Make communication tasks vanish when running non-MPI version of the code.

src/cell.h

@@ -23,6 +23,9 @@
 #ifndef SWIFT_CELL_H
 #define SWIFT_CELL_H
 
+/* Config parameters. */
+#include "../config.h"
+
 /* Includes. */
 #include <stddef.h>
 
@@ -124,11 +127,13 @@ struct cell {
   /* The hierarchical tasks. */
   struct task *ghost, *init, *kick;
 
+#ifdef WITH_MPI
   /* Task receiving data. */
   struct task *recv_xv, *recv_rho, *recv_ti;
 
   /* Task send data. */
   struct link *send_xv, *send_rho, *send_ti;
+#endif
 
   /* Tasks for gravity tree. */
   struct task *grav_up, *grav_down;

src/engine.c

@@ -1865,6 +1865,8 @@ void engine_marktasks_mapper(void *map_data, int num_elements,
         }
       }
 
+#ifdef WITH_MPI
+
       /* Activate the send/recv flags. */
       if (ci->nodeID != engine_rank) {
 
@@ -1919,6 +1921,8 @@ void engine_marktasks_mapper(void *map_data, int num_elements,
         if (l == NULL) error("Missing link to send_ti task.");
         l->t->skip = 0;
       }
+
+#endif
     }
 
     /* Kick? */