title: Difference between GCC and Clang optimization options
body: <p>Precondition: I invoke gcc with -O2 optimization flag and clang with -O2 optimization flag.<br>
  Does it means the options list passed to the compilers will be the same?<br>
  Do clang understand standard GCC options like -funroll-loops?</p>
  
  <p>I did not find anything useful about this question in manual:<br>
  <a href="http://llvm.org/releases/3.3/tools/clang/docs/UsersManual.html" rel="nofollow">http://llvm.org/releases/3.3/tools/clang/docs/UsersManual.html</a><br>
  I can not even find a list of possible GCC compatible options that can be used with clang.</p>
  
  <p>Do clang even do anything with GCC options (or it just ignore them?)<br>
  I just need some clarifications on how it work.</p>