merlin/bridge: load user subcomponent for networkIF

pymerlin expects to override a SimpleNetwork subcomponent with its own
network subcomponent (e.g., LinkControl). When using a Bridge, this
subcomponent is ignored and link initialization crashes on
SST::Link::sendUntimedData when trying to access a null rtr object. This
patch extends the Bridge component to use the user subcomponent if the
subcomponent slot is populated and if not then fall back to using an
anonymous subcomponent as before.

src/sst/elements/merlin/bridge.h

@@ -204,25 +204,29 @@ class Bridge : public SST::Component {
         dbg.debug(CALL_INFO, 2, 0, "Initializing network interface %d\n", id);
         Nic_t &nic = interfaces[id];
 
-        Params if_params;
-
-        if_params.insert("link_bw",params.find<std::string>("network_bw","80GiB/s"));
-        if_params.insert("input_buf_size",params.find<std::string>("network_input_buffer_size", "1KiB"));
-        if_params.insert("output_buf_size",params.find<std::string>("network_output_buffer_size", "1KiB"));
-        if_params.insert("port_name","network" + std::to_string(id));
-
-        nic.nic = loadAnonymousSubComponent<SST::Interfaces::SimpleNetwork>
-            ("merlin.linkcontrol", "networkIF", id,
-             ComponentInfo::SHARE_PORTS | ComponentInfo::INSERT_STATS, if_params, 1 /* vns */);
-
+        SubComponentSlotInfo *info = getSubComponentSlotInfo("networkIF");
+        if (info) {
+            int maxSlot = info->getMaxPopulatedSlotNumber();
+            if (maxSlot > 1) {
+                dbg.fatal(CALL_INFO, 1,
+                          "May only specify slots 0 and 1 for 'networkIF'; maximum slot given: %d.\n",
+                          maxSlot);
+            }
+        }
+        if (!info || !info->isPopulated(id)) {
+            Params if_params;
+            if_params.insert("link_bw",params.find<std::string>("network_bw","80GiB/s"));
+            if_params.insert("input_buf_size",params.find<std::string>("network_input_buffer_size", "1KiB"));
+            if_params.insert("output_buf_size",params.find<std::string>("network_output_buffer_size", "1KiB"));
+            if_params.insert("port_name","network" + std::to_string(id));
+
+            nic.nic = loadAnonymousSubComponent<SimpleNetwork>
+                ("merlin.linkcontrol", "networkIF", id,
+                 ComponentInfo::SHARE_PORTS | ComponentInfo::INSERT_STATS, if_params, 1 /* vns */);
+        } else {
+            nic.nic = info->create<SimpleNetwork>(id, ComponentInfo::SHARE_PORTS, 1 /* vns */);
+        }
 
-        // nic.nic = (SimpleNetwork*)loadSubComponent("merlin.linkcontrol", this, params);
-        // nic.nic->initialize( "network" + std::to_string(id),
-        //         params.find<SST::UnitAlgebra>("network_bw", SST::UnitAlgebra("80GiB/s")),
-        //         1, /* should be num VN */
-        //         params.find<SST::UnitAlgebra>("network_input_buffer_size", SST::UnitAlgebra("1KiB")),
-        //         params.find<SST::UnitAlgebra>("network_output_buffer_size", SST::UnitAlgebra("1KiB")));
-
         nic.nic->setNotifyOnReceive(new SimpleNetwork::Handler<Bridge, uint8_t>(this, &Bridge::handleIncoming, id));
         sendNotify[id] = new SimpleNetwork::Handler<Bridge, uint8_t>(this, &Bridge::spaceAvailable, id);