Documentation on Clang Optimization Levels

Is there documentation about what types of optimizations clang performs with
the different optimization levels? For example, GCC documents somewhat the
optimization levels here:
http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

On that GCC page, they also state "You can invoke GCC with -Q
--help=optimizers to find out the exact set of optimizations that are
enabled at each level". Does Clang have something similar?

I'm also using LLVM 2.9. I did find this post:
http://stackoverflow.com/questions/7796151/where-to-find-the-optimization-sequence-for-clang-ox
but I wasn't able to get this to work with llvm-as version 2.9.