ghc -O

Hello GHC gurus, specifying "-O" or "-O2" to GHC enables various optimisations to the frontend of the compiler, but I wonder does it turn on any optimistions to the backend/code-generator that are independent of the frontend? I can imagine that knowledge such as strictness which is computed by frontend would enable optimisations in the backend, but I'm more interested in whether the backend would do anything independent (e.g. peephole optimistion, C compiler options) with "-O" but not without. Thanks, Matt.