Auto merge of #120527 - GnomedDev:atomicu32-handle, r=petrochenkov

Switch OwnedStore handle count to AtomicU32

This is already panics if overflowing a u32, so let's use the smaller int size to save a tiny bit of memory.

library/proc_macro/src/bridge/client.rs

@@ -3,6 +3,7 @@
 use super::*;
 
 use std::marker::PhantomData;
+use std::sync::atomic::AtomicU32;
 
 macro_rules! define_handles {
     (
@@ -12,8 +13,8 @@ macro_rules! define_handles {
         #[repr(C)]
         #[allow(non_snake_case)]
         pub struct HandleCounters {
-            $($oty: AtomicUsize,)*
-            $($ity: AtomicUsize,)*
+            $($oty: AtomicU32,)*
+            $($ity: AtomicU32,)*
         }
 
         impl HandleCounters {
@@ -21,8 +22,8 @@ impl HandleCounters {
             // a wrapper `fn` pointer, once `const fn` can reference `static`s.
             extern "C" fn get() -> &'static Self {
                 static COUNTERS: HandleCounters = HandleCounters {
-                    $($oty: AtomicUsize::new(1),)*
-                    $($ity: AtomicUsize::new(1),)*
+                    $($oty: AtomicU32::new(1),)*
+                    $($ity: AtomicU32::new(1),)*
                 };
                 &COUNTERS
             }

library/proc_macro/src/bridge/handle.rs

@@ -4,7 +4,7 @@
 use std::hash::Hash;
 use std::num::NonZeroU32;
 use std::ops::{Index, IndexMut};
-use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicU32, Ordering};
 
 use super::fxhash::FxHashMap;
 
@@ -13,12 +13,12 @@
 /// A store that associates values of type `T` with numeric handles. A value can
 /// be looked up using its handle.
 pub(super) struct OwnedStore<T: 'static> {
-    counter: &'static AtomicUsize,
+    counter: &'static AtomicU32,
     data: BTreeMap<Handle, T>,
 }
 
 impl<T> OwnedStore<T> {
-    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
+    pub(super) fn new(counter: &'static AtomicU32) -> Self {
         // Ensure the handle counter isn't 0, which would panic later,
         // when `NonZeroU32::new` (aka `Handle::new`) is called in `alloc`.
         assert_ne!(counter.load(Ordering::SeqCst), 0);
@@ -30,7 +30,7 @@ pub(super) fn new(counter: &'static AtomicUsize) -> Self {
 impl<T> OwnedStore<T> {
     pub(super) fn alloc(&mut self, x: T) -> Handle {
         let counter = self.counter.fetch_add(1, Ordering::SeqCst);
-        let handle = Handle::new(counter as u32).expect("`proc_macro` handle counter overflowed");
+        let handle = Handle::new(counter).expect("`proc_macro` handle counter overflowed");
         assert!(self.data.insert(handle, x).is_none());
         handle
     }
@@ -60,7 +60,7 @@ pub(super) struct InternedStore<T: 'static> {
 }
 
 impl<T: Copy + Eq + Hash> InternedStore<T> {
-    pub(super) fn new(counter: &'static AtomicUsize) -> Self {
+    pub(super) fn new(counter: &'static AtomicU32) -> Self {
         InternedStore { owned: OwnedStore::new(counter), interner: FxHashMap::default() }
     }
 

library/proc_macro/src/bridge/mod.rs

@@ -16,7 +16,6 @@
 use std::ops::Bound;
 use std::ops::Range;
 use std::panic;
-use std::sync::atomic::AtomicUsize;
 use std::sync::Once;
 use std::thread;