Add regression test

Author: oli-obk

tests/ui/statics/const_generics.rs

@@ -0,0 +1,26 @@
+//! Check that we lose the information that `BAR` points to `FOO`
+//! when going through a const generic.
+//! This is not an intentional guarantee, it just describes the status quo.
+
+//@ run-pass
+// With optimizations, LLVM will deduplicate the constant `X` whose
+// value is `&42` to just be a reference to the static. This is correct,
+// but obscures the issue we're trying to show.
+//@ revisions: opt noopt
+//@[noopt] compile-flags: -Copt-level=0
+//@[opt] compile-flags: -O
+
+#![feature(const_refs_to_static)]
+#![feature(adt_const_params)]
+#![allow(incomplete_features)]
+
+static FOO: usize = 42;
+const BAR: &usize = &FOO;
+fn foo<const X: &'static usize>() {
+    // Without optimizations, `X` ends up pointing to a copy of `FOO` instead of `FOO` itself.
+    assert_eq!(cfg!(opt), std::ptr::eq(X, &FOO));
+}
+
+fn main() {
+    foo::<BAR>();
+}