1 files changed, 34 insertions, 0 deletions
diff --git a/tests/codegen/try_identity.rs b/tests/codegen/try_identity.rs
new file mode 100644
index 000000000..92be90014
--- /dev/null
+++ b/tests/codegen/try_identity.rs
@@ -0,0 +1,34 @@
+// compile-flags: -C no-prepopulate-passes -O -Z mir-opt-level=3 -Zunsound-mir-opts
+
+// Ensure that `x?` has no overhead on `Result<T, E>` due to identity `match`es in lowering.
+// This requires inlining to trigger the MIR optimizations in `SimplifyArmIdentity`.
+
+#![crate_type = "lib"]
+
+type R = Result<u64, i32>;
+
+// This was written to the `?` from `try_trait`, but `try_trait_v2` uses a different structure,
+// so the relevant desugar is copied inline in order to keep the test testing the same thing.
+// FIXME(#85133): while this might be useful for `r#try!`, it would be nice to have a MIR
+// optimization that picks up the `?` desugaring, as `SimplifyArmIdentity` does not.
+#[no_mangle]
+pub fn try_identity(x: R) -> R {
+// CHECK: start:
+// FIXME(JakobDegen): Broken by deaggregation change CHECK-NOT\: br {{.*}}
+// CHECK ret void
+    let y = match into_result(x) {
+        Err(e) => return from_error(From::from(e)),
+        Ok(v) => v,
+    };
+    Ok(y)
+}
+
+#[inline]
+fn into_result<T, E>(r: Result<T, E>) -> Result<T, E> {
+    r
+}
+
+#[inline]
+fn from_error<T, E>(e: E) -> Result<T, E> {
+    Err(e)
+}