1 files changed, 38 insertions, 0 deletions

diff --git a/tests/codegen-llvm/issues/str-to-string-128690.rs b/tests/codegen-llvm/issues/str-to-string-128690.rs
new file mode 100644
index 00000000000..d9e69764be2
--- /dev/null
+++ b/tests/codegen-llvm/issues/str-to-string-128690.rs
@@ -0,0 +1,38 @@
+//@ 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.
+//!
+//! Note that the `CHECK-NOT`s here try to match on calls to functions under `core::fmt`.
+
+// CHECK-LABEL: define {{(dso_local )?}}void @one_ref
+#[no_mangle]
+pub fn one_ref(input: &str) -> String {
+    // CHECK-NOT: {{(call|invoke)}}{{.*}}@{{.*}}core{{.*}}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)}}{{.*}}@{{.*}}core{{.*}}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)}}{{.*}}@{{.*}}core{{.*}}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)}}{{.*}}@{{.*}}core{{.*}}fmt{{.*}}
+    input.to_string()
+}