fix(to_backend): Clean up to_backend implementation

Signed-off-by: Naren Dasan <naren@narendasan.com>
Signed-off-by: Naren Dasan <narens@nvidia.com>

Author: narendasan

py/trtorch/csrc/tensorrt_backend.cpp

@@ -24,40 +24,29 @@ c10::IValue preprocess(const torch::jit::Module& mod, const c10::Dict<c10::IValu
 
 c10::impl::GenericDict TensorRTBackend::compile(c10::IValue mod_val, c10::impl::GenericDict method_compile_spec) {
   auto mod = mod_val.toModule();
-  mod = core::lowering::LowerModule(mod);
-
   auto spec = c10::impl::toTypedDict<std::string, at::IValue>(method_compile_spec);
-  core::lowering::LowerInfo lower_info;
-  for (auto it = spec.begin(), end = spec.end(); it != end; ++it) {
-    const auto& method_name = it->key();
-    auto method = mod.get_method(method_name);
-    auto graph = method.graph();
-    core::lowering::LowerGraph(graph, lower_info);
-  }
 
   auto handles = c10::impl::GenericDict(
       c10::StringType::get(), c10::getCustomClassType<c10::intrusive_ptr<core::runtime::TRTEngine>>());
 
   for (auto it = spec.begin(), end = spec.end(); it != end; ++it) {
+    auto mod_ = mod.clone();
     const auto& method_name = it->key();
-    auto method = mod.get_method(method_name);
-    auto g = method.graph();
-
     auto raw_spec = it->value().toCustomClass<trtorch::pyapi::CompileSpec>();
     LOG_DEBUG(raw_spec->stringify());
     auto cfg = raw_spec->toInternalCompileSpec();
-    auto convert_cfg = std::move(cfg.convert_info);
-    auto graph_and_ivalues = torch::jit::LowerGraph(*g, mod._ivalue());
+    auto graph_and_ivals = Lower(mod_, method_name, cfg.lower_info);
 
-    g = graph_and_ivalues.first;
-    auto params = graph_and_ivalues.second;
+    auto g = graph_and_ivals.first;
+    auto params = graph_and_ivals.second;
     auto named_params = core::conversion::get_named_params(g->inputs(), params);
 
+    auto convert_cfg = std::move(cfg.convert_info);
     auto device_spec = convert_cfg.engine_settings.device;
     auto device = core::runtime::CudaDevice(device_spec.gpu_id, device_spec.device_type);
     auto serialized_engine = core::conversion::ConvertBlockToEngine(g->block(), convert_cfg, named_params);
     auto engine_handle = c10::make_intrusive<core::runtime::TRTEngine>(it->key(), serialized_engine, device);
-    handles.insert(method.name(), at::IValue(engine_handle));
+    handles.insert(method_name, at::IValue(engine_handle));
   }
 
   return c10::impl::toGenericDict(handles);