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BTreeMap: bundle the duplication of node references in navigate.rs #81332

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BTreeMap: bundle the duplication of node references in navigate.rs #81332

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28 changes: 16 additions & 12 deletions library/alloc/src/collections/btree/navigate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -130,6 +130,16 @@ fn full_range<BorrowType, K, V>(
}
}

impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
/// Duplicates a NodeRef, even for a non-immutable borrow type.
/// # Safety
/// Never visit the same KV twice, and never end up with overlapping
/// value references.
unsafe fn fork(self) -> (Self, Self) {
unsafe { (ptr::read(&self), self) }
}
}

impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal> {
/// Creates a pair of leaf edges delimiting a specified range in or underneath a node.
///
Expand Down Expand Up @@ -180,10 +190,8 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::ValMut<'a>, K, V, marker::LeafOrInternal>
K: Borrow<Q>,
R: RangeBounds<Q>,
{
// We duplicate the root NodeRef here -- we will never visit the same KV
// twice, and never end up with overlapping value references.
let self2 = unsafe { ptr::read(&self) };
range_search(self, self2, range)
let (self1, self2) = unsafe { self.fork() };
range_search(self1, self2, range)
}

/// Splits a unique reference into a pair of leaf edges delimiting the full range of the tree.
Expand All @@ -195,10 +203,8 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::ValMut<'a>, K, V, marker::LeafOrInternal>
Handle<NodeRef<marker::ValMut<'a>, K, V, marker::Leaf>, marker::Edge>,
Handle<NodeRef<marker::ValMut<'a>, K, V, marker::Leaf>, marker::Edge>,
) {
// We duplicate the root NodeRef here -- we will never visit the same KV
// twice, and never end up with overlapping value references.
let self2 = unsafe { ptr::read(&self) };
full_range(self, self2)
let (self1, self2) = unsafe { self.fork() };
full_range(self1, self2)
}
}

Expand All @@ -212,10 +218,8 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge>,
Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge>,
) {
// We duplicate the root NodeRef here -- we will never access it in a way
// that overlaps references obtained from the root.
let self2 = unsafe { ptr::read(&self) };
full_range(self, self2)
let (self1, self2) = unsafe { self.fork() };
full_range(self1, self2)
}
}

Expand Down