diff --git a/tests/codegen/string-push.rs b/tests/codegen/string-push.rs
index 72ecc6d04c5e..cf5f6bb1aa39 100644
--- a/tests/codegen/string-push.rs
+++ b/tests/codegen/string-push.rs
@@ -1,3 +1,5 @@
+//! Check that `String::push` is optimized enough not to call `memcpy`.
+
 //@ compile-flags: -O
 #![crate_type = "lib"]