move WriteCloneIntoRaw into alloc::alloc

library/alloc/src/alloc.rs

@@ -397,3 +397,26 @@ pub mod __alloc_error_handler {
         unsafe { oom_impl(layout) }
     }
 }
+
+/// Specialize clones into pre-allocated, uninitialized memory.
+/// Used by `Box::clone` and `Rc`/`Arc::make_mut`.
+pub(crate) trait WriteCloneIntoRaw: Sized {
+    unsafe fn write_clone_into_raw(&self, target: *mut Self);
+}
+
+impl<T: Clone> WriteCloneIntoRaw for T {
+    #[inline]
+    default unsafe fn write_clone_into_raw(&self, target: *mut Self) {
+        // Having allocated *first* may allow the optimizer to create
+        // the cloned value in-place, skipping the local and move.
+        unsafe { target.write(self.clone()) };
+    }
+}
+
+impl<T: Copy> WriteCloneIntoRaw for T {
+    #[inline]
+    unsafe fn write_clone_into_raw(&self, target: *mut Self) {
+        // We can always copy in-place, without ever involving a local value.
+        unsafe { target.copy_from_nonoverlapping(self, 1) };
+    }
+}

library/alloc/src/boxed.rs

@@ -151,7 +151,7 @@ use core::pin::Pin;
 use core::ptr::{self, Unique};
 use core::task::{Context, Poll};
 
-use crate::alloc::{handle_alloc_error, AllocError, Allocator, Global, Layout};
+use crate::alloc::{handle_alloc_error, AllocError, Allocator, Global, Layout, WriteCloneIntoRaw};
 use crate::borrow::Cow;
 use crate::raw_vec::RawVec;
 use crate::str::from_boxed_utf8_unchecked;
@@ -1047,28 +1047,6 @@ impl<T: Clone, A: Allocator + Clone> Clone for Box<T, A> {
     }
 }
 
-/// Specialize clones into pre-allocated, uninitialized memory.
-pub(crate) trait WriteCloneIntoRaw: Sized {
-    unsafe fn write_clone_into_raw(&self, target: *mut Self);
-}
-
-impl<T: Clone> WriteCloneIntoRaw for T {
-    #[inline]
-    default unsafe fn write_clone_into_raw(&self, target: *mut Self) {
-        // Having allocated *first* may allow the optimizer to create
-        // the cloned value in-place, skipping the local and move.
-        unsafe { target.write(self.clone()) };
-    }
-}
-
-impl<T: Copy> WriteCloneIntoRaw for T {
-    #[inline]
-    unsafe fn write_clone_into_raw(&self, target: *mut Self) {
-        // We can always copy in-place, without ever involving a local value.
-        unsafe { target.copy_from_nonoverlapping(self, 1) };
-    }
-}
-
 #[stable(feature = "box_slice_clone", since = "1.3.0")]
 impl Clone for Box<str> {
     fn clone(&self) -> Self {

library/alloc/src/rc.rs

@@ -263,9 +263,10 @@ use core::pin::Pin;
 use core::ptr::{self, NonNull};
 use core::slice::from_raw_parts_mut;
 
-use crate::alloc::{box_free, handle_alloc_error, AllocError, Allocator, Global, Layout};
+use crate::alloc::{
+    box_free, handle_alloc_error, AllocError, Allocator, Global, Layout, WriteCloneIntoRaw,
+};
 use crate::borrow::{Cow, ToOwned};
-use crate::boxed::WriteCloneIntoRaw;
 use crate::string::String;
 use crate::vec::Vec;
 

library/alloc/src/sync.rs

@@ -22,9 +22,11 @@ use core::slice::from_raw_parts_mut;
 use core::sync::atomic;
 use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
 
-use crate::alloc::{box_free, handle_alloc_error, AllocError, Allocator, Global, Layout};
+use crate::alloc::{
+    box_free, handle_alloc_error, AllocError, Allocator, Global, Layout, WriteCloneIntoRaw,
+};
 use crate::borrow::{Cow, ToOwned};
-use crate::boxed::{Box, WriteCloneIntoRaw};
+use crate::boxed::Box;
 use crate::rc::is_dangling;
 use crate::string::String;
 use crate::vec::Vec;