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BTreeMap: prefer bulk_steal functions over specialized ones #81115

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Jan 19, 2021
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BTreeMap: prefer bulk_steal functions over specialized ones #81115

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121 changes: 4 additions & 117 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -592,17 +592,6 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
self.val_area_mut(idx).write(val);
}
}

/// Adds a key-value pair to the beginning of the node.
fn push_front(&mut self, key: K, val: V) {
let new_len = self.len() + 1;
assert!(new_len <= CAPACITY);
unsafe {
slice_insert(self.key_area_mut(..new_len), 0, key);
slice_insert(self.val_area_mut(..new_len), 0, val);
*self.len_mut() = new_len as u16;
}
}
}

impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
Expand Down Expand Up @@ -638,88 +627,6 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
Handle::new_edge(self.reborrow_mut(), idx + 1).correct_parent_link();
}
}

/// Adds a key-value pair, and an edge to go to the left of that pair,
/// to the beginning of the node.
fn push_front(&mut self, key: K, val: V, edge: Root<K, V>) {
let new_len = self.len() + 1;
assert!(edge.height == self.height - 1);
assert!(new_len <= CAPACITY);

unsafe {
slice_insert(self.key_area_mut(..new_len), 0, key);
slice_insert(self.val_area_mut(..new_len), 0, val);
slice_insert(self.edge_area_mut(..new_len + 1), 0, edge.node);
*self.len_mut() = new_len as u16;
}

self.correct_all_childrens_parent_links();
}
}

impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
/// Removes a key-value pair from the end of the node and returns the pair.
/// Also removes the edge that was to the right of that pair and, if the node
/// is internal, returns the orphaned subtree that this edge owned.
///
/// # Safety
/// The node must not be empty.
unsafe fn pop(&mut self) -> (K, V, Option<Root<K, V>>) {
debug_assert!(self.len() > 0);

let idx = self.len() - 1;

unsafe {
let key = self.key_area_mut(idx).assume_init_read();
let val = self.val_area_mut(idx).assume_init_read();
let edge = match self.reborrow_mut().force() {
ForceResult::Leaf(_) => None,
ForceResult::Internal(mut internal) => {
let node = internal.edge_area_mut(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.
edge.clear_parent_link();
Some(edge)
}
};

*self.len_mut() -= 1;
(key, val, edge)
}
}

/// Removes a key-value pair from the beginning of the node and returns the pair.
/// Also removes the edge that was to the left of that pair and, if the node is
/// internal, returns the orphaned subtree that this edge owned.
fn pop_front(&mut self) -> (K, V, Option<Root<K, V>>) {
debug_assert!(self.len() > 0);

let old_len = self.len();

unsafe {
let key = slice_remove(self.key_area_mut(..old_len), 0);
let val = slice_remove(self.val_area_mut(..old_len), 0);
let edge = match self.reborrow_mut().force() {
ForceResult::Leaf(_) => None,
ForceResult::Internal(mut internal) => {
let node = slice_remove(internal.edge_area_mut(..old_len + 1), 0);
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.
edge.clear_parent_link();

internal.correct_childrens_parent_links(0..old_len);

Some(edge)
}
};

*self.len_mut() -= 1;

(key, val, edge)
}
}
}

impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
Expand Down Expand Up @@ -1399,18 +1306,8 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
mut self,
track_right_edge_idx: usize,
) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
unsafe {
let (k, v, edge) = self.left_child.pop();

let (k, v) = self.parent.replace_kv(k, v);

match self.right_child.reborrow_mut().force() {
ForceResult::Leaf(mut leaf) => leaf.push_front(k, v),
ForceResult::Internal(mut internal) => internal.push_front(k, v, edge.unwrap()),
}

Handle::new_edge(self.right_child, 1 + track_right_edge_idx)
}
self.bulk_steal_left(1);
unsafe { Handle::new_edge(self.right_child, 1 + track_right_edge_idx) }
}

/// Removes a key-value pair from the right child and places it in the key-value storage
Expand All @@ -1421,18 +1318,8 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
mut self,
track_left_edge_idx: usize,
) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
unsafe {
let (k, v, edge) = self.right_child.pop_front();

let (k, v) = self.parent.replace_kv(k, v);

match self.left_child.reborrow_mut().force() {
ForceResult::Leaf(mut leaf) => leaf.push(k, v),
ForceResult::Internal(mut internal) => internal.push(k, v, edge.unwrap()),
}

Handle::new_edge(self.left_child, track_left_edge_idx)
}
self.bulk_steal_right(1);
unsafe { Handle::new_edge(self.left_child, track_left_edge_idx) }
}

/// This does stealing similar to `steal_left` but steals multiple elements at once.
Expand Down
8 changes: 4 additions & 4 deletions library/alloc/src/collections/btree/remove.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -121,25 +121,25 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
self,
) -> Option<NodeRef<marker::Mut<'a>, K, V, marker::Internal>> {
match self.forget_type().choose_parent_kv() {
Ok(Left(left_parent_kv)) => {
Ok(Left(mut left_parent_kv)) => {
debug_assert_eq!(left_parent_kv.right_child_len(), MIN_LEN - 1);
if left_parent_kv.can_merge() {
let parent = left_parent_kv.merge_tracking_parent();
Some(parent)
} else {
debug_assert!(left_parent_kv.left_child_len() > MIN_LEN);
left_parent_kv.steal_left(0);
left_parent_kv.bulk_steal_left(1);
None
}
}
Ok(Right(right_parent_kv)) => {
Ok(Right(mut right_parent_kv)) => {
debug_assert_eq!(right_parent_kv.left_child_len(), MIN_LEN - 1);
if right_parent_kv.can_merge() {
let parent = right_parent_kv.merge_tracking_parent();
Some(parent)
} else {
debug_assert!(right_parent_kv.right_child_len() > MIN_LEN);
right_parent_kv.steal_right(0);
right_parent_kv.bulk_steal_right(1);
None
}
}
Expand Down