Guard a query invocation out of perf reasons

Author: oli-obk

Diff for: compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1314,8 +1314,10 @@ fn build_generic_type_param_di_nodes<'ll, 'tcx>(
     ty: Ty<'tcx>,
 ) -> SmallVec<Option<&'ll DIType>> {
     if let ty::Adt(def, args) = *ty.kind() {
-        let generics = cx.tcx.generics_of(def.did());
-        return get_template_parameters(cx, generics, args);
+        if args.types().next().is_some() {
+            let generics = cx.tcx.generics_of(def.did());
+            return get_template_parameters(cx, generics, args);
+        }
     }
 
     return smallvec![];