Merge pull request #2215 from Kobzol/pull

rustc pull

1 files changed, 9 insertions, 3 deletions

diff --git a/library/core/src/ptr/alignment.rs b/library/core/src/ptr/alignment.rs
index 74a1d40f4e7..2da94e72566 100644
--- a/library/core/src/ptr/alignment.rs
+++ b/library/core/src/ptr/alignment.rs
@@ -42,9 +42,10 @@ impl Alignment {
     /// but in an `Alignment` instead of a `usize`.
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
+    #[must_use]
     pub const fn of<T>() -> Self {
-        // SAFETY: rustc ensures that type alignment is always a power of two.
-        unsafe { Alignment::new_unchecked(mem::align_of::<T>()) }
+        // This can't actually panic since type alignment is always a power of two.
+        const { Alignment::new(mem::align_of::<T>()).unwrap() }
     }
 
     /// Creates an `Alignment` from a `usize`, or returns `None` if it's
@@ -95,8 +96,13 @@ impl Alignment {
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
     pub const fn as_nonzero(self) -> NonZero<usize> {
+        // This transmutes directly to avoid the UbCheck in `NonZero::new_unchecked`
+        // since there's no way for the user to trip that check anyway -- the
+        // validity invariant of the type would have to have been broken earlier --
+        // and emitting it in an otherwise simple method is bad for compile time.
+
         // SAFETY: All the discriminants are non-zero.
-        unsafe { NonZero::new_unchecked(self.as_usize()) }
+        unsafe { mem::transmute::<Alignment, NonZero<usize>>(self) }
     }
 
     /// Returns the base-2 logarithm of the alignment.