Use InstanceDef::Item for clone_from shims

Author: Manishearth

src/librustc/ty/instance.rs

@@ -289,8 +289,14 @@ fn resolve_associated_item<'a, 'tcx>(
         }
         traits::VtableBuiltin(..) => {
             if let Some(_) = tcx.lang_items().clone_trait() {
+                let name = tcx.item_name(def_id);
+                let def = if name == "clone" {
+                    ty::InstanceDef::CloneShim(def_id, trait_ref.self_ty())
+                } else {
+                    ty::InstanceDef::Item(def_id)
+                };
                 Some(Instance {
-                    def: ty::InstanceDef::CloneShim(def_id, trait_ref.self_ty()),
+                    def,
                     substs: rcvr_substs
                 })
             } else {

src/librustc_mir/shim.rs

@@ -100,15 +100,7 @@ fn make_shim<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             build_drop_shim(tcx, def_id, ty)
         }
         ty::InstanceDef::CloneShim(def_id, ty) => {
-            let name = tcx.item_name(def_id);
-            if name == "clone" {
-                build_clone_shim(tcx, def_id, ty)
-            } else if name == "clone_from" {
-                debug!("make_shim({:?}: using default trait implementation", instance);
-                return tcx.optimized_mir(def_id);
-            } else {
-                bug!("builtin clone shim {:?} not supported", instance)
-            }
+            build_clone_shim(tcx, def_id, ty)
         }
         ty::InstanceDef::Intrinsic(_) => {
             bug!("creating shims from intrinsics ({:?}) is unsupported", instance)