Remove `HybridBitSet`.

It's no longer used.

3 files changed, 3 insertions, 692 deletions

diff --git a/compiler/rustc_index/Cargo.toml b/compiler/rustc_index/Cargo.toml
index f7d18f84e34..33e8e2824c7 100644
--- a/compiler/rustc_index/Cargo.toml
+++ b/compiler/rustc_index/Cargo.toml
@@ -5,7 +5,6 @@ edition = "2021"
 
 [dependencies]
 # tidy-alphabetical-start
-arrayvec = { version = "0.7", default-features = false }
 rustc_index_macros = { path = "../rustc_index_macros", default-features = false }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }
diff --git a/compiler/rustc_index/src/bit_set.rs b/compiler/rustc_index/src/bit_set.rs
index 5446894374f..de6fa132ca0 100644
--- a/compiler/rustc_index/src/bit_set.rs
+++ b/compiler/rustc_index/src/bit_set.rs
@@ -4,7 +4,6 @@ use std::rc::Rc;
 use std::{fmt, iter, mem, slice};
 
 use Chunk::*;
-use arrayvec::ArrayVec;
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_Generic, Encodable_Generic};
 use smallvec::{SmallVec, smallvec};
@@ -240,45 +239,6 @@ impl<T: Idx> BitSet<T> {
         BitIter::new(&self.words)
     }
 
-    /// Set `self = self | other`. In contrast to `union` returns `true` if the set contains at
-    /// least one bit that is not in `other` (i.e. `other` is not a superset of `self`).
-    ///
-    /// This is an optimization for union of a hybrid bitset.
-    fn reverse_union_sparse(&mut self, sparse: &SparseBitSet<T>) -> bool {
-        assert!(sparse.domain_size == self.domain_size);
-        self.clear_excess_bits();
-
-        let mut not_already = false;
-        // Index of the current word not yet merged.
-        let mut current_index = 0;
-        // Mask of bits that came from the sparse set in the current word.
-        let mut new_bit_mask = 0;
-        for (word_index, mask) in sparse.iter().map(|x| word_index_and_mask(*x)) {
-            // Next bit is in a word not inspected yet.
-            if word_index > current_index {
-                self.words[current_index] |= new_bit_mask;
-                // Were there any bits in the old word that did not occur in the sparse set?
-                not_already |= (self.words[current_index] ^ new_bit_mask) != 0;
-                // Check all words we skipped for any set bit.
-                not_already |= self.words[current_index + 1..word_index].iter().any(|&x| x != 0);
-                // Update next word.
-                current_index = word_index;
-                // Reset bit mask, no bits have been merged yet.
-                new_bit_mask = 0;
-            }
-            // Add bit and mark it as coming from the sparse set.
-            // self.words[word_index] |= mask;
-            new_bit_mask |= mask;
-        }
-        self.words[current_index] |= new_bit_mask;
-        // Any bits in the last inspected word that were not in the sparse set?
-        not_already |= (self.words[current_index] ^ new_bit_mask) != 0;
-        // Any bits in the tail? Note `clear_excess_bits` before.
-        not_already |= self.words[current_index + 1..].iter().any(|&x| x != 0);
-
-        not_already
-    }
-
     pub fn last_set_in(&self, range: impl RangeBounds<T>) -> Option<T> {
         let (start, end) = inclusive_start_end(range, self.domain_size)?;
         let (start_word_index, _) = word_index_and_mask(start);
@@ -829,30 +789,6 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
     }
 }
 
-impl<T: Idx> BitRelations<HybridBitSet<T>> for ChunkedBitSet<T> {
-    fn union(&mut self, other: &HybridBitSet<T>) -> bool {
-        // FIXME: This is slow if `other` is dense, but it hasn't been a problem
-        // in practice so far.
-        // If a faster implementation of this operation is required, consider
-        // reopening https://github.com/rust-lang/rust/pull/94625
-        assert_eq!(self.domain_size, other.domain_size());
-        sequential_update(|elem| self.insert(elem), other.iter())
-    }
-
-    fn subtract(&mut self, other: &HybridBitSet<T>) -> bool {
-        // FIXME: This is slow if `other` is dense, but it hasn't been a problem
-        // in practice so far.
-        // If a faster implementation of this operation is required, consider
-        // reopening https://github.com/rust-lang/rust/pull/94625
-        assert_eq!(self.domain_size, other.domain_size());
-        sequential_update(|elem| self.remove(elem), other.iter())
-    }
-
-    fn intersect(&mut self, _other: &HybridBitSet<T>) -> bool {
-        unimplemented!("implement if/when necessary");
-    }
-}
-
 impl<T: Idx> BitRelations<ChunkedBitSet<T>> for BitSet<T> {
     fn union(&mut self, other: &ChunkedBitSet<T>) -> bool {
         sequential_update(|elem| self.insert(elem), other.iter())
@@ -1022,176 +958,6 @@ fn sequential_update<T: Idx>(
     it.fold(false, |changed, elem| self_update(elem) | changed)
 }
 
-// Optimization of intersection for SparseBitSet that's generic
-// over the RHS
-fn sparse_intersect<T: Idx>(
-    set: &mut SparseBitSet<T>,
-    other_contains: impl Fn(&T) -> bool,
-) -> bool {
-    let size = set.elems.len();
-    set.elems.retain(|elem| other_contains(elem));
-    set.elems.len() != size
-}
-
-// Optimization of dense/sparse intersection. The resulting set is
-// guaranteed to be at most the size of the sparse set, and hence can be
-// represented as a sparse set. Therefore the sparse set is copied and filtered,
-// then returned as the new set.
-fn dense_sparse_intersect<T: Idx>(
-    dense: &BitSet<T>,
-    sparse: &SparseBitSet<T>,
-) -> (SparseBitSet<T>, bool) {
-    let mut sparse_copy = sparse.clone();
-    sparse_intersect(&mut sparse_copy, |el| dense.contains(*el));
-    let n = sparse_copy.len();
-    (sparse_copy, n != dense.count())
-}
-
-// hybrid REL dense
-impl<T: Idx> BitRelations<BitSet<T>> for HybridBitSet<T> {
-    fn union(&mut self, other: &BitSet<T>) -> bool {
-        assert_eq!(self.domain_size(), other.domain_size);
-        match self {
-            HybridBitSet::Sparse(sparse) => {
-                // `self` is sparse and `other` is dense. To
-                // merge them, we have two available strategies:
-                // * Densify `self` then merge other
-                // * Clone other then integrate bits from `self`
-                // The second strategy requires dedicated method
-                // since the usual `union` returns the wrong
-                // result. In the dedicated case the computation
-                // is slightly faster if the bits of the sparse
-                // bitset map to only few words of the dense
-                // representation, i.e. indices are near each
-                // other.
-                //
-                // Benchmarking seems to suggest that the second
-                // option is worth it.
-                let mut new_dense = other.clone();
-                let changed = new_dense.reverse_union_sparse(sparse);
-                *self = HybridBitSet::Dense(new_dense);
-                changed
-            }
-
-            HybridBitSet::Dense(dense) => dense.union(other),
-        }
-    }
-
-    fn subtract(&mut self, other: &BitSet<T>) -> bool {
-        assert_eq!(self.domain_size(), other.domain_size);
-        match self {
-            HybridBitSet::Sparse(sparse) => {
-                sequential_update(|elem| sparse.remove(elem), other.iter())
-            }
-            HybridBitSet::Dense(dense) => dense.subtract(other),
-        }
-    }
-
-    fn intersect(&mut self, other: &BitSet<T>) -> bool {
-        assert_eq!(self.domain_size(), other.domain_size);
-        match self {
-            HybridBitSet::Sparse(sparse) => sparse_intersect(sparse, |elem| other.contains(*elem)),
-            HybridBitSet::Dense(dense) => dense.intersect(other),
-        }
-    }
-}
-
-// dense REL hybrid
-impl<T: Idx> BitRelations<HybridBitSet<T>> for BitSet<T> {
-    fn union(&mut self, other: &HybridBitSet<T>) -> bool {
-        assert_eq!(self.domain_size, other.domain_size());
-        match other {
-            HybridBitSet::Sparse(sparse) => {
-                sequential_update(|elem| self.insert(elem), sparse.iter().cloned())
-            }
-            HybridBitSet::Dense(dense) => self.union(dense),
-        }
-    }
-
-    fn subtract(&mut self, other: &HybridBitSet<T>) -> bool {
-        assert_eq!(self.domain_size, other.domain_size());
-        match other {
-            HybridBitSet::Sparse(sparse) => {
-                sequential_update(|elem| self.remove(elem), sparse.iter().cloned())
-            }
-            HybridBitSet::Dense(dense) => self.subtract(dense),
-        }
-    }
-
-    fn intersect(&mut self, other: &HybridBitSet<T>) -> bool {
-        assert_eq!(self.domain_size, other.domain_size());
-        match other {
-            HybridBitSet::Sparse(sparse) => {
-                let (updated, changed) = dense_sparse_intersect(self, sparse);
-
-                // We can't directly assign the SparseBitSet to the BitSet, and
-                // doing `*self = updated.to_dense()` would cause a drop / reallocation. Instead,
-                // the BitSet is cleared and `updated` is copied into `self`.
-                self.clear();
-                for elem in updated.iter() {
-                    self.insert(*elem);
-                }
-                changed
-            }
-            HybridBitSet::Dense(dense) => self.intersect(dense),
-        }
-    }
-}
-
-// hybrid REL hybrid
-impl<T: Idx> BitRelations<HybridBitSet<T>> for HybridBitSet<T> {
-    fn union(&mut self, other: &HybridBitSet<T>) -> bool {
-        assert_eq!(self.domain_size(), other.domain_size());
-        match self {
-            HybridBitSet::Sparse(_) => {
-                match other {
-                    HybridBitSet::Sparse(other_sparse) => {
-                        // Both sets are sparse. Add the elements in
-                        // `other_sparse` to `self` one at a time. This
-                        // may or may not cause `self` to be densified.
-                        let mut changed = false;
-                        for elem in other_sparse.iter() {
-                            changed |= self.insert(*elem);
-                        }
-                        changed
-                    }
-
-                    HybridBitSet::Dense(other_dense) => self.union(other_dense),
-                }
-            }
-
-            HybridBitSet::Dense(self_dense) => self_dense.union(other),
-        }
-    }
-
-    fn subtract(&mut self, other: &HybridBitSet<T>) -> bool {
-        assert_eq!(self.domain_size(), other.domain_size());
-        match self {
-            HybridBitSet::Sparse(self_sparse) => {
-                sequential_update(|elem| self_sparse.remove(elem), other.iter())
-            }
-            HybridBitSet::Dense(self_dense) => self_dense.subtract(other),
-        }
-    }
-
-    fn intersect(&mut self, other: &HybridBitSet<T>) -> bool {
-        assert_eq!(self.domain_size(), other.domain_size());
-        match self {
-            HybridBitSet::Sparse(self_sparse) => {
-                sparse_intersect(self_sparse, |elem| other.contains(*elem))
-            }
-            HybridBitSet::Dense(self_dense) => match other {
-                HybridBitSet::Sparse(other_sparse) => {
-                    let (updated, changed) = dense_sparse_intersect(self_dense, other_sparse);
-                    *self = HybridBitSet::Sparse(updated);
-                    changed
-                }
-                HybridBitSet::Dense(other_dense) => self_dense.intersect(other_dense),
-            },
-        }
-    }
-}
-
 impl<T> Clone for BitSet<T> {
     fn clone(&self) -> Self {
         BitSet { domain_size: self.domain_size, words: self.words.clone(), marker: PhantomData }
@@ -1340,286 +1106,6 @@ where
     false
 }
 
-const SPARSE_MAX: usize = 8;
-
-/// A fixed-size bitset type with a sparse representation and a maximum of
-/// `SPARSE_MAX` elements. The elements are stored as a sorted `ArrayVec` with
-/// no duplicates.
-///
-/// This type is used by `HybridBitSet`; do not use directly.
-#[derive(Clone, Debug)]
-pub struct SparseBitSet<T> {
-    domain_size: usize,
-    elems: ArrayVec<T, SPARSE_MAX>,
-}
-
-impl<T: Idx> SparseBitSet<T> {
-    fn new_empty(domain_size: usize) -> Self {
-        SparseBitSet { domain_size, elems: ArrayVec::new() }
-    }
-
-    fn len(&self) -> usize {
-        self.elems.len()
-    }
-
-    fn is_empty(&self) -> bool {
-        self.elems.len() == 0
-    }
-
-    fn contains(&self, elem: T) -> bool {
-        assert!(elem.index() < self.domain_size);
-        self.elems.contains(&elem)
-    }
-
-    fn insert(&mut self, elem: T) -> bool {
-        assert!(elem.index() < self.domain_size);
-        let changed = if let Some(i) = self.elems.iter().position(|&e| e.index() >= elem.index()) {
-            if self.elems[i] == elem {
-                // `elem` is already in the set.
-                false
-            } else {
-                // `elem` is smaller than one or more existing elements.
-                self.elems.insert(i, elem);
-                true
-            }
-        } else {
-            // `elem` is larger than all existing elements.
-            self.elems.push(elem);
-            true
-        };
-        assert!(self.len() <= SPARSE_MAX);
-        changed
-    }
-
-    fn remove(&mut self, elem: T) -> bool {
-        assert!(elem.index() < self.domain_size);
-        if let Some(i) = self.elems.iter().position(|&e| e == elem) {
-            self.elems.remove(i);
-            true
-        } else {
-            false
-        }
-    }
-
-    fn to_dense(&self) -> BitSet<T> {
-        let mut dense = BitSet::new_empty(self.domain_size);
-        for elem in self.elems.iter() {
-            dense.insert(*elem);
-        }
-        dense
-    }
-
-    fn iter(&self) -> slice::Iter<'_, T> {
-        self.elems.iter()
-    }
-
-    bit_relations_inherent_impls! {}
-}
-
-impl<T: Idx + Ord> SparseBitSet<T> {
-    pub fn last_set_in(&self, range: impl RangeBounds<T>) -> Option<T> {
-        let mut last_leq = None;
-        for e in self.iter() {
-            if range.contains(e) {
-                last_leq = Some(*e);
-            }
-        }
-        last_leq
-    }
-}
-
-/// A fixed-size bitset type with a hybrid representation: sparse when there
-/// are up to a `SPARSE_MAX` elements in the set, but dense when there are more
-/// than `SPARSE_MAX`.
-///
-/// This type is especially efficient for sets that typically have a small
-/// number of elements, but a large `domain_size`, and are cleared frequently.
-///
-/// `T` is an index type, typically a newtyped `usize` wrapper, but it can also
-/// just be `usize`.
-///
-/// All operations that involve an element will panic if the element is equal
-/// to or greater than the domain size. All operations that involve two bitsets
-/// will panic if the bitsets have differing domain sizes.
-#[derive(Clone)]
-pub enum HybridBitSet<T> {
-    Sparse(SparseBitSet<T>),
-    Dense(BitSet<T>),
-}
-
-impl<T: Idx> fmt::Debug for HybridBitSet<T> {
-    fn fmt(&self, w: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::Sparse(b) => b.fmt(w),
-            Self::Dense(b) => b.fmt(w),
-        }
-    }
-}
-
-impl<T: Idx> HybridBitSet<T> {
-    pub fn new_empty(domain_size: usize) -> Self {
-        HybridBitSet::Sparse(SparseBitSet::new_empty(domain_size))
-    }
-
-    pub fn domain_size(&self) -> usize {
-        match self {
-            HybridBitSet::Sparse(sparse) => sparse.domain_size,
-            HybridBitSet::Dense(dense) => dense.domain_size,
-        }
-    }
-
-    pub fn clear(&mut self) {
-        let domain_size = self.domain_size();
-        *self = HybridBitSet::new_empty(domain_size);
-    }
-
-    pub fn contains(&self, elem: T) -> bool {
-        match self {
-            HybridBitSet::Sparse(sparse) => sparse.contains(elem),
-            HybridBitSet::Dense(dense) => dense.contains(elem),
-        }
-    }
-
-    pub fn superset(&self, other: &HybridBitSet<T>) -> bool {
-        match (self, other) {
-            (HybridBitSet::Dense(self_dense), HybridBitSet::Dense(other_dense)) => {
-                self_dense.superset(other_dense)
-            }
-            _ => {
-                assert!(self.domain_size() == other.domain_size());
-                other.iter().all(|elem| self.contains(elem))
-            }
-        }
-    }
-
-    pub fn is_empty(&self) -> bool {
-        match self {
-            HybridBitSet::Sparse(sparse) => sparse.is_empty(),
-            HybridBitSet::Dense(dense) => dense.is_empty(),
-        }
-    }
-
-    /// Returns the previous element present in the bitset from `elem`,
-    /// inclusively of elem. That is, will return `Some(elem)` if elem is in the
-    /// bitset.
-    pub fn last_set_in(&self, range: impl RangeBounds<T>) -> Option<T>
-    where
-        T: Ord,
-    {
-        match self {
-            HybridBitSet::Sparse(sparse) => sparse.last_set_in(range),
-            HybridBitSet::Dense(dense) => dense.last_set_in(range),
-        }
-    }
-
-    pub fn insert(&mut self, elem: T) -> bool {
-        // No need to check `elem` against `self.domain_size` here because all
-        // the match cases check it, one way or another.
-        match self {
-            HybridBitSet::Sparse(sparse) if sparse.len() < SPARSE_MAX => {
-                // The set is sparse and has space for `elem`.
-                sparse.insert(elem)
-            }
-            HybridBitSet::Sparse(sparse) if sparse.contains(elem) => {
-                // The set is sparse and does not have space for `elem`, but
-                // that doesn't matter because `elem` is already present.
-                false
-            }
-            HybridBitSet::Sparse(sparse) => {
-                // The set is sparse and full. Convert to a dense set.
-                let mut dense = sparse.to_dense();
-                let changed = dense.insert(elem);
-                assert!(changed);
-                *self = HybridBitSet::Dense(dense);
-                changed
-            }
-            HybridBitSet::Dense(dense) => dense.insert(elem),
-        }
-    }
-
-    pub fn insert_range(&mut self, elems: impl RangeBounds<T>) {
-        // No need to check `elem` against `self.domain_size` here because all
-        // the match cases check it, one way or another.
-        let start = match elems.start_bound().cloned() {
-            Bound::Included(start) => start.index(),
-            Bound::Excluded(start) => start.index() + 1,
-            Bound::Unbounded => 0,
-        };
-        let end = match elems.end_bound().cloned() {
-            Bound::Included(end) => end.index() + 1,
-            Bound::Excluded(end) => end.index(),
-            Bound::Unbounded => self.domain_size() - 1,
-        };
-        let Some(len) = end.checked_sub(start) else { return };
-        match self {
-            HybridBitSet::Sparse(sparse) if sparse.len() + len < SPARSE_MAX => {
-                // The set is sparse and has space for `elems`.
-                for elem in start..end {
-                    sparse.insert(T::new(elem));
-                }
-            }
-            HybridBitSet::Sparse(sparse) => {
-                // The set is sparse and full. Convert to a dense set.
-                let mut dense = sparse.to_dense();
-                dense.insert_range(elems);
-                *self = HybridBitSet::Dense(dense);
-            }
-            HybridBitSet::Dense(dense) => dense.insert_range(elems),
-        }
-    }
-
-    pub fn insert_all(&mut self) {
-        let domain_size = self.domain_size();
-        match self {
-            HybridBitSet::Sparse(_) => {
-                *self = HybridBitSet::Dense(BitSet::new_filled(domain_size));
-            }
-            HybridBitSet::Dense(dense) => dense.insert_all(),
-        }
-    }
-
-    pub fn remove(&mut self, elem: T) -> bool {
-        // Note: we currently don't bother going from Dense back to Sparse.
-        match self {
-            HybridBitSet::Sparse(sparse) => sparse.remove(elem),
-            HybridBitSet::Dense(dense) => dense.remove(elem),
-        }
-    }
-
-    /// Converts to a dense set, consuming itself in the process.
-    pub fn to_dense(self) -> BitSet<T> {
-        match self {
-            HybridBitSet::Sparse(sparse) => sparse.to_dense(),
-            HybridBitSet::Dense(dense) => dense,
-        }
-    }
-
-    pub fn iter(&self) -> HybridIter<'_, T> {
-        match self {
-            HybridBitSet::Sparse(sparse) => HybridIter::Sparse(sparse.iter()),
-            HybridBitSet::Dense(dense) => HybridIter::Dense(dense.iter()),
-        }
-    }
-
-    bit_relations_inherent_impls! {}
-}
-
-pub enum HybridIter<'a, T: Idx> {
-    Sparse(slice::Iter<'a, T>),
-    Dense(BitIter<'a, T>),
-}
-
-impl<'a, T: Idx> Iterator for HybridIter<'a, T> {
-    type Item = T;
-
-    fn next(&mut self) -> Option<T> {
-        match self {
-            HybridIter::Sparse(sparse) => sparse.next().copied(),
-            HybridIter::Dense(dense) => dense.next(),
-        }
-    }
-}
-
 /// A resizable bitset type with a dense representation.
 ///
 /// `T` is an index type, typically a newtyped `usize` wrapper, but it can also
diff --git a/compiler/rustc_index/src/bit_set/tests.rs b/compiler/rustc_index/src/bit_set/tests.rs
index 21e681d63f6..3f9198ce37f 100644
--- a/compiler/rustc_index/src/bit_set/tests.rs
+++ b/compiler/rustc_index/src/bit_set/tests.rs
@@ -76,96 +76,6 @@ fn union_two_sets() {
 }
 
 #[test]
-fn hybrid_bitset() {
-    let mut sparse038: HybridBitSet<usize> = HybridBitSet::new_empty(256);
-    assert!(sparse038.is_empty());
-    assert!(sparse038.insert(0));
-    assert!(sparse038.insert(1));
-    assert!(sparse038.insert(8));
-    assert!(sparse038.insert(3));
-    assert!(!sparse038.insert(3));
-    assert!(sparse038.remove(1));
-    assert!(!sparse038.is_empty());
-    assert_eq!(sparse038.iter().collect::<Vec<_>>(), [0, 3, 8]);
-
-    for i in 0..256 {
-        if i == 0 || i == 3 || i == 8 {
-            assert!(sparse038.contains(i));
-        } else {
-            assert!(!sparse038.contains(i));
-        }
-    }
-
-    let mut sparse01358 = sparse038.clone();
-    assert!(sparse01358.insert(1));
-    assert!(sparse01358.insert(5));
-    assert_eq!(sparse01358.iter().collect::<Vec<_>>(), [0, 1, 3, 5, 8]);
-
-    let mut dense10 = HybridBitSet::new_empty(256);
-    for i in 0..10 {
-        assert!(dense10.insert(i));
-    }
-    assert!(!dense10.is_empty());
-    assert_eq!(dense10.iter().collect::<Vec<_>>(), [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
-
-    let mut dense256 = HybridBitSet::new_empty(256);
-    assert!(dense256.is_empty());
-    dense256.insert_all();
-    assert!(!dense256.is_empty());
-    for i in 0..256 {
-        assert!(dense256.contains(i));
-    }
-
-    assert!(sparse038.superset(&sparse038)); // sparse + sparse (self)
-    assert!(sparse01358.superset(&sparse038)); // sparse + sparse
-    assert!(dense10.superset(&sparse038)); // dense + sparse
-    assert!(dense10.superset(&dense10)); // dense + dense (self)
-    assert!(dense256.superset(&dense10)); // dense + dense
-
-    let mut hybrid = sparse038.clone();
-    assert!(!sparse01358.union(&hybrid)); // no change
-    assert!(hybrid.union(&sparse01358));
-    assert!(hybrid.superset(&sparse01358) && sparse01358.superset(&hybrid));
-    assert!(!dense256.union(&dense10));
-
-    // dense / sparse where dense superset sparse
-    assert!(!dense10.clone().union(&sparse01358));
-    assert!(sparse01358.clone().union(&dense10));
-    assert!(dense10.clone().intersect(&sparse01358));
-    assert!(!sparse01358.clone().intersect(&dense10));
-    assert!(dense10.clone().subtract(&sparse01358));
-    assert!(sparse01358.clone().subtract(&dense10));
-
-    // dense / sparse where sparse superset dense
-    let dense038 = sparse038.to_dense();
-    assert!(!sparse01358.clone().union(&dense038));
-    assert!(dense038.clone().union(&sparse01358));
-    assert!(sparse01358.clone().intersect(&dense038));
-    assert!(!dense038.clone().intersect(&sparse01358));
-    assert!(sparse01358.clone().subtract(&dense038));
-    assert!(dense038.clone().subtract(&sparse01358));
-
-    let mut dense = dense10.clone();
-    assert!(dense.union(&dense256));
-    assert!(dense.superset(&dense256) && dense256.superset(&dense));
-    assert!(hybrid.union(&dense256));
-    assert!(hybrid.superset(&dense256) && dense256.superset(&hybrid));
-
-    assert!(!dense10.clone().intersect(&dense256));
-    assert!(dense256.clone().intersect(&dense10));
-    assert!(dense10.clone().subtract(&dense256));
-    assert!(dense256.clone().subtract(&dense10));
-
-    assert_eq!(dense256.iter().count(), 256);
-    let mut dense0 = dense256;
-    for i in 0..256 {
-        assert!(dense0.remove(i));
-    }
-    assert!(!dense0.remove(0));
-    assert!(dense0.is_empty());
-}
-
-#[test]
 fn chunked_bitset() {
     let mut b0 = ChunkedBitSet::<usize>::new_empty(0);
     let b0b = b0.clone();
@@ -593,15 +503,15 @@ fn sparse_matrix_operations() {
     matrix.insert(2, 99);
     matrix.insert(4, 0);
 
-    let mut disjoint: HybridBitSet<usize> = HybridBitSet::new_empty(100);
+    let mut disjoint: ChunkedBitSet<usize> = ChunkedBitSet::new_empty(100);
     disjoint.insert(33);
 
-    let mut superset = HybridBitSet::new_empty(100);
+    let mut superset = ChunkedBitSet::new_empty(100);
     superset.insert(22);
     superset.insert(75);
     superset.insert(33);
 
-    let mut subset = HybridBitSet::new_empty(100);
+    let mut subset = ChunkedBitSet::new_empty(100);
     subset.insert(22);
 
     // SparseBitMatrix::remove
@@ -746,90 +656,6 @@ fn dense_last_set_before() {
     }
 }
 
-/// Merge dense hybrid set into empty sparse hybrid set.
-#[bench]
-fn union_hybrid_sparse_empty_to_dense(b: &mut Bencher) {
-    let mut pre_dense: HybridBitSet<usize> = HybridBitSet::new_empty(256);
-    for i in 0..10 {
-        assert!(pre_dense.insert(i));
-    }
-    let pre_sparse: HybridBitSet<usize> = HybridBitSet::new_empty(256);
-    b.iter(|| {
-        let dense = pre_dense.clone();
-        let mut sparse = pre_sparse.clone();
-        sparse.union(&dense);
-    })
-}
-
-/// Merge dense hybrid set into full hybrid set with same indices.
-#[bench]
-fn union_hybrid_sparse_full_to_dense(b: &mut Bencher) {
-    let mut pre_dense: HybridBitSet<usize> = HybridBitSet::new_empty(256);
-    for i in 0..10 {
-        assert!(pre_dense.insert(i));
-    }
-    let mut pre_sparse: HybridBitSet<usize> = HybridBitSet::new_empty(256);
-    for i in 0..SPARSE_MAX {
-        assert!(pre_sparse.insert(i));
-    }
-    b.iter(|| {
-        let dense = pre_dense.clone();
-        let mut sparse = pre_sparse.clone();
-        sparse.union(&dense);
-    })
-}
-
-/// Merge dense hybrid set into full hybrid set with indices over the whole domain.
-#[bench]
-fn union_hybrid_sparse_domain_to_dense(b: &mut Bencher) {
-    let mut pre_dense: HybridBitSet<usize> = HybridBitSet::new_empty(SPARSE_MAX * 64);
-    for i in 0..10 {
-        assert!(pre_dense.insert(i));
-    }
-    let mut pre_sparse: HybridBitSet<usize> = HybridBitSet::new_empty(SPARSE_MAX * 64);
-    for i in 0..SPARSE_MAX {
-        assert!(pre_sparse.insert(i * 64));
-    }
-    b.iter(|| {
-        let dense = pre_dense.clone();
-        let mut sparse = pre_sparse.clone();
-        sparse.union(&dense);
-    })
-}
-
-/// Merge dense hybrid set into empty hybrid set where the domain is very small.
-#[bench]
-fn union_hybrid_sparse_empty_small_domain(b: &mut Bencher) {
-    let mut pre_dense: HybridBitSet<usize> = HybridBitSet::new_empty(SPARSE_MAX);
-    for i in 0..SPARSE_MAX {
-        assert!(pre_dense.insert(i));
-    }
-    let pre_sparse: HybridBitSet<usize> = HybridBitSet::new_empty(SPARSE_MAX);
-    b.iter(|| {
-        let dense = pre_dense.clone();
-        let mut sparse = pre_sparse.clone();
-        sparse.union(&dense);
-    })
-}
-
-/// Merge dense hybrid set into full hybrid set where the domain is very small.
-#[bench]
-fn union_hybrid_sparse_full_small_domain(b: &mut Bencher) {
-    let mut pre_dense: HybridBitSet<usize> = HybridBitSet::new_empty(SPARSE_MAX);
-    for i in 0..SPARSE_MAX {
-        assert!(pre_dense.insert(i));
-    }
-    let mut pre_sparse: HybridBitSet<usize> = HybridBitSet::new_empty(SPARSE_MAX);
-    for i in 0..SPARSE_MAX {
-        assert!(pre_sparse.insert(i));
-    }
-    b.iter(|| {
-        let dense = pre_dense.clone();
-        let mut sparse = pre_sparse.clone();
-        sparse.union(&dense);
-    })
-}
-
 #[bench]
 fn bench_insert(b: &mut Bencher) {
     let mut bs = BitSet::new_filled(99999usize);