let help = "set the default level of slicing used to propagate to the calls
0 : don't slice the called functions
1 : don't slice the called functions but propagate the marks anyway
2 : try to use existing slices, create at most one
3 : most precise slices
note: this value (defaults to 2) is not used for calls to undefined functions
except when '-slice-undef-functions' option is set"