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Use `drop_in_place` in `array::IntoIter::drop`

This skips the loop when the element type is known not to have drop glue, even in debug mode.
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SimonSapin committed Oct 25, 2019
1 parent a0d40f8 commit 74b571402f980f70a4d87ec3c778af568e4fa329
Showing with 18 additions and 4 deletions.
  1. +18 −4 src/libcore/array/iter.rs
@@ -92,6 +92,18 @@ where
mem::transmute::<&[MaybeUninit<T>], &[T]>(slice)
}
}

/// Returns a mutable slice of all elements that have not been yielded yet.
fn as_mut_slice(&mut self) -> &mut [T] {
// This transmute is safe, same as in `as_slice` above.
let slice = &mut self.data[self.alive.clone()];
// SAFETY: This transmute is safe. As mentioned in `new`, `MaybeUninit` retains
// the size and alignment of `T`. Furthermore, we know that all
// elements within `alive` are properly initialized.
unsafe {
mem::transmute::<&mut [MaybeUninit<T>], &mut [T]>(slice)
}
}
}


@@ -184,10 +196,12 @@ where
[T; N]: LengthAtMost32,
{
fn drop(&mut self) {
// We simply drop each element via `for_each`. This should not incur
// any significant runtime overhead and avoids adding another `unsafe`
// block.
self.by_ref().for_each(drop);
// SAFETY: This is safe: `as_mut_slice` returns exactly the sub-slice
// of elements that have not been moved out yet and that remain
// to be dropped.
unsafe {
ptr::drop_in_place(self.as_mut_slice())
}
}
}

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