llvm/polly/lib/External/isl/test_inputs/flow/multi_source2-tree.ai

sink: "{ S[] -> a[] }"
must_source: "{ T[] -> a[] }"
may_source: "{ U[] -> a[] }"
schedule:
  domain: "{ U[]; S[]; T[] }"
  child:
    sequence:
    - filter: "{ T[]; U[] }"
    - filter: "{ S[] }"