isl_schedule_constraints_compute_schedule: strongly satisfy dependences
The core scheduling algorithm only ensures that dependences are weakly
satisfied. In particular, instances of different statements may
still be mapped together. These statements are therefore separated
apart in a final step by sorting them according to the remaining
dependences. In some pathological cases, however, different dependences
may impose a different order on the statements.
In such cases, we add an extra schedule row to carry at least one
more dependence.
Reported-by: Tobias Grosser <tobias@grosser.es>
Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>