clean up const stability around UB checks

Author: RalfJung

library/core/src/intrinsics/mod.rs

@@ -4013,9 +4013,9 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
             count: usize = count,
         ) => {
             let zero_size = count == 0 || size == 0;
-            ub_checks::is_aligned_and_not_null(src, align, zero_size)
-                && ub_checks::is_aligned_and_not_null(dst, align, zero_size)
-                && ub_checks::is_nonoverlapping(src, dst, size, count)
+            ub_checks::maybe_is_aligned_and_not_null(src, align, zero_size)
+                && ub_checks::maybe_is_aligned_and_not_null(dst, align, zero_size)
+                && ub_checks::maybe_is_nonoverlapping(src, dst, size, count)
         }
     );
 
@@ -4119,8 +4119,8 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
                 align: usize = align_of::<T>(),
                 zero_size: bool = T::IS_ZST || count == 0,
             ) =>
-            ub_checks::is_aligned_and_not_null(src, align, zero_size)
-                && ub_checks::is_aligned_and_not_null(dst, align, zero_size)
+            ub_checks::maybe_is_aligned_and_not_null(src, align, zero_size)
+                && ub_checks::maybe_is_aligned_and_not_null(dst, align, zero_size)
         );
         copy(src, dst, count)
     }
@@ -4201,7 +4201,7 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
                 addr: *const () = dst as *const (),
                 align: usize = align_of::<T>(),
                 zero_size: bool = T::IS_ZST || count == 0,
-            ) => ub_checks::is_aligned_and_not_null(addr, align, zero_size)
+            ) => ub_checks::maybe_is_aligned_and_not_null(addr, align, zero_size)
         );
         write_bytes(dst, val, count)
     }

library/core/src/lib.rs

@@ -109,6 +109,7 @@
 // tidy-alphabetical-start
 #![cfg_attr(bootstrap, feature(const_exact_div))]
 #![cfg_attr(bootstrap, feature(const_fmt_arguments_new))]
+#![cfg_attr(bootstrap, feature(const_ub_checks))]
 #![feature(array_ptr_get)]
 #![feature(asm_experimental_arch)]
 #![feature(const_align_of_val)]
@@ -131,7 +132,6 @@
 #![feature(const_type_id)]
 #![feature(const_type_name)]
 #![feature(const_typed_swap)]
-#![feature(const_ub_checks)]
 #![feature(core_intrinsics)]
 #![feature(coverage_attribute)]
 #![feature(do_not_recommend)]

library/core/src/ptr/mod.rs

@@ -1103,9 +1103,9 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
             count: usize = count,
         ) => {
             let zero_size = size == 0 || count == 0;
-            ub_checks::is_aligned_and_not_null(x, align, zero_size)
-                && ub_checks::is_aligned_and_not_null(y, align, zero_size)
-                && ub_checks::is_nonoverlapping(x, y, size, count)
+            ub_checks::maybe_is_aligned_and_not_null(x, align, zero_size)
+                && ub_checks::maybe_is_aligned_and_not_null(y, align, zero_size)
+                && ub_checks::maybe_is_nonoverlapping(x, y, size, count)
         }
     );
 
@@ -1216,7 +1216,7 @@ pub const unsafe fn replace<T>(dst: *mut T, src: T) -> T {
                 addr: *const () = dst as *const (),
                 align: usize = align_of::<T>(),
                 is_zst: bool = T::IS_ZST,
-            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
+            ) => ub_checks::maybe_is_aligned_and_not_null(addr, align, is_zst)
         );
         mem::replace(&mut *dst, src)
     }
@@ -1369,7 +1369,7 @@ pub const unsafe fn read<T>(src: *const T) -> T {
                 addr: *const () = src as *const (),
                 align: usize = align_of::<T>(),
                 is_zst: bool = T::IS_ZST,
-            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
+            ) => ub_checks::maybe_is_aligned_and_not_null(addr, align, is_zst)
         );
         crate::intrinsics::read_via_copy(src)
     }
@@ -1573,7 +1573,7 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
                 addr: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
                 is_zst: bool = T::IS_ZST,
-            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
+            ) => ub_checks::maybe_is_aligned_and_not_null(addr, align, is_zst)
         );
         intrinsics::write_via_move(dst, src)
     }
@@ -1745,7 +1745,7 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
                 addr: *const () = src as *const (),
                 align: usize = align_of::<T>(),
                 is_zst: bool = T::IS_ZST,
-            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
+            ) => ub_checks::maybe_is_aligned_and_not_null(addr, align, is_zst)
         );
         intrinsics::volatile_load(src)
     }
@@ -1825,7 +1825,7 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
                 addr: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
                 is_zst: bool = T::IS_ZST,
-            ) => ub_checks::is_aligned_and_not_null(addr, align, is_zst)
+            ) => ub_checks::maybe_is_aligned_and_not_null(addr, align, is_zst)
         );
         intrinsics::volatile_store(dst, src);
     }

library/core/src/slice/raw.rs

@@ -132,7 +132,7 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
                 align: usize = align_of::<T>(),
                 len: usize = len,
             ) =>
-            ub_checks::is_aligned_and_not_null(data, align, false)
+            ub_checks::maybe_is_aligned_and_not_null(data, align, false)
                 && ub_checks::is_valid_allocation_size(size, len)
         );
         &*ptr::slice_from_raw_parts(data, len)
@@ -186,7 +186,7 @@ pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a m
                 align: usize = align_of::<T>(),
                 len: usize = len,
             ) =>
-            ub_checks::is_aligned_and_not_null(data, align, false)
+            ub_checks::maybe_is_aligned_and_not_null(data, align, false)
                 && ub_checks::is_valid_allocation_size(size, len)
         );
         &mut *ptr::slice_from_raw_parts_mut(data, len)

library/core/src/ub_checks.rs

@@ -64,8 +64,6 @@ macro_rules! assert_unsafe_precondition {
             #[rustc_no_mir_inline]
             #[inline]
             #[rustc_nounwind]
-            #[cfg_attr(bootstrap, rustc_const_unstable(feature = "const_ub_checks", issue = "none"))]
-            #[rustc_allow_const_fn_unstable(const_ub_checks)] // only for UB checks
             const fn precondition_check($($name:$ty),*) {
                 if !$e {
                     ::core::panicking::panic_nounwind(
@@ -116,12 +114,16 @@ pub(crate) const fn check_language_ub() -> bool {
 /// for `assert_unsafe_precondition!` with `check_language_ub`, in which case the
 /// check is anyway not executed in `const`.
 #[inline]
-#[rustc_const_unstable(feature = "const_ub_checks", issue = "none")]
-pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize, is_zst: bool) -> bool {
+#[rustc_allow_const_fn_unstable(const_eval_select)]
+pub(crate) const fn maybe_is_aligned_and_not_null(
+    ptr: *const (),
+    align: usize,
+    is_zst: bool,
+) -> bool {
     // This is just for safety checks so we can const_eval_select.
     const_eval_select!(
         @capture { ptr: *const (), align: usize, is_zst: bool } -> bool:
-        if const #[rustc_const_unstable(feature = "const_ub_checks", issue = "none")] {
+        if const {
             is_zst || !ptr.is_null()
         } else {
             ptr.is_aligned_to(align) && (is_zst || !ptr.is_null())
@@ -141,8 +143,8 @@ pub(crate) const fn is_valid_allocation_size(size: usize, len: usize) -> bool {
 /// Note that in const-eval this function just returns `true` and therefore must
 /// only be used with `assert_unsafe_precondition!`, similar to `is_aligned_and_not_null`.
 #[inline]
-#[rustc_const_unstable(feature = "const_ub_checks", issue = "none")]
-pub(crate) const fn is_nonoverlapping(
+#[rustc_allow_const_fn_unstable(const_eval_select)]
+pub(crate) const fn maybe_is_nonoverlapping(
     src: *const (),
     dst: *const (),
     size: usize,