move calling miri_promise_symbolic_alignment to a shared helper

library/core/src/intrinsics.rs

@@ -2859,3 +2859,28 @@ pub const unsafe fn write_bytes<T>(dst: *mut T, val: u8, count: usize) {
  write_bytes(dst, val, count)
  }
 }
+
+/// Inform Miri that a given pointer definitely has a certain alignment.
+#[cfg(miri)]
+pub(crate) const fn miri_promise_symbolic_alignment(ptr: *const (), align: usize) {
+ extern "Rust" {
+ /// Miri-provided extern function to promise that a given pointer is properly aligned for
+ /// "symbolic" alignment checks. Will fail if the pointer is not actually aligned or `align` is
+ /// not a power of two. Has no effect when alignment checks are concrete (which is the default).
+ fn miri_promise_symbolic_alignment(ptr: *const (), align: usize);
+ }
+
+ fn runtime(ptr: *const (), align: usize) {
+ // SAFETY: this call is always safe.
+ unsafe {
+ miri_promise_symbolic_alignment(ptr, align);
+ }
+ }
+
+ const fn compiletime(_ptr: *const (), _align: usize) {}
+
+ // SAFETY: the extra behavior at runtime is for UB checks only.
+ unsafe {
+ const_eval_select((ptr, align), compiletime, runtime);
+ }
+}

library/core/src/ptr/const_ptr.rs

@@ -1374,27 +1374,7 @@ impl<T: ?Sized> *const T {
  // Inform Miri that we want to consider the resulting pointer to be suitably aligned.
  #[cfg(miri)]
  if ret != usize::MAX {
- fn runtime(ptr: *const (), align: usize) {
- extern "Rust" {
- pub fn miri_promise_symbolic_alignment(ptr: *const (), align: usize);
- }
-
- // SAFETY: this call is always safe.
- unsafe {
- miri_promise_symbolic_alignment(ptr, align);
- }
- }
-
- const fn compiletime(_ptr: *const (), _align: usize) {}
-
- // SAFETY: the extra behavior at runtime is for UB checks only.
- unsafe {
- intrinsics::const_eval_select(
- (self.wrapping_add(ret).cast(), align),
- compiletime,
- runtime,
- );
- }
+ intrinsics::miri_promise_symbolic_alignment(self.wrapping_add(ret).cast(), align);
  }
 
  ret

library/core/src/ptr/mut_ptr.rs

@@ -1641,27 +1641,10 @@ impl<T: ?Sized> *mut T {
  // Inform Miri that we want to consider the resulting pointer to be suitably aligned.
  #[cfg(miri)]
  if ret != usize::MAX {
- fn runtime(ptr: *const (), align: usize) {
- extern "Rust" {
- pub fn miri_promise_symbolic_alignment(ptr: *const (), align: usize);
- }
-
- // SAFETY: this call is always safe.
- unsafe {
- miri_promise_symbolic_alignment(ptr, align);
- }
- }
-
- const fn compiletime(_ptr: *const (), _align: usize) {}
-
- // SAFETY: the extra behavior at runtime is for UB checks only.
- unsafe {
- intrinsics::const_eval_select(
- (self.wrapping_add(ret).cast_const().cast(), align),
- compiletime,
- runtime,
- );
- }
+ intrinsics::miri_promise_symbolic_alignment(
+ self.wrapping_add(ret).cast_const().cast(),
+ align,
+ );
  }
 
  ret

library/core/src/slice/mod.rs

@@ -3870,16 +3870,10 @@ impl<T> [T] {
  let (us_len, ts_len) = rest.align_to_offsets::<U>();
  // Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
  #[cfg(miri)]
- {
- extern "Rust" {
- pub fn miri_promise_symbolic_alignment(ptr: *const (), align: usize);
- }
-
- // SAFETY: this call is always safe.
- unsafe {
- miri_promise_symbolic_alignment(rest.as_ptr().cast(), mem::align_of::<U>());
- }
- }
+ crate::intrinsics::miri_promise_symbolic_alignment(
+ rest.as_ptr().cast(),
+ mem::align_of::<U>(),
+ );
  // SAFETY: now `rest` is definitely aligned, so `from_raw_parts` below is okay,
  // since the caller guarantees that we can transmute `T` to `U` safely.
  unsafe {
@@ -3952,19 +3946,10 @@ impl<T> [T] {
  let mut_ptr = rest.as_mut_ptr();
  // Inform Miri that we want to consider the "middle" pointer to be suitably aligned.
  #[cfg(miri)]
- {
- extern "Rust" {
- pub fn miri_promise_symbolic_alignment(ptr: *const (), align: usize);
- }
-
- // SAFETY: this call is always safe.
- unsafe {
- miri_promise_symbolic_alignment(
- mut_ptr.cast() as *const (),
- mem::align_of::<U>(),
- );
- }
- }
+ crate::intrinsics::miri_promise_symbolic_alignment(
+ mut_ptr.cast() as *const (),
+ mem::align_of::<U>(),
+ );
  // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
  // SAFETY: see comments for `align_to`.
  unsafe {