code: func FindMains(p *loader.Program, s *ssa.Program) []*ssa.Package {
  	ips := p.InitialPackages()
  	mains := make([]*ssa.Package, 0, len(ips))
  	for _, info := range ips {
  		ssaPkg := s.Package(info.Pkg)
  		if ssaPkg.Func("main") != nil {
  			mains = append(mains, ssaPkg)
  		}
  	}
  	return mains
  }
docs: // FindMains returns the set of all packages loaded into the given
  // loader.Program which contain main functions