GPU TPC bugfix: break cyclic merged track graphs

Author: davidrohr

GPU/GPUTracking/Merger/GPUTPCGMMerger.cxx

@@ -1772,7 +1772,11 @@ GPUd() void GPUTPCGMMerger::PrepareForFit1(int32_t nBlocks, int32_t nThreads, in
       if (!trk.CCE() && !trk.MergedLooper()) {
         GPUTPCGMMergedTrack* updTrk = &trk;
         while (updTrk->PrevSegment() >= 0) {
-          updTrk = &mMergedTracks[updTrk->PrevSegment()];
+          auto next = &mMergedTracks[updTrk->PrevSegment()];
+          if (next == &trk) {
+            break;
+          }
+          updTrk = next;
         }
         const auto &cl0 = mClusters[trk.FirstClusterRef()], &cln = mClusters[updTrk->FirstClusterRef() + updTrk->NClusters() - 1];
         const auto& GPUrestrict() cls = GetConstantMem()->ioPtrs.clustersNative->clustersLinear;
@@ -1781,7 +1785,11 @@ GPUd() void GPUTPCGMMerger::PrepareForFit1(int32_t nBlocks, int32_t nThreads, in
         trk.Param().ShiftZ(this, cl0.sector, tmp[0], tmp[1], tmp[2]);
         updTrk = &trk;
         while (updTrk->PrevSegment() >= 0) {
-          updTrk = &mMergedTracks[updTrk->PrevSegment()];
+          auto next = &mMergedTracks[updTrk->PrevSegment()];
+          if (next == &trk) {
+            break;
+          }
+          updTrk = next;
           updTrk->Param().TOffset() = trk.Param().TOffset();
         }
       }

GPU/GPUTracking/Merger/GPUTPCGMO2Output.cxx

@@ -214,7 +214,11 @@ GPUdii() void GPUTPCGMO2Output::Thread<GPUTPCGMO2Output::output>(int32_t nBlocks
     if (track.PrevSegment() >= 0) {
       const GPUTPCGMMergedTrack* chkTrk = &tracks[track.PrevSegment()];
       while (chkTrk->PrevSegment() >= 0) {
-        chkTrk = &tracks[chkTrk->PrevSegment()];
+        auto next = &tracks[chkTrk->PrevSegment()];
+        if (next == &track) {
+          break;
+        }
+        chkTrk = next;
       }
       const auto& firstPrevCluster = trackClusters[chkTrk->FirstClusterRef()];
       t1 = clusters->clustersLinear[firstPrevCluster.num].getTime();