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BTreeMap: type-specific variants of node_as_mut and cast_unchecked #77569

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Oct 14, 2020
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BTreeMap: type-specific variants of node_as_mut and cast_unchecked #77569

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52 changes: 28 additions & 24 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,22 @@ impl<K, V> Root<K, V> {
NodeRef { height: self.height, node: self.node.as_ptr(), _marker: PhantomData }
}

/// Borrows and returns a mutable reference to the leaf node owned by the root.
/// # Safety
/// The root node is a leaf.
unsafe fn leaf_node_as_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::Leaf> {
debug_assert!(self.height == 0);
NodeRef { height: self.height, node: self.node.as_ptr(), _marker: PhantomData }
}

/// Borrows and returns a mutable reference to the internal node owned by the root.
/// # Safety
/// The root node is not a leaf.
unsafe fn internal_node_as_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
debug_assert!(self.height > 0);
NodeRef { height: self.height, node: self.node.as_ptr(), _marker: PhantomData }
}

pub fn node_as_valmut(&mut self) -> NodeRef<marker::ValMut<'_>, K, V, marker::LeafOrInternal> {
NodeRef { height: self.height, node: self.node.as_ptr(), _marker: PhantomData }
}
Expand All @@ -188,14 +204,11 @@ impl<K, V> Root<K, V> {
self.node = BoxedNode::from_internal(new_node);
self.height += 1;

let mut ret =
NodeRef { height: self.height, node: self.node.as_ptr(), _marker: PhantomData };

unsafe {
let mut ret = self.internal_node_as_mut();
ret.reborrow_mut().first_edge().correct_parent_link();
ret
}

ret
}

/// Removes the internal root node, using its first child as the new root node.
Expand All @@ -212,11 +225,8 @@ impl<K, V> Root<K, V> {

let top = self.node.ptr;

self.node = unsafe {
BoxedNode::from_ptr(
self.node_as_mut().cast_unchecked::<marker::Internal>().first_edge().descend().node,
)
};
let internal_node = unsafe { self.internal_node_as_mut() };
self.node = unsafe { BoxedNode::from_ptr(internal_node.first_edge().descend().node) };
self.height -= 1;
self.node_as_mut().as_leaf_mut().parent = None;

Expand Down Expand Up @@ -443,9 +453,9 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
}

impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
/// Unsafely asserts to the compiler some static information about whether this
/// node is a `Leaf` or an `Internal`.
unsafe fn cast_unchecked<NewType>(self) -> NodeRef<marker::Mut<'a>, K, V, NewType> {
/// Unsafely asserts to the compiler the static information that this node is an `Internal`.
unsafe fn cast_to_internal_unchecked(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
debug_assert!(self.height > 0);
NodeRef { height: self.height, node: self.node, _marker: PhantomData }
}

Expand Down Expand Up @@ -943,10 +953,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
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,
)
Handle::new_edge(right.leaf_node_as_mut(), insert_idx)
},
};
let val_ptr = insertion_edge.insert_fit(key, val);
Expand Down Expand Up @@ -1006,10 +1013,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
Handle::new_edge(left.reborrow_mut(), insert_idx)
},
InsertionPlace::Right(insert_idx) => unsafe {
Handle::new_edge(
right.node_as_mut().cast_unchecked::<marker::Internal>(),
insert_idx,
)
Handle::new_edge(right.internal_node_as_mut(), insert_idx)
},
};
insertion_edge.insert_fit(key, val, edge);
Expand Down Expand Up @@ -1205,7 +1209,7 @@ 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 };

new_root.node_as_mut().cast_unchecked().correct_childrens_parent_links(0..=new_len);
new_root.internal_node_as_mut().correct_childrens_parent_links(0..=new_len);

(self.node, k, v, new_root)
}
Expand Down Expand Up @@ -1258,8 +1262,8 @@ 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::<marker::Internal>();
let right_node = right_node.cast_unchecked::<marker::Internal>();
let mut left_node = left_node.cast_to_internal_unchecked();
let right_node = right_node.cast_to_internal_unchecked();
ptr::copy_nonoverlapping(
right_node.edge_at(0),
left_node.edges_mut().as_mut_ptr().add(left_len + 1),
Expand Down