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Add a != check to ChunkedBitSet::union. #147619

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Add a != check to ChunkedBitSet::union. #147619

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20cc4da
Refactor some `ChunkedBitSet` operations.
nnethercote Oct 13, 2025
ad8b2e0
Add a `!=` check to ChunkedBitSet::union.
nnethercote Oct 13, 2025
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122 changes: 69 additions & 53 deletions compiler/rustc_index/src/bit_set.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -803,29 +803,41 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
// words, and this happens often enough that it's a
// performance win. Also, we only need to operate on the
// in-use words, hence the slicing.
let op = |a, b| a | b;
let num_words = num_words(chunk_domain_size as usize);
if bitwise_changes(

// If both sides are the same, nothing will change. This
// case is very common and it's a pretty fast check, so
// it's a performance win to do it.
if self_chunk_words[0..num_words] == other_chunk_words[0..num_words] {
continue;
}

// Do a more precise "will anything change?" test.
let op = |a, b| a | b;
if !bitwise_changes(
&self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
) {
let self_chunk_words = Rc::make_mut(self_chunk_words);
let has_changed = bitwise(
&mut self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
);
debug_assert!(has_changed);
*self_chunk_count = self_chunk_words[0..num_words]
.iter()
.map(|w| w.count_ones() as ChunkSize)
.sum();
if *self_chunk_count == chunk_domain_size {
*self_chunk = Ones;
}
changed = true;
continue;
}

// If we reach here, `self_chunk_words` is definitely changing.
let self_chunk_words = Rc::make_mut(self_chunk_words);
let has_changed = bitwise(
&mut self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
);
debug_assert!(has_changed);
*self_chunk_count = self_chunk_words[0..num_words]
.iter()
.map(|w| w.count_ones() as ChunkSize)
.sum();
if *self_chunk_count == chunk_domain_size {
*self_chunk = Ones;
}
changed = true;
}
}
}
Expand Down Expand Up @@ -882,30 +894,32 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
Mixed(self_chunk_count, self_chunk_words),
Mixed(_other_chunk_count, other_chunk_words),
) => {
// See [`<Self as BitRelations<ChunkedBitSet<T>>>::union`] for the explanation
let op = |a: u64, b: u64| a & !b;
// See `ChunkedBitSet::union` for details on what is happening here.
let num_words = num_words(chunk_domain_size as usize);
if bitwise_changes(
let op = |a: u64, b: u64| a & !b;
if !bitwise_changes(
&self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
) {
let self_chunk_words = Rc::make_mut(self_chunk_words);
let has_changed = bitwise(
&mut self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
);
debug_assert!(has_changed);
*self_chunk_count = self_chunk_words[0..num_words]
.iter()
.map(|w| w.count_ones() as ChunkSize)
.sum();
if *self_chunk_count == 0 {
*self_chunk = Zeros;
}
changed = true;
continue;
}

let self_chunk_words = Rc::make_mut(self_chunk_words);
let has_changed = bitwise(
&mut self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
);
debug_assert!(has_changed);
*self_chunk_count = self_chunk_words[0..num_words]
.iter()
.map(|w| w.count_ones() as ChunkSize)
.sum();
if *self_chunk_count == 0 {
*self_chunk = Zeros;
}
changed = true;
}
}
}
Expand Down Expand Up @@ -941,30 +955,32 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
Mixed(self_chunk_count, self_chunk_words),
Mixed(_other_chunk_count, other_chunk_words),
) => {
// See [`<Self as BitRelations<ChunkedBitSet<T>>>::union`] for the explanation
let op = |a, b| a & b;
// See `ChunkedBitSet::union` for details on what is happening here.
let num_words = num_words(chunk_domain_size as usize);
if bitwise_changes(
let op = |a, b| a & b;
if !bitwise_changes(
&self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
) {
let self_chunk_words = Rc::make_mut(self_chunk_words);
let has_changed = bitwise(
&mut self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
);
debug_assert!(has_changed);
*self_chunk_count = self_chunk_words[0..num_words]
.iter()
.map(|w| w.count_ones() as ChunkSize)
.sum();
if *self_chunk_count == 0 {
*self_chunk = Zeros;
}
changed = true;
continue;
}

let self_chunk_words = Rc::make_mut(self_chunk_words);
let has_changed = bitwise(
&mut self_chunk_words[0..num_words],
&other_chunk_words[0..num_words],
op,
);
debug_assert!(has_changed);
*self_chunk_count = self_chunk_words[0..num_words]
.iter()
.map(|w| w.count_ones() as ChunkSize)
.sum();
if *self_chunk_count == 0 {
*self_chunk = Zeros;
}
changed = true;
}
}
}
Expand Down
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