1 files changed, 40 insertions, 0 deletions
diff --git a/src/test/mir-opt/issue-41697.rs b/src/test/mir-opt/issue-41697.rs
new file mode 100644
index 000000000..5c34d8e68
--- /dev/null
+++ b/src/test/mir-opt/issue-41697.rs
@@ -0,0 +1,40 @@
+// Regression test for #41697. Using dump-mir was triggering
+// artificial cycles: during type-checking, we had to get the MIR for
+// the constant expressions in `[u8; 2]`, which in turn would trigger
+// an attempt to get the def-path, which in turn would request the
+// types of the impl, which would trigger a cycle. We suppressed this
+// cycle now by forcing mir-dump to avoid asking for types of an impl.
+
+#![feature(rustc_attrs)]
+
+use std::sync::Arc;
+
+trait Foo {
+    fn get(&self) -> [u8; 2];
+}
+
+// EMIT_MIR_FOR_EACH_BIT_WIDTH
+// EMIT_MIR issue_41697.{impl#0}-{constant#0}.SimplifyCfg-promote-consts.after.mir
+impl Foo for [u8; 1+1] {
+    fn get(&self) -> [u8; 2] {
+        *self
+    }
+}
+
+struct Bar<T: ?Sized>(T);
+
+fn unsize_fat_ptr<'a>(x: &'a Bar<Foo + Send + 'a>) -> &'a Bar<Foo + 'a> {
+    x
+}
+
+fn unsize_nested_fat_ptr(x: Arc<Foo + Send>) -> Arc<Foo> {
+    x
+}
+
+fn main() {
+    let x: Box<Bar<Foo + Send>> = Box::new(Bar([1,2]));
+    assert_eq!(unsize_fat_ptr(&*x).0.get(), [1, 2]);
+
+    let x: Arc<Foo + Send> = Arc::new([3, 4]);
+    assert_eq!(unsize_nested_fat_ptr(x).get(), [3, 4]);
+}