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BTreeMap: cut out the ceremony around BoxedNode #79354

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Nov 24, 2020
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BTreeMap: cut out the ceremony around BoxedNode #79354

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50 changes: 12 additions & 38 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -112,20 +112,8 @@ impl<K, V> InternalNode<K, V> {
///
/// However, `BoxedNode` contains no information as to which of the two types
/// of nodes it actually contains, and, partially due to this lack of information,
/// has no destructor.
struct BoxedNode<K, V> {
ptr: NonNull<LeafNode<K, V>>,
}

impl<K, V> BoxedNode<K, V> {
fn from_owned(ptr: NonNull<LeafNode<K, V>>) -> Self {
BoxedNode { ptr }
}

fn as_ptr(&self) -> NonNull<LeafNode<K, V>> {
self.ptr
}
}
/// is not a separate type and has no destructor.
type BoxedNode<K, V> = NonNull<LeafNode<K, V>>;

/// An owned tree.
///
Expand Down Expand Up @@ -168,11 +156,6 @@ impl<K, V, Type> NodeRef<marker::Owned, K, V, Type> {
pub fn borrow_valmut(&mut self) -> NodeRef<marker::ValMut<'_>, K, V, Type> {
NodeRef { height: self.height, node: self.node, _marker: PhantomData }
}

/// Packs the reference, aware of type and height, into a type-agnostic pointer.
fn into_boxed_node(self) -> BoxedNode<K, V> {
BoxedNode::from_owned(self.node)
}
}

impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
Expand All @@ -181,7 +164,7 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
/// 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(BoxedNode::from_owned(self.node));
new_node.edges[0].write(self.node);
let mut new_root = NodeRef::from_new_internal(new_node, self.height + 1);
new_root.borrow_mut().first_edge().correct_parent_link();
*self = new_root.forget_type();
Expand Down Expand Up @@ -288,13 +271,6 @@ unsafe impl<'a, K: Send + 'a, V: Send + 'a, Type> Send for NodeRef<marker::Mut<'
unsafe impl<'a, K: Send + 'a, V: Send + 'a, Type> Send for NodeRef<marker::ValMut<'a>, K, V, Type> {}
unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Owned, K, V, Type> {}

impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
/// Unpack a node reference that was packed by `Root::into_boxed_node`.
fn from_boxed_node(boxed_node: BoxedNode<K, V>, height: usize) -> Self {
NodeRef { height, node: boxed_node.as_ptr(), _marker: PhantomData }
}
}

impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
/// Unpack a node reference that was packed as `NodeRef::parent`.
fn from_internal(node: NonNull<InternalNode<K, V>>, height: usize) -> Self {
Expand Down Expand Up @@ -695,7 +671,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
unsafe {
self.reborrow_mut().into_key_area_mut_at(idx).write(key);
self.reborrow_mut().into_val_area_mut_at(idx).write(val);
self.reborrow_mut().into_edge_area_mut_at(idx + 1).write(edge.into_boxed_node());
self.reborrow_mut().into_edge_area_mut_at(idx + 1).write(edge.node);
Handle::new_edge(self.reborrow_mut(), idx + 1).correct_parent_link();
}
}
Expand All @@ -710,7 +686,7 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
*self.reborrow_mut().into_len_mut() += 1;
slice_insert(self.reborrow_mut().into_key_area_slice(), 0, key);
slice_insert(self.reborrow_mut().into_val_area_slice(), 0, val);
slice_insert(self.reborrow_mut().into_edge_area_slice(), 0, edge.into_boxed_node());
slice_insert(self.reborrow_mut().into_edge_area_slice(), 0, edge.node);
}

self.correct_all_childrens_parent_links();
Expand All @@ -732,8 +708,8 @@ 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(internal) => {
let boxed_node = ptr::read(internal.reborrow().edge_at(idx + 1));
let mut edge = Root::from_boxed_node(boxed_node, internal.height - 1);
let node = ptr::read(internal.reborrow().edge_at(idx + 1));
let mut edge = Root { node, height: internal.height - 1, _marker: PhantomData };
// In practice, clearing the parent is a waste of time, because we will
// insert the node elsewhere and set its parent link again.
edge.borrow_mut().clear_parent_link();
Expand All @@ -760,9 +736,8 @@ 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 boxed_node =
slice_remove(internal.reborrow_mut().into_edge_area_slice(), 0);
let mut edge = Root::from_boxed_node(boxed_node, internal.height - 1);
let node = slice_remove(internal.reborrow_mut().into_edge_area_slice(), 0);
let mut edge = Root { node, height: internal.height - 1, _marker: PhantomData };
// In practice, clearing the parent is a waste of time, because we will
// insert the node elsewhere and set its parent link again.
edge.borrow_mut().clear_parent_link();
Expand Down Expand Up @@ -1041,12 +1016,11 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
debug_assert!(self.node.len() < CAPACITY);
debug_assert!(edge.height == self.node.height - 1);

let boxed_node = edge.into_boxed_node();
unsafe {
*self.node.reborrow_mut().into_len_mut() += 1;
slice_insert(self.node.reborrow_mut().into_key_area_slice(), self.idx, key);
slice_insert(self.node.reborrow_mut().into_val_area_slice(), self.idx, val);
slice_insert(self.node.reborrow_mut().into_edge_area_slice(), self.idx + 1, boxed_node);
slice_insert(self.node.reborrow_mut().into_edge_area_slice(), self.idx + 1, edge.node);

self.node.correct_childrens_parent_links((self.idx + 1)..=self.node.len());
}
Expand Down Expand Up @@ -1135,8 +1109,8 @@ impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marke
// reference (Rust issue #73987) and invalidate any other references
// to or inside the array, should any be around.
let parent_ptr = NodeRef::as_internal_ptr(&self.node);
let boxed_node = unsafe { (*parent_ptr).edges.get_unchecked(self.idx).assume_init_read() };
NodeRef::from_boxed_node(boxed_node, self.node.height - 1)
let node = unsafe { (*parent_ptr).edges.get_unchecked(self.idx).assume_init_read() };
NodeRef { node, height: self.node.height - 1, _marker: PhantomData }
}
}

Expand Down
12 changes: 6 additions & 6 deletions src/etc/gdb_providers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -216,6 +216,10 @@ def cast_to_internal(node):
internal_type = lookup_type(internal_type_name)
return node.cast(internal_type.pointer())

if node_ptr.type.name.startswith("alloc::collections::btree::node::BoxedNode<"):
# BACKCOMPAT: rust 1.49
node_ptr = node_ptr["ptr"]
node_ptr = unwrap_unique_or_non_null(node_ptr)
leaf = node_ptr.dereference()
keys = leaf["keys"]
vals = leaf["vals"]
Expand All @@ -224,9 +228,8 @@ def cast_to_internal(node):

for i in xrange(0, length + 1):
if height > 0:
boxed_child_node = edges[i]["value"]["value"]
child_node = unwrap_unique_or_non_null(boxed_child_node["ptr"])
for child in children_of_node(child_node, height - 1):
child_ptr = edges[i]["value"]["value"]
for child in children_of_node(child_ptr, height - 1):
yield child
if i < length:
# Avoid "Cannot perform pointer math on incomplete type" on zero-sized arrays.
Expand All @@ -239,9 +242,6 @@ def cast_to_internal(node):
if root.type.name.startswith("core::option::Option<"):
root = root.cast(gdb.lookup_type(root.type.name[21:-1]))
node_ptr = root["node"]
if node_ptr.type.name.startswith("alloc::collections::btree::node::BoxedNode<"):
node_ptr = node_ptr["ptr"]
node_ptr = unwrap_unique_or_non_null(node_ptr)
height = root["height"]
for child in children_of_node(node_ptr, height):
yield child
Expand Down