Swarm comm debug fix

CHANGELOG.md

@@ -24,6 +24,7 @@
 - [[PR 1172]](https://github.com/parthenon-hpc-lab/parthenon/pull/1172) Make parthenon manager robust against external MPI init and finalize calls
 
 ### Fixed (not changing behavior/API/variables/...)
+- [[PR 1217]](https://github.com/parthenon-hpc-lab/parthenon/pull/1217) Swarm comm debug fix
 - [[PR 1215]](https://github.com/parthenon-hpc-lab/parthenon/pull/1215) Fix issue with uninitialized input parameter block data
 - [[PR 1211]](https://github.com/parthenon-hpc-lab/parthenon/pull/1211) remove inline from WriteTaskGraph
 - [[PR 1188]](https://github.com/parthenon-hpc-lab/parthenon/pull/1188) Fix hdf5 output issue for metadata none variables, update test.

src/interface/swarm_comms.cpp

@@ -250,18 +250,20 @@ void Swarm::LoadBuffers_() {
           auto p_index = buffer_sorted(n).swarm_idx_;
           if (swarm_d.IsActive(p_index)) {
             const int m = buffer_sorted(n).sort_idx_;
-            const int bufid = neighbor_buffer_index(m);
             if (m >= 0) {
-              const int bid = n - buffer_start[m];
-              int buffer_index = bid * particle_size;
-              swarm_d.MarkParticleForRemoval(p_index);
-              for (int i = 0; i < realPackDim; i++) {
-                bdvar.send[bufid](buffer_index) = vreal(i, p_index);
-                buffer_index++;
-              }
-              for (int i = 0; i < intPackDim; i++) {
-                bdvar.send[bufid](buffer_index) = static_cast<Real>(vint(i, p_index));
-                buffer_index++;
+              const int bufid = neighbor_buffer_index(m);
+              if (m >= 0) {
+                const int bid = n - buffer_start[m];
+                int buffer_index = bid * particle_size;
+                swarm_d.MarkParticleForRemoval(p_index);
+                for (int i = 0; i < realPackDim; i++) {
+                  bdvar.send[bufid](buffer_index) = vreal(i, p_index);
+                  buffer_index++;
+                }
+                for (int i = 0; i < intPackDim; i++) {
+                  bdvar.send[bufid](buffer_index) = static_cast<Real>(vint(i, p_index));
+                  buffer_index++;
+                }
               }
             }
           }