Merge pull request #1202 from artpol84/alltoall_fix

Fix MPI_Alltoall to support inter-communicators.

ompi/mpi/c/alltoall.c

@@ -92,12 +92,10 @@ int MPI_Alltoall(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
         }
     }
 
-    /* Do we need to do anything? Per MPI standard the (v3.1 page 168 line 48)
-     * the amount of data sent must be equal to the amount of data received.
-     */
-    ompi_datatype_type_size(recvtype, &recvtype_size);
-    if( (0 == recvcount) || (0 == recvtype_size) ) {
-        return MPI_SUCCESS;
+    if( !OMPI_COMM_IS_INTER(comm) ){
+        if( (0 == recvcount) || (0 == recvtype_size) ) {
+            return MPI_SUCCESS;
+        }
     }
 
     OPAL_CR_ENTER_LIBRARY();