coll/base: Fix collective module selection preference treatment

The selectable list is sorted with lowest to highest priority so the
user-defined preferences should be appended to the list.
The preference treatment should also maintain the order provided by the user
(first item has highest priority) so switch the loop order.

Signed-off-by: Joseph Schuchart <schuchart@icl.utk.edu>

ompi/mca/coll/base/coll_base_comm_select.c

@@ -337,6 +337,7 @@ static opal_list_t *check_components(opal_list_t * components,
                                      ompi_communicator_t * comm)
 {
     int priority, flag;
+    int count_include = 0;
     const mca_base_component_t *component;
     mca_base_component_list_item_t *cli;
     mca_coll_base_module_2_3_0_t *module;
@@ -363,7 +364,8 @@ static opal_list_t *check_components(opal_list_t * components,
         if(NULL == coll_argv) {
             goto proceed_to_select;
         }
-        int idx2, count_include = opal_argv_count(coll_argv);
+        int idx2;
+        count_include = opal_argv_count(coll_argv);
         /* Allocate the coll_include argv */
         coll_include = (char**)malloc((count_include + 1) * sizeof(char*));
         coll_include[count_include] = NULL; /* NULL terminated array */
@@ -385,15 +387,6 @@ static opal_list_t *check_components(opal_list_t * components,
             }
             coll_include[idx] = coll_argv[idx];
         }
-        /* Reverse the order of the coll_inclide argv to faciliate the ordering of
-         * the selected components reverse.
-         */
-        for( idx2 = 0; idx2 < (count_include - 1); idx2++ ) {
-            char* temp = coll_include[idx2];
-            coll_include[idx2] = coll_include[count_include - 1];
-            coll_include[count_include - 1] = temp;
-            count_include--;
-        }
     }
  proceed_to_select:
     /* Make a list of the components that query successfully */
@@ -453,14 +446,17 @@ static opal_list_t *check_components(opal_list_t * components,
 
     /* For all valid component reorder them not on their provided priorities but on
      * the order requested in the info key. As at this point the coll_include is
-     * already ordered backward we can simply prepend the components.
+     * already ordered backward we can simply append the components.
+     * Note that the last element in selectable will have the highest priorty.
      */
-    mca_coll_base_avail_coll_t *item, *item_next;
-    OPAL_LIST_FOREACH_SAFE(item, item_next,
-                           selectable, mca_coll_base_avail_coll_t) {
-        if( component_in_argv(coll_include, item->ac_component_name) ) {
-            opal_list_remove_item(selectable, &item->super);
-            opal_list_prepend(selectable, &item->super);
+    for (int idx = count_include-1; idx >= 0; --idx) {
+        mca_coll_base_avail_coll_t *item;
+        OPAL_LIST_FOREACH(item, selectable, mca_coll_base_avail_coll_t) {
+            if (0 == strcmp(item->ac_component_name, coll_include[idx])) {
+                opal_list_remove_item(selectable, &item->super);
+                opal_list_append(selectable, &item->super);
+                break;
+            }
         }
     }