How do I enable specific LLVM passes?

I’m trying to compile a c++ library with clang++ with some optimizations. I see that for some I can find a corresponding flag to pass to clang (e.g. -funroll-loops), but this doesn’t seem to be the case for others. Specifially, I want to turn on indirect call promotion, and I am also curious if there is a general guideline on how to turn on passes.