1 files changed, 23 insertions, 0 deletions
diff --git a/src/test/mir-opt/simplify-arm-identity.rs b/src/test/mir-opt/simplify-arm-identity.rs
new file mode 100644
index 000000000..bedc86bba
--- /dev/null
+++ b/src/test/mir-opt/simplify-arm-identity.rs
@@ -0,0 +1,23 @@
+// Checks that `SimplifyArmIdentity` is not applied if enums have incompatible layouts.
+// Regression test for issue #66856.
+//
+// compile-flags: -Zmir-opt-level=3
+// EMIT_MIR_FOR_EACH_BIT_WIDTH
+
+enum Src {
+    Foo(u8),
+    Bar,
+}
+
+enum Dst {
+    Foo(u8),
+}
+
+// EMIT_MIR simplify_arm_identity.main.SimplifyArmIdentity.diff
+fn main() {
+    let e: Src = Src::Foo(0);
+    let _: Dst = match e {
+        Src::Foo(x) => Dst::Foo(x),
+        Src::Bar => Dst::Foo(0),
+    };
+}