(trivial) Use the exact CLI file name for single function. (pytorch#3747

)

Summary:
**Summary**
When the module has a single function, even if the CLI parameter is given as (for example)

> -dump-graph-DAG=graph.dot

the generated file name is "_graph.dot" which is not clean (pre-pending the function name makes sense when multiple functions are in the module).

Documentation/test:
Not required.
Pull Request resolved: pytorch#3747

Differential Revision: D18376400

Pulled By: jfix71

fbshipit-source-id: 609ecbba99c9b45e7957f2cfa9e6aec8e3174258

tools/loader/Loader.cpp

@@ -516,6 +516,9 @@ void Loader::compile(CompilationContext &cctx) {
     for (auto function : module->getFunctions()) {
       std::string filename =
           function->getFilename() + "_" + dumpGraphDAGFileOpt;
+      if (module->getFunctions().size() == 1) {
+        filename = dumpGraphDAGFileOpt;
+      }
       function->dumpDAG(filename.c_str());
     }
   }