Always align Waiter to 4 bytes

diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index 4c14fe75643a891d43060e8a28db41c80b3d6ba0..c135471e2f2ea3503869594b6ed8e44ead712025 100644 (file)
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -171,6 +171,7 @@ pub struct OnceState {
 // `wait` would both hand out a mutable reference to its `Waiter` node, and keep
 // a shared reference to check `signaled`. Instead we hold shared references and
 // use interior mutability.
+#[repr(align(4))] // Ensure the two lower bits are free to use as state bits.
 struct Waiter {
     thread: Cell<Option<Thread>>,
     signaled: AtomicBool,