to allow more flexible address range configuration.
With only one AddressSet, we can not even represent
very simple address ranges like [2G, 32G).

probe.

test_gen_0             test_gen_1
    |                      |
   \ /                    \ /
    L1                     L1
    |                      |
   \ /                    \ /
    L2                     L2
     \                    /
      \                  /
       \                /
        \              /
         \            /
               L3