Don't consider !Unpin references as noalias

Such structures may contain self-references, in which case the
same location may be accessible through a pointer that is not
based-on the noalias pointer.

This is still grey area as far as language semantics are concerned,
but checking for !Unpin as an indicator for self-referential
sturctures seems like a good approach for the meantime.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/test/codegen/noalias-unpin.rs b/src/test/codegen/noalias-unpin.rs
new file mode 100644
index 00000000000..46f18d7f891
--- /dev/null
+++ b/src/test/codegen/noalias-unpin.rs
@@ -0,0 +1,15 @@
+// compile-flags: -Z mutable-noalias=yes
+
+#![crate_type = "lib"]
+
+pub struct SelfRef {
+    self_ref: *mut SelfRef,
+    _pin: std::marker::PhantomPinned
+}
+
+// CHECK-LABEL: @test_self_ref(
+// CHECK-NOT: noalias
+#[no_mangle]
+pub unsafe fn test_self_ref(s: &mut SelfRef) {
+    (*s.self_ref).self_ref = std::ptr::null_mut();
+}