Use Vec::append

src/librustc_mir/transform/simplify.rs

@@ -124,7 +124,7 @@ pub fn simplify(mut self) {
                 }
 
                 let data = &mut self.basic_blocks[bb];
-                data.statements.extend(new_stmts.drain(..));
+                data.statements.append(&mut new_stmts);
                 data.terminator = Some(terminator);
 
                 changed |= inner_changed;