The various GHC optimisations aren't very well documented. Simply a one line description of their name:

http://www.haskell.org/ghc/docs/latest/html/users_guide/flag-reference.html\#id494409

It would be nice if we documented them with an explanation of what the pass does, i.e how GCC documents their flags:

http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html