To make use of the profiling system all modules must be compiled and linked with the -prof option. Any SCC annotations you've put in your source will spring to life.

Without a -prof option, your SCCs are ignored; so you can compile SCC-laden code without changing it.

GHC will automatically add _scc_ constructs for all top-level, exported functions.

All top-level functions, exported or not, will be automatically _scc_'d.

The costs of all CAFs in a module are usually attributed to one “big” CAF cost-centre. With this option, all CAFs get their own cost-centre. An “if all else fails” option…

Ignore any _scc_ constructs, so a module which already has _scc_s can be compiled for profiling with the annotations ignored.