title: No "Variable is assigned but never used" warning
body: <p>I have the following C# code, I'm using VS 2012 and all my warnings are treated as errors (although this probably doesn't have much relevance).</p>
  
  <pre><code>private static readonly int MAX_RADIUS_KM = 16;
  
  private void Test() {
      int i = 2 * MAX_RADIUS_KM;
      int i2 = 2;
  }
  </code></pre>
  
  <p>"The variable [x] is assigned, but its value is never used" is shown for <code>i2</code>, but not for <code>i</code>. Why? Is this a bug or something's happening behind the scenes? I'd be surprised by the latter, but if so, what's happening that makes <code>i</code> to avoid that warning?</p>
  
  <p>The following also exhibits failure to emit warning for unused <code>i</code>:</p>
  
  <pre><code>private void Test(int foo) {
      int i = 2 * foo;
      int i2 = 2;
  }
  </code></pre>
  
  <p>And another (<code>i2</code> in this case):</p>
  
  <pre><code>private void Test()
  {
    int i = 2 * 3;
    int i2 = i;
  }
  </code></pre>