llvm/polly/lib/External/isl/test_inputs/flow/multi_source3.ai

sink: { S[] -> a[] }
must_source: { T[] -> a[]; U[] -> a[] }
may_source: { V[] -> a[] }
schedule_map: { T[] -> [0,0]; U[] -> [0,0]; V[] -> [0,1]; S[] -> [1,0] }