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Use ManuallyDrop instead of Option in Hole implementation

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The Option is always Some until drop, where it becomes None. Make
this more explicit and avoid unwraps by using ManuallyDrop.

This change should be performance-neutral as LLVM already optimizes
the unwraps away in the inlined code.
This commit is contained in:
Nikita Popov 2018-05-06 16:55:04 +02:00
parent 6f721f54c6
commit 9f8f366eea
1 changed files with 5 additions and 6 deletions
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11
src/liballoc/binary_heap.rs
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@ -157,7 +157,7 @@
use core::ops::{Deref, DerefMut};
use core::iter::{FromIterator, FusedIterator};
use core::mem::{swap, size_of};
use core::mem::{swap, size_of, ManuallyDrop};
use core::ptr;
use core::fmt;
@ -864,8 +864,7 @@ impl<T: Ord> BinaryHeap<T> {
/// position with the value that was originally removed.
struct Hole<'a, T: 'a> {
data: &'a mut [T],
/// `elt` is always `Some` from new until drop.
elt: Option<T>,
elt: ManuallyDrop<T>,
pos: usize,
}
@ -879,7 +878,7 @@ impl<'a, T> Hole<'a, T> {
let elt = ptr::read(&data[pos]);
Hole {
data,
elt: Some(elt),
elt: ManuallyDrop::new(elt),
pos,
}
}
@ -892,7 +891,7 @@ impl<'a, T> Hole<'a, T> {
/// Returns a reference to the element removed.
#[inline]
fn element(&self) -> &T {
self.elt.as_ref().unwrap()
&self.elt
}
/// Returns a reference to the element at `index`.
@ -925,7 +924,7 @@ impl<'a, T> Drop for Hole<'a, T> {
// fill the hole again
unsafe {
let pos = self.pos;
ptr::write(self.data.get_unchecked_mut(pos), self.elt.take().unwrap());
ptr::copy_nonoverlapping(&*self.elt, self.data.get_unchecked_mut(pos), 1);
}
}
}