NCCL_TREES variable and rome model fixes (#856)

[ROCm/rccl commit: d33cd5a233]

projects/rccl/src/init.cc

@@ -1110,6 +1110,8 @@ static ncclResult_t initTransportsRank(struct ncclComm* comm, struct ncclComm* p
   comm->topo->ll128Enabled = false;
   // Topology hint for MSCCL internal scheduler about whether to enable MSCCL
   comm->topo->mscclEnabled = false;
+  // Topology hint if tree has been defined by model or User
+  comm->topo->treeDefined = false;
   // Compute paths between GPUs and NICs
   NCCLCHECKGOTO(ncclTopoComputePaths(comm->topo, comm), ret, fail);
   // Remove inaccessible GPUs and unused NICs
@@ -1362,7 +1364,7 @@ static ncclResult_t initTransportsRank(struct ncclComm* comm, struct ncclComm* p
   NCCLCHECKGOTO(ncclCalloc(&rings, nranks*MAXCHANNELS), ret, fail);
 
   NCCLCHECKGOTO(ncclTopoPostset(comm, nodesFirstRank, nodesTreePatterns, allTopoRanks, rings, graphs, nc), ret, fail);
-  if (comm->topo->pivotA2ANumBiRings == 3) NCCLCHECK(ncclTreeBasePostset(comm, &treeGraph));
+  if (comm->topo->treeDefined) NCCLCHECK(ncclTreeBasePostset(comm, &treeGraph));
 
   // AllGather3 - end