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Auto merge of #147619 - nnethercote:union-ne-check, r=Zalathar

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Add a `!=` check to `ChunkedBitSet::union`.

It's a big speed win for `cranelift-codegen-0.119.0`.

r? `@Zalathar`
This commit is contained in:
bors 2025-10-15 10:04:49 +00:00
commit 4f08307f6e
1 changed files with 61 additions and 47 deletions
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108
compiler/rustc_index/src/bit_set.rs
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@ -800,27 +800,39 @@ 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. Also a
// performance win.
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 =
count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
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 = count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
if *self_chunk_count == chunk_domain_size {
*self_chunk = Ones;
}
changed = true;
}
}
}
@ -874,28 +886,29 @@ 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 =
count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
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 = count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
if *self_chunk_count == 0 {
*self_chunk = Zeros;
}
changed = true;
}
}
}
@ -931,28 +944,29 @@ 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 =
count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
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 = count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
if *self_chunk_count == 0 {
*self_chunk = Zeros;
}
changed = true;
}
}
}