Dependency relation between SUnits

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Hi,
I am trying to modify LLVM scheduler and I have a question on SDep. I would be grateful if anyone could answer it:

  1. Does the Pred–> Succ relation between Scheduling Units represent the fact that the execution of Succ is dependent to execution of Pred? for example:
    I1: Add a,b,c
    I2: Mul d,a,5
    I2 needs the result of I1. Does this represented as I1(Pred)–>I2(Succ)? I am confused since the direction in the DAG graph is the opposite of the dependency graph.
    If so, for two SUnits: SU and N, can checking SU->isSUcc(N) reveals if N is in anyway dependent to SU?
    Thanks,
    Fami