Add a unique cell ID for all the non top-level cells.

src/cell.c

@@ -182,6 +182,9 @@ int cell_pack(struct cell *restrict c, struct pcell *restrict pc) {
   pc->gcount = c->gcount;
   pc->scount = c->scount;
   c->tag = pc->tag = atomic_inc(&cell_next_tag) % cell_max_tag;
+#ifdef SWIFT_DEBUG_CHECKS
+  pc->cellID = c->cellID;
+#endif
 
   /* Fill in the progeny, depth-first recursion. */
   int count = 1;
@@ -227,6 +230,9 @@ int cell_unpack(struct pcell *restrict pc, struct cell *restrict c,
   c->gcount = pc->gcount;
   c->scount = pc->scount;
   c->tag = pc->tag;
+#ifdef SWIFT_DEBUG_CHECKS
+  c->cellID = pc->cellID;
+#endif
 
   /* Number of new cells created. */
   int count = 1;

src/cell.h

@@ -113,6 +113,11 @@ struct pcell {
   /*! Relative indices of the cell's progeny. */
   int progeny[8];
 
+#ifdef SWIFT_DEBUG_CHECKS
+  /* Cell ID (for debugging) */
+  int cellID;
+#endif
+
 } SWIFT_STRUCT_ALIGN;
 
 /**
@@ -406,6 +411,9 @@ struct cell {
   char do_sub_sort;
 
 #ifdef SWIFT_DEBUG_CHECKS
+  /* Cell ID (for debugging) */
+  int cellID;
+
   /*! Last (integer) time the cell's sort arrays were updated. */
   integertime_t ti_sort;
 

src/space.c

@@ -64,6 +64,9 @@ int space_subsize_pair = space_subsize_pair_default;
 int space_subsize_self = space_subsize_self_default;
 int space_subsize_self_grav = space_subsize_self_grav_default;
 int space_maxsize = space_maxsize_default;
+#ifdef SWIFT_DEBUG_CHECKS
+int last_cell_id;
+#endif
 
 /**
  * @brief Interval stack necessary for parallel particle sorting.
@@ -463,7 +466,7 @@ void space_regrid(struct space *s, int verbose) {
           c->ti_old_part = ti_old;
           c->ti_old_gpart = ti_old;
           c->ti_old_multipole = ti_old;
-          if (s->gravity) c->multipole = &s->multipoles_top[cid];
+	  if (s->gravity) c->multipole = &s->multipoles_top[cid];
         }
 
     /* Be verbose about the change. */
@@ -2082,6 +2085,9 @@ void space_split_recursive(struct space *s, struct cell *c,
       cp->nodeID = c->nodeID;
       cp->parent = c;
       cp->super = NULL;
+#ifdef SWIFT_DEBUG_CHECKS
+      cp->cellID = last_cell_id++;
+#endif
     }
 
     /* Split the cell data. */