Question about SUnits in a ScheduleDAG

Hello,

While trying to move upwards in a DAG using the Preds vector of a SUnit, I encountered a situation where;

Given a SUnit A, and a successor B. SUnit A was not in the vector Preds of B, even though B was in Succs of A.

I’m curious as to why this could be. Have I misinterpret the use of Succs and Preds?

/Erik