Auto merge of #102795 - lukas-code:constify-is-aligned-via-align-offset, r=oli-obk

Constify `is_aligned` via `align_offset`

Alternative to #102753

Make `align_offset` work in const eval (and not always return `usize::MAX`) and then use that to constify `is_aligned{_to}`.

Tracking Issue: #104203

Author: bors

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -1,8 +1,12 @@
 use rustc_hir::def::DefKind;
+use rustc_hir::LangItem;
 use rustc_middle::mir;
+use rustc_middle::mir::interpret::PointerArithmetic;
+use rustc_middle::ty::layout::FnAbiOf;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use std::borrow::Borrow;
 use std::hash::Hash;
+use std::ops::ControlFlow;
 
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::fx::IndexEntry;
@@ -17,58 +21,12 @@ use rustc_target::abi::{Align, Size};
 use rustc_target::spec::abi::Abi as CallAbi;
 
 use crate::interpret::{
-    self, compile_time_machine, AllocId, ConstAllocation, Frame, ImmTy, InterpCx, InterpResult,
-    OpTy, PlaceTy, Pointer, Scalar, StackPopUnwind,
+    self, compile_time_machine, AllocId, ConstAllocation, FnVal, Frame, ImmTy, InterpCx,
+    InterpResult, OpTy, PlaceTy, Pointer, Scalar, StackPopUnwind,
 };
 
 use super::error::*;
 
-impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
-    /// "Intercept" a function call to a panic-related function
-    /// because we have something special to do for it.
-    /// If this returns successfully (`Ok`), the function should just be evaluated normally.
-    fn hook_special_const_fn(
-        &mut self,
-        instance: ty::Instance<'tcx>,
-        args: &[OpTy<'tcx>],
-    ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
-        // All `#[rustc_do_not_const_check]` functions should be hooked here.
-        let def_id = instance.def_id();
-
-        if Some(def_id) == self.tcx.lang_items().panic_display()
-            || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
-        {
-            // &str or &&str
-            assert!(args.len() == 1);
-
-            let mut msg_place = self.deref_operand(&args[0])?;
-            while msg_place.layout.ty.is_ref() {
-                msg_place = self.deref_operand(&msg_place.into())?;
-            }
-
-            let msg = Symbol::intern(self.read_str(&msg_place)?);
-            let span = self.find_closest_untracked_caller_location();
-            let (file, line, col) = self.location_triple_for_span(span);
-            return Err(ConstEvalErrKind::Panic { msg, file, line, col }.into());
-        } else if Some(def_id) == self.tcx.lang_items().panic_fmt() {
-            // For panic_fmt, call const_panic_fmt instead.
-            if let Some(const_panic_fmt) = self.tcx.lang_items().const_panic_fmt() {
-                return Ok(Some(
-                    ty::Instance::resolve(
-                        *self.tcx,
-                        ty::ParamEnv::reveal_all(),
-                        const_panic_fmt,
-                        self.tcx.intern_substs(&[]),
-                    )
-                    .unwrap()
-                    .unwrap(),
-                ));
-            }
-        }
-        Ok(None)
-    }
-}
-
 /// Extra machine state for CTFE, and the Machine instance
 pub struct CompileTimeInterpreter<'mir, 'tcx> {
     /// For now, the number of terminators that can be evaluated before we throw a resource
@@ -191,6 +149,125 @@ impl interpret::MayLeak for ! {
 }
 
 impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
+    /// "Intercept" a function call, because we have something special to do for it.
+    /// All `#[rustc_do_not_const_check]` functions should be hooked here.
+    /// If this returns `Some` function, which may be `instance` or a different function with
+    /// compatible arguments, then evaluation should continue with that function.
+    /// If this returns `None`, the function call has been handled and the function has returned.
+    fn hook_special_const_fn(
+        &mut self,
+        instance: ty::Instance<'tcx>,
+        args: &[OpTy<'tcx>],
+        dest: &PlaceTy<'tcx>,
+        ret: Option<mir::BasicBlock>,
+    ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
+        let def_id = instance.def_id();
+
+        if Some(def_id) == self.tcx.lang_items().panic_display()
+            || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
+        {
+            // &str or &&str
+            assert!(args.len() == 1);
+
+            let mut msg_place = self.deref_operand(&args[0])?;
+            while msg_place.layout.ty.is_ref() {
+                msg_place = self.deref_operand(&msg_place.into())?;
+            }
+
+            let msg = Symbol::intern(self.read_str(&msg_place)?);
+            let span = self.find_closest_untracked_caller_location();
+            let (file, line, col) = self.location_triple_for_span(span);
+            return Err(ConstEvalErrKind::Panic { msg, file, line, col }.into());
+        } else if Some(def_id) == self.tcx.lang_items().panic_fmt() {
+            // For panic_fmt, call const_panic_fmt instead.
+            let const_def_id = self.tcx.require_lang_item(LangItem::ConstPanicFmt, None);
+            let new_instance = ty::Instance::resolve(
+                *self.tcx,
+                ty::ParamEnv::reveal_all(),
+                const_def_id,
+                instance.substs,
+            )
+            .unwrap()
+            .unwrap();
+
+            return Ok(Some(new_instance));
+        } else if Some(def_id) == self.tcx.lang_items().align_offset_fn() {
+            // For align_offset, we replace the function call if the pointer has no address.
+            match self.align_offset(instance, args, dest, ret)? {
+                ControlFlow::Continue(()) => return Ok(Some(instance)),
+                ControlFlow::Break(()) => return Ok(None),
+            }
+        }
+        Ok(Some(instance))
+    }
+
+    /// `align_offset(ptr, target_align)` needs special handling in const eval, because the pointer
+    /// may not have an address.
+    ///
+    /// If `ptr` does have a known address, then we return `CONTINUE` and the function call should
+    /// proceed as normal.
+    ///
+    /// If `ptr` doesn't have an address, but its underlying allocation's alignment is at most
+    /// `target_align`, then we call the function again with an dummy address relative to the
+    /// allocation.
+    ///
+    /// If `ptr` doesn't have an address and `target_align` is stricter than the underlying
+    /// allocation's alignment, then we return `usize::MAX` immediately.
+    fn align_offset(
+        &mut self,
+        instance: ty::Instance<'tcx>,
+        args: &[OpTy<'tcx>],
+        dest: &PlaceTy<'tcx>,
+        ret: Option<mir::BasicBlock>,
+    ) -> InterpResult<'tcx, ControlFlow<()>> {
+        assert_eq!(args.len(), 2);
+
+        let ptr = self.read_pointer(&args[0])?;
+        let target_align = self.read_scalar(&args[1])?.to_machine_usize(self)?;
+
+        if !target_align.is_power_of_two() {
+            throw_ub_format!("`align_offset` called with non-power-of-two align: {}", target_align);
+        }
+
+        match self.ptr_try_get_alloc_id(ptr) {
+            Ok((alloc_id, offset, _extra)) => {
+                let (_size, alloc_align, _kind) = self.get_alloc_info(alloc_id);
+
+                if target_align <= alloc_align.bytes() {
+                    // Extract the address relative to the allocation base that is definitely
+                    // sufficiently aligned and call `align_offset` again.
+                    let addr = ImmTy::from_uint(offset.bytes(), args[0].layout).into();
+                    let align = ImmTy::from_uint(target_align, args[1].layout).into();
+                    let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
+
+                    // We replace the entire entire function call with a "tail call".
+                    // Note that this happens before the frame of the original function
+                    // is pushed on the stack.
+                    self.eval_fn_call(
+                        FnVal::Instance(instance),
+                        (CallAbi::Rust, fn_abi),
+                        &[addr, align],
+                        /* with_caller_location = */ false,
+                        dest,
+                        ret,
+                        StackPopUnwind::NotAllowed,
+                    )?;
+                    Ok(ControlFlow::BREAK)
+                } else {
+                    // Not alignable in const, return `usize::MAX`.
+                    let usize_max = Scalar::from_machine_usize(self.machine_usize_max(), self);
+                    self.write_scalar(usize_max, dest)?;
+                    self.return_to_block(ret)?;
+                    Ok(ControlFlow::BREAK)
+                }
+            }
+            Err(_addr) => {
+                // The pointer has an address, continue with function call.
+                Ok(ControlFlow::CONTINUE)
+            }
+        }
+    }
+
     /// See documentation on the `ptr_guaranteed_cmp` intrinsic.
     fn guaranteed_cmp(&mut self, a: Scalar, b: Scalar) -> InterpResult<'tcx, u8> {
         Ok(match (a, b) {
@@ -271,8 +348,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         instance: ty::Instance<'tcx>,
         _abi: CallAbi,
         args: &[OpTy<'tcx>],
-        _dest: &PlaceTy<'tcx>,
-        _ret: Option<mir::BasicBlock>,
+        dest: &PlaceTy<'tcx>,
+        ret: Option<mir::BasicBlock>,
         _unwind: StackPopUnwind, // unwinding is not supported in consts
     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
         debug!("find_mir_or_eval_fn: {:?}", instance);
@@ -291,7 +368,11 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
                 }
             }
 
-            if let Some(new_instance) = ecx.hook_special_const_fn(instance, args)? {
+            let Some(new_instance) = ecx.hook_special_const_fn(instance, args, dest, ret)? else {
+                return Ok(None);
+            };
+
+            if new_instance != instance {
                 // We call another const fn instead.
                 // However, we return the *original* instance to make backtraces work out
                 // (and we hope this does not confuse the FnAbi checks too much).
@@ -300,13 +381,14 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
                     new_instance,
                     _abi,
                     args,
-                    _dest,
-                    _ret,
+                    dest,
+                    ret,
                     _unwind,
                 )?
                 .map(|(body, _instance)| (body, instance)));
             }
         }
+
         // This is a const fn. Call it.
         Ok(Some((ecx.load_mir(instance.def, None)?, instance)))
     }

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -243,6 +243,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let discr_val = self.read_discriminant(&place.into())?.0;
                 self.write_scalar(discr_val, dest)?;
             }
+            sym::exact_div => {
+                let l = self.read_immediate(&args[0])?;
+                let r = self.read_immediate(&args[1])?;
+                self.exact_div(&l, &r, dest)?;
+            }
             sym::unchecked_shl
             | sym::unchecked_shr
             | sym::unchecked_add

library/core/src/intrinsics.rs

@@ -1851,6 +1851,7 @@ extern "rust-intrinsic" {
     /// `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`
     ///
     /// This intrinsic does not have a stable counterpart.
+    #[rustc_const_unstable(feature = "const_exact_div", issue = "none")]
     pub fn exact_div<T: Copy>(x: T, y: T) -> T;
 
     /// Performs an unchecked division, resulting in undefined behavior

library/core/src/lib.rs

@@ -109,6 +109,7 @@
 #![feature(const_cmp)]
 #![feature(const_discriminant)]
 #![feature(const_eval_select)]
+#![feature(const_exact_div)]
 #![feature(const_float_bits_conv)]
 #![feature(const_float_classify)]
 #![feature(const_fmt_arguments_new)]
@@ -129,6 +130,7 @@
 #![feature(const_option)]
 #![feature(const_option_ext)]
 #![feature(const_pin)]
+#![feature(const_pointer_is_aligned)]
 #![feature(const_ptr_sub_ptr)]
 #![feature(const_replace)]
 #![feature(const_result_drop)]

library/core/src/ptr/const_ptr.rs

@@ -1320,6 +1320,8 @@ impl<T: ?Sized> *const T {
     /// }
     /// # }
     /// ```
+    #[must_use]
+    #[inline]
     #[stable(feature = "align_offset", since = "1.36.0")]
     #[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
     pub const fn align_offset(self, align: usize) -> usize
@@ -1330,32 +1332,149 @@ impl<T: ?Sized> *const T {
             panic!("align_offset: align is not a power-of-two");
         }
 
-        fn rt_impl<T>(p: *const T, align: usize) -> usize {
-            // SAFETY: `align` has been checked to be a power of 2 above
-            unsafe { align_offset(p, align) }
-        }
+        #[cfg(bootstrap)]
+        {
+            fn rt_impl<T>(p: *const T, align: usize) -> usize {
+                // SAFETY: `align` has been checked to be a power of 2 above
+                unsafe { align_offset(p, align) }
+            }
+
+            const fn ctfe_impl<T>(_: *const T, _: usize) -> usize {
+                usize::MAX
+            }
 
-        const fn ctfe_impl<T>(_: *const T, _: usize) -> usize {
-            usize::MAX
+            // SAFETY:
+            // It is permissible for `align_offset` to always return `usize::MAX`,
+            // algorithm correctness can not depend on `align_offset` returning non-max values.
+            //
+            // As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
+            unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
         }
 
-        // SAFETY:
-        // It is permissible for `align_offset` to always return `usize::MAX`,
-        // algorithm correctness can not depend on `align_offset` returning non-max values.
-        //
-        // As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
-        unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
+        #[cfg(not(bootstrap))]
+        {
+            // SAFETY: `align` has been checked to be a power of 2 above
+            unsafe { align_offset(self, align) }
+        }
     }
 
     /// Returns whether the pointer is properly aligned for `T`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(pointer_byte_offsets)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// let data = AlignedI32(42);
+    /// let ptr = &data as *const AlignedI32;
+    ///
+    /// assert!(ptr.is_aligned());
+    /// assert!(!ptr.wrapping_byte_add(1).is_aligned());
+    /// ```
+    ///
+    /// # At compiletime
+    /// **Note: Alignment at compiletime is experimental and subject to change. See the
+    /// [tracking issue] for details.**
+    ///
+    /// At compiletime, the compiler may not know where a value will end up in memory.
+    /// Calling this function on a pointer created from a reference at compiletime will only
+    /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
+    /// is never aligned if cast to a type with a stricter alignment than the reference's
+    /// underlying allocation.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// const _: () = {
+    ///     let data = AlignedI32(42);
+    ///     let ptr = &data as *const AlignedI32;
+    ///     assert!(ptr.is_aligned());
+    ///
+    ///     // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
+    ///     let ptr1 = ptr.cast::<AlignedI64>();
+    ///     let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
+    ///     assert!(!ptr1.is_aligned());
+    ///     assert!(!ptr2.is_aligned());
+    /// };
+    /// ```
+    ///
+    /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
+    /// pointer is aligned, even if the compiletime pointer wasn't aligned.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
+    /// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
+    /// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
+    /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());
+    ///
+    /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
+    /// let runtime_ptr = COMPTIME_PTR;
+    /// assert_ne!(
+    ///     runtime_ptr.cast::<AlignedI64>().is_aligned(),
+    ///     runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
+    /// );
+    /// ```
+    ///
+    /// If a pointer is created from a fixed address, this function behaves the same during
+    /// runtime and compiletime.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// const _: () = {
+    ///     let ptr = 40 as *const AlignedI32;
+    ///     assert!(ptr.is_aligned());
+    ///
+    ///     // For pointers with a known address, runtime and compiletime behavior are identical.
+    ///     let ptr1 = ptr.cast::<AlignedI64>();
+    ///     let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
+    ///     assert!(ptr1.is_aligned());
+    ///     assert!(!ptr2.is_aligned());
+    /// };
+    /// ```
+    ///
+    /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned(self) -> bool
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
+    pub const fn is_aligned(self) -> bool
     where
         T: Sized,
     {
-        self.is_aligned_to(core::mem::align_of::<T>())
+        self.is_aligned_to(mem::align_of::<T>())
     }
 
     /// Returns whether the pointer is aligned to `align`.
@@ -1366,16 +1485,121 @@ impl<T: ?Sized> *const T {
     /// # Panics
     ///
     /// The function panics if `align` is not a power-of-two (this includes 0).
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(pointer_byte_offsets)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// let data = AlignedI32(42);
+    /// let ptr = &data as *const AlignedI32;
+    ///
+    /// assert!(ptr.is_aligned_to(1));
+    /// assert!(ptr.is_aligned_to(2));
+    /// assert!(ptr.is_aligned_to(4));
+    ///
+    /// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
+    /// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
+    ///
+    /// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
+    /// ```
+    ///
+    /// # At compiletime
+    /// **Note: Alignment at compiletime is experimental and subject to change. See the
+    /// [tracking issue] for details.**
+    ///
+    /// At compiletime, the compiler may not know where a value will end up in memory.
+    /// Calling this function on a pointer created from a reference at compiletime will only
+    /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
+    /// cannot be stricter aligned than the reference's underlying allocation.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// const _: () = {
+    ///     let data = AlignedI32(42);
+    ///     let ptr = &data as *const AlignedI32;
+    ///
+    ///     assert!(ptr.is_aligned_to(1));
+    ///     assert!(ptr.is_aligned_to(2));
+    ///     assert!(ptr.is_aligned_to(4));
+    ///
+    ///     // At compiletime, we know for sure that the pointer isn't aligned to 8.
+    ///     assert!(!ptr.is_aligned_to(8));
+    ///     assert!(!ptr.wrapping_add(1).is_aligned_to(8));
+    /// };
+    /// ```
+    ///
+    /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
+    /// pointer is aligned, even if the compiletime pointer wasn't aligned.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
+    /// const COMPTIME_PTR: *const AlignedI32 = &AlignedI32(42);
+    /// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
+    /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));
+    ///
+    /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
+    /// let runtime_ptr = COMPTIME_PTR;
+    /// assert_ne!(
+    ///     runtime_ptr.is_aligned_to(8),
+    ///     runtime_ptr.wrapping_add(1).is_aligned_to(8),
+    /// );
+    /// ```
+    ///
+    /// If a pointer is created from a fixed address, this function behaves the same during
+    /// runtime and compiletime.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// const _: () = {
+    ///     let ptr = 40 as *const u8;
+    ///     assert!(ptr.is_aligned_to(1));
+    ///     assert!(ptr.is_aligned_to(2));
+    ///     assert!(ptr.is_aligned_to(4));
+    ///     assert!(ptr.is_aligned_to(8));
+    ///     assert!(!ptr.is_aligned_to(16));
+    /// };
+    /// ```
+    ///
+    /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned_to(self, align: usize) -> bool {
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
+    pub const fn is_aligned_to(self, align: usize) -> bool {
         if !align.is_power_of_two() {
             panic!("is_aligned_to: align is not a power-of-two");
         }
 
-        // Cast is needed for `T: !Sized`
-        self.cast::<u8>().addr() & align - 1 == 0
+        // We can't use the address of `self` in a `const fn`, so we use `align_offset` instead.
+        // The cast to `()` is used to
+        //   1. deal with fat pointers; and
+        //   2. ensure that `align_offset` doesn't actually try to compute an offset.
+        self.cast::<()>().align_offset(align) == 0
     }
 }
 

library/core/src/ptr/mod.rs

@@ -1574,10 +1574,14 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
 
 /// Align pointer `p`.
 ///
-/// Calculate offset (in terms of elements of `stride` stride) that has to be applied
+/// Calculate offset (in terms of elements of `size_of::<T>()` stride) that has to be applied
 /// to pointer `p` so that pointer `p` would get aligned to `a`.
 ///
-/// Note: This implementation has been carefully tailored to not panic. It is UB for this to panic.
+/// # Safety
+/// `a` must be a power of two.
+///
+/// # Notes
+/// This implementation has been carefully tailored to not panic. It is UB for this to panic.
 /// The only real change that can be made here is change of `INV_TABLE_MOD_16` and associated
 /// constants.
 ///
@@ -1587,7 +1591,7 @@ pub unsafe fn write_volatile<T>(dst: *mut T, src: T) {
 ///
 /// Any questions go to @nagisa.
 #[lang = "align_offset"]
-pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
+pub(crate) const unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
     // FIXME(#75598): Direct use of these intrinsics improves codegen significantly at opt-level <=
     // 1, where the method versions of these operations are not inlined.
     use intrinsics::{
@@ -1604,7 +1608,7 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
     ///
     /// Implementation of this function shall not panic. Ever.
     #[inline]
-    unsafe fn mod_inv(x: usize, m: usize) -> usize {
+    const unsafe fn mod_inv(x: usize, m: usize) -> usize {
         /// Multiplicative modular inverse table modulo 2⁴ = 16.
         ///
         /// Note, that this table does not contain values where inverse does not exist (i.e., for
@@ -1646,8 +1650,14 @@ pub(crate) unsafe fn align_offset<T: Sized>(p: *const T, a: usize) -> usize {
         inverse & m_minus_one
     }
 
-    let addr = p.addr();
     let stride = mem::size_of::<T>();
+
+    // SAFETY: This is just an inlined `p.addr()` (which is not
+    // a `const fn` so we cannot call it).
+    // During const eval, we hook this function to ensure that the pointer never
+    // has provenance, making this sound.
+    let addr: usize = unsafe { mem::transmute(p) };
+
     // SAFETY: `a` is a power-of-two, therefore non-zero.
     let a_minus_one = unsafe { unchecked_sub(a, 1) };
 

library/core/src/ptr/mut_ptr.rs

@@ -1588,6 +1588,8 @@ impl<T: ?Sized> *mut T {
     /// }
     /// # }
     /// ```
+    #[must_use]
+    #[inline]
     #[stable(feature = "align_offset", since = "1.36.0")]
     #[rustc_const_unstable(feature = "const_align_offset", issue = "90962")]
     pub const fn align_offset(self, align: usize) -> usize
@@ -1598,32 +1600,151 @@ impl<T: ?Sized> *mut T {
             panic!("align_offset: align is not a power-of-two");
         }
 
-        fn rt_impl<T>(p: *mut T, align: usize) -> usize {
-            // SAFETY: `align` has been checked to be a power of 2 above
-            unsafe { align_offset(p, align) }
+        #[cfg(bootstrap)]
+        {
+            fn rt_impl<T>(p: *mut T, align: usize) -> usize {
+                // SAFETY: `align` has been checked to be a power of 2 above
+                unsafe { align_offset(p, align) }
+            }
+
+            const fn ctfe_impl<T>(_: *mut T, _: usize) -> usize {
+                usize::MAX
+            }
+
+            // SAFETY:
+            // It is permissible for `align_offset` to always return `usize::MAX`,
+            // algorithm correctness can not depend on `align_offset` returning non-max values.
+            //
+            // As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
+            unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
         }
 
-        const fn ctfe_impl<T>(_: *mut T, _: usize) -> usize {
-            usize::MAX
+        #[cfg(not(bootstrap))]
+        {
+            // SAFETY: `align` has been checked to be a power of 2 above
+            unsafe { align_offset(self, align) }
         }
-
-        // SAFETY:
-        // It is permissible for `align_offset` to always return `usize::MAX`,
-        // algorithm correctness can not depend on `align_offset` returning non-max values.
-        //
-        // As such the behaviour can't change after replacing `align_offset` with `usize::MAX`, only performance can.
-        unsafe { intrinsics::const_eval_select((self, align), ctfe_impl, rt_impl) }
     }
 
     /// Returns whether the pointer is properly aligned for `T`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(pointer_byte_offsets)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// let mut data = AlignedI32(42);
+    /// let ptr = &mut data as *mut AlignedI32;
+    ///
+    /// assert!(ptr.is_aligned());
+    /// assert!(!ptr.wrapping_byte_add(1).is_aligned());
+    /// ```
+    ///
+    /// # At compiletime
+    /// **Note: Alignment at compiletime is experimental and subject to change. See the
+    /// [tracking issue] for details.**
+    ///
+    /// At compiletime, the compiler may not know where a value will end up in memory.
+    /// Calling this function on a pointer created from a reference at compiletime will only
+    /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
+    /// is never aligned if cast to a type with a stricter alignment than the reference's
+    /// underlying allocation.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    /// #![feature(const_mut_refs)]
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// const _: () = {
+    ///     let mut data = AlignedI32(42);
+    ///     let ptr = &mut data as *mut AlignedI32;
+    ///     assert!(ptr.is_aligned());
+    ///
+    ///     // At runtime either `ptr1` or `ptr2` would be aligned, but at compiletime neither is aligned.
+    ///     let ptr1 = ptr.cast::<AlignedI64>();
+    ///     let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
+    ///     assert!(!ptr1.is_aligned());
+    ///     assert!(!ptr2.is_aligned());
+    /// };
+    /// ```
+    ///
+    /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
+    /// pointer is aligned, even if the compiletime pointer wasn't aligned.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
+    /// // Also, note that mutable references are not allowed in the final value of constants.
+    /// const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
+    /// const _: () = assert!(!COMPTIME_PTR.cast::<AlignedI64>().is_aligned());
+    /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).cast::<AlignedI64>().is_aligned());
+    ///
+    /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
+    /// let runtime_ptr = COMPTIME_PTR;
+    /// assert_ne!(
+    ///     runtime_ptr.cast::<AlignedI64>().is_aligned(),
+    ///     runtime_ptr.wrapping_add(1).cast::<AlignedI64>().is_aligned(),
+    /// );
+    /// ```
+    ///
+    /// If a pointer is created from a fixed address, this function behaves the same during
+    /// runtime and compiletime.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of primitives is less than their size.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    /// #[repr(align(8))]
+    /// struct AlignedI64(i64);
+    ///
+    /// const _: () = {
+    ///     let ptr = 40 as *mut AlignedI32;
+    ///     assert!(ptr.is_aligned());
+    ///
+    ///     // For pointers with a known address, runtime and compiletime behavior are identical.
+    ///     let ptr1 = ptr.cast::<AlignedI64>();
+    ///     let ptr2 = ptr.wrapping_add(1).cast::<AlignedI64>();
+    ///     assert!(ptr1.is_aligned());
+    ///     assert!(!ptr2.is_aligned());
+    /// };
+    /// ```
+    ///
+    /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned(self) -> bool
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
+    pub const fn is_aligned(self) -> bool
     where
         T: Sized,
     {
-        self.is_aligned_to(core::mem::align_of::<T>())
+        self.is_aligned_to(mem::align_of::<T>())
     }
 
     /// Returns whether the pointer is aligned to `align`.
@@ -1634,16 +1755,123 @@ impl<T: ?Sized> *mut T {
     /// # Panics
     ///
     /// The function panics if `align` is not a power-of-two (this includes 0).
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    /// ```
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(pointer_byte_offsets)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// let mut data = AlignedI32(42);
+    /// let ptr = &mut data as *mut AlignedI32;
+    ///
+    /// assert!(ptr.is_aligned_to(1));
+    /// assert!(ptr.is_aligned_to(2));
+    /// assert!(ptr.is_aligned_to(4));
+    ///
+    /// assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
+    /// assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
+    ///
+    /// assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
+    /// ```
+    ///
+    /// # At compiletime
+    /// **Note: Alignment at compiletime is experimental and subject to change. See the
+    /// [tracking issue] for details.**
+    ///
+    /// At compiletime, the compiler may not know where a value will end up in memory.
+    /// Calling this function on a pointer created from a reference at compiletime will only
+    /// return `true` if the pointer is guaranteed to be aligned. This means that the pointer
+    /// cannot be stricter aligned than the reference's underlying allocation.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    /// #![feature(const_mut_refs)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// const _: () = {
+    ///     let mut data = AlignedI32(42);
+    ///     let ptr = &mut data as *mut AlignedI32;
+    ///
+    ///     assert!(ptr.is_aligned_to(1));
+    ///     assert!(ptr.is_aligned_to(2));
+    ///     assert!(ptr.is_aligned_to(4));
+    ///
+    ///     // At compiletime, we know for sure that the pointer isn't aligned to 8.
+    ///     assert!(!ptr.is_aligned_to(8));
+    ///     assert!(!ptr.wrapping_add(1).is_aligned_to(8));
+    /// };
+    /// ```
+    ///
+    /// Due to this behavior, it is possible that a runtime pointer derived from a compiletime
+    /// pointer is aligned, even if the compiletime pointer wasn't aligned.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// // On some platforms, the alignment of i32 is less than 4.
+    /// #[repr(align(4))]
+    /// struct AlignedI32(i32);
+    ///
+    /// // At compiletime, neither `COMPTIME_PTR` nor `COMPTIME_PTR + 1` is aligned.
+    /// // Also, note that mutable references are not allowed in the final value of constants.
+    /// const COMPTIME_PTR: *mut AlignedI32 = (&AlignedI32(42) as *const AlignedI32).cast_mut();
+    /// const _: () = assert!(!COMPTIME_PTR.is_aligned_to(8));
+    /// const _: () = assert!(!COMPTIME_PTR.wrapping_add(1).is_aligned_to(8));
+    ///
+    /// // At runtime, either `runtime_ptr` or `runtime_ptr + 1` is aligned.
+    /// let runtime_ptr = COMPTIME_PTR;
+    /// assert_ne!(
+    ///     runtime_ptr.is_aligned_to(8),
+    ///     runtime_ptr.wrapping_add(1).is_aligned_to(8),
+    /// );
+    /// ```
+    ///
+    /// If a pointer is created from a fixed address, this function behaves the same during
+    /// runtime and compiletime.
+    ///
+    #[cfg_attr(bootstrap, doc = "```ignore")]
+    #[cfg_attr(not(bootstrap), doc = "```")]
+    /// #![feature(pointer_is_aligned)]
+    /// #![feature(const_pointer_is_aligned)]
+    ///
+    /// const _: () = {
+    ///     let ptr = 40 as *mut u8;
+    ///     assert!(ptr.is_aligned_to(1));
+    ///     assert!(ptr.is_aligned_to(2));
+    ///     assert!(ptr.is_aligned_to(4));
+    ///     assert!(ptr.is_aligned_to(8));
+    ///     assert!(!ptr.is_aligned_to(16));
+    /// };
+    /// ```
+    ///
+    /// [tracking issue]: https://github.com/rust-lang/rust/issues/104203
     #[must_use]
     #[inline]
     #[unstable(feature = "pointer_is_aligned", issue = "96284")]
-    pub fn is_aligned_to(self, align: usize) -> bool {
+    #[rustc_const_unstable(feature = "const_pointer_is_aligned", issue = "104203")]
+    pub const fn is_aligned_to(self, align: usize) -> bool {
         if !align.is_power_of_two() {
             panic!("is_aligned_to: align is not a power-of-two");
         }
 
-        // Cast is needed for `T: !Sized`
-        self.cast::<u8>().addr() & align - 1 == 0
+        // We can't use the address of `self` in a `const fn`, so we use `align_offset` instead.
+        // The cast to `()` is used to
+        //   1. deal with fat pointers; and
+        //   2. ensure that `align_offset` doesn't actually try to compute an offset.
+        self.cast::<()>().align_offset(align) == 0
     }
 }
 

library/core/tests/lib.rs

@@ -4,6 +4,7 @@
 #![feature(array_windows)]
 #![feature(bigint_helper_methods)]
 #![feature(cell_update)]
+#![feature(const_align_offset)]
 #![feature(const_assume)]
 #![feature(const_align_of_val_raw)]
 #![feature(const_black_box)]
@@ -18,6 +19,7 @@
 #![feature(const_nonnull_new)]
 #![feature(const_num_from_num)]
 #![feature(const_pointer_byte_offsets)]
+#![feature(const_pointer_is_aligned)]
 #![feature(const_ptr_as_ref)]
 #![feature(const_ptr_read)]
 #![feature(const_ptr_write)]
@@ -81,6 +83,7 @@
 #![feature(never_type)]
 #![feature(unwrap_infallible)]
 #![feature(pointer_byte_offsets)]
+#![feature(pointer_is_aligned)]
 #![feature(portable_simd)]
 #![feature(ptr_metadata)]
 #![feature(once_cell)]

library/core/tests/ptr.rs

@@ -358,6 +358,23 @@ fn align_offset_zst() {
     }
 }
 
+#[test]
+#[cfg(not(bootstrap))]
+fn align_offset_zst_const() {
+    const {
+        // For pointers of stride = 0, the pointer is already aligned or it cannot be aligned at
+        // all, because no amount of elements will align the pointer.
+        let mut p = 1;
+        while p < 1024 {
+            assert!(ptr::invalid::<()>(p).align_offset(p) == 0);
+            if p != 1 {
+                assert!(ptr::invalid::<()>(p + 1).align_offset(p) == !0);
+            }
+            p = (p + 1).next_power_of_two();
+        }
+    }
+}
+
 #[test]
 fn align_offset_stride_one() {
     // For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
@@ -379,6 +396,26 @@ fn align_offset_stride_one() {
     }
 }
 
+#[test]
+#[cfg(not(bootstrap))]
+fn align_offset_stride_one_const() {
+    const {
+        // For pointers of stride = 1, the pointer can always be aligned. The offset is equal to
+        // number of bytes.
+        let mut align = 1;
+        while align < 1024 {
+            let mut ptr = 1;
+            while ptr < 2 * align {
+                let expected = ptr % align;
+                let offset = if expected == 0 { 0 } else { align - expected };
+                assert!(ptr::invalid::<u8>(ptr).align_offset(align) == offset);
+                ptr += 1;
+            }
+            align = (align + 1).next_power_of_two();
+        }
+    }
+}
+
 #[test]
 fn align_offset_various_strides() {
     unsafe fn test_stride<T>(ptr: *const T, align: usize) -> bool {
@@ -455,6 +492,182 @@ fn align_offset_various_strides() {
     assert!(!x);
 }
 
+#[test]
+#[cfg(not(bootstrap))]
+fn align_offset_various_strides_const() {
+    const unsafe fn test_stride<T>(ptr: *const T, numptr: usize, align: usize) {
+        let mut expected = usize::MAX;
+        // Naive but definitely correct way to find the *first* aligned element of stride::<T>.
+        let mut el = 0;
+        while el < align {
+            if (numptr + el * ::std::mem::size_of::<T>()) % align == 0 {
+                expected = el;
+                break;
+            }
+            el += 1;
+        }
+        let got = ptr.align_offset(align);
+        assert!(got == expected);
+    }
+
+    const {
+        // For pointers of stride != 1, we verify the algorithm against the naivest possible
+        // implementation
+        let mut align = 1;
+        let limit = 32;
+        while align < limit {
+            let mut ptr = 1;
+            while ptr < 4 * align {
+                unsafe {
+                    #[repr(packed)]
+                    struct A3(u16, u8);
+                    test_stride::<A3>(ptr::invalid::<A3>(ptr), ptr, align);
+
+                    struct A4(u32);
+                    test_stride::<A4>(ptr::invalid::<A4>(ptr), ptr, align);
+
+                    #[repr(packed)]
+                    struct A5(u32, u8);
+                    test_stride::<A5>(ptr::invalid::<A5>(ptr), ptr, align);
+
+                    #[repr(packed)]
+                    struct A6(u32, u16);
+                    test_stride::<A6>(ptr::invalid::<A6>(ptr), ptr, align);
+
+                    #[repr(packed)]
+                    struct A7(u32, u16, u8);
+                    test_stride::<A7>(ptr::invalid::<A7>(ptr), ptr, align);
+
+                    #[repr(packed)]
+                    struct A8(u32, u32);
+                    test_stride::<A8>(ptr::invalid::<A8>(ptr), ptr, align);
+
+                    #[repr(packed)]
+                    struct A9(u32, u32, u8);
+                    test_stride::<A9>(ptr::invalid::<A9>(ptr), ptr, align);
+
+                    #[repr(packed)]
+                    struct A10(u32, u32, u16);
+                    test_stride::<A10>(ptr::invalid::<A10>(ptr), ptr, align);
+
+                    test_stride::<u32>(ptr::invalid::<u32>(ptr), ptr, align);
+                    test_stride::<u128>(ptr::invalid::<u128>(ptr), ptr, align);
+                }
+                ptr += 1;
+            }
+            align = (align + 1).next_power_of_two();
+        }
+    }
+}
+
+#[test]
+#[cfg(not(bootstrap))]
+fn align_offset_with_provenance_const() {
+    const {
+        // On some platforms (e.g. msp430-none-elf), the alignment of `i32` is less than 4.
+        #[repr(align(4))]
+        struct AlignedI32(i32);
+
+        let data = AlignedI32(42);
+
+        // `stride % align == 0` (usual case)
+
+        let ptr: *const i32 = &data.0;
+        assert!(ptr.align_offset(1) == 0);
+        assert!(ptr.align_offset(2) == 0);
+        assert!(ptr.align_offset(4) == 0);
+        assert!(ptr.align_offset(8) == usize::MAX);
+        assert!(ptr.wrapping_byte_add(1).align_offset(1) == 0);
+        assert!(ptr.wrapping_byte_add(1).align_offset(2) == usize::MAX);
+        assert!(ptr.wrapping_byte_add(2).align_offset(1) == 0);
+        assert!(ptr.wrapping_byte_add(2).align_offset(2) == 0);
+        assert!(ptr.wrapping_byte_add(2).align_offset(4) == usize::MAX);
+        assert!(ptr.wrapping_byte_add(3).align_offset(1) == 0);
+        assert!(ptr.wrapping_byte_add(3).align_offset(2) == usize::MAX);
+
+        assert!(ptr.wrapping_add(42).align_offset(4) == 0);
+        assert!(ptr.wrapping_add(42).align_offset(8) == usize::MAX);
+
+        let ptr1: *const i8 = ptr.cast();
+        assert!(ptr1.align_offset(1) == 0);
+        assert!(ptr1.align_offset(2) == 0);
+        assert!(ptr1.align_offset(4) == 0);
+        assert!(ptr1.align_offset(8) == usize::MAX);
+        assert!(ptr1.wrapping_byte_add(1).align_offset(1) == 0);
+        assert!(ptr1.wrapping_byte_add(1).align_offset(2) == 1);
+        assert!(ptr1.wrapping_byte_add(1).align_offset(4) == 3);
+        assert!(ptr1.wrapping_byte_add(1).align_offset(8) == usize::MAX);
+        assert!(ptr1.wrapping_byte_add(2).align_offset(1) == 0);
+        assert!(ptr1.wrapping_byte_add(2).align_offset(2) == 0);
+        assert!(ptr1.wrapping_byte_add(2).align_offset(4) == 2);
+        assert!(ptr1.wrapping_byte_add(2).align_offset(8) == usize::MAX);
+        assert!(ptr1.wrapping_byte_add(3).align_offset(1) == 0);
+        assert!(ptr1.wrapping_byte_add(3).align_offset(2) == 1);
+        assert!(ptr1.wrapping_byte_add(3).align_offset(4) == 1);
+        assert!(ptr1.wrapping_byte_add(3).align_offset(8) == usize::MAX);
+
+        let ptr2: *const i16 = ptr.cast();
+        assert!(ptr2.align_offset(1) == 0);
+        assert!(ptr2.align_offset(2) == 0);
+        assert!(ptr2.align_offset(4) == 0);
+        assert!(ptr2.align_offset(8) == usize::MAX);
+        assert!(ptr2.wrapping_byte_add(1).align_offset(1) == 0);
+        assert!(ptr2.wrapping_byte_add(1).align_offset(2) == usize::MAX);
+        assert!(ptr2.wrapping_byte_add(2).align_offset(1) == 0);
+        assert!(ptr2.wrapping_byte_add(2).align_offset(2) == 0);
+        assert!(ptr2.wrapping_byte_add(2).align_offset(4) == 1);
+        assert!(ptr2.wrapping_byte_add(2).align_offset(8) == usize::MAX);
+        assert!(ptr2.wrapping_byte_add(3).align_offset(1) == 0);
+        assert!(ptr2.wrapping_byte_add(3).align_offset(2) == usize::MAX);
+
+        let ptr3: *const i64 = ptr.cast();
+        assert!(ptr3.align_offset(1) == 0);
+        assert!(ptr3.align_offset(2) == 0);
+        assert!(ptr3.align_offset(4) == 0);
+        assert!(ptr3.align_offset(8) == usize::MAX);
+        assert!(ptr3.wrapping_byte_add(1).align_offset(1) == 0);
+        assert!(ptr3.wrapping_byte_add(1).align_offset(2) == usize::MAX);
+
+        // `stride % align != 0` (edge case)
+
+        let ptr4: *const [u8; 3] = ptr.cast();
+        assert!(ptr4.align_offset(1) == 0);
+        assert!(ptr4.align_offset(2) == 0);
+        assert!(ptr4.align_offset(4) == 0);
+        assert!(ptr4.align_offset(8) == usize::MAX);
+        assert!(ptr4.wrapping_byte_add(1).align_offset(1) == 0);
+        assert!(ptr4.wrapping_byte_add(1).align_offset(2) == 1);
+        assert!(ptr4.wrapping_byte_add(1).align_offset(4) == 1);
+        assert!(ptr4.wrapping_byte_add(1).align_offset(8) == usize::MAX);
+        assert!(ptr4.wrapping_byte_add(2).align_offset(1) == 0);
+        assert!(ptr4.wrapping_byte_add(2).align_offset(2) == 0);
+        assert!(ptr4.wrapping_byte_add(2).align_offset(4) == 2);
+        assert!(ptr4.wrapping_byte_add(2).align_offset(8) == usize::MAX);
+        assert!(ptr4.wrapping_byte_add(3).align_offset(1) == 0);
+        assert!(ptr4.wrapping_byte_add(3).align_offset(2) == 1);
+        assert!(ptr4.wrapping_byte_add(3).align_offset(4) == 3);
+        assert!(ptr4.wrapping_byte_add(3).align_offset(8) == usize::MAX);
+
+        let ptr5: *const [u8; 5] = ptr.cast();
+        assert!(ptr5.align_offset(1) == 0);
+        assert!(ptr5.align_offset(2) == 0);
+        assert!(ptr5.align_offset(4) == 0);
+        assert!(ptr5.align_offset(8) == usize::MAX);
+        assert!(ptr5.wrapping_byte_add(1).align_offset(1) == 0);
+        assert!(ptr5.wrapping_byte_add(1).align_offset(2) == 1);
+        assert!(ptr5.wrapping_byte_add(1).align_offset(4) == 3);
+        assert!(ptr5.wrapping_byte_add(1).align_offset(8) == usize::MAX);
+        assert!(ptr5.wrapping_byte_add(2).align_offset(1) == 0);
+        assert!(ptr5.wrapping_byte_add(2).align_offset(2) == 0);
+        assert!(ptr5.wrapping_byte_add(2).align_offset(4) == 2);
+        assert!(ptr5.wrapping_byte_add(2).align_offset(8) == usize::MAX);
+        assert!(ptr5.wrapping_byte_add(3).align_offset(1) == 0);
+        assert!(ptr5.wrapping_byte_add(3).align_offset(2) == 1);
+        assert!(ptr5.wrapping_byte_add(3).align_offset(4) == 1);
+        assert!(ptr5.wrapping_byte_add(3).align_offset(8) == usize::MAX);
+    }
+}
+
 #[test]
 fn align_offset_issue_103361() {
     #[cfg(target_pointer_width = "64")]
@@ -467,6 +680,72 @@ fn align_offset_issue_103361() {
     let _ = (SIZE as *const HugeSize).align_offset(SIZE);
 }
 
+#[test]
+#[cfg(not(bootstrap))]
+fn align_offset_issue_103361_const() {
+    #[cfg(target_pointer_width = "64")]
+    const SIZE: usize = 1 << 47;
+    #[cfg(target_pointer_width = "32")]
+    const SIZE: usize = 1 << 30;
+    #[cfg(target_pointer_width = "16")]
+    const SIZE: usize = 1 << 13;
+    struct HugeSize([u8; SIZE - 1]);
+
+    const {
+        assert!(ptr::invalid::<HugeSize>(SIZE - 1).align_offset(SIZE) == SIZE - 1);
+        assert!(ptr::invalid::<HugeSize>(SIZE).align_offset(SIZE) == 0);
+        assert!(ptr::invalid::<HugeSize>(SIZE + 1).align_offset(SIZE) == 1);
+    }
+}
+
+#[test]
+fn is_aligned() {
+    let data = 42;
+    let ptr: *const i32 = &data;
+    assert!(ptr.is_aligned());
+    assert!(ptr.is_aligned_to(1));
+    assert!(ptr.is_aligned_to(2));
+    assert!(ptr.is_aligned_to(4));
+    assert!(ptr.wrapping_byte_add(2).is_aligned_to(1));
+    assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
+    assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
+
+    // At runtime either `ptr` or `ptr+1` is aligned to 8.
+    assert_ne!(ptr.is_aligned_to(8), ptr.wrapping_add(1).is_aligned_to(8));
+}
+
+#[test]
+#[cfg(not(bootstrap))]
+fn is_aligned_const() {
+    const {
+        let data = 42;
+        let ptr: *const i32 = &data;
+        assert!(ptr.is_aligned());
+        assert!(ptr.is_aligned_to(1));
+        assert!(ptr.is_aligned_to(2));
+        assert!(ptr.is_aligned_to(4));
+        assert!(ptr.wrapping_byte_add(2).is_aligned_to(1));
+        assert!(ptr.wrapping_byte_add(2).is_aligned_to(2));
+        assert!(!ptr.wrapping_byte_add(2).is_aligned_to(4));
+
+        // At comptime neither `ptr` nor `ptr+1` is aligned to 8.
+        assert!(!ptr.is_aligned_to(8));
+        assert!(!ptr.wrapping_add(1).is_aligned_to(8));
+    }
+}
+
+#[test]
+#[cfg(bootstrap)]
+fn is_aligned_const() {
+    const {
+        let data = 42;
+        let ptr: *const i32 = &data;
+        // The bootstrap compiler always returns false for is_aligned.
+        assert!(!ptr.is_aligned());
+        assert!(!ptr.is_aligned_to(1));
+    }
+}
+
 #[test]
 fn offset_from() {
     let mut a = [0; 5];

src/test/assembly/is_aligned.rs

@@ -0,0 +1,58 @@
+// assembly-output: emit-asm
+// min-llvm-version: 14.0
+// only-x86_64
+// revisions: opt-speed opt-size
+// [opt-speed] compile-flags: -Copt-level=1
+// [opt-size] compile-flags: -Copt-level=s
+#![crate_type="rlib"]
+
+#![feature(core_intrinsics)]
+#![feature(pointer_is_aligned)]
+
+// CHECK-LABEL: is_aligned_to_unchecked
+// CHECK: decq
+// CHECK-NEXT: testq
+// CHECK-NEXT: sete
+// CHECK: retq
+#[no_mangle]
+pub unsafe fn is_aligned_to_unchecked(ptr: *const u8, align: usize) -> bool {
+    unsafe {
+        std::intrinsics::assume(align.is_power_of_two())
+    }
+    ptr.is_aligned_to(align)
+}
+
+// CHECK-LABEL: is_aligned_1
+// CHECK: movb $1
+// CHECK: retq
+#[no_mangle]
+pub fn is_aligned_1(ptr: *const u8) -> bool {
+    ptr.is_aligned()
+}
+
+// CHECK-LABEL: is_aligned_2
+// CHECK: testb $1
+// CHECK-NEXT: sete
+// CHECK: retq
+#[no_mangle]
+pub fn is_aligned_2(ptr: *const u16) -> bool {
+    ptr.is_aligned()
+}
+
+// CHECK-LABEL: is_aligned_4
+// CHECK: testb $3
+// CHECK-NEXT: sete
+// CHECK: retq
+#[no_mangle]
+pub fn is_aligned_4(ptr: *const u32) -> bool {
+    ptr.is_aligned()
+}
+
+// CHECK-LABEL: is_aligned_8
+// CHECK: testb $7
+// CHECK-NEXT: sete
+// CHECK: retq
+#[no_mangle]
+pub fn is_aligned_8(ptr: *const u64) -> bool {
+    ptr.is_aligned()
+}

src/tools/miri/src/shims/intrinsics/mod.rs

@@ -368,11 +368,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             }
 
             // Other
-            "exact_div" => {
-                let [num, denom] = check_arg_count(args)?;
-                this.exact_div(&this.read_immediate(num)?, &this.read_immediate(denom)?, dest)?;
-            }
-
             "breakpoint" => {
                 let [] = check_arg_count(args)?;
                 // normally this would raise a SIGTRAP, which aborts if no debugger is connected