Take the filename as argument

passes/cmds/example_dt.cc

@@ -46,7 +46,7 @@ struct ExampleDtPass : public Pass
     log("\n");
   }
 
-  void generate_json(const ComputeGraph<ExampleFn, int, IdString, IdString>& compute_graph) {
+  void generate_json(const ComputeGraph<ExampleFn, int, IdString, IdString>& compute_graph, const std::string& filename) {
     Json::array json_nodes;
 
     for (int i = 0; i < compute_graph.size(); ++i) {
@@ -83,15 +83,23 @@ struct ExampleDtPass : public Pass
       {"nodes", json_nodes},
       {"outputs", json_outputs}
     };
-    std::ofstream outfile("compute_graph.json");
+    std::ofstream outfile(filename);
     outfile << json.dump() << std::endl;
 
     // return json.dump();
   }
 
   void execute(std::vector<std::string> args, RTLIL::Design *design) override
-  {
-    size_t argidx = 1;
+  { 
+    size_t argidx;
+    std::string filename;
+    for (argidx = 1; argidx < args.size(); argidx++)
+      {
+	if (args[argidx] == "-o" && argidx+1 < args.size()) {
+	  filename = args[++argidx];
+	  continue;
+	}
+      }
     extra_args(args, argidx, design);
 
     for (auto module : design->selected_modules()) {
@@ -289,7 +297,7 @@ struct ExampleDtPass : public Pass
 	  log("return %d as %s \n", key.second, log_id(key.first));
 	}
 
-      generate_json(compute_graph);
+      generate_json(compute_graph, filename);
     }
     log("Plugin test passed!\n");
   }