Rollup merge of rust-lang#45610 - strake:atomic_from, r=nagisa

impl From<T> for AtomicT

src/libcore/sync/atomic.rs

@@ -927,6 +927,12 @@ impl<T> AtomicPtr<T> {
     }
 }
 
+#[stable(feature = "atomic_from", since = "1.23.0")]
+impl<T> From<*mut T> for AtomicPtr<T> {
+    #[inline]
+    fn from(p: *mut T) -> Self { Self::new(p) }
+}
+
 #[cfg(target_has_atomic = "ptr")]
 macro_rules! atomic_int {
     ($stable:meta, $const_unstable:meta,
@@ -967,6 +973,12 @@ macro_rules! atomic_int {
             }
         }
 
+        #[stable(feature = "atomic_from", since = "1.23.0")]
+        impl From<$int_type> for $atomic_type {
+            #[inline]
+            fn from(v: $int_type) -> Self { Self::new(v) }
+        }
+
         #[$stable_debug]
         impl fmt::Debug for $atomic_type {
             fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {