llvm/polly/lib/External/isl/test_inputs/cg1.pip

2 4
  1  1  0 -1
  1 -1  1  0

-1

8 7
  1  0  1  0 -1  0  0
  1  0 -1  0  1  0  0
  1  1  0  0  0 -1  0
  1 -1  0  0  0  1  0
  1  0  1  0  0  0 -1
  1  0 -1  0  0  1  0
  1  0 -1  1  0  0 -1
  1  0  0 -1  0  1  0