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Auto merge of #79520 - ssomers:btree_cleanup_1, r=Mark-Simulacrum
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BTreeMap: clean up access to MaybeUninit arrays

Stop exposing and using immutable access to `MaybeUninit` slices when we need and have exclusive access to the tree.

r? `@Mark-Simulacrum`
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@bors
bors committed Dec 26, 2020
2 parents 30a4273 + 0d2548a commit 89524d0
Showing 1 changed file with 17 additions and 64 deletions.
81 changes: 17 additions & 64 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -295,15 +295,6 @@ impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
}
}

impl<'a, K, V> NodeRef<marker::Immut<'a>, K, V, marker::Internal> {
/// Exposes the data of an internal node in an immutable tree.
fn as_internal(this: &Self) -> &'a InternalNode<K, V> {
let ptr = Self::as_internal_ptr(this);
// SAFETY: there can be no mutable references into this tree borrowed as `Immut`.
unsafe { &*ptr }
}
}

impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
/// Borrows exclusive access to the data of an internal node.
fn as_internal_mut(&mut self) -> &mut InternalNode<K, V> {
Expand Down Expand Up @@ -368,17 +359,6 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
}
}

impl<'a, K, V> NodeRef<marker::Immut<'a>, K, V, marker::Internal> {
/// Exposes the contents of one of the edges in the node.
///
/// # Safety
/// The node has more than `idx` initialized elements.
unsafe fn edge_at(self, idx: usize) -> &'a BoxedNode<K, V> {
debug_assert!(idx <= self.len());
unsafe { Self::as_internal(&self).edges.get_unchecked(idx).assume_init_ref() }
}
}

impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
/// Finds the parent of the current node. Returns `Ok(handle)` if the current
/// node actually has a parent, where `handle` points to the edge of the parent
Expand Down Expand Up @@ -550,31 +530,6 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
}
}

impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
/// Exposes the entire key storage area in the node,
/// regardless of the node's current length,
/// having exclusive access to the entire node.
unsafe fn key_area(self) -> &'a [MaybeUninit<K>] {
self.into_leaf().keys.as_slice()
}

/// Exposes the entire value storage area in the node,
/// regardless of the node's current length,
/// having exclusive access to the entire node.
unsafe fn val_area(self) -> &'a [MaybeUninit<V>] {
self.into_leaf().vals.as_slice()
}
}

impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::Internal> {
/// Exposes the entire storage area for edge contents in the node,
/// regardless of the node's current length,
/// having exclusive access to the entire node.
unsafe fn edge_area(self) -> &'a [MaybeUninit<BoxedNode<K, V>>] {
Self::as_internal(&self).edges.as_slice()
}
}

impl<'a, K, V, Type> NodeRef<marker::ValMut<'a>, K, V, Type> {
/// # Safety
/// - The node has more than `idx` initialized elements.
Expand Down Expand Up @@ -707,12 +662,12 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
let idx = self.len() - 1;

unsafe {
let key = ptr::read(self.reborrow().key_at(idx));
let val = ptr::read(self.reborrow().val_at(idx));
let key = self.key_area_mut_at(idx).assume_init_read();
let val = self.val_area_mut_at(idx).assume_init_read();
let edge = match self.reborrow_mut().force() {
ForceResult::Leaf(_) => None,
ForceResult::Internal(internal) => {
let node = ptr::read(internal.reborrow().edge_at(idx + 1));
ForceResult::Internal(mut internal) => {
let node = internal.edge_area_mut_at(idx + 1).assume_init_read();
let mut edge = Root { node, height: internal.height - 1, _marker: PhantomData };
// Currently, clearing the parent link is superfluous, because we will
// insert the node elsewhere and set its parent link again.
Expand Down Expand Up @@ -1172,16 +1127,16 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>
let new_len = self.node.len() - self.idx - 1;
new_node.len = new_len as u16;
unsafe {
let k = ptr::read(self.node.reborrow().key_at(self.idx));
let v = ptr::read(self.node.reborrow().val_at(self.idx));
let k = self.node.key_area_mut_at(self.idx).assume_init_read();
let v = self.node.val_area_mut_at(self.idx).assume_init_read();

ptr::copy_nonoverlapping(
self.node.reborrow().key_area().as_ptr().add(self.idx + 1),
self.node.key_area_mut_at(self.idx + 1..).as_ptr(),
new_node.keys.as_mut_ptr(),
new_len,
);
ptr::copy_nonoverlapping(
self.node.reborrow().val_area().as_ptr().add(self.idx + 1),
self.node.val_area_mut_at(self.idx + 1..).as_ptr(),
new_node.vals.as_mut_ptr(),
new_len,
);
Expand Down Expand Up @@ -1240,7 +1195,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
let kv = self.split_leaf_data(&mut new_node.data);
let new_len = usize::from(new_node.data.len);
ptr::copy_nonoverlapping(
self.node.reborrow().edge_area().as_ptr().add(self.idx + 1),
self.node.edge_area_mut_at(self.idx + 1..).as_ptr(),
new_node.edges.as_mut_ptr(),
new_len + 1,
);
Expand Down Expand Up @@ -1352,7 +1307,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
let old_parent_len = parent_node.len();
let mut left_node = self.left_child;
let old_left_len = left_node.len();
let right_node = self.right_child;
let mut right_node = self.right_child;
let right_len = right_node.len();
let new_left_len = old_left_len + 1 + right_len;

Expand All @@ -1370,7 +1325,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
slice_remove(parent_node.key_area_mut_at(..old_parent_len), parent_idx);
left_node.key_area_mut_at(old_left_len).write(parent_key);
ptr::copy_nonoverlapping(
right_node.reborrow().key_area().as_ptr(),
right_node.key_area_mut_at(..).as_ptr(),
left_node.key_area_mut_at(old_left_len + 1..).as_mut_ptr(),
right_len,
);
Expand All @@ -1379,7 +1334,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
slice_remove(parent_node.val_area_mut_at(..old_parent_len), parent_idx);
left_node.val_area_mut_at(old_left_len).write(parent_val);
ptr::copy_nonoverlapping(
right_node.reborrow().val_area().as_ptr(),
right_node.val_area_mut_at(..).as_ptr(),
left_node.val_area_mut_at(old_left_len + 1..).as_mut_ptr(),
right_len,
);
Expand All @@ -1392,9 +1347,9 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
// SAFETY: the height of the nodes being merged is one below the height
// of the node of this edge, thus above zero, so they are internal.
let mut left_node = left_node.reborrow_mut().cast_to_internal_unchecked();
let right_node = right_node.cast_to_internal_unchecked();
let mut right_node = right_node.cast_to_internal_unchecked();
ptr::copy_nonoverlapping(
right_node.reborrow().edge_area().as_ptr(),
right_node.edge_area_mut_at(..).as_ptr(),
left_node.edge_area_mut_at(old_left_len + 1..).as_mut_ptr(),
right_len + 1,
);
Expand Down Expand Up @@ -1503,7 +1458,6 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
(ForceResult::Internal(left), ForceResult::Internal(mut right)) => {
// Make room for stolen edges.
let left = left.reborrow();
let right_edges = right.edge_area_mut_at(..).as_mut_ptr();
ptr::copy(right_edges, right_edges.add(count), old_right_len + 1);
right.correct_childrens_parent_links(count..new_right_len + 1);
Expand Down Expand Up @@ -1561,7 +1515,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
(ForceResult::Internal(left), ForceResult::Internal(mut right)) => {
// Steal edges.
move_edges(right.reborrow(), 0, left, old_left_len + 1, count);
move_edges(right.reborrow_mut(), 0, left, old_left_len + 1, count);

// Fill gap where stolen edges used to be.
let right_edges = right.edge_area_mut_at(..).as_mut_ptr();
Expand Down Expand Up @@ -1590,14 +1544,14 @@ unsafe fn move_kv<K, V>(

// Source and destination must have the same height.
unsafe fn move_edges<'a, K: 'a, V: 'a>(
source: NodeRef<marker::Immut<'a>, K, V, marker::Internal>,
mut source: NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
source_offset: usize,
mut dest: NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
dest_offset: usize,
count: usize,
) {
unsafe {
let source_ptr = source.edge_area().as_ptr();
let source_ptr = source.edge_area_mut_at(..).as_ptr();
let dest_ptr = dest.edge_area_mut_at(dest_offset..).as_mut_ptr();
ptr::copy_nonoverlapping(source_ptr.add(source_offset), dest_ptr, count);
dest.correct_childrens_parent_links(dest_offset..dest_offset + count);
Expand Down Expand Up @@ -1699,7 +1653,6 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, ma

match (left_node.force(), right_node.force()) {
(ForceResult::Internal(left), ForceResult::Internal(right)) => {
let left = left.reborrow();
move_edges(left, new_left_len + 1, right, 1, new_right_len);
}
(ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
Expand Down

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