From df7be435d3a1ad05ba8b71b2966b4ec9b2a1229e Mon Sep 17 00:00:00 2001
From: scalexm <martin.alex32@hotmail.fr>
Date: Mon, 7 Aug 2017 17:14:20 +0200
Subject: [PATCH] Optimize clone shim for `Copy` types

---
 src/librustc_mir/shim.rs | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/src/librustc_mir/shim.rs b/src/librustc_mir/shim.rs
index 818e713cf48..a9fa596a567 100644
--- a/src/librustc_mir/shim.rs
+++ b/src/librustc_mir/shim.rs
@@ -347,7 +347,20 @@ fn build_clone_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
         loc
     };
 
+    let is_copy = !self_ty.moves_by_default(tcx, tcx.param_env(def_id), span);
+
     match self_ty.sty {
+        _ if is_copy => {
+            // `return *self;`
+            let statement = Statement {
+                source_info: source_info,
+                kind: StatementKind::Assign(
+                    Lvalue::Local(RETURN_POINTER),
+                    Rvalue::Use(Operand::Consume(rcvr))
+                )
+            };
+            block(&mut blocks, statement, TerminatorKind::Return);
+        }
         ty::TyArray(ty, len) => {
             let mut returns = Vec::new();
             for i in 0..len {
@@ -402,15 +415,7 @@ fn build_clone_shim<'a, 'tcx>(tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
             block(&mut blocks, statement, TerminatorKind::Return);
         }
         _ => {
-            // `return *self;`
-            let statement = Statement {
-                source_info: source_info,
-                kind: StatementKind::Assign(
-                    Lvalue::Local(RETURN_POINTER),
-                    Rvalue::Use(Operand::Consume(rcvr))
-                )
-            };
-            block(&mut blocks, statement, TerminatorKind::Return);
+            bug!("builtin shim for `{:?}` which is not `Copy` and is not an aggregate", self_ty);
         }
     };