assume

Author: bend-n

library/core/src/slice/index.rs

@@ -214,8 +214,7 @@ unsafe impl<T> SliceIndex<[T]> for usize {
     #[inline]
     fn get(self, slice: &[T]) -> Option<&T> {
         // SAFETY: `self` is checked to be in bounds.
-        // The call to `add` is safe, as we check the bounds.
-        if self < slice.len() { unsafe { Some(&*slice.as_ptr().add(self)) } } else { None }
+        if self < slice.len() { unsafe { Some(&*self.get_unchecked(slice)) } } else { None }
     }
 
     #[inline]
@@ -230,14 +229,14 @@ unsafe impl<T> SliceIndex<[T]> for usize {
         // SAFETY: the caller guarantees that `slice` is not dangling, so it
         // cannot be longer than `isize::MAX`. They also guarantee that
         // `self` is in bounds of `slice` so `self` cannot overflow an `isize`,
-        // so we can `unwrap_unchecked`.
-        // We use `get().unwrap_unchecked()` for better codegen: see issue #116878
+        // so the call to `add` is safe.
         unsafe {
             assert_unsafe_precondition!(
                 "slice::get_unchecked requires that the index is within the slice",
                 [T](this: usize, slice: *const [T]) => this < slice.len()
             );
-            self.get(&*slice).unwrap_unchecked() as *const _
+            crate::intrinsics::assume(self < slice.len());
+            slice.as_ptr().add(self)
         }
     }