title: What is option -O3 for g++ and nvcc?
body: <p>I'm new to nvcc and I've seen a library where compilation is done with option -O3, for g++ and nvcc.</p>
  
  <pre><code>CC=g++
  CFLAGS=--std=c++11 -O3
  NVCC=nvcc
  NVCCFLAGS=--std=c++11 -arch sm_20 -O3
  </code></pre>
  
  <p>What is -O3 doing ?</p>