title: Find loops in LLVM bytecode
body: <p>I want to find simple loops in LLVM bytecode, and extract the basic 
  information of the loop.</p>
  
  <p>For example:  </p>
  
  <pre><code> for (i=0; i&lt;1000; i++)
      sum += i;
  </code></pre>
  
  <p>I want to extract the bound [0, 1000), the loop variable "i" and the 
  loop body (sum += i).<br>
  What should I do?</p>
  
  <p>I read the LLVM API document, and find some useful classes like "Loop", 
  "LoopInfo".<br>
  But I do not know how to use them in detail.</p>
  
  <p>Could you please give me some help? A detailed usage may be more helpful.</p>