116d1a7056
Try to avoid locals when cloning into Box/Rc/Arc For generic `T: Clone`, we can allocate an uninitialized box beforehand, which gives the optimizer a chance to create the clone directly in the heap. For `T: Copy`, we can go further and do a simple memory copy, regardless of optimization level. The same applies to `Rc`/`Arc::make_mut` when they must clone the data.