[MISched] Compare right next cluster node

We support bottom-up and bidirectonal postra scheduling now, but we
only compare successive next cluster node as if we are doing topdown
scheduling. This makes load/store clustering and macro fusions wrong.

This patch makes sure that we can get the right cluster node by the
scheduling direction.

Author: wangpc-pp

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -3955,9 +3955,12 @@ bool PostGenericScheduler::tryCandidate(SchedCandidate &Cand,
     return TryCand.Reason != NoCand;
 
   // Keep clustered nodes together.
-  if (tryGreater(TryCand.SU == DAG->getNextClusterSucc(),
-                 Cand.SU == DAG->getNextClusterSucc(),
-                 TryCand, Cand, Cluster))
+  const SUnit *CandNextClusterSU =
+      Cand.AtTop ? DAG->getNextClusterSucc() : DAG->getNextClusterPred();
+  const SUnit *TryCandNextClusterSU =
+      TryCand.AtTop ? DAG->getNextClusterSucc() : DAG->getNextClusterPred();
+  if (tryGreater(TryCand.SU == TryCandNextClusterSU,
+                 Cand.SU == CandNextClusterSU, TryCand, Cand, Cluster))
     return TryCand.Reason != NoCand;
 
   // Avoid critical resource consumption and balance the schedule.