How do -ON optimization levels relate to -passes pipeline?

It looks like -passes is the new way to specify what optimizations opt would perform.

But is there a relationship between -ON and -passes strings? What -passes strings would correspond to -O0 -O1 -O2 -Os -Oz -O3 -O4, or any particular "old style" command line? Is opt able to print this information?

Yuri