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:

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:
but I wasn't able to get this to work with llvm-as version 2.9.