Merging upstream version 1.73.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
index c6f438578..9dbb3f9d3 100644
--- a/library/core/src/ptr/mut_ptr.rs
+++ b/library/core/src/ptr/mut_ptr.rs
@@ -1,6 +1,7 @@
 use super::*;
 use crate::cmp::Ordering::{self, Equal, Greater, Less};
 use crate::intrinsics::{self, const_eval_select};
+use crate::mem::SizedTypeProperties;
 use crate::slice::{self, SliceIndex};
 
 impl<T: ?Sized> *mut T {
@@ -29,6 +30,7 @@ impl<T: ?Sized> *mut T {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
+    #[rustc_diagnostic_item = "ptr_is_null"]
     #[inline]
     pub const fn is_null(self) -> bool {
         #[inline]
@@ -53,6 +55,7 @@ impl<T: ?Sized> *mut T {
     /// Casts to a pointer of another type.
     #[stable(feature = "ptr_cast", since = "1.38.0")]
     #[rustc_const_stable(feature = "const_ptr_cast", since = "1.38.0")]
+    #[rustc_diagnostic_item = "ptr_cast"]
     #[inline(always)]
     pub const fn cast<U>(self) -> *mut U {
         self as _
@@ -109,6 +112,7 @@ impl<T: ?Sized> *mut T {
     /// [`cast_mut`]: #method.cast_mut
     #[stable(feature = "ptr_const_cast", since = "1.65.0")]
     #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")]
+    #[rustc_diagnostic_item = "ptr_cast_const"]
     #[inline(always)]
     pub const fn cast_const(self) -> *const T {
         self as _
@@ -1093,14 +1097,23 @@ impl<T: ?Sized> *mut T {
     #[stable(feature = "pointer_methods", since = "1.26.0")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
     #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
+    // We could always go back to wrapping if unchecked becomes unacceptable
+    #[rustc_allow_const_fn_unstable(const_int_unchecked_arith)]
     #[inline(always)]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub const unsafe fn sub(self, count: usize) -> Self
     where
         T: Sized,
     {
-        // SAFETY: the caller must uphold the safety contract for `offset`.
-        unsafe { self.offset((count as isize).wrapping_neg()) }
+        if T::IS_ZST {
+            // Pointer arithmetic does nothing when the pointee is a ZST.
+            self
+        } else {
+            // SAFETY: the caller must uphold the safety contract for `offset`.
+            // Because the pointee is *not* a ZST, that means that `count` is
+            // at most `isize::MAX`, and thus the negation cannot overflow.
+            unsafe { self.offset(intrinsics::unchecked_sub(0, count as isize)) }
+        }
     }
 
     /// Calculates the offset from a pointer in bytes (convenience for