title: Accelerator restriction: unsupported operation: RSQRTSS
body: <p>I have a simple nbody implementation code and try to compile it for launching on NVIDIA GPUs (Tesla K20m/Geforce GTX 650 Ti). I use the following compiler options:</p>
  
  <p><code>-Minfo=all -acc -Minline -Mfpapprox -ta=tesla:cc35/nvidia</code></p>
  
  <p>Everything works without <code>-Mfpapprox</code>, but when I use it, the compilation fails with the following output:</p>
  
  <p><code>346, Accelerator restriction: unsupported operation: RSQRTSS</code></p>
  
  <p>The 346 line writes as: </p>
  
  <pre><code>float rdistance=1.0f/sqrtf(drSquared); 
  </code></pre>
  
  <p>where</p>
  
  <pre><code>float drSquared=dx*dx+dy*dy+dz*dz+softening;
  </code></pre>
  
  <p>and <code>dx</code>, <code>dy</code>, <code>dz</code> are float values. This line is inside the #pragma acc parallel loop independent for() construction.
  What is the problem with <code>-Mfpapprox</code>?</p>