Auto merge of #107329 - joboet:optimize_lazylock, r=m-ou-se

Optimize `LazyLock` size

The initialization function was unnecessarily stored separately from the data to be initialized. Since both cannot exist at the same time, a `union` can be used, with the `Once` acting as discriminant. This unfortunately requires some extra methods on `Once` so that `Drop` can be implemented correctly and efficiently.

`@rustbot` label +T-libs +A-atomic

1 files changed, 11 insertions, 0 deletions

diff --git a/library/std/src/sys/unsupported/once.rs b/library/std/src/sys/unsupported/once.rs
index b4bb4975f41..11fde1888ba 100644
--- a/library/std/src/sys/unsupported/once.rs
+++ b/library/std/src/sys/unsupported/once.rs
@@ -1,5 +1,6 @@
 use crate::cell::Cell;
 use crate::sync as public;
+use crate::sync::once::ExclusiveState;
 
 pub struct Once {
     state: Cell<State>,
@@ -44,6 +45,16 @@ impl Once {
         self.state.get() == State::Complete
     }
 
+    #[inline]
+    pub(crate) fn state(&mut self) -> ExclusiveState {
+        match self.state.get() {
+            State::Incomplete => ExclusiveState::Incomplete,
+            State::Poisoned => ExclusiveState::Poisoned,
+            State::Complete => ExclusiveState::Complete,
+            _ => unreachable!("invalid Once state"),
+        }
+    }
+
     #[cold]
     #[track_caller]
     pub fn call(&self, ignore_poisoning: bool, f: &mut impl FnMut(&public::OnceState)) {