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Rollup merge of #77005 - ssomers:btree_cleanup_3, r=Mark-Simulacrum 

BtreeMap: refactoring around edges

Parts chipped off a more daring effort, that the btree benchmarks judge to be performance-neutral.

r? @Mark-Simulacrum
This commit is contained in:
Jonas Schievink 2020-09-25 19:42:31 +02:00 committed by GitHub
parent 1b8c939a8d 55fa8afe94
commit e8dc07c242
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 99 additions and 110 deletions
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209
library/alloc/src/collections/btree/node.rs
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@ -47,8 +47,7 @@ const KV_IDX_CENTER: usize = B - 1;
const EDGE_IDX_LEFT_OF_CENTER: usize = B - 1;
const EDGE_IDX_RIGHT_OF_CENTER: usize = B;
/// The underlying representation of leaf nodes.
#[repr(C)]
/// The underlying representation of leaf nodes and part of the representation of internal nodes.
struct LeafNode<K, V> {
/// We want to be covariant in `K` and `V`.
parent: Option<NonNull<InternalNode<K, V>>>,
@ -59,9 +58,6 @@ struct LeafNode<K, V> {
parent_idx: MaybeUninit<u16>,
/// The number of keys and values this node stores.
///
/// This next to `parent_idx` to encourage the compiler to join `len` and
/// `parent_idx` into the same 32-bit word, reducing space overhead.
len: u16,
/// The arrays storing the actual data of the node. Only the first `len` elements of each
@ -92,7 +88,9 @@ impl<K, V> LeafNode<K, V> {
/// node, allowing code to act on leaf and internal nodes generically without having to even check
/// which of the two a pointer is pointing at. This property is enabled by the use of `repr(C)`.
#[repr(C)]
// gdb_providers.py uses this type name for introspection.
struct InternalNode<K, V> {
// gdb_providers.py uses this field name for introspection.
data: LeafNode<K, V>,
/// The pointers to the children of this node. `len + 1` of these are considered
@ -183,9 +181,9 @@ impl<K, V> Root<K, V> {
NodeRef { height: self.height, node: self.node.as_ptr(), _marker: PhantomData }
}
/// Adds a new internal node with a single edge, pointing to the previous root, and make that
/// new node the root. This increases the height by 1 and is the opposite of
/// `pop_internal_level`.
/// Adds a new internal node with a single edge pointing to the previous root node,
/// make that new node the root node, and return it. This increases the height by 1
/// and is the opposite of `pop_internal_level`.
pub fn push_internal_level(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
let mut new_node = Box::new(unsafe { InternalNode::new() });
new_node.edges[0].write(unsafe { BoxedNode::from_ptr(self.node.as_ptr()) });
@ -322,7 +320,7 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
NodeRef { height: self.height, node: self.node, _marker: PhantomData }
}
/// Exposes the leaf "portion" of any leaf or internal node.
/// Exposes the leaf portion of any leaf or internal node.
/// If the node is a leaf, this function simply opens up its data.
/// If the node is an internal node, so not a leaf, it does have all the data a leaf has
/// (header, keys and values), and this function exposes that.
@ -351,7 +349,22 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
unsafe fn val_at(&self, idx: usize) -> &V {
unsafe { self.reborrow().into_val_at(idx) }
}
}
impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
/// Borrows a reference to the contents of one of the edges that delimit
/// the elements of the node, without invalidating other references.
///
/// # Safety
/// The node has more than `idx` initialized elements.
unsafe fn edge_at(&self, idx: usize) -> &BoxedNode<K, V> {
debug_assert!(idx <= self.len());
let node = self.as_internal_ptr();
unsafe { (*node).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
/// that points to the current node. Returns `Err(self)` if the current node has
@ -457,7 +470,7 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
NodeRef { height: self.height, node: self.node, _marker: PhantomData }
}
/// Exposes the leaf "portion" of any leaf or internal node for writing.
/// Exposes the leaf portion of any leaf or internal node for writing.
/// If the node is a leaf, this function simply opens up its data.
/// If the node is an internal node, so not a leaf, it does have all the data a leaf has
/// (header, keys and values), and this function exposes that.
@ -483,18 +496,49 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
unsafe { self.reborrow_mut().into_val_mut_at(idx) }
}
fn keys_mut(&mut self) -> &mut [K] {
fn keys_mut(&mut self) -> &mut [K]
where
K: 'a,
V: 'a,
{
// SAFETY: the caller will not be able to call further methods on self
// until the key slice reference is dropped, as we have unique access
// for the lifetime of the borrow.
unsafe { self.reborrow_mut().into_key_slice_mut() }
// SAFETY: The keys of a node must always be initialized up to length.
unsafe {
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.as_leaf_mut().keys),
self.len(),
)
}
}
fn vals_mut(&mut self) -> &mut [V] {
fn vals_mut(&mut self) -> &mut [V]
where
K: 'a,
V: 'a,
{
// SAFETY: the caller will not be able to call further methods on self
// until the value slice reference is dropped, as we have unique access
// for the lifetime of the borrow.
unsafe { self.reborrow_mut().into_val_slice_mut() }
// SAFETY: The values of a node must always be initialized up to length.
unsafe {
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.as_leaf_mut().vals),
self.len(),
)
}
}
}
impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
fn edges_mut(&mut self) -> &mut [BoxedNode<K, V>] {
unsafe {
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.as_internal_mut().edges),
self.len() + 1,
)
}
}
}
@ -513,26 +557,6 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
}
impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
fn into_key_slice_mut(mut self) -> &'a mut [K] {
// SAFETY: The keys of a node must always be initialized up to length.
unsafe {
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.as_leaf_mut().keys),
self.len(),
)
}
}
fn into_val_slice_mut(mut self) -> &'a mut [V] {
// SAFETY: The values of a node must always be initialized up to length.
unsafe {
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.as_leaf_mut().vals),
self.len(),
)
}
}
/// # Safety
/// The node has more than `idx` initialized elements.
unsafe fn into_key_mut_at(mut self, idx: usize) -> &'a mut K {
@ -584,8 +608,8 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
}
/// Adds a key/value pair to the beginning of the node.
pub fn push_front(&mut self, key: K, val: V) {
assert!(self.len() < CAPACITY);
fn push_front(&mut self, key: K, val: V) {
debug_assert!(self.len() < CAPACITY);
unsafe {
slice_insert(self.keys_mut(), 0, key);
@ -597,18 +621,17 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
/// # Safety
/// 'first' and 'after_last' must be in range.
unsafe fn correct_childrens_parent_links(&mut self, first: usize, after_last: usize) {
debug_assert!(first <= self.len());
debug_assert!(after_last <= self.len() + 1);
for i in first..after_last {
/// Every item returned by `range` is a valid edge index for the node.
unsafe fn correct_childrens_parent_links<R: Iterator<Item = usize>>(&mut self, range: R) {
for i in range {
debug_assert!(i <= self.len());
unsafe { Handle::new_edge(self.reborrow_mut(), i) }.correct_parent_link();
}
}
fn correct_all_childrens_parent_links(&mut self) {
let len = self.len();
unsafe { self.correct_childrens_parent_links(0, len + 1) };
unsafe { self.correct_childrens_parent_links(0..=len) };
}
}
@ -658,10 +681,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
/// Removes a key/value pair from the end of this node and returns the pair.
/// If this is an internal node, also removes the edge that was to the right
/// of that pair and returns the orphaned node that this edge owned with its
/// parent erased.
pub fn pop(&mut self) -> (K, V, Option<Root<K, V>>) {
assert!(self.len() > 0);
/// of that pair and returns the orphaned node that this edge owned.
fn pop(&mut self) -> (K, V, Option<Root<K, V>>) {
debug_assert!(self.len() > 0);
let idx = self.len() - 1;
@ -670,9 +692,8 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
let val = ptr::read(self.val_at(idx));
let edge = match self.reborrow_mut().force() {
ForceResult::Leaf(_) => None,
ForceResult::Internal(mut internal) => {
let edge =
ptr::read(internal.as_internal().edges.get_unchecked(idx + 1).as_ptr());
ForceResult::Internal(internal) => {
let edge = ptr::read(internal.edge_at(idx + 1));
let mut new_root = Root { node: edge, height: internal.height - 1 };
new_root.node_as_mut().as_leaf_mut().parent = None;
Some(new_root)
@ -684,10 +705,11 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
}
}
/// Removes a key/value pair from the beginning of this node. If this is an internal node,
/// also removes the edge that was to the left of that pair.
pub fn pop_front(&mut self) -> (K, V, Option<Root<K, V>>) {
assert!(self.len() > 0);
/// Removes a key/value pair from the beginning of this node and returns the pair.
/// If this is an internal node, also removes the edge that was to the left
/// of that pair and returns the orphaned node 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();
@ -697,20 +719,11 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
let edge = match self.reborrow_mut().force() {
ForceResult::Leaf(_) => None,
ForceResult::Internal(mut internal) => {
let edge = slice_remove(
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut internal.as_internal_mut().edges),
old_len + 1,
),
0,
);
let edge = slice_remove(internal.edges_mut(), 0);
let mut new_root = Root { node: edge, height: internal.height - 1 };
new_root.node_as_mut().as_leaf_mut().parent = None;
for i in 0..old_len {
Handle::new_edge(internal.reborrow_mut(), i).correct_parent_link();
}
internal.correct_childrens_parent_links(0..old_len);
Some(new_root)
}
@ -898,7 +911,6 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>
/// this edge. This method assumes that there is enough space in the node for the new
/// pair to fit.
fn leafy_insert_fit(&mut self, key: K, val: V) {
// Necessary for correctness, but in a private module
debug_assert!(self.node.len() < CAPACITY);
unsafe {
@ -936,18 +948,18 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
let (middle_kv_idx, insertion) = splitpoint(self.idx);
let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
let (mut left, k, v, mut right) = middle.split();
let val_ptr = match insertion {
let mut insertion_edge = match insertion {
InsertionPlace::Left(insert_idx) => unsafe {
Handle::new_edge(left.reborrow_mut(), insert_idx).insert_fit(key, val)
Handle::new_edge(left.reborrow_mut(), insert_idx)
},
InsertionPlace::Right(insert_idx) => unsafe {
Handle::new_edge(
right.node_as_mut().cast_unchecked::<marker::Leaf>(),
insert_idx,
)
.insert_fit(key, val)
},
};
let val_ptr = insertion_edge.insert_fit(key, val);
(InsertResult::Split(SplitResult { left: left.forget_type(), k, v, right }), val_ptr)
}
}
@ -970,25 +982,13 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
/// between this edge and the key/value pair to the right of this edge. This method assumes
/// that there is enough space in the node for the new pair to fit.
fn insert_fit(&mut self, key: K, val: V, edge: Root<K, V>) {
// Necessary for correctness, but in an internal module
debug_assert!(self.node.len() < CAPACITY);
debug_assert!(edge.height == self.node.height - 1);
unsafe {
slice_insert(self.node.edges_mut(), self.idx + 1, edge.node);
self.leafy_insert_fit(key, val);
slice_insert(
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.node.as_internal_mut().edges),
self.node.len(),
),
self.idx + 1,
edge.node,
);
for i in (self.idx + 1)..(self.node.len() + 1) {
Handle::new_edge(self.node.reborrow_mut(), i).correct_parent_link();
}
self.node.correct_childrens_parent_links((self.idx + 1)..=self.node.len());
}
}
@ -1131,12 +1131,12 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>
ptr::copy_nonoverlapping(
self.node.key_at(self.idx + 1),
new_node.keys.as_mut_ptr() as *mut K,
MaybeUninit::slice_as_mut_ptr(&mut new_node.keys),
new_len,
);
ptr::copy_nonoverlapping(
self.node.val_at(self.idx + 1),
new_node.vals.as_mut_ptr() as *mut V,
MaybeUninit::slice_as_mut_ptr(&mut new_node.vals),
new_len,
);
@ -1215,9 +1215,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
let mut new_root = Root { node: BoxedNode::from_internal(new_node), height };
for i in 0..(new_len + 1) {
Handle::new_edge(new_root.node_as_mut().cast_unchecked(), i).correct_parent_link();
}
new_root.node_as_mut().cast_unchecked().correct_childrens_parent_links(0..=new_len);
(self.node, k, v, new_root)
}
@ -1260,10 +1258,9 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
right_len,
);
slice_remove(&mut self.node.as_internal_mut().edges, self.idx + 1);
for i in self.idx + 1..self.node.len() {
Handle::new_edge(self.node.reborrow_mut(), i).correct_parent_link();
}
slice_remove(&mut self.node.edges_mut(), self.idx + 1);
let self_len = self.node.len();
self.node.correct_childrens_parent_links(self.idx + 1..self_len);
self.node.as_leaf_mut().len -= 1;
left_node.as_leaf_mut().len += right_len as u16 + 1;
@ -1271,17 +1268,15 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
if self.node.height > 1 {
// 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.cast_unchecked();
let mut right_node = right_node.cast_unchecked();
let mut left_node = left_node.cast_unchecked::<marker::Internal>();
let right_node = right_node.cast_unchecked::<marker::Internal>();
ptr::copy_nonoverlapping(
right_node.as_internal().edges.as_ptr(),
left_node.as_internal_mut().edges.as_mut_ptr().add(left_len + 1),
right_node.edge_at(0),
left_node.edges_mut().as_mut_ptr().add(left_len + 1),
right_len + 1,
);
for i in left_len + 1..left_len + right_len + 2 {
Handle::new_edge(left_node.reborrow_mut(), i).correct_parent_link();
}
left_node.correct_childrens_parent_links(left_len + 1..=left_len + 1 + right_len);
Global.dealloc(right_node.node.cast(), Layout::new::<InternalNode<K, V>>());
} else {
@ -1371,14 +1366,12 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
// Make room for stolen edges.
let right_edges = right.reborrow_mut().as_internal_mut().edges.as_mut_ptr();
ptr::copy(right_edges, right_edges.add(count), right_len + 1);
right.correct_childrens_parent_links(count, count + right_len + 1);
right.correct_childrens_parent_links(count..count + right_len + 1);
move_edges(left, new_left_len + 1, right, 0, count);
}
(ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
_ => {
unreachable!();
}
_ => unreachable!(),
}
}
}
@ -1430,12 +1423,10 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
// Fix right indexing.
let right_edges = right.reborrow_mut().as_internal_mut().edges.as_mut_ptr();
ptr::copy(right_edges.add(count), right_edges, new_right_len + 1);
right.correct_childrens_parent_links(0, new_right_len + 1);
right.correct_childrens_parent_links(0..=new_right_len);
}
(ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
_ => {
unreachable!();
}
_ => unreachable!(),
}
}
}
@ -1466,7 +1457,7 @@ unsafe fn move_edges<K, V>(
let dest_ptr = dest.as_internal_mut().edges.as_mut_ptr();
unsafe {
ptr::copy_nonoverlapping(source_ptr.add(source_offset), dest_ptr.add(dest_offset), count);
dest.correct_childrens_parent_links(dest_offset, dest_offset + count);
dest.correct_childrens_parent_links(dest_offset..dest_offset + count);
}
}
@ -1568,9 +1559,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, ma
move_edges(left, left_new_len + 1, right, 1, right_new_len);
}
(ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
_ => {
unreachable!();
}
_ => unreachable!(),
}
}
}