Rollup merge of #114794 - RalfJung:swap-safety, r=m-ou-se

clarify safety documentation of ptr::swap and ptr::copy

Closes https://github.com/rust-lang/rust/issues/81005

2 files changed, 9 insertions, 3 deletions

diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index 5a9c900f643..4c76662ac09 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -2707,9 +2707,13 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
 ///
 /// Behavior is undefined if any of the following conditions are violated:
 ///
-/// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes.
+/// * `src` must be [valid] for reads of `count * size_of::<T>()` bytes, and must remain valid even
+///   when `dst` is written for `count * size_of::<T>()` bytes. (This means if the memory ranges
+///   overlap, the two pointers must not be subject to aliasing restrictions relative to each
+///   other.)
 ///
-/// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes.
+/// * `dst` must be [valid] for writes of `count * size_of::<T>()` bytes, and must remain valid even
+///   when `src` is read for `count * size_of::<T>()` bytes.
 ///
 /// * Both `src` and `dst` must be properly aligned.
 ///
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index 01e36044899..41e67fd8435 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -795,7 +795,9 @@ pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
 ///
 /// Behavior is undefined if any of the following conditions are violated:
 ///
-/// * Both `x` and `y` must be [valid] for both reads and writes.
+/// * Both `x` and `y` must be [valid] for both reads and writes. They must remain valid even when the
+///   other pointer is written. (This means if the memory ranges overlap, the two pointers must not
+///   be subject to aliasing restrictions relative to each other.)
 ///
 /// * Both `x` and `y` must be properly aligned.
 ///