coll: Don't allocate space for zero requests

Refs #2402

Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>

ompi/mca/coll/base/coll_base_alltoall.c

@@ -395,8 +395,10 @@ int ompi_coll_base_alltoall_intra_linear_sync(const void *sbuf, int scount,
     total_reqs =  (((max_outstanding_reqs > (size - 1)) ||
                     (max_outstanding_reqs <= 0)) ?
                    (size - 1) : (max_outstanding_reqs));
-    reqs = coll_base_comm_get_reqs(module->base_data, 2 * total_reqs);
-    if (NULL == reqs) { error = -1; line = __LINE__; goto error_hndl; }
+    if (0 < total_reqs) {
+        reqs = coll_base_comm_get_reqs(module->base_data, 2 * total_reqs);
+        if (NULL == reqs) { error = -1; line = __LINE__; goto error_hndl; }
+    }
 
     prcv = (char *) rbuf;
     psnd = (char *) sbuf;

ompi/mca/coll/base/coll_base_bcast.c

@@ -10,7 +10,9 @@
  *                         University of Stuttgart.  All rights reserved.
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
- * Copyright (c) 2012 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2012      Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2016      Research Organization for Information Science
+ *                         and Technology (RIST). All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -615,6 +617,8 @@ ompi_coll_base_bcast_intra_basic_linear(void *buff, int count,
 
     OPAL_OUTPUT((ompi_coll_base_framework.framework_output,"ompi_coll_base_bcast_intra_basic_linear rank %d root %d", rank, root));
 
+    if (1 == size) return OMPI_SUCCESS;
+
     /* Non-root receive the data. */
 
     if (rank != root) {

ompi/mca/coll/basic/coll_basic_allreduce.c

@@ -108,8 +108,10 @@ mca_coll_basic_allreduce_inter(const void *sbuf, void *rbuf, int count,
         if (NULL == tmpbuf) { err = OMPI_ERR_OUT_OF_RESOURCE; line = __LINE__; goto exit; }
         pml_buffer = tmpbuf - gap;
 
-        reqs = coll_base_comm_get_reqs(module->base_data, rsize - 1);
-        if( NULL == reqs ) { err = OMPI_ERR_OUT_OF_RESOURCE; line = __LINE__; goto exit; }
+        if (rsize > 1) {
+            reqs = coll_base_comm_get_reqs(module->base_data, rsize - 1);
+            if( NULL == reqs ) { err = OMPI_ERR_OUT_OF_RESOURCE; line = __LINE__; goto exit; }
+        }
 
         /* Do a send-recv between the two root procs. to avoid deadlock */
         err = MCA_PML_CALL(irecv(rbuf, count, dtype, 0,

ompi/mca/coll/basic/coll_basic_neighbor_alltoallw.c

@@ -12,7 +12,7 @@
  *                         All rights reserved.
  * Copyright (c) 2013      Los Alamos National Security, LLC. All rights
  *                         reserved.
- * Copyright (c) 2014-2015 Research Organization for Information Science
+ * Copyright (c) 2014-2016 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  * $COPYRIGHT$
  *
@@ -46,6 +46,8 @@ mca_coll_basic_neighbor_alltoallw_cart(const void *sbuf, const int scounts[], co
     int rc = MPI_SUCCESS, dim, i, nreqs;
     ompi_request_t **reqs, **preqs;
 
+    if (0 == cart->ndims) return OMPI_SUCCESS;
+
     reqs = preqs = coll_base_comm_get_reqs( module->base_data, 4 * cart->ndims );
     if( NULL == reqs ) { return OMPI_ERR_OUT_OF_RESOURCE; }
 
@@ -129,6 +131,8 @@ mca_coll_basic_neighbor_alltoallw_graph(const void *sbuf, const int scounts[], c
     const int *edges;
 
     mca_topo_base_graph_neighbors_count (comm, rank, &degree);
+    if (0 == degree) return OMPI_SUCCESS;
+
     reqs = preqs = coll_base_comm_get_reqs( module->base_data, 2 * degree );
     if( NULL == reqs ) { return OMPI_ERR_OUT_OF_RESOURCE; }
 
@@ -187,6 +191,8 @@ mca_coll_basic_neighbor_alltoallw_dist_graph(const void *sbuf, const int scounts
     inedges = dist_graph->in;
     outedges = dist_graph->out;
 
+    if (0 == indegree+outdegree) return OMPI_SUCCESS;
+
     reqs = preqs = coll_base_comm_get_reqs( module->base_data, indegree + outdegree );
     if( NULL == reqs ) { return OMPI_ERR_OUT_OF_RESOURCE; }