1 files changed, 36 insertions, 0 deletions

diff --git a/tests/codegen/issues/str-to-string-128690.rs b/tests/codegen/issues/str-to-string-128690.rs
new file mode 100644
index 00000000000..8b416306ba6
--- /dev/null
+++ b/tests/codegen/issues/str-to-string-128690.rs
@@ -0,0 +1,36 @@
+//@ compile-flags: -C opt-level=3 -Z merge-functions=disabled
+#![crate_type = "lib"]
+
+//! Make sure str::to_string is specialized not to use fmt machinery.
+
+// CHECK-LABEL: define {{(dso_local )?}}void @one_ref
+#[no_mangle]
+pub fn one_ref(input: &str) -> String {
+    // CHECK-NOT: {{(call|invoke).*}}fmt
+    input.to_string()
+}
+
+// CHECK-LABEL: define {{(dso_local )?}}void @two_ref
+#[no_mangle]
+pub fn two_ref(input: &&str) -> String {
+    // CHECK-NOT: {{(call|invoke).*}}fmt
+    input.to_string()
+}
+
+// CHECK-LABEL: define {{(dso_local )?}}void @thirteen_ref
+#[no_mangle]
+pub fn thirteen_ref(input: &&&&&&&&&&&&&str) -> String {
+    // CHECK-NOT: {{(call|invoke).*}}fmt
+    input.to_string()
+}
+
+// This is a known performance cliff because of the macro-generated
+// specialized impl. If this test suddenly starts failing,
+// consider removing the `to_string_str!` macro in `alloc/str/string.rs`.
+//
+// CHECK-LABEL: define {{(dso_local )?}}void @fourteen_ref
+#[no_mangle]
+pub fn fourteen_ref(input: &&&&&&&&&&&&&&str) -> String {
+    // CHECK: {{(call|invoke).*}}fmt
+    input.to_string()
+}