Reinstate the two flavours of cell_can_use_pair_mm()

src/cell.c

@@ -3332,7 +3332,7 @@ void cell_activate_subcell_grav_tasks(struct cell *ci, struct cell *cj,
     if (lock_unlock(&cj->grav.mlock) != 0) error("Impossible to unlock m-pole");
 
     /* Can we use multipoles ? */
-    if (cell_can_use_pair_mm(ci, cj, e, sp)) {
+    if (cell_can_use_pair_mm(ci, cj, e, sp, /*use_rebuild_sizes=*/0)) {
       /* Ok, no need to drift anything */
       return;
     }
@@ -6382,15 +6382,16 @@ void cell_reorder_extra_gparts(struct cell *c, struct part *parts,
 /**
  * @brief Can we use the MM interactions fo a given pair of cells?
  *
- * This uses the information from the last tree-build.
- *
  * @param ci The first #cell.
  * @param cj The second #cell.
  * @param e The #engine.
  * @param s The #space.
+ * @param use_rebuild_sizes Are we considering the sizes at the last tree-build
+ * (1) or current sizes (0)?
  */
 int cell_can_use_pair_mm(const struct cell *ci, const struct cell *cj,
-                         const struct engine *e, const struct space *s) {
+                         const struct engine *e, const struct space *s,
+                         const int use_rebuild_sizes) {
 
   const struct gravity_props *props = e->gravity_properties;
   const int periodic = s->periodic;
@@ -6414,5 +6415,5 @@ int cell_can_use_pair_mm(const struct cell *ci, const struct cell *cj,
   const double r2 = dx * dx + dy * dy + dz * dz;
 
   return gravity_M2L_accept_symmetric(props, multi_i, multi_j, r2,
-                                      /*use_rebuild_sizes=*/1);
+                                      use_rebuild_sizes);
 }

src/cell.h

@@ -959,7 +959,8 @@ void cell_reorder_extra_gparts(struct cell *c, struct part *parts,
                                struct spart *sparts);
 void cell_reorder_extra_sparts(struct cell *c, const ptrdiff_t sparts_offset);
 int cell_can_use_pair_mm(const struct cell *ci, const struct cell *cj,
-                         const struct engine *e, const struct space *s);
+                         const struct engine *e, const struct space *s,
+                         const int use_rebuild_sizes);
 
 /**
  * @brief Compute the square of the minimal distance between any two points in

src/engine_maketasks.c

@@ -1381,7 +1381,7 @@ void engine_make_self_gravity_tasks_mapper(void *map_data, int num_elements,
           if (periodic && min_radius2 > max_distance2) continue;
 
           /* Are the cells too close for a MM interaction ? */
-          if (!cell_can_use_pair_mm(ci, cj, e, s)) {
+          if (!cell_can_use_pair_mm(ci, cj, e, s, /*use_rebuild_sizes=*/1)) {
 
             /* Ok, we need to add a direct pair calculation */
             scheduler_addtask(sched, task_type_pair, task_subtype_grav, 0, 0,

src/scheduler.c

@@ -873,7 +873,7 @@ static void scheduler_splittask_gravity(struct task *t, struct scheduler *s) {
                 if (cj->progeny[j] != NULL) {
                   /* Can we use a M-M interaction here? */
                   if (cell_can_use_pair_mm(ci->progeny[i], cj->progeny[j], e,
-                                           sp)) {
+                                           sp, /*use_rebuild_sizes=*/1)) {
 
                     /* Flag this pair as being treated by the M-M task.
                      * We use the 64 bits in the task->flags field to store