title: Why does vectorization fail?
body: <p>I want to optimize my code for vectorization using </p>
  
  <pre><code>-msse2 -ftree-vectorizer-verbose=2.
  </code></pre>
  
  <p>I have the following simple code:</p>
  
  <pre><code>int main(){
    int a[2048], b[2048], c[2048];
    int i;
  
    for (i=0; i&lt;2048; i++){
        b[i]=0;
        c[i]=0;
    }
  
    for (i=0; i&lt;2048; i++){
      a[i] = b[i] + c[i];
    }
    return 0;
  }
  </code></pre>
  
  <p>Why do I get the note</p>
  
  <pre><code> test.cpp:10: note: not vectorized: not enough data-refs in basic block.
  </code></pre>
  
  <p>Thanks!</p>