1 files changed, 32 insertions, 0 deletions
diff --git a/tests/mir-opt/copy-prop/mutate_through_pointer.rs b/tests/mir-opt/copy-prop/mutate_through_pointer.rs
new file mode 100644
index 000000000..da142e339
--- /dev/null
+++ b/tests/mir-opt/copy-prop/mutate_through_pointer.rs
@@ -0,0 +1,32 @@
+// This attempts to mutate `a` via a pointer derived from `addr_of!(a)`. That is UB
+// according to Miri. However, the decision to make this UB - and to allow
+// rustc to rely on that fact for the purpose of optimizations - has not been
+// finalized.
+//
+// As such, we include this test to ensure that copy prop does not rely on that
+// fact. Specifically, if `addr_of!(a)` could not be used to modify a, it would
+// be correct for CopyProp to replace all occurrences of `a` with `c` - but that
+// would cause `f(true)` to output `false` instead of `true`.
+
+#![feature(custom_mir, core_intrinsics)]
+#![allow(unused_assignments)]
+extern crate core;
+use core::intrinsics::mir::*;
+
+#[custom_mir(dialect = "analysis", phase = "post-cleanup")]
+fn f(c: bool) -> bool {
+    mir!({
+        let a = c;
+        let p = core::ptr::addr_of!(a);
+        let p2 = core::ptr::addr_of_mut!(*p);
+        *p2 = false;
+        RET = c;
+        Return()
+    })
+}
+
+fn main() {
+    assert_eq!(true, f(true));
+}
+
+// EMIT_MIR mutate_through_pointer.f.CopyProp.diff