diff --git a/tests/pass/upcast.rs b/tests/pass/upcast.rs
new file mode 100644
index 0000000000..030c2a7cbf
--- /dev/null
+++ b/tests/pass/upcast.rs
@@ -0,0 +1,418 @@
+#![feature(trait_upcasting)]
+#![allow(incomplete_features)]
+
+fn main() {
+    basic();
+    diamond();
+    struct_();
+    replace_vptr();
+}
+
+fn basic() {
+    trait Foo: PartialEq<i32> + std::fmt::Debug + Send + Sync {
+        fn a(&self) -> i32 {
+            10
+        }
+
+        fn z(&self) -> i32 {
+            11
+        }
+
+        fn y(&self) -> i32 {
+            12
+        }
+    }
+
+    trait Bar: Foo {
+        fn b(&self) -> i32 {
+            20
+        }
+
+        fn w(&self) -> i32 {
+            21
+        }
+    }
+
+    trait Baz: Bar {
+        fn c(&self) -> i32 {
+            30
+        }
+    }
+
+    impl Foo for i32 {
+        fn a(&self) -> i32 {
+            100
+        }
+    }
+
+    impl Bar for i32 {
+        fn b(&self) -> i32 {
+            200
+        }
+    }
+
+    impl Baz for i32 {
+        fn c(&self) -> i32 {
+            300
+        }
+    }
+
+    let baz: &dyn Baz = &1;
+    let _: &dyn std::fmt::Debug = baz;
+    assert_eq!(*baz, 1);
+    assert_eq!(baz.a(), 100);
+    assert_eq!(baz.b(), 200);
+    assert_eq!(baz.c(), 300);
+    assert_eq!(baz.z(), 11);
+    assert_eq!(baz.y(), 12);
+    assert_eq!(baz.w(), 21);
+
+    let bar: &dyn Bar = baz;
+    let _: &dyn std::fmt::Debug = bar;
+    assert_eq!(*bar, 1);
+    assert_eq!(bar.a(), 100);
+    assert_eq!(bar.b(), 200);
+    assert_eq!(bar.z(), 11);
+    assert_eq!(bar.y(), 12);
+    assert_eq!(bar.w(), 21);
+
+    let foo: &dyn Foo = baz;
+    let _: &dyn std::fmt::Debug = foo;
+    assert_eq!(*foo, 1);
+    assert_eq!(foo.a(), 100);
+    assert_eq!(foo.z(), 11);
+    assert_eq!(foo.y(), 12);
+
+    let foo: &dyn Foo = bar;
+    let _: &dyn std::fmt::Debug = foo;
+    assert_eq!(*foo, 1);
+    assert_eq!(foo.a(), 100);
+    assert_eq!(foo.z(), 11);
+    assert_eq!(foo.y(), 12);
+}
+
+fn diamond() {
+    trait Foo: PartialEq<i32> + std::fmt::Debug + Send + Sync {
+        fn a(&self) -> i32 {
+            10
+        }
+
+        fn z(&self) -> i32 {
+            11
+        }
+
+        fn y(&self) -> i32 {
+            12
+        }
+    }
+
+    trait Bar1: Foo {
+        fn b(&self) -> i32 {
+            20
+        }
+
+        fn w(&self) -> i32 {
+            21
+        }
+    }
+
+    trait Bar2: Foo {
+        fn c(&self) -> i32 {
+            30
+        }
+
+        fn v(&self) -> i32 {
+            31
+        }
+    }
+
+    trait Baz: Bar1 + Bar2 {
+        fn d(&self) -> i32 {
+            40
+        }
+    }
+
+    impl Foo for i32 {
+        fn a(&self) -> i32 {
+            100
+        }
+    }
+
+    impl Bar1 for i32 {
+        fn b(&self) -> i32 {
+            200
+        }
+    }
+
+    impl Bar2 for i32 {
+        fn c(&self) -> i32 {
+            300
+        }
+    }
+
+    impl Baz for i32 {
+        fn d(&self) -> i32 {
+            400
+        }
+    }
+
+    let baz: &dyn Baz = &1;
+    let _: &dyn std::fmt::Debug = baz;
+    assert_eq!(*baz, 1);
+    assert_eq!(baz.a(), 100);
+    assert_eq!(baz.b(), 200);
+    assert_eq!(baz.c(), 300);
+    assert_eq!(baz.d(), 400);
+    assert_eq!(baz.z(), 11);
+    assert_eq!(baz.y(), 12);
+    assert_eq!(baz.w(), 21);
+    assert_eq!(baz.v(), 31);
+
+    let bar1: &dyn Bar1 = baz;
+    let _: &dyn std::fmt::Debug = bar1;
+    assert_eq!(*bar1, 1);
+    assert_eq!(bar1.a(), 100);
+    assert_eq!(bar1.b(), 200);
+    assert_eq!(bar1.z(), 11);
+    assert_eq!(bar1.y(), 12);
+    assert_eq!(bar1.w(), 21);
+
+    let bar2: &dyn Bar2 = baz;
+    let _: &dyn std::fmt::Debug = bar2;
+    assert_eq!(*bar2, 1);
+    assert_eq!(bar2.a(), 100);
+    assert_eq!(bar2.c(), 300);
+    assert_eq!(bar2.z(), 11);
+    assert_eq!(bar2.y(), 12);
+    assert_eq!(bar2.v(), 31);
+
+    let foo: &dyn Foo = baz;
+    let _: &dyn std::fmt::Debug = foo;
+    assert_eq!(*foo, 1);
+    assert_eq!(foo.a(), 100);
+
+    let foo: &dyn Foo = bar1;
+    let _: &dyn std::fmt::Debug = foo;
+    assert_eq!(*foo, 1);
+    assert_eq!(foo.a(), 100);
+
+    let foo: &dyn Foo = bar2;
+    let _: &dyn std::fmt::Debug = foo;
+    assert_eq!(*foo, 1);
+    assert_eq!(foo.a(), 100);
+}
+
+fn struct_() {
+    use std::rc::Rc;
+    use std::sync::Arc;
+
+    trait Foo: PartialEq<i32> + std::fmt::Debug + Send + Sync {
+        fn a(&self) -> i32 {
+            10
+        }
+
+        fn z(&self) -> i32 {
+            11
+        }
+
+        fn y(&self) -> i32 {
+            12
+        }
+    }
+
+    trait Bar: Foo {
+        fn b(&self) -> i32 {
+            20
+        }
+
+        fn w(&self) -> i32 {
+            21
+        }
+    }
+
+    trait Baz: Bar {
+        fn c(&self) -> i32 {
+            30
+        }
+    }
+
+    impl Foo for i32 {
+        fn a(&self) -> i32 {
+            100
+        }
+    }
+
+    impl Bar for i32 {
+        fn b(&self) -> i32 {
+            200
+        }
+    }
+
+    impl Baz for i32 {
+        fn c(&self) -> i32 {
+            300
+        }
+    }
+
+    fn test_box() {
+        let v = Box::new(1);
+
+        let baz: Box<dyn Baz> = v.clone();
+        assert_eq!(*baz, 1);
+        assert_eq!(baz.a(), 100);
+        assert_eq!(baz.b(), 200);
+        assert_eq!(baz.c(), 300);
+        assert_eq!(baz.z(), 11);
+        assert_eq!(baz.y(), 12);
+        assert_eq!(baz.w(), 21);
+
+        let baz: Box<dyn Baz> = v.clone();
+        let bar: Box<dyn Bar> = baz;
+        assert_eq!(*bar, 1);
+        assert_eq!(bar.a(), 100);
+        assert_eq!(bar.b(), 200);
+        assert_eq!(bar.z(), 11);
+        assert_eq!(bar.y(), 12);
+        assert_eq!(bar.w(), 21);
+
+        let baz: Box<dyn Baz> = v.clone();
+        let foo: Box<dyn Foo> = baz;
+        assert_eq!(*foo, 1);
+        assert_eq!(foo.a(), 100);
+        assert_eq!(foo.z(), 11);
+        assert_eq!(foo.y(), 12);
+
+        let baz: Box<dyn Baz> = v.clone();
+        let bar: Box<dyn Bar> = baz;
+        let foo: Box<dyn Foo> = bar;
+        assert_eq!(*foo, 1);
+        assert_eq!(foo.a(), 100);
+        assert_eq!(foo.z(), 11);
+        assert_eq!(foo.y(), 12);
+    }
+
+    fn test_rc() {
+        let v = Rc::new(1);
+
+        let baz: Rc<dyn Baz> = v.clone();
+        assert_eq!(*baz, 1);
+        assert_eq!(baz.a(), 100);
+        assert_eq!(baz.b(), 200);
+        assert_eq!(baz.c(), 300);
+        assert_eq!(baz.z(), 11);
+        assert_eq!(baz.y(), 12);
+        assert_eq!(baz.w(), 21);
+
+        let baz: Rc<dyn Baz> = v.clone();
+        let bar: Rc<dyn Bar> = baz;
+        assert_eq!(*bar, 1);
+        assert_eq!(bar.a(), 100);
+        assert_eq!(bar.b(), 200);
+        assert_eq!(bar.z(), 11);
+        assert_eq!(bar.y(), 12);
+        assert_eq!(bar.w(), 21);
+
+        let baz: Rc<dyn Baz> = v.clone();
+        let foo: Rc<dyn Foo> = baz;
+        assert_eq!(*foo, 1);
+        assert_eq!(foo.a(), 100);
+        assert_eq!(foo.z(), 11);
+        assert_eq!(foo.y(), 12);
+
+        let baz: Rc<dyn Baz> = v.clone();
+        let bar: Rc<dyn Bar> = baz;
+        let foo: Rc<dyn Foo> = bar;
+        assert_eq!(*foo, 1);
+        assert_eq!(foo.a(), 100);
+        assert_eq!(foo.z(), 11);
+        assert_eq!(foo.y(), 12);
+        assert_eq!(foo.z(), 11);
+        assert_eq!(foo.y(), 12);
+    }
+
+    fn test_arc() {
+        let v = Arc::new(1);
+
+        let baz: Arc<dyn Baz> = v.clone();
+        assert_eq!(*baz, 1);
+        assert_eq!(baz.a(), 100);
+        assert_eq!(baz.b(), 200);
+        assert_eq!(baz.c(), 300);
+        assert_eq!(baz.z(), 11);
+        assert_eq!(baz.y(), 12);
+        assert_eq!(baz.w(), 21);
+
+        let baz: Arc<dyn Baz> = v.clone();
+        let bar: Arc<dyn Bar> = baz;
+        assert_eq!(*bar, 1);
+        assert_eq!(bar.a(), 100);
+        assert_eq!(bar.b(), 200);
+        assert_eq!(bar.z(), 11);
+        assert_eq!(bar.y(), 12);
+        assert_eq!(bar.w(), 21);
+
+        let baz: Arc<dyn Baz> = v.clone();
+        let foo: Arc<dyn Foo> = baz;
+        assert_eq!(*foo, 1);
+        assert_eq!(foo.a(), 100);
+        assert_eq!(foo.z(), 11);
+        assert_eq!(foo.y(), 12);
+
+        let baz: Arc<dyn Baz> = v.clone();
+        let bar: Arc<dyn Bar> = baz;
+        let foo: Arc<dyn Foo> = bar;
+        assert_eq!(*foo, 1);
+        assert_eq!(foo.a(), 100);
+        assert_eq!(foo.z(), 11);
+        assert_eq!(foo.y(), 12);
+    }
+
+    test_box();
+    test_rc();
+    test_arc();
+}
+
+fn replace_vptr() {
+    trait A {
+        fn foo_a(&self);
+    }
+
+    trait B {
+        fn foo_b(&self);
+    }
+
+    trait C: A + B {
+        fn foo_c(&self);
+    }
+
+    struct S(i32);
+
+    impl A for S {
+        fn foo_a(&self) {
+            unreachable!();
+        }
+    }
+
+    impl B for S {
+        fn foo_b(&self) {
+            assert_eq!(42, self.0);
+        }
+    }
+
+    impl C for S {
+        fn foo_c(&self) {
+            unreachable!();
+        }
+    }
+
+    fn invoke_inner(b: &dyn B) {
+        b.foo_b();
+    }
+
+    fn invoke_outer(c: &dyn C) {
+        invoke_inner(c);
+    }
+
+    let s = S(42);
+    invoke_outer(&s);
+}