Merge from rustc

10 files changed, 262 insertions, 178 deletions

diff --git a/library/core/src/char/mod.rs b/library/core/src/char/mod.rs
index 12bca0b438c..a860c7c6aaa 100644
--- a/library/core/src/char/mod.rs
+++ b/library/core/src/char/mod.rs
@@ -42,7 +42,7 @@ use crate::ascii;
 use crate::error::Error;
 use crate::escape;
 use crate::fmt::{self, Write};
-use crate::iter::FusedIterator;
+use crate::iter::{FusedIterator, TrustedLen, TrustedRandomAccess, TrustedRandomAccessNoCoerce};
 use crate::num::NonZero;
 
 pub(crate) use self::methods::EscapeDebugExtArgs;
@@ -373,176 +373,229 @@ impl fmt::Display for EscapeDebug {
     }
 }
 
-/// Returns an iterator that yields the lowercase equivalent of a `char`.
-///
-/// This `struct` is created by the [`to_lowercase`] method on [`char`]. See
-/// its documentation for more.
-///
-/// [`to_lowercase`]: char::to_lowercase
-#[stable(feature = "rust1", since = "1.0.0")]
-#[derive(Debug, Clone)]
-pub struct ToLowercase(CaseMappingIter);
+macro_rules! casemappingiter_impls {
+    ($(#[$attr:meta])* $ITER_NAME:ident) => {
+        $(#[$attr])*
+        #[stable(feature = "rust1", since = "1.0.0")]
+        #[derive(Debug, Clone)]
+        pub struct $ITER_NAME(CaseMappingIter);
+
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl Iterator for $ITER_NAME {
+            type Item = char;
+            fn next(&mut self) -> Option<char> {
+                self.0.next()
+            }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Iterator for ToLowercase {
-    type Item = char;
-    fn next(&mut self) -> Option<char> {
-        self.0.next()
-    }
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.0.size_hint()
-    }
-}
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                self.0.size_hint()
+            }
 
-#[stable(feature = "case_mapping_double_ended", since = "1.59.0")]
-impl DoubleEndedIterator for ToLowercase {
-    fn next_back(&mut self) -> Option<char> {
-        self.0.next_back()
-    }
-}
+            fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+            where
+                Fold: FnMut(Acc, Self::Item) -> Acc,
+            {
+                self.0.fold(init, fold)
+            }
 
-#[stable(feature = "fused", since = "1.26.0")]
-impl FusedIterator for ToLowercase {}
+            fn count(self) -> usize {
+                self.0.count()
+            }
 
-#[stable(feature = "exact_size_case_mapping_iter", since = "1.35.0")]
-impl ExactSizeIterator for ToLowercase {}
+            fn last(self) -> Option<Self::Item> {
+                self.0.last()
+            }
 
-/// Returns an iterator that yields the uppercase equivalent of a `char`.
-///
-/// This `struct` is created by the [`to_uppercase`] method on [`char`]. See
-/// its documentation for more.
-///
-/// [`to_uppercase`]: char::to_uppercase
-#[stable(feature = "rust1", since = "1.0.0")]
-#[derive(Debug, Clone)]
-pub struct ToUppercase(CaseMappingIter);
+            fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+                self.0.advance_by(n)
+            }
 
-#[stable(feature = "rust1", since = "1.0.0")]
-impl Iterator for ToUppercase {
-    type Item = char;
-    fn next(&mut self) -> Option<char> {
-        self.0.next()
-    }
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.0.size_hint()
-    }
-}
+            unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+                // SAFETY: just forwarding requirements to caller
+                unsafe { self.0.__iterator_get_unchecked(idx) }
+            }
+        }
 
-#[stable(feature = "case_mapping_double_ended", since = "1.59.0")]
-impl DoubleEndedIterator for ToUppercase {
-    fn next_back(&mut self) -> Option<char> {
-        self.0.next_back()
+        #[stable(feature = "case_mapping_double_ended", since = "1.59.0")]
+        impl DoubleEndedIterator for $ITER_NAME {
+            fn next_back(&mut self) -> Option<char> {
+                self.0.next_back()
+            }
+
+            fn rfold<Acc, Fold>(self, init: Acc, rfold: Fold) -> Acc
+            where
+                Fold: FnMut(Acc, Self::Item) -> Acc,
+            {
+                self.0.rfold(init, rfold)
+            }
+
+            fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+                self.0.advance_back_by(n)
+            }
+        }
+
+        #[stable(feature = "fused", since = "1.26.0")]
+        impl FusedIterator for $ITER_NAME {}
+
+        #[stable(feature = "exact_size_case_mapping_iter", since = "1.35.0")]
+        impl ExactSizeIterator for $ITER_NAME {
+            fn len(&self) -> usize {
+                self.0.len()
+            }
+
+            fn is_empty(&self) -> bool {
+                self.0.is_empty()
+            }
+        }
+
+        // SAFETY: forwards to inner `array::IntoIter`
+        #[unstable(feature = "trusted_len", issue = "37572")]
+        unsafe impl TrustedLen for $ITER_NAME {}
+
+        // SAFETY: forwards to inner `array::IntoIter`
+        #[doc(hidden)]
+        #[unstable(feature = "std_internals", issue = "none")]
+        unsafe impl TrustedRandomAccessNoCoerce for $ITER_NAME {
+            const MAY_HAVE_SIDE_EFFECT: bool = false;
+        }
+
+        // SAFETY: this iter has no subtypes/supertypes
+        #[doc(hidden)]
+        #[unstable(feature = "std_internals", issue = "none")]
+        unsafe impl TrustedRandomAccess for $ITER_NAME {}
+
+        #[stable(feature = "char_struct_display", since = "1.16.0")]
+        impl fmt::Display for $ITER_NAME {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                fmt::Display::fmt(&self.0, f)
+            }
+        }
     }
 }
 
-#[stable(feature = "fused", since = "1.26.0")]
-impl FusedIterator for ToUppercase {}
+casemappingiter_impls! {
+    /// Returns an iterator that yields the lowercase equivalent of a `char`.
+    ///
+    /// This `struct` is created by the [`to_lowercase`] method on [`char`]. See
+    /// its documentation for more.
+    ///
+    /// [`to_lowercase`]: char::to_lowercase
+    ToLowercase
+}
 
-#[stable(feature = "exact_size_case_mapping_iter", since = "1.35.0")]
-impl ExactSizeIterator for ToUppercase {}
+casemappingiter_impls! {
+    /// Returns an iterator that yields the uppercase equivalent of a `char`.
+    ///
+    /// This `struct` is created by the [`to_uppercase`] method on [`char`]. See
+    /// its documentation for more.
+    ///
+    /// [`to_uppercase`]: char::to_uppercase
+    ToUppercase
+}
 
 #[derive(Debug, Clone)]
-enum CaseMappingIter {
-    Three(char, char, char),
-    Two(char, char),
-    One(char),
-    Zero,
-}
+struct CaseMappingIter(core::array::IntoIter<char, 3>);
 
 impl CaseMappingIter {
+    #[inline]
     fn new(chars: [char; 3]) -> CaseMappingIter {
+        let mut iter = chars.into_iter();
         if chars[2] == '\0' {
+            iter.next_back();
             if chars[1] == '\0' {
-                CaseMappingIter::One(chars[0]) // Including if chars[0] == '\0'
-            } else {
-                CaseMappingIter::Two(chars[0], chars[1])
+                iter.next_back();
+
+                // Deliberately don't check `chars[0]`,
+                // as '\0' lowercases to itself
             }
-        } else {
-            CaseMappingIter::Three(chars[0], chars[1], chars[2])
         }
+        CaseMappingIter(iter)
     }
 }
 
 impl Iterator for CaseMappingIter {
     type Item = char;
+
     fn next(&mut self) -> Option<char> {
-        match *self {
-            CaseMappingIter::Three(a, b, c) => {
-                *self = CaseMappingIter::Two(b, c);
-                Some(a)
-            }
-            CaseMappingIter::Two(b, c) => {
-                *self = CaseMappingIter::One(c);
-                Some(b)
-            }
-            CaseMappingIter::One(c) => {
-                *self = CaseMappingIter::Zero;
-                Some(c)
-            }
-            CaseMappingIter::Zero => None,
-        }
+        self.0.next()
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        let size = match self {
-            CaseMappingIter::Three(..) => 3,
-            CaseMappingIter::Two(..) => 2,
-            CaseMappingIter::One(_) => 1,
-            CaseMappingIter::Zero => 0,
-        };
-        (size, Some(size))
+        self.0.size_hint()
+    }
+
+    fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+    where
+        Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.0.fold(init, fold)
+    }
+
+    fn count(self) -> usize {
+        self.0.count()
+    }
+
+    fn last(self) -> Option<Self::Item> {
+        self.0.last()
+    }
+
+    fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+        self.0.advance_by(n)
+    }
+
+    unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item {
+        // SAFETY: just forwarding requirements to caller
+        unsafe { self.0.__iterator_get_unchecked(idx) }
     }
 }
 
 impl DoubleEndedIterator for CaseMappingIter {
     fn next_back(&mut self) -> Option<char> {
-        match *self {
-            CaseMappingIter::Three(a, b, c) => {
-                *self = CaseMappingIter::Two(a, b);
-                Some(c)
-            }
-            CaseMappingIter::Two(b, c) => {
-                *self = CaseMappingIter::One(b);
-                Some(c)
-            }
-            CaseMappingIter::One(c) => {
-                *self = CaseMappingIter::Zero;
-                Some(c)
-            }
-            CaseMappingIter::Zero => None,
-        }
+        self.0.next_back()
     }
-}
 
-impl fmt::Display for CaseMappingIter {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            CaseMappingIter::Three(a, b, c) => {
-                f.write_char(a)?;
-                f.write_char(b)?;
-                f.write_char(c)
-            }
-            CaseMappingIter::Two(b, c) => {
-                f.write_char(b)?;
-                f.write_char(c)
-            }
-            CaseMappingIter::One(c) => f.write_char(c),
-            CaseMappingIter::Zero => Ok(()),
-        }
+    fn rfold<Acc, Fold>(self, init: Acc, rfold: Fold) -> Acc
+    where
+        Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.0.rfold(init, rfold)
+    }
+
+    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+        self.0.advance_back_by(n)
     }
 }
 
-#[stable(feature = "char_struct_display", since = "1.16.0")]
-impl fmt::Display for ToLowercase {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Display::fmt(&self.0, f)
+impl ExactSizeIterator for CaseMappingIter {
+    fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.0.is_empty()
     }
 }
 
-#[stable(feature = "char_struct_display", since = "1.16.0")]
-impl fmt::Display for ToUppercase {
+impl FusedIterator for CaseMappingIter {}
+
+// SAFETY: forwards to inner `array::IntoIter`
+unsafe impl TrustedLen for CaseMappingIter {}
+
+// SAFETY: forwards to inner `array::IntoIter`
+unsafe impl TrustedRandomAccessNoCoerce for CaseMappingIter {
+    const MAY_HAVE_SIDE_EFFECT: bool = false;
+}
+
+// SAFETY: `CaseMappingIter` has no subtypes/supertypes
+unsafe impl TrustedRandomAccess for CaseMappingIter {}
+
+impl fmt::Display for CaseMappingIter {
+    #[inline]
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Display::fmt(&self.0, f)
+        for c in self.0.clone() {
+            f.write_char(c)?;
+        }
+        Ok(())
     }
 }
 
diff --git a/library/core/src/cmp.rs b/library/core/src/cmp.rs
index a2f07814726..cc9ef673da7 100644
--- a/library/core/src/cmp.rs
+++ b/library/core/src/cmp.rs
@@ -848,6 +848,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     #[stable(feature = "ord_max_min", since = "1.21.0")]
     #[inline]
     #[must_use]
+    #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "cmp_ord_max")]
     fn max(self, other: Self) -> Self
     where
         Self: Sized,
@@ -868,6 +869,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     #[stable(feature = "ord_max_min", since = "1.21.0")]
     #[inline]
     #[must_use]
+    #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "cmp_ord_min")]
     fn min(self, other: Self) -> Self
     where
         Self: Sized,
@@ -1154,6 +1156,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "cmp_partialord_cmp")]
     fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;
 
     /// This method tests less than (for `self` and `other`) and is used by the `<` operator.
@@ -1168,6 +1171,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "cmp_partialord_lt")]
     fn lt(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Less))
     }
@@ -1185,6 +1189,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "cmp_partialord_le")]
     fn le(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Less | Equal))
     }
@@ -1201,6 +1206,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "cmp_partialord_gt")]
     fn gt(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Greater))
     }
@@ -1218,6 +1224,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "cmp_partialord_ge")]
     fn ge(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Greater | Equal))
     }
diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index ae6e39d19e1..26e813346be 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -2240,24 +2240,27 @@ extern "rust-intrinsic" {
     /// Returns the result of an unchecked addition, resulting in
     /// undefined behavior when `x + y > T::MAX` or `x + y < T::MIN`.
     ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
+    /// The stable counterpart of this intrinsic is `unchecked_add` on the various
+    /// integer types, such as [`u16::unchecked_add`] and [`i64::unchecked_add`].
+    #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
     #[rustc_nounwind]
     pub fn unchecked_add<T: Copy>(x: T, y: T) -> T;
 
     /// Returns the result of an unchecked subtraction, resulting in
     /// undefined behavior when `x - y > T::MAX` or `x - y < T::MIN`.
     ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
+    /// The stable counterpart of this intrinsic is `unchecked_sub` on the various
+    /// integer types, such as [`u16::unchecked_sub`] and [`i64::unchecked_sub`].
+    #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
     #[rustc_nounwind]
     pub fn unchecked_sub<T: Copy>(x: T, y: T) -> T;
 
     /// Returns the result of an unchecked multiplication, resulting in
     /// undefined behavior when `x * y > T::MAX` or `x * y < T::MIN`.
     ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_int_unchecked_arith", issue = "none")]
+    /// The stable counterpart of this intrinsic is `unchecked_mul` on the various
+    /// integer types, such as [`u16::unchecked_mul`] and [`i64::unchecked_mul`].
+    #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
     #[rustc_nounwind]
     pub fn unchecked_mul<T: Copy>(x: T, y: T) -> T;
 
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index cf13496b367..18dd3440b6e 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -137,7 +137,6 @@
 #![feature(const_heap)]
 #![feature(const_hint_assert_unchecked)]
 #![feature(const_index_range_slice_index)]
-#![feature(const_int_unchecked_arith)]
 #![feature(const_intrinsic_copy)]
 #![feature(const_intrinsic_forget)]
 #![feature(const_ipv4)]
@@ -197,7 +196,6 @@
 #![feature(str_split_inclusive_remainder)]
 #![feature(str_split_remainder)]
 #![feature(strict_provenance)]
-#![feature(unchecked_math)]
 #![feature(unchecked_shifts)]
 #![feature(utf16_extra)]
 #![feature(utf16_extra_const)]
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
index fa37ee4ffb2..2fec8ef2381 100644
--- a/library/core/src/num/int_macros.rs
+++ b/library/core/src/num/int_macros.rs
@@ -492,21 +492,25 @@ macro_rules! int_impl {
         /// Unchecked integer addition. Computes `self + rhs`, assuming overflow
         /// cannot occur.
         ///
+        /// Calling `x.unchecked_add(y)` is semantically equivalent to calling
+        /// `x.`[`checked_add`]`(y).`[`unwrap_unchecked`]`()`.
+        ///
+        /// If you're just trying to avoid the panic in debug mode, then **do not**
+        /// use this.  Instead, you're looking for [`wrapping_add`].
+        ///
         /// # Safety
         ///
         /// This results in undefined behavior when
         #[doc = concat!("`self + rhs > ", stringify!($SelfT), "::MAX` or `self + rhs < ", stringify!($SelfT), "::MIN`,")]
         /// i.e. when [`checked_add`] would return `None`.
         ///
+        /// [`unwrap_unchecked`]: option/enum.Option.html#method.unwrap_unchecked
         #[doc = concat!("[`checked_add`]: ", stringify!($SelfT), "::checked_add")]
-        #[unstable(
-            feature = "unchecked_math",
-            reason = "niche optimization path",
-            issue = "85122",
-        )]
+        #[doc = concat!("[`wrapping_add`]: ", stringify!($SelfT), "::wrapping_add")]
+        #[stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
+        #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
-        #[rustc_const_unstable(feature = "unchecked_math", issue = "85122")]
         #[inline(always)]
         #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
         pub const unsafe fn unchecked_add(self, rhs: Self) -> Self {
@@ -630,21 +634,25 @@ macro_rules! int_impl {
         /// Unchecked integer subtraction. Computes `self - rhs`, assuming overflow
         /// cannot occur.
         ///
+        /// Calling `x.unchecked_sub(y)` is semantically equivalent to calling
+        /// `x.`[`checked_sub`]`(y).`[`unwrap_unchecked`]`()`.
+        ///
+        /// If you're just trying to avoid the panic in debug mode, then **do not**
+        /// use this.  Instead, you're looking for [`wrapping_sub`].
+        ///
         /// # Safety
         ///
         /// This results in undefined behavior when
         #[doc = concat!("`self - rhs > ", stringify!($SelfT), "::MAX` or `self - rhs < ", stringify!($SelfT), "::MIN`,")]
         /// i.e. when [`checked_sub`] would return `None`.
         ///
+        /// [`unwrap_unchecked`]: option/enum.Option.html#method.unwrap_unchecked
         #[doc = concat!("[`checked_sub`]: ", stringify!($SelfT), "::checked_sub")]
-        #[unstable(
-            feature = "unchecked_math",
-            reason = "niche optimization path",
-            issue = "85122",
-        )]
+        #[doc = concat!("[`wrapping_sub`]: ", stringify!($SelfT), "::wrapping_sub")]
+        #[stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
+        #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
-        #[rustc_const_unstable(feature = "unchecked_math", issue = "85122")]
         #[inline(always)]
         #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
         pub const unsafe fn unchecked_sub(self, rhs: Self) -> Self {
@@ -768,21 +776,25 @@ macro_rules! int_impl {
         /// Unchecked integer multiplication. Computes `self * rhs`, assuming overflow
         /// cannot occur.
         ///
+        /// Calling `x.unchecked_mul(y)` is semantically equivalent to calling
+        /// `x.`[`checked_mul`]`(y).`[`unwrap_unchecked`]`()`.
+        ///
+        /// If you're just trying to avoid the panic in debug mode, then **do not**
+        /// use this.  Instead, you're looking for [`wrapping_mul`].
+        ///
         /// # Safety
         ///
         /// This results in undefined behavior when
         #[doc = concat!("`self * rhs > ", stringify!($SelfT), "::MAX` or `self * rhs < ", stringify!($SelfT), "::MIN`,")]
         /// i.e. when [`checked_mul`] would return `None`.
         ///
+        /// [`unwrap_unchecked`]: option/enum.Option.html#method.unwrap_unchecked
         #[doc = concat!("[`checked_mul`]: ", stringify!($SelfT), "::checked_mul")]
-        #[unstable(
-            feature = "unchecked_math",
-            reason = "niche optimization path",
-            issue = "85122",
-        )]
+        #[doc = concat!("[`wrapping_mul`]: ", stringify!($SelfT), "::wrapping_mul")]
+        #[stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
+        #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
-        #[rustc_const_unstable(feature = "unchecked_math", issue = "85122")]
         #[inline(always)]
         #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
         pub const unsafe fn unchecked_mul(self, rhs: Self) -> Self {
diff --git a/library/core/src/num/uint_macros.rs b/library/core/src/num/uint_macros.rs
index 081a3c0b118..f76f110fc4e 100644
--- a/library/core/src/num/uint_macros.rs
+++ b/library/core/src/num/uint_macros.rs
@@ -500,21 +500,25 @@ macro_rules! uint_impl {
         /// Unchecked integer addition. Computes `self + rhs`, assuming overflow
         /// cannot occur.
         ///
+        /// Calling `x.unchecked_add(y)` is semantically equivalent to calling
+        /// `x.`[`checked_add`]`(y).`[`unwrap_unchecked`]`()`.
+        ///
+        /// If you're just trying to avoid the panic in debug mode, then **do not**
+        /// use this.  Instead, you're looking for [`wrapping_add`].
+        ///
         /// # Safety
         ///
         /// This results in undefined behavior when
         #[doc = concat!("`self + rhs > ", stringify!($SelfT), "::MAX` or `self + rhs < ", stringify!($SelfT), "::MIN`,")]
         /// i.e. when [`checked_add`] would return `None`.
         ///
+        /// [`unwrap_unchecked`]: option/enum.Option.html#method.unwrap_unchecked
         #[doc = concat!("[`checked_add`]: ", stringify!($SelfT), "::checked_add")]
-        #[unstable(
-            feature = "unchecked_math",
-            reason = "niche optimization path",
-            issue = "85122",
-        )]
+        #[doc = concat!("[`wrapping_add`]: ", stringify!($SelfT), "::wrapping_add")]
+        #[stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
+        #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
-        #[rustc_const_unstable(feature = "unchecked_math", issue = "85122")]
         #[inline(always)]
         #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
         pub const unsafe fn unchecked_add(self, rhs: Self) -> Self {
@@ -644,21 +648,25 @@ macro_rules! uint_impl {
         /// Unchecked integer subtraction. Computes `self - rhs`, assuming overflow
         /// cannot occur.
         ///
+        /// Calling `x.unchecked_sub(y)` is semantically equivalent to calling
+        /// `x.`[`checked_sub`]`(y).`[`unwrap_unchecked`]`()`.
+        ///
+        /// If you're just trying to avoid the panic in debug mode, then **do not**
+        /// use this.  Instead, you're looking for [`wrapping_sub`].
+        ///
         /// # Safety
         ///
         /// This results in undefined behavior when
         #[doc = concat!("`self - rhs > ", stringify!($SelfT), "::MAX` or `self - rhs < ", stringify!($SelfT), "::MIN`,")]
         /// i.e. when [`checked_sub`] would return `None`.
         ///
+        /// [`unwrap_unchecked`]: option/enum.Option.html#method.unwrap_unchecked
         #[doc = concat!("[`checked_sub`]: ", stringify!($SelfT), "::checked_sub")]
-        #[unstable(
-            feature = "unchecked_math",
-            reason = "niche optimization path",
-            issue = "85122",
-        )]
+        #[doc = concat!("[`wrapping_sub`]: ", stringify!($SelfT), "::wrapping_sub")]
+        #[stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
+        #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
-        #[rustc_const_unstable(feature = "unchecked_math", issue = "85122")]
         #[inline(always)]
         #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
         pub const unsafe fn unchecked_sub(self, rhs: Self) -> Self {
@@ -726,21 +734,25 @@ macro_rules! uint_impl {
         /// Unchecked integer multiplication. Computes `self * rhs`, assuming overflow
         /// cannot occur.
         ///
+        /// Calling `x.unchecked_mul(y)` is semantically equivalent to calling
+        /// `x.`[`checked_mul`]`(y).`[`unwrap_unchecked`]`()`.
+        ///
+        /// If you're just trying to avoid the panic in debug mode, then **do not**
+        /// use this.  Instead, you're looking for [`wrapping_mul`].
+        ///
         /// # Safety
         ///
         /// This results in undefined behavior when
         #[doc = concat!("`self * rhs > ", stringify!($SelfT), "::MAX` or `self * rhs < ", stringify!($SelfT), "::MIN`,")]
         /// i.e. when [`checked_mul`] would return `None`.
         ///
+        /// [`unwrap_unchecked`]: option/enum.Option.html#method.unwrap_unchecked
         #[doc = concat!("[`checked_mul`]: ", stringify!($SelfT), "::checked_mul")]
-        #[unstable(
-            feature = "unchecked_math",
-            reason = "niche optimization path",
-            issue = "85122",
-        )]
+        #[doc = concat!("[`wrapping_mul`]: ", stringify!($SelfT), "::wrapping_mul")]
+        #[stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
+        #[rustc_const_stable(feature = "unchecked_math", since = "CURRENT_RUSTC_VERSION")]
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
-        #[rustc_const_unstable(feature = "unchecked_math", issue = "85122")]
         #[inline(always)]
         #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
         pub const unsafe fn unchecked_mul(self, rhs: Self) -> Self {
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index a6c00ff28d4..68ce80ee321 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -1029,8 +1029,6 @@ impl<T: ?Sized> *const 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
@@ -1857,6 +1855,7 @@ impl<T: ?Sized> Ord for *const T {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> PartialOrd for *const T {
     #[inline]
+    #[allow(ambiguous_wide_pointer_comparisons)]
     fn partial_cmp(&self, other: &*const T) -> Option<Ordering> {
         Some(self.cmp(other))
     }
diff --git a/library/core/src/ptr/metadata.rs b/library/core/src/ptr/metadata.rs
index fe19f66a31a..7f9d8e677d2 100644
--- a/library/core/src/ptr/metadata.rs
+++ b/library/core/src/ptr/metadata.rs
@@ -258,6 +258,7 @@ impl<Dyn: ?Sized> PartialEq for DynMetadata<Dyn> {
 
 impl<Dyn: ?Sized> Ord for DynMetadata<Dyn> {
     #[inline]
+    #[allow(ambiguous_wide_pointer_comparisons)]
     fn cmp(&self, other: &Self) -> crate::cmp::Ordering {
         (self.vtable_ptr as *const VTable).cmp(&(other.vtable_ptr as *const VTable))
     }
diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
index 1add9ca2311..3dde83541d4 100644
--- a/library/core/src/ptr/mut_ptr.rs
+++ b/library/core/src/ptr/mut_ptr.rs
@@ -1119,8 +1119,6 @@ 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
@@ -2275,6 +2273,7 @@ impl<T: ?Sized> Ord for *mut T {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: ?Sized> PartialOrd for *mut T {
     #[inline(always)]
+    #[allow(ambiguous_wide_pointer_comparisons)]
     fn partial_cmp(&self, other: &*mut T) -> Option<Ordering> {
         Some(self.cmp(other))
     }
diff --git a/library/core/src/ptr/non_null.rs b/library/core/src/ptr/non_null.rs
index e9488917acc..c0a36bb405e 100644
--- a/library/core/src/ptr/non_null.rs
+++ b/library/core/src/ptr/non_null.rs
@@ -702,8 +702,6 @@ impl<T: ?Sized> NonNull<T> {
     #[unstable(feature = "non_null_convenience", issue = "117691")]
     #[rustc_const_unstable(feature = "non_null_convenience", issue = "117691")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
-    // 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
@@ -1821,6 +1819,7 @@ impl<T: ?Sized> PartialEq for NonNull<T> {
 #[stable(feature = "nonnull", since = "1.25.0")]
 impl<T: ?Sized> Ord for NonNull<T> {
     #[inline]
+    #[allow(ambiguous_wide_pointer_comparisons)]
     fn cmp(&self, other: &Self) -> Ordering {
         self.as_ptr().cmp(&other.as_ptr())
     }
@@ -1829,6 +1828,7 @@ impl<T: ?Sized> Ord for NonNull<T> {
 #[stable(feature = "nonnull", since = "1.25.0")]
 impl<T: ?Sized> PartialOrd for NonNull<T> {
     #[inline]
+    #[allow(ambiguous_wide_pointer_comparisons)]
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         self.as_ptr().partial_cmp(&other.as_ptr())
     }