Fixed the benchmark file to reflect the updated compile function usage (#2248)

* Fixed the benchmark file to reflect the updated compile function usage.  Compile returns the compiled function now

* Removed redundant compilation

src/tools/nbench/benchmark.cpp

@@ -168,7 +168,7 @@ vector<runtime::PerformanceCounter> run_benchmark(shared_ptr<Function> f,
     timer.start();
     auto backend = runtime::Backend::create(backend_name);
     backend->enable_performance_data(f, timing_detail);
-    backend->compile(f);
+    auto compiled_func = backend->compile(f);
     timer.stop();
     cout.imbue(locale(""));
     cout << "compile time: " << timer.get_milliseconds() << "ms" << endl;
@@ -214,7 +214,7 @@ vector<runtime::PerformanceCounter> run_benchmark(shared_ptr<Function> f,
     {
         for (int i = 0; i < warmup_iterations; i++)
         {
-            backend->call(f, results, args);
+            backend->call(compiled_func, results, args);
         }
     }
 
@@ -236,7 +236,7 @@ vector<runtime::PerformanceCounter> run_benchmark(shared_ptr<Function> f,
                 }
             }
         }
-        backend->call(f, results, args);
+        backend->call(compiled_func, results, args);
         if (copy_data)
         {
             for (size_t result_index = 0; result_index < results.size(); result_index++)