use strict;
use warnings;

sub get_subs {
  my $pkg = shift;
  my $subs = shift || +{};
  my $seen = shift || +{};
  return if $seen->{ $pkg }++;
  my $pkg_and_dots = $pkg . '::';
  my @ancestors;

  {
    no strict 'refs';
    $subs->{ $_ } ||= $pkg
      for grep exists &{ "$pkg_and_dots$_" }, keys %{ $pkg_and_dots };
    @ancestors = @{ "${pkg_and_dots}ISA" };
  }

  @ancestors = 'UNIVERSAL' unless @ancestors || $seen->{ UNIVERSAL };
  get_subs( $_, $subs, $seen ) for @ancestors;

  return $subs;
}

sub Foo::baz { 1 }
@Bar::ISA = 'Foo';

my $subs = get_subs( 'Bar' );

__END__