h3>What I am doing in one sentence</h3>
  
  <p>Checking out the branch <code>Update-1</code> from the <a href="https://github.com/dotnet/roslyn.git" rel="noreferrer">Roslyn github repository</a>, building the csc.exe, and compiling a random Solution with the csc.exe version I just built myself.</p>
  
  <h3>Expected result</h3>
  
  <p>I expect the performance to be comparable to the original Roslyn version which was shipped with VS 2015 Update 1, located in the path: <code>C:\Program Files (x86)\MSBuild\14.0\Bin</code></p>
  
  <h3>Actual result</h3>
  
  <p>The build performance of the Roslyn version I built myself is significantly worse, compared to the original one. In the solution I used in my tests: roughly 30 seconds vs. 65 seconds.</p>
  
  <h3>My procedure in more detail</h3>
  
  <ul>
  <li>Cloned <a href="https://github.com/dotnet/roslyn.git" rel="noreferrer">https://github.com/dotnet/roslyn.git</a> and checked out branch update-1</li>
  <li>Built Roslyn using <code>Release</code> configuration (tried with both, <code>Mixed Configuration</code> as well as <code>x64</code> for the solution platform.)</li>
  <li><p>To compile a test solution, I altered all project files to use a specific location for the csc path:</p>
  
  <p><code>&lt;CscToolPath&gt;C:\Path\To\Output\Location\Of\Roslyn\Binaries\&lt;/CscToolPath&gt;</code></p></li>
  <li><p>For testing purposes I am building the test solution from command line with</p>
  
  <p><code>MSBuild.exe /t:Rebuild /m:1 /verbosity:m MySolutionName.sln</code></p></li>
  <li><p>I am currently also doing a clean before: </p>
  
  <p><code>MSBuild.exe /t:Clean /m:1 /verbosity:m MySolutionName.sln</code></p></li>
  <li><p>To test against the original compiler, shipped with VS 2015 Update 1, I am changing the configuration in the project files to:</p>
  
  <p><code>&lt;CscToolPath&gt;C:\Program Files (x86)\MSBuild\14.0\Bin\&lt;/CscToolPath&gt;</code></p></li>
  </ul>
  
  <h3>Questions</h3>
  
  <ul>
  <li>What can I do to to achieve a similar performance with my self-compiled Roslyn version, like with the originally shipped Roslyn dlls? </li>
  <li>Are there any further things (like optimizations etc.) to be considered when building Roslyn itself?</li>
  </ul>