diff options
Diffstat (limited to 'library/core/src/ptr/mod.rs')
| -rw-r--r-- | library/core/src/ptr/mod.rs | 38 |
1 files changed, 1 insertions, 37 deletions
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs index dbe3999b4a4..7339ccd4048 100644 --- a/library/core/src/ptr/mod.rs +++ b/library/core/src/ptr/mod.rs @@ -1345,40 +1345,6 @@ pub const unsafe fn swap<T>(x: *mut T, y: *mut T) { /// assert_eq!(x, [7, 8, 3, 4]); /// assert_eq!(y, [1, 2, 9]); /// ``` -/// -/// # Const evaluation limitations -/// -/// If this function is invoked during const-evaluation, the current implementation has a small (and -/// rarely relevant) limitation: if `count` is at least 2 and the data pointed to by `x` or `y` -/// contains a pointer that crosses the boundary of two `T`-sized chunks of memory, the function may -/// fail to evaluate (similar to a panic during const-evaluation). This behavior may change in the -/// future. -/// -/// The limitation is illustrated by the following example: -/// -/// ``` -/// use std::mem::size_of; -/// use std::ptr; -/// -/// const { unsafe { -/// const PTR_SIZE: usize = size_of::<*const i32>(); -/// let mut data1 = [0u8; PTR_SIZE]; -/// let mut data2 = [0u8; PTR_SIZE]; -/// // Store a pointer in `data1`. -/// data1.as_mut_ptr().cast::<*const i32>().write_unaligned(&42); -/// // Swap the contents of `data1` and `data2` by swapping `PTR_SIZE` many `u8`-sized chunks. -/// // This call will fail, because the pointer in `data1` crosses the boundary -/// // between several of the 1-byte chunks that are being swapped here. -/// //ptr::swap_nonoverlapping(data1.as_mut_ptr(), data2.as_mut_ptr(), PTR_SIZE); -/// // Swap the contents of `data1` and `data2` by swapping a single chunk of size -/// // `[u8; PTR_SIZE]`. That works, as there is no pointer crossing the boundary between -/// // two chunks. -/// ptr::swap_nonoverlapping(&mut data1, &mut data2, 1); -/// // Read the pointer from `data2` and dereference it. -/// let ptr = data2.as_ptr().cast::<*const i32>().read_unaligned(); -/// assert!(*ptr == 42); -/// } } -/// ``` #[inline] #[stable(feature = "swap_nonoverlapping", since = "1.27.0")] #[rustc_const_stable(feature = "const_swap_nonoverlapping", since = "1.88.0")] @@ -1407,9 +1373,7 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) { const_eval_select!( @capture[T] { x: *mut T, y: *mut T, count: usize }: if const { - // At compile-time we want to always copy this in chunks of `T`, to ensure that if there - // are pointers inside `T` we will copy them in one go rather than trying to copy a part - // of a pointer (which would not work). + // At compile-time we don't need all the special code below. // SAFETY: Same preconditions as this function unsafe { swap_nonoverlapping_const(x, y, count) } } else { |