Skip AddAgentsToRm when no contexts have pending agents

AddAgentsToRm runs every step in both SetupIterationAll and
TearDownIterationAll. On steps where no agents were created, the
function still allocated NUMA vectors, called ResizeAgentUidMap,
GrowAgentContainer(0), and entered an OMP parallel region. Add an
early-out scan that checks all execution contexts for empty
new_agents_ and returns immediately when nothing to commit.

Author: stanbot8

src/core/execution_context/in_place_exec_ctxt.cc

@@ -318,6 +318,19 @@ void InPlaceExecutionContext::RemoveAgent(const AgentUid& uid) {
 
 void InPlaceExecutionContext::AddAgentsToRm(
     const std::vector<ExecutionContext*>& all_exec_ctxts) {
+  // Skip entirely when no execution context has pending agents
+  bool any_new = false;
+  for (int i = 0; i < tinfo_->GetMaxThreads(); ++i) {
+    auto* ctxt = bdm_static_cast<InPlaceExecutionContext*>(all_exec_ctxts[i]);
+    if (!ctxt->new_agents_.empty()) {
+      any_new = true;
+      break;
+    }
+  }
+  if (!any_new) {
+    return;
+  }
+
   // group execution contexts by numa domain
   std::vector<uint64_t> new_agent_per_numa(tinfo_->GetNumaNodes());
   std::vector<uint64_t> thread_offsets(tinfo_->GetMaxThreads());