1 files changed, 50 insertions, 0 deletions
diff --git a/src/test/ui/structs-enums/enum-layout-optimization.rs b/src/test/ui/structs-enums/enum-layout-optimization.rs
new file mode 100644
index 000000000..05d297906
--- /dev/null
+++ b/src/test/ui/structs-enums/enum-layout-optimization.rs
@@ -0,0 +1,50 @@
+// run-pass
+// Test that we will do various size optimizations to enum layout, but
+// *not* if `#[repr(u8)]` or `#[repr(C)]` is passed. See also #40029.
+
+#![allow(dead_code)]
+
+use std::mem;
+
+enum Nullable<T> {
+    Alive(T),
+    Dropped,
+}
+
+#[repr(u8)]
+enum NullableU8<T> {
+    Alive(T),
+    Dropped,
+}
+
+#[repr(C)]
+enum NullableC<T> {
+    Alive(T),
+    Dropped,
+}
+
+struct StructNewtype<T>(T);
+
+#[repr(C)]
+struct StructNewtypeC<T>(T);
+
+enum EnumNewtype<T> { Variant(T) }
+
+#[repr(u8)]
+enum EnumNewtypeU8<T> { Variant(T) }
+
+#[repr(C)]
+enum EnumNewtypeC<T> { Variant(T) }
+
+fn main() {
+    assert!(mem::size_of::<Box<i32>>() == mem::size_of::<Nullable<Box<i32>>>());
+    assert!(mem::size_of::<Box<i32>>() < mem::size_of::<NullableU8<Box<i32>>>());
+    assert!(mem::size_of::<Box<i32>>() < mem::size_of::<NullableC<Box<i32>>>());
+
+    assert!(mem::size_of::<i32>() == mem::size_of::<StructNewtype<i32>>());
+    assert!(mem::size_of::<i32>() == mem::size_of::<StructNewtypeC<i32>>());
+
+    assert!(mem::size_of::<i32>() == mem::size_of::<EnumNewtype<i32>>());
+    assert!(mem::size_of::<i32>() < mem::size_of::<EnumNewtypeU8<i32>>());
+    assert!(mem::size_of::<i32>() < mem::size_of::<EnumNewtypeC<i32>>());
+}