refactor check_{lang,library}_ub: use a single intrinsic

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -2000,7 +2000,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     ConstraintCategory::SizedBound,
                 );
             }
-            &Rvalue::NullaryOp(NullOp::UbCheck(_), _) => {}
+            &Rvalue::NullaryOp(NullOp::UbChecks, _) => {}
 
             Rvalue::ShallowInitBox(operand, ty) => {
                 self.check_operand(operand, location);

compiler/rustc_codegen_cranelift/src/base.rs

@@ -780,7 +780,7 @@ fn codegen_stmt<'tcx>(
                         NullOp::OffsetOf(fields) => {
                             layout.offset_of_subfield(fx, fields.iter()).bytes()
                         }
-                        NullOp::UbCheck(_) => {
+                        NullOp::UbChecks => {
                             let val = fx.tcx.sess.opts.debug_assertions;
                             let val = CValue::by_val(
                                 fx.bcx.ins().iconst(types::I8, i64::try_from(val).unwrap()),

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -680,8 +680,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         let val = layout.offset_of_subfield(bx.cx(), fields.iter()).bytes();
                         bx.cx().const_usize(val)
                     }
-                    mir::NullOp::UbCheck(_) => {
-                        // In codegen, we want to check for language UB and library UB
+                    mir::NullOp::UbChecks => {
                         let val = bx.tcx().sess.opts.debug_assertions;
                         bx.cx().const_bool(val)
                     }

compiler/rustc_const_eval/src/interpret/step.rs

@@ -258,17 +258,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         let val = layout.offset_of_subfield(self, fields.iter()).bytes();
                         Scalar::from_target_usize(val, self)
                     }
-                    mir::NullOp::UbCheck(kind) => {
-                        // We want to enable checks for library UB, because the interpreter doesn't
-                        // know about those on its own.
-                        // But we want to disable checks for language UB, because the interpreter
-                        // has its own better checks for that.
-                        let should_check = match kind {
-                            mir::UbKind::LibraryUb => self.tcx.sess.opts.debug_assertions,
-                            mir::UbKind::LanguageUb => false,
-                        };
-                        Scalar::from_bool(should_check)
-                    }
+                    mir::NullOp::UbChecks => Scalar::from_bool(self.tcx.sess.opts.debug_assertions),
                 };
                 self.write_scalar(val, &dest)?;
             }

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -558,7 +558,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
             Rvalue::Cast(_, _, _) => {}
 
             Rvalue::NullaryOp(
-                NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbCheck(_),
+                NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbChecks,
                 _,
             ) => {}
             Rvalue::ShallowInitBox(_, _) => {}

compiler/rustc_const_eval/src/transform/validate.rs

@@ -1168,7 +1168,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
             Rvalue::Repeat(_, _)
             | Rvalue::ThreadLocalRef(_)
             | Rvalue::AddressOf(_, _)
-            | Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::UbCheck(_), _)
+            | Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::UbChecks, _)
             | Rvalue::Discriminant(_) => {}
         }
         self.super_rvalue(rvalue, location);

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -127,8 +127,7 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -
         | sym::variant_count
         | sym::is_val_statically_known
         | sym::ptr_mask
-        | sym::check_language_ub
-        | sym::check_library_ub
+        | sym::ub_checks
         | sym::fadd_algebraic
         | sym::fsub_algebraic
         | sym::fmul_algebraic
@@ -571,7 +570,7 @@ pub fn check_intrinsic_type(
                 (0, 0, vec![Ty::new_imm_ptr(tcx, Ty::new_unit(tcx))], tcx.types.usize)
             }
 
-            sym::check_language_ub | sym::check_library_ub => (0, 1, Vec::new(), tcx.types.bool),
+            sym::ub_checks => (0, 1, Vec::new(), tcx.types.bool),
 
             sym::simd_eq
             | sym::simd_ne

compiler/rustc_middle/src/mir/mod.rs

@@ -796,7 +796,7 @@ impl<'tcx> Body<'tcx> {
         }
 
         match rvalue {
-            Rvalue::NullaryOp(NullOp::UbCheck(_), _) => {
+            Rvalue::NullaryOp(NullOp::UbChecks, _) => {
                 Some((tcx.sess.opts.debug_assertions as u128, targets))
             }
             Rvalue::Use(Operand::Constant(constant)) => {

compiler/rustc_middle/src/mir/pretty.rs

@@ -944,7 +944,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                     NullOp::SizeOf => write!(fmt, "SizeOf({t})"),
                     NullOp::AlignOf => write!(fmt, "AlignOf({t})"),
                     NullOp::OffsetOf(fields) => write!(fmt, "OffsetOf({t}, {fields:?})"),
-                    NullOp::UbCheck(kind) => write!(fmt, "UbCheck({kind:?})"),
+                    NullOp::UbChecks => write!(fmt, "UbChecks()"),
                 }
             }
             ThreadLocalRef(did) => ty::tls::with(|tcx| {

compiler/rustc_middle/src/mir/syntax.rs

@@ -1367,16 +1367,9 @@ pub enum NullOp<'tcx> {
     AlignOf,
     /// Returns the offset of a field
     OffsetOf(&'tcx List<(VariantIdx, FieldIdx)>),
-    /// Returns whether we want to check for library UB or language UB at monomorphization time.
-    /// Both kinds of UB evaluate to `true` in codegen, and only library UB evalutes to `true` in
-    /// const-eval/Miri, because the interpreter has its own better checks for language UB.
-    UbCheck(UbKind),
-}
-
-#[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
-pub enum UbKind {
-    LanguageUb,
-    LibraryUb,
+    /// Returns whether we want to check for UB.
+    /// This returns the value of `cfg!(debug_assertions)` at monomorphization time.
+    UbChecks,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]

compiler/rustc_middle/src/mir/tcx.rs

@@ -194,7 +194,7 @@ impl<'tcx> Rvalue<'tcx> {
             Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..), _) => {
                 tcx.types.usize
             }
-            Rvalue::NullaryOp(NullOp::UbCheck(_), _) => tcx.types.bool,
+            Rvalue::NullaryOp(NullOp::UbChecks, _) => tcx.types.bool,
             Rvalue::Aggregate(ref ak, ref ops) => match **ak {
                 AggregateKind::Array(ty) => Ty::new_array(tcx, ty, ops.len() as u64),
                 AggregateKind::Tuple => {

compiler/rustc_mir_dataflow/src/move_paths/builder.rs

@@ -433,7 +433,7 @@ impl<'b, 'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> Gatherer<'b, 'a, 'tcx, F> {
             | Rvalue::Discriminant(..)
             | Rvalue::Len(..)
             | Rvalue::NullaryOp(
-                NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..) | NullOp::UbCheck(_),
+                NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..) | NullOp::UbChecks,
                 _,
             ) => {}
         }

compiler/rustc_mir_transform/src/gvn.rs

@@ -487,7 +487,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                     NullOp::OffsetOf(fields) => {
                         layout.offset_of_subfield(&self.ecx, fields.iter()).bytes()
                     }
-                    NullOp::UbCheck(_) => return None,
+                    NullOp::UbChecks => return None,
                 };
                 let usize_layout = self.ecx.layout_of(self.tcx.types.usize).unwrap();
                 let imm = ImmTy::try_from_uint(val, usize_layout)?;

compiler/rustc_mir_transform/src/known_panics_lint.rs

@@ -639,7 +639,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                     NullOp::OffsetOf(fields) => {
                         op_layout.offset_of_subfield(self, fields.iter()).bytes()
                     }
-                    NullOp::UbCheck(_) => return None,
+                    NullOp::UbChecks => return None,
                 };
                 ImmTy::from_scalar(Scalar::from_target_usize(val, self), layout).into()
             }

compiler/rustc_mir_transform/src/lower_intrinsics.rs

@@ -20,30 +20,13 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                     sym::unreachable => {
                         terminator.kind = TerminatorKind::Unreachable;
                     }
-                    sym::check_language_ub => {
+                    sym::ub_checks => {
                         let target = target.unwrap();
                         block.statements.push(Statement {
                             source_info: terminator.source_info,
                             kind: StatementKind::Assign(Box::new((
                                 *destination,
-                                Rvalue::NullaryOp(
-                                    NullOp::UbCheck(UbKind::LanguageUb),
-                                    tcx.types.bool,
-                                ),
-                            ))),
-                        });
-                        terminator.kind = TerminatorKind::Goto { target };
-                    }
-                    sym::check_library_ub => {
-                        let target = target.unwrap();
-                        block.statements.push(Statement {
-                            source_info: terminator.source_info,
-                            kind: StatementKind::Assign(Box::new((
-                                *destination,
-                                Rvalue::NullaryOp(
-                                    NullOp::UbCheck(UbKind::LibraryUb),
-                                    tcx.types.bool,
-                                ),
+                                Rvalue::NullaryOp(NullOp::UbChecks, tcx.types.bool),
                             ))),
                         });
                         terminator.kind = TerminatorKind::Goto { target };

compiler/rustc_mir_transform/src/promote_consts.rs

@@ -446,7 +446,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                 NullOp::SizeOf => {}
                 NullOp::AlignOf => {}
                 NullOp::OffsetOf(_) => {}
-                NullOp::UbCheck(_) => {}
+                NullOp::UbChecks => {}
             },
 
             Rvalue::ShallowInitBox(_, _) => return Err(Unpromotable),

compiler/rustc_smir/src/rustc_smir/convert/mir.rs

@@ -251,19 +251,13 @@ impl<'tcx> Stable<'tcx> for mir::NullOp<'tcx> {
     type T = stable_mir::mir::NullOp;
     fn stable(&self, tables: &mut Tables<'_>) -> Self::T {
         use rustc_middle::mir::NullOp::*;
-        use rustc_middle::mir::UbKind;
         match self {
             SizeOf => stable_mir::mir::NullOp::SizeOf,
             AlignOf => stable_mir::mir::NullOp::AlignOf,
             OffsetOf(indices) => stable_mir::mir::NullOp::OffsetOf(
                 indices.iter().map(|idx| idx.stable(tables)).collect(),
             ),
-            UbCheck(UbKind::LanguageUb) => {
-                stable_mir::mir::NullOp::UbCheck(stable_mir::mir::UbKind::LanguageUb)
-            }
-            UbCheck(UbKind::LibraryUb) => {
-                stable_mir::mir::NullOp::UbCheck(stable_mir::mir::UbKind::LibraryUb)
-            }
+            UbChecks => stable_mir::mir::NullOp::UbChecks,
         }
     }
 }

compiler/rustc_span/src/symbol.rs

@@ -518,8 +518,6 @@ symbols! {
         cfi,
         cfi_encoding,
         char,
-        check_language_ub,
-        check_library_ub,
         client,
         clippy,
         clobber_abi,
@@ -1867,6 +1865,7 @@ symbols! {
         u8_legacy_fn_max_value,
         u8_legacy_fn_min_value,
         u8_legacy_mod,
+        ub_checks,
         unaligned_volatile_load,
         unaligned_volatile_store,
         unboxed_closures,

compiler/stable_mir/src/mir/body.rs

@@ -621,7 +621,7 @@ impl Rvalue {
             Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(..), _) => {
                 Ok(Ty::usize_ty())
             }
-            Rvalue::NullaryOp(NullOp::UbCheck(_), _) => Ok(Ty::bool_ty()),
+            Rvalue::NullaryOp(NullOp::UbChecks, _) => Ok(Ty::bool_ty()),
             Rvalue::Aggregate(ak, ops) => match *ak {
                 AggregateKind::Array(ty) => Ty::try_new_array(ty, ops.len() as u64),
                 AggregateKind::Tuple => Ok(Ty::new_tuple(
@@ -989,13 +989,7 @@ pub enum NullOp {
     /// Returns the offset of a field.
     OffsetOf(Vec<(VariantIdx, FieldIdx)>),
     /// cfg!(debug_assertions), but at codegen time
-    UbCheck(UbKind),
-}
-
-#[derive(Clone, Debug, Eq, PartialEq)]
-pub enum UbKind {
-    LanguageUb,
-    LibraryUb,
+    UbChecks,
 }
 
 impl Operand {

library/core/src/char/convert.rs

@@ -4,9 +4,9 @@ use crate::char::TryFromCharError;
 use crate::convert::TryFrom;
 use crate::error::Error;
 use crate::fmt;
-use crate::intrinsics::assert_unsafe_precondition;
 use crate::mem::transmute;
 use crate::str::FromStr;
+use crate::ub_checks::assert_unsafe_precondition;
 
 /// Converts a `u32` to a `char`. See [`char::from_u32`].
 #[must_use]

library/core/src/hint.rs

@@ -4,6 +4,7 @@
 //! Hints may be compile time or runtime.
 
 use crate::intrinsics;
+use crate::ub_checks;
 
 /// Informs the compiler that the site which is calling this function is not
 /// reachable, possibly enabling further optimizations.
@@ -98,7 +99,7 @@ use crate::intrinsics;
 #[rustc_const_stable(feature = "const_unreachable_unchecked", since = "1.57.0")]
 #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
 pub const unsafe fn unreachable_unchecked() -> ! {
-    intrinsics::assert_unsafe_precondition!(
+    ub_checks::assert_unsafe_precondition!(
         check_language_ub,
         "hint::unreachable_unchecked must never be reached",
         () => false
@@ -148,7 +149,7 @@ pub const unsafe fn unreachable_unchecked() -> ! {
 pub const unsafe fn assert_unchecked(cond: bool) {
     // SAFETY: The caller promised `cond` is true.
     unsafe {
-        intrinsics::assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "hint::assert_unchecked must never be called when the condition is false",
             (cond: bool = cond) => cond,

library/core/src/intrinsics.rs

@@ -67,6 +67,7 @@ use crate::marker::DiscriminantKind;
 use crate::marker::Tuple;
 use crate::mem::align_of;
 use crate::ptr;
+use crate::ub_checks;
 
 pub mod mir;
 pub mod simd;
@@ -2660,38 +2661,22 @@ pub const unsafe fn typed_swap<T>(x: *mut T, y: *mut T) {
     unsafe { ptr::swap_nonoverlapping(x, y, 1) };
 }
 
-/// Returns whether we should check for library UB. This evaluate to the value of `cfg!(debug_assertions)`
-/// during monomorphization.
-///
-/// This intrinsic is evaluated after monomorphization, and therefore branching on this value can
-/// be used to implement debug assertions that are included in the precompiled standard library,
-/// but can be optimized out by builds that monomorphize the standard library code with debug
-/// assertions disabled. This intrinsic is primarily used by [`assert_unsafe_precondition`].
-///
-/// We have separate intrinsics for library UB and language UB because checkers like the const-eval
-/// interpreter and Miri already implement checks for language UB. Since such checkers do not know
-/// about library preconditions, checks guarded by this intrinsic let them find more UB.
-#[rustc_const_unstable(feature = "ub_checks", issue = "none")]
-#[unstable(feature = "core_intrinsics", issue = "none")]
-#[inline(always)]
-#[rustc_intrinsic]
-pub(crate) const fn check_library_ub() -> bool {
-    cfg!(debug_assertions)
-}
-
-/// Returns whether we should check for language UB. This evaluate to the value of `cfg!(debug_assertions)`
-/// during monomorphization.
-///
-/// Since checks implemented at the source level must come strictly before the operation that
-/// executes UB, if we enabled language UB checks in const-eval/Miri we would miss out on the
-/// interpreter's improved diagnostics for the cases that our source-level checks catch.
-///
-/// See `check_library_ub` for more information.
-#[rustc_const_unstable(feature = "ub_checks", issue = "none")]
+/// Returns whether we should perform some UB-checking at runtime. This evaluate to the value of
+/// `cfg!(debug_assertions)` during monomorphization.
+///
+/// This intrinsic is evaluated after monomorphization, which is relevant when mixing crates
+/// compiled with and without debug_assertions. The common case here is a user program built with
+/// debug_assertions linked against the distributed sysroot which is built without debug_assertions.
+/// For code that gets monomorphized in the user crate (i.e., generic functions and functions with
+/// `#[inline]`), gating assertions on `ub_checks()` rather than `cfg!(debug_assertions)` means that
+/// assertions are enabled whenever the *user crate* has debug assertions enabled. However if the
+/// user has debug assertions disabled, the checks will still get optimized out. This intrinsic is
+/// primarily used by [`ub_checks::assert_unsafe_precondition`].
+#[rustc_const_unstable(feature = "const_ub_checks", issue = "none")]
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[inline(always)]
-#[rustc_intrinsic]
-pub(crate) const fn check_language_ub() -> bool {
+#[cfg_attr(not(bootstrap), rustc_intrinsic)] // just make it a regular fn in bootstrap
+pub(crate) const fn ub_checks() -> bool {
     cfg!(debug_assertions)
 }
 
@@ -2755,132 +2740,6 @@ pub unsafe fn vtable_align(_ptr: *const ()) -> usize {
 // (`transmute` also falls into this category, but it cannot be wrapped due to the
 // check that `T` and `U` have the same size.)
 
-/// Check that the preconditions of an unsafe function are followed. The check is enabled at
-/// runtime if debug assertions are enabled when the caller is monomorphized. In const-eval/Miri
-/// checks implemented with this macro for language UB are always ignored.
-///
-/// This macro should be called as
-/// `assert_unsafe_precondition!(check_{library,lang}_ub, "message", (ident: type = expr, ident: type = expr) => check_expr)`
-/// where each `expr` will be evaluated and passed in as function argument `ident: type`. Then all
-/// those arguments are passed to a function with the body `check_expr`.
-/// Pick `check_language_ub` when this is guarding a violation of language UB, i.e., immediate UB
-/// according to the Rust Abstract Machine. Pick `check_library_ub` when this is guarding a violation
-/// of a documented library precondition that does not *immediately* lead to language UB.
-///
-/// If `check_library_ub` is used but the check is actually guarding language UB, the check will
-/// slow down const-eval/Miri and we'll get the panic message instead of the interpreter's nice
-/// diagnostic, but our ability to detect UB is unchanged.
-/// But if `check_language_ub` is used when the check is actually for library UB, the check is
-/// omitted in const-eval/Miri and thus if we eventually execute language UB which relies on the
-/// library UB, the backtrace Miri reports may be far removed from original cause.
-///
-/// These checks are behind a condition which is evaluated at codegen time, not expansion time like
-/// [`debug_assert`]. This means that a standard library built with optimizations and debug
-/// assertions disabled will have these checks optimized out of its monomorphizations, but if a
-/// caller of the standard library has debug assertions enabled and monomorphizes an expansion of
-/// this macro, that monomorphization will contain the check.
-///
-/// Since these checks cannot be optimized out in MIR, some care must be taken in both call and
-/// implementation to mitigate their compile-time overhead. Calls to this macro always expand to
-/// this structure:
-/// ```ignore (pseudocode)
-/// if ::core::intrinsics::check_language_ub() {
-///     precondition_check(args)
-/// }
-/// ```
-/// where `precondition_check` is monomorphic with the attributes `#[rustc_nounwind]`, `#[inline]` and
-/// `#[rustc_no_mir_inline]`. This combination of attributes ensures that the actual check logic is
-/// compiled only once and generates a minimal amount of IR because the check cannot be inlined in
-/// MIR, but *can* be inlined and fully optimized by a codegen backend.
-///
-/// Callers should avoid introducing any other `let` bindings or any code outside this macro in
-/// order to call it. Since the precompiled standard library is built with full debuginfo and these
-/// variables cannot be optimized out in MIR, an innocent-looking `let` can produce enough
-/// debuginfo to have a measurable compile-time impact on debug builds.
-#[allow_internal_unstable(ub_checks)] // permit this to be called in stably-const fn
-macro_rules! assert_unsafe_precondition {
-    ($kind:ident, $message:expr, ($($name:ident:$ty:ty = $arg:expr),*$(,)?) => $e:expr $(,)?) => {
-        {
-            // This check is inlineable, but not by the MIR inliner.
-            // The reason for this is that the MIR inliner is in an exceptionally bad position
-            // to think about whether or not to inline this. In MIR, this call is gated behind `debug_assertions`,
-            // which will codegen to `false` in release builds. Inlining the check would be wasted work in that case and
-            // would be bad for compile times.
-            //
-            // LLVM on the other hand sees the constant branch, so if it's `false`, it can immediately delete it without
-            // inlining the check. If it's `true`, it can inline it and get significantly better performance.
-            #[rustc_no_mir_inline]
-            #[inline]
-            #[rustc_nounwind]
-            #[rustc_const_unstable(feature = "ub_checks", issue = "none")]
-            const fn precondition_check($($name:$ty),*) {
-                if !$e {
-                    ::core::panicking::panic_nounwind(
-                        concat!("unsafe precondition(s) violated: ", $message)
-                    );
-                }
-            }
-
-            if ::core::intrinsics::$kind() {
-                precondition_check($($arg,)*);
-            }
-        }
-    };
-}
-pub(crate) use assert_unsafe_precondition;
-
-/// Checks whether `ptr` is properly aligned with respect to
-/// `align_of::<T>()`.
-///
-/// In `const` this is approximate and can fail spuriously. It is primarily intended
-/// for `assert_unsafe_precondition!` with `check_language_ub`, in which case the
-/// check is anyway not executed in `const`.
-#[inline]
-pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize) -> bool {
-    !ptr.is_null() && ptr.is_aligned_to(align)
-}
-
-#[inline]
-pub(crate) const fn is_valid_allocation_size(size: usize, len: usize) -> bool {
-    let max_len = if size == 0 { usize::MAX } else { isize::MAX as usize / size };
-    len <= max_len
-}
-
-/// Checks whether the regions of memory starting at `src` and `dst` of size
-/// `count * size` do *not* overlap.
-///
-/// 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]
-pub(crate) const fn is_nonoverlapping(
-    src: *const (),
-    dst: *const (),
-    size: usize,
-    count: usize,
-) -> bool {
-    #[inline]
-    fn runtime(src: *const (), dst: *const (), size: usize, count: usize) -> bool {
-        let src_usize = src.addr();
-        let dst_usize = dst.addr();
-        let Some(size) = size.checked_mul(count) else {
-            crate::panicking::panic_nounwind(
-                "is_nonoverlapping: `size_of::<T>() * count` overflows a usize",
-            )
-        };
-        let diff = src_usize.abs_diff(dst_usize);
-        // If the absolute distance between the ptrs is at least as big as the size of the buffer,
-        // they do not overlap.
-        diff >= size
-    }
-
-    #[inline]
-    const fn comptime(_: *const (), _: *const (), _: usize, _: usize) -> bool {
-        true
-    }
-
-    const_eval_select((src, dst, size, count), comptime, runtime)
-}
-
 /// Copies `count * size_of::<T>()` bytes from `src` to `dst`. The source
 /// and destination must *not* overlap.
 ///
@@ -2979,7 +2838,7 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
         pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
     }
 
-    assert_unsafe_precondition!(
+    ub_checks::assert_unsafe_precondition!(
         check_language_ub,
         "ptr::copy_nonoverlapping requires that both pointer arguments are aligned and non-null \
         and the specified memory ranges do not overlap",
@@ -2990,9 +2849,9 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
             align: usize = align_of::<T>(),
             count: usize = count,
         ) =>
-        is_aligned_and_not_null(src, align)
-            && is_aligned_and_not_null(dst, align)
-            && is_nonoverlapping(src, dst, size, count)
+        ub_checks::is_aligned_and_not_null(src, align)
+            && ub_checks::is_aligned_and_not_null(dst, align)
+            && ub_checks::is_nonoverlapping(src, dst, size, count)
     );
 
     // SAFETY: the safety contract for `copy_nonoverlapping` must be
@@ -3083,7 +2942,7 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
 
     // SAFETY: the safety contract for `copy` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::copy_nonoverlapping requires that both pointer arguments are aligned and non-null \
             and the specified memory ranges do not overlap",
@@ -3092,8 +2951,8 @@ pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
                 dst: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
             ) =>
-            is_aligned_and_not_null(src, align)
-                && is_aligned_and_not_null(dst, align)
+            ub_checks::is_aligned_and_not_null(src, align)
+                && ub_checks::is_aligned_and_not_null(dst, align)
         );
         copy(src, dst, count)
     }
@@ -3164,13 +3023,13 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
 
     // SAFETY: the safety contract for `write_bytes` must be upheld by the caller.
     unsafe {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::write_bytes requires that the destination pointer is aligned and non-null",
             (
                 addr: *const () = dst as *const (),
                 align: usize = align_of::<T>(),
-            ) => is_aligned_and_not_null(addr, align)
+            ) => ub_checks::is_aligned_and_not_null(addr, align)
         );
         write_bytes(dst, val, count)
     }

library/core/src/lib.rs

@@ -171,6 +171,7 @@
 #![feature(const_type_id)]
 #![feature(const_type_name)]
 #![feature(const_typed_swap)]
+#![feature(const_ub_checks)]
 #![feature(const_unicode_case_lookup)]
 #![feature(const_unsafecell_get_mut)]
 #![feature(const_waker)]
@@ -367,6 +368,7 @@ pub mod hint;
 pub mod intrinsics;
 pub mod mem;
 pub mod ptr;
+mod ub_checks;
 
 /* Core language traits */
 

library/core/src/num/nonzero.rs

@@ -9,6 +9,7 @@ use crate::ops::{BitOr, BitOrAssign, Div, DivAssign, Neg, Rem, RemAssign};
 use crate::panic::{RefUnwindSafe, UnwindSafe};
 use crate::ptr;
 use crate::str::FromStr;
+use crate::ub_checks;
 
 use super::from_str_radix;
 use super::{IntErrorKind, ParseIntError};
@@ -369,7 +370,7 @@ where
             None => {
                 // SAFETY: The caller guarantees that `n` is non-zero, so this is unreachable.
                 unsafe {
-                    intrinsics::assert_unsafe_precondition!(
+                    ub_checks::assert_unsafe_precondition!(
                         check_language_ub,
                         "NonZero::new_unchecked requires the argument to be non-zero",
                         () => false,
@@ -409,7 +410,7 @@ where
             None => {
                 // SAFETY: The caller guarantees that `n` references a value that is non-zero, so this is unreachable.
                 unsafe {
-                    intrinsics::assert_unsafe_precondition!(
+                    ub_checks::assert_unsafe_precondition!(
                         check_library_ub,
                         "NonZero::from_mut_unchecked requires the argument to dereference as non-zero",
                         () => false,

library/core/src/ops/index_range.rs

@@ -1,6 +1,7 @@
-use crate::intrinsics::{assert_unsafe_precondition, unchecked_add, unchecked_sub};
+use crate::intrinsics::{unchecked_add, unchecked_sub};
 use crate::iter::{FusedIterator, TrustedLen};
 use crate::num::NonZero;
+use crate::ub_checks;
 
 /// Like a `Range<usize>`, but with a safety invariant that `start <= end`.
 ///
@@ -19,7 +20,7 @@ impl IndexRange {
     /// - `start <= end`
     #[inline]
     pub const unsafe fn new_unchecked(start: usize, end: usize) -> Self {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_library_ub,
             "IndexRange::new_unchecked requires `start <= end`",
             (start: usize = start, end: usize = end) => start <= end,

library/core/src/ptr/alignment.rs

@@ -1,7 +1,7 @@
 use crate::convert::{TryFrom, TryInto};
-#[cfg(debug_assertions)]
-use crate::intrinsics::assert_unsafe_precondition;
 use crate::num::NonZero;
+#[cfg(debug_assertions)]
+use crate::ub_checks::assert_unsafe_precondition;
 use crate::{cmp, fmt, hash, mem, num};
 
 /// A type storing a `usize` which is a power of two, and thus

library/core/src/ptr/const_ptr.rs

@@ -818,7 +818,7 @@ impl<T: ?Sized> *const T {
             intrinsics::const_eval_select((this, origin), comptime, runtime)
         }
 
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::sub_ptr requires `self >= origin`",
             (

library/core/src/ptr/mod.rs

@@ -388,10 +388,9 @@
 use crate::cmp::Ordering;
 use crate::fmt;
 use crate::hash;
-use crate::intrinsics::{
-    self, assert_unsafe_precondition, is_aligned_and_not_null, is_nonoverlapping,
-};
+use crate::intrinsics;
 use crate::marker::FnPtr;
+use crate::ub_checks;
 
 use crate::mem::{self, align_of, size_of, MaybeUninit};
 
@@ -1019,7 +1018,7 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
         };
     }
 
-    assert_unsafe_precondition!(
+    ub_checks::assert_unsafe_precondition!(
         check_language_ub,
         "ptr::swap_nonoverlapping requires that both pointer arguments are aligned and non-null \
         and the specified memory ranges do not overlap",
@@ -1030,9 +1029,9 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
             align: usize = align_of::<T>(),
             count: usize = count,
         ) =>
-        is_aligned_and_not_null(x, align)
-            && is_aligned_and_not_null(y, align)
-            && is_nonoverlapping(x, y, size, count)
+        ub_checks::is_aligned_and_not_null(x, align)
+            && ub_checks::is_aligned_and_not_null(y, align)
+            && ub_checks::is_nonoverlapping(x, y, size, count)
     );
 
     // Split up the slice into small power-of-two-sized chunks that LLVM is able
@@ -1135,13 +1134,13 @@ pub const unsafe fn replace<T>(dst: *mut T, src: T) -> T {
     // and cannot overlap `src` since `dst` must point to a distinct
     // allocated object.
     unsafe {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::replace requires that the pointer argument is aligned and non-null",
             (
                 addr: *const () = dst as *const (),
                 align: usize = align_of::<T>(),
-            ) => is_aligned_and_not_null(addr, align)
+            ) => ub_checks::is_aligned_and_not_null(addr, align)
         );
         mem::replace(&mut *dst, src)
     }
@@ -1287,13 +1286,13 @@ pub const unsafe fn read<T>(src: *const T) -> T {
     // SAFETY: the caller must guarantee that `src` is valid for reads.
     unsafe {
         #[cfg(debug_assertions)] // Too expensive to always enable (for now?)
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::read requires that the pointer argument is aligned and non-null",
             (
                 addr: *const () = src as *const (),
                 align: usize = align_of::<T>(),
-            ) => is_aligned_and_not_null(addr, align)
+            ) => ub_checks::is_aligned_and_not_null(addr, align)
         );
         crate::intrinsics::read_via_copy(src)
     }
@@ -1496,13 +1495,13 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
     // to `dst` while `src` is owned by this function.
     unsafe {
         #[cfg(debug_assertions)] // Too expensive to always enable (for now?)
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::write requires that the pointer argument is aligned and non-null",
             (
                 addr: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
-            ) => is_aligned_and_not_null(addr, align)
+            ) => ub_checks::is_aligned_and_not_null(addr, align)
         );
         intrinsics::write_via_move(dst, src)
     }
@@ -1668,13 +1667,13 @@ pub const unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 pub unsafe fn read_volatile<T>(src: *const T) -> T {
     // SAFETY: the caller must uphold the safety contract for `volatile_load`.
     unsafe {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::read_volatile requires that the pointer argument is aligned and non-null",
             (
                 addr: *const () = src as *const (),
                 align: usize = align_of::<T>(),
-            ) => is_aligned_and_not_null(addr, align)
+            ) => ub_checks::is_aligned_and_not_null(addr, align)
         );
         intrinsics::volatile_load(src)
     }
@@ -1747,13 +1746,13 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
 pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
     // SAFETY: the caller must uphold the safety contract for `volatile_store`.
     unsafe {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "ptr::write_volatile requires that the pointer argument is aligned and non-null",
             (
                 addr: *mut () = dst as *mut (),
                 align: usize = align_of::<T>(),
-            ) => is_aligned_and_not_null(addr, align)
+            ) => ub_checks::is_aligned_and_not_null(addr, align)
         );
         intrinsics::volatile_store(dst, src);
     }

library/core/src/ptr/non_null.rs

@@ -2,14 +2,14 @@ use crate::cmp::Ordering;
 use crate::fmt;
 use crate::hash;
 use crate::intrinsics;
-use crate::intrinsics::assert_unsafe_precondition;
 use crate::marker::Unsize;
 use crate::mem::{MaybeUninit, SizedTypeProperties};
 use crate::num::NonZero;
 use crate::ops::{CoerceUnsized, DispatchFromDyn};
 use crate::ptr;
 use crate::ptr::Unique;
 use crate::slice::{self, SliceIndex};
+use crate::ub_checks::assert_unsafe_precondition;
 
 /// `*mut T` but non-zero and [covariant].
 ///

library/core/src/slice/index.rs

@@ -1,10 +1,10 @@
 //! Indexing implementations for `[T]`.
 
-use crate::intrinsics::assert_unsafe_precondition;
 use crate::intrinsics::const_eval_select;
 use crate::intrinsics::unchecked_sub;
 use crate::ops;
 use crate::ptr;
+use crate::ub_checks::assert_unsafe_precondition;
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T, I> ops::Index<I> for [T]

library/core/src/slice/mod.rs

@@ -9,14 +9,14 @@
 use crate::cmp::Ordering::{self, Equal, Greater, Less};
 use crate::fmt;
 use crate::hint;
-use crate::intrinsics::assert_unsafe_precondition;
 use crate::intrinsics::exact_div;
 use crate::mem::{self, SizedTypeProperties};
 use crate::num::NonZero;
 use crate::ops::{Bound, OneSidedRange, Range, RangeBounds};
 use crate::ptr;
 use crate::simd::{self, Simd};
 use crate::slice;
+use crate::ub_checks::assert_unsafe_precondition;
 
 #[unstable(
     feature = "slice_internals",

library/core/src/slice/raw.rs

@@ -1,12 +1,10 @@
 //! Free functions to create `&[T]` and `&mut [T]`.
 
 use crate::array;
-use crate::intrinsics::{
-    assert_unsafe_precondition, is_aligned_and_not_null, is_valid_allocation_size,
-};
 use crate::mem::{align_of, size_of};
 use crate::ops::Range;
 use crate::ptr;
+use crate::ub_checks;
 
 /// Forms a slice from a pointer and a length.
 ///
@@ -95,7 +93,7 @@ use crate::ptr;
 pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
     unsafe {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "slice::from_raw_parts requires the pointer to be aligned and non-null, and the total size of the slice not to exceed `isize::MAX`",
             (
@@ -104,8 +102,8 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
                 align: usize = align_of::<T>(),
                 len: usize = len,
             ) =>
-                is_aligned_and_not_null(data, align)
-                && is_valid_allocation_size(size, len)
+            ub_checks::is_aligned_and_not_null(data, align)
+                && ub_checks::is_valid_allocation_size(size, len)
         );
         &*ptr::slice_from_raw_parts(data, len)
     }
@@ -149,7 +147,7 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
 pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.
     unsafe {
-        assert_unsafe_precondition!(
+        ub_checks::assert_unsafe_precondition!(
             check_language_ub,
             "slice::from_raw_parts_mut requires the pointer to be aligned and non-null, and the total size of the slice not to exceed `isize::MAX`",
             (
@@ -158,8 +156,8 @@ 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,
             ) =>
-                is_aligned_and_not_null(data, align)
-                && is_valid_allocation_size(size, len)
+            ub_checks::is_aligned_and_not_null(data, align)
+                && ub_checks::is_valid_allocation_size(size, len)
         );
         &mut *ptr::slice_from_raw_parts_mut(data, len)
     }

library/core/src/str/traits.rs

@@ -1,10 +1,10 @@
 //! Trait implementations for `str`.
 
 use crate::cmp::Ordering;
-use crate::intrinsics::assert_unsafe_precondition;
 use crate::ops;
 use crate::ptr;
 use crate::slice::SliceIndex;
+use crate::ub_checks::assert_unsafe_precondition;
 
 use super::ParseBoolError;
 

library/core/src/ub_checks.rs

@@ -0,0 +1,158 @@
+//! Provides the [`assert_unsafe_precondition`] macro as well as some utility functions that cover
+//! common preconditions.
+
+use crate::intrinsics::{self, const_eval_select};
+
+/// Check that the preconditions of an unsafe function are followed. The check is enabled at
+/// runtime if debug assertions are enabled when the caller is monomorphized. In const-eval/Miri
+/// checks implemented with this macro for language UB are always ignored.
+///
+/// This macro should be called as
+/// `assert_unsafe_precondition!(check_{library,lang}_ub, "message", (ident: type = expr, ident: type = expr) => check_expr)`
+/// where each `expr` will be evaluated and passed in as function argument `ident: type`. Then all
+/// those arguments are passed to a function with the body `check_expr`.
+/// Pick `check_language_ub` when this is guarding a violation of language UB, i.e., immediate UB
+/// according to the Rust Abstract Machine. Pick `check_library_ub` when this is guarding a violation
+/// of a documented library precondition that does not *immediately* lead to language UB.
+///
+/// If `check_library_ub` is used but the check is actually guarding language UB, the check will
+/// slow down const-eval/Miri and we'll get the panic message instead of the interpreter's nice
+/// diagnostic, but our ability to detect UB is unchanged.
+/// But if `check_language_ub` is used when the check is actually for library UB, the check is
+/// omitted in const-eval/Miri and thus if we eventually execute language UB which relies on the
+/// library UB, the backtrace Miri reports may be far removed from original cause.
+///
+/// These checks are behind a condition which is evaluated at codegen time, not expansion time like
+/// [`debug_assert`]. This means that a standard library built with optimizations and debug
+/// assertions disabled will have these checks optimized out of its monomorphizations, but if a
+/// caller of the standard library has debug assertions enabled and monomorphizes an expansion of
+/// this macro, that monomorphization will contain the check.
+///
+/// Since these checks cannot be optimized out in MIR, some care must be taken in both call and
+/// implementation to mitigate their compile-time overhead. Calls to this macro always expand to
+/// this structure:
+/// ```ignore (pseudocode)
+/// if ::core::intrinsics::check_language_ub() {
+///     precondition_check(args)
+/// }
+/// ```
+/// where `precondition_check` is monomorphic with the attributes `#[rustc_nounwind]`, `#[inline]` and
+/// `#[rustc_no_mir_inline]`. This combination of attributes ensures that the actual check logic is
+/// compiled only once and generates a minimal amount of IR because the check cannot be inlined in
+/// MIR, but *can* be inlined and fully optimized by a codegen backend.
+///
+/// Callers should avoid introducing any other `let` bindings or any code outside this macro in
+/// order to call it. Since the precompiled standard library is built with full debuginfo and these
+/// variables cannot be optimized out in MIR, an innocent-looking `let` can produce enough
+/// debuginfo to have a measurable compile-time impact on debug builds.
+#[allow_internal_unstable(const_ub_checks)] // permit this to be called in stably-const fn
+macro_rules! assert_unsafe_precondition {
+    ($kind:ident, $message:expr, ($($name:ident:$ty:ty = $arg:expr),*$(,)?) => $e:expr $(,)?) => {
+        {
+            // This check is inlineable, but not by the MIR inliner.
+            // The reason for this is that the MIR inliner is in an exceptionally bad position
+            // to think about whether or not to inline this. In MIR, this call is gated behind `debug_assertions`,
+            // which will codegen to `false` in release builds. Inlining the check would be wasted work in that case and
+            // would be bad for compile times.
+            //
+            // LLVM on the other hand sees the constant branch, so if it's `false`, it can immediately delete it without
+            // inlining the check. If it's `true`, it can inline it and get significantly better performance.
+            #[rustc_no_mir_inline]
+            #[inline]
+            #[rustc_nounwind]
+            #[rustc_const_unstable(feature = "const_ub_checks", issue = "none")]
+            const fn precondition_check($($name:$ty),*) {
+                if !$e {
+                    ::core::panicking::panic_nounwind(
+                        concat!("unsafe precondition(s) violated: ", $message)
+                    );
+                }
+            }
+
+            if ::core::ub_checks::$kind() {
+                precondition_check($($arg,)*);
+            }
+        }
+    };
+}
+pub(crate) use assert_unsafe_precondition;
+
+/// Checking library UB is always enabled when UB-checking is done
+/// (and we use a reexport so that there is no unnecessary wrapper function).
+pub(crate) use intrinsics::ub_checks as check_library_ub;
+
+/// Determines whether we should check for language UB.
+///
+/// The intention is to not do that when running in the interpreter, as that one has its own
+/// language UB checks which generally produce better errors.
+#[rustc_const_unstable(feature = "const_ub_checks", issue = "none")]
+#[inline]
+pub(crate) const fn check_language_ub() -> bool {
+    #[inline]
+    fn runtime() -> bool {
+        // Disable UB checks in Miri.
+        !cfg!(miri)
+    }
+
+    #[inline]
+    const fn comptime() -> bool {
+        // Always disable UB checks.
+        false
+    }
+
+    // Only used for UB checks so we may const_eval_select.
+    intrinsics::ub_checks() && const_eval_select((), comptime, runtime)
+}
+
+/// Checks whether `ptr` is properly aligned with respect to
+/// `align_of::<T>()`.
+///
+/// In `const` this is approximate and can fail spuriously. It is primarily intended
+/// for `assert_unsafe_precondition!` with `check_language_ub`, in which case the
+/// check is anyway not executed in `const`.
+#[inline]
+pub(crate) const fn is_aligned_and_not_null(ptr: *const (), align: usize) -> bool {
+    !ptr.is_null() && ptr.is_aligned_to(align)
+}
+
+#[inline]
+pub(crate) const fn is_valid_allocation_size(size: usize, len: usize) -> bool {
+    let max_len = if size == 0 { usize::MAX } else { isize::MAX as usize / size };
+    len <= max_len
+}
+
+/// Checks whether the regions of memory starting at `src` and `dst` of size
+/// `count * size` do *not* overlap.
+///
+/// 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]
+pub(crate) const fn is_nonoverlapping(
+    src: *const (),
+    dst: *const (),
+    size: usize,
+    count: usize,
+) -> bool {
+    #[inline]
+    fn runtime(src: *const (), dst: *const (), size: usize, count: usize) -> bool {
+        let src_usize = src.addr();
+        let dst_usize = dst.addr();
+        let Some(size) = size.checked_mul(count) else {
+            crate::panicking::panic_nounwind(
+                "is_nonoverlapping: `size_of::<T>() * count` overflows a usize",
+            )
+        };
+        let diff = src_usize.abs_diff(dst_usize);
+        // If the absolute distance between the ptrs is at least as big as the size of the buffer,
+        // they do not overlap.
+        diff >= size
+    }
+
+    #[inline]
+    const fn comptime(_: *const (), _: *const (), _: usize, _: usize) -> bool {
+        true
+    }
+
+    // This is just for safety checks so we can const_eval_select.
+    const_eval_select((src, dst, size, count), comptime, runtime)
+}

src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs

@@ -174,7 +174,7 @@ fn check_rvalue<'tcx>(
                 ))
             }
         },
-        Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbCheck(_), _)
+        Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbChecks, _)
         | Rvalue::ShallowInitBox(_, _) => Ok(()),
         Rvalue::UnaryOp(_, operand) => {
             let ty = operand.ty(body, tcx);

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.DataflowConstProp.32bit.panic-abort.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -60,7 +64,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb4, otherwise: bb2];
       }
 

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.DataflowConstProp.32bit.panic-unwind.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -60,7 +64,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb5, otherwise: bb3];
       }
 

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.DataflowConstProp.64bit.panic-abort.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -60,7 +64,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb4, otherwise: bb2];
       }
 

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.DataflowConstProp.64bit.panic-unwind.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -60,7 +64,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb5, otherwise: bb3];
       }
 

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.32bit.panic-abort.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -62,7 +66,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb4, otherwise: bb2];
       }
 

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.32bit.panic-unwind.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -62,7 +66,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb5, otherwise: bb3];
       }
 

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.64bit.panic-abort.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -62,7 +66,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb4, otherwise: bb2];
       }
 

tests/mir-opt/dataflow-const-prop/default_boxed_slice.main.GVN.64bit.panic-unwind.diff

@@ -28,6 +28,10 @@
                               let mut _10: *mut ();
                               let mut _11: *const [bool; 0];
                               scope 13 {
+                                  scope 14 (inlined core::ub_checks::check_language_ub) {
+                                      scope 15 (inlined core::ub_checks::check_language_ub::runtime) {
+                                      }
+                                  }
                               }
                           }
                       }
@@ -62,7 +66,7 @@
           StorageDead(_7);
           StorageLive(_11);
           StorageLive(_8);
-          _8 = UbCheck(LanguageUb);
+          _8 = UbChecks();
           switchInt(move _8) -> [0: bb5, otherwise: bb3];
       }
 

tests/mir-opt/inline/unwrap_unchecked.unwrap_unchecked.Inline.panic-abort.diff

@@ -17,6 +17,10 @@
 +                 let _5: ();
 +                 scope 5 {
 +                 }
++                 scope 6 (inlined core::ub_checks::check_language_ub) {
++                     scope 7 (inlined core::ub_checks::check_language_ub::runtime) {
++                     }
++                 }
 +             }
 +         }
 +     }
@@ -37,7 +41,7 @@
 + 
 +     bb2: {
 +         StorageLive(_4);
-+         _4 = UbCheck(LanguageUb);
++         _4 = UbChecks();
 +         assume(_4);
 +         _5 = unreachable_unchecked::precondition_check() -> [return: bb1, unwind unreachable];
 +     }

tests/mir-opt/inline/unwrap_unchecked.unwrap_unchecked.Inline.panic-unwind.diff

@@ -17,6 +17,10 @@
 +                 let _5: ();
 +                 scope 5 {
 +                 }
++                 scope 6 (inlined core::ub_checks::check_language_ub) {
++                     scope 7 (inlined core::ub_checks::check_language_ub::runtime) {
++                     }
++                 }
 +             }
 +         }
 +     }
@@ -41,7 +45,7 @@
 -         resume;
 +     bb2: {
 +         StorageLive(_4);
-+         _4 = UbCheck(LanguageUb);
++         _4 = UbChecks();
 +         assume(_4);
 +         _5 = unreachable_unchecked::precondition_check() -> [return: bb1, unwind unreachable];
 +     }

tests/mir-opt/inline/unwrap_unchecked.unwrap_unchecked.PreCodegen.after.panic-abort.mir

@@ -15,6 +15,10 @@ fn unwrap_unchecked(_1: Option<T>) -> T {
                 let _4: ();
                 scope 5 {
                 }
+                scope 6 (inlined core::ub_checks::check_language_ub) {
+                    scope 7 (inlined core::ub_checks::check_language_ub::runtime) {
+                    }
+                }
             }
         }
     }
@@ -27,7 +31,7 @@ fn unwrap_unchecked(_1: Option<T>) -> T {
 
     bb1: {
         StorageLive(_3);
-        _3 = UbCheck(LanguageUb);
+        _3 = UbChecks();
         assume(_3);
         _4 = unreachable_unchecked::precondition_check() -> [return: bb3, unwind unreachable];
     }

tests/mir-opt/inline/unwrap_unchecked.unwrap_unchecked.PreCodegen.after.panic-unwind.mir

@@ -15,6 +15,10 @@ fn unwrap_unchecked(_1: Option<T>) -> T {
                 let _4: ();
                 scope 5 {
                 }
+                scope 6 (inlined core::ub_checks::check_language_ub) {
+                    scope 7 (inlined core::ub_checks::check_language_ub::runtime) {
+                    }
+                }
             }
         }
     }
@@ -27,7 +31,7 @@ fn unwrap_unchecked(_1: Option<T>) -> T {
 
     bb1: {
         StorageLive(_3);
-        _3 = UbCheck(LanguageUb);
+        _3 = UbChecks();
         assume(_3);
         _4 = unreachable_unchecked::precondition_check() -> [return: bb3, unwind unreachable];
     }

tests/mir-opt/pre-codegen/duplicate_switch_targets.ub_if_b.PreCodegen.after.mir

@@ -9,6 +9,10 @@ fn ub_if_b(_1: Thing) -> Thing {
         let _4: ();
         scope 2 {
         }
+        scope 3 (inlined core::ub_checks::check_language_ub) {
+            scope 4 (inlined core::ub_checks::check_language_ub::runtime) {
+            }
+        }
     }
 
     bb0: {
@@ -23,7 +27,7 @@ fn ub_if_b(_1: Thing) -> Thing {
 
     bb2: {
         StorageLive(_3);
-        _3 = UbCheck(LanguageUb);
+        _3 = UbChecks();
         assume(_3);
         _4 = unreachable_unchecked::precondition_check() -> [return: bb3, unwind unreachable];
     }