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Rollup merge of #151178 - ua/fixme, r=Kivooeo

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simplify words initialization using Rc::new_zeroed

Now that Rc::new_zeroed is stable, remove the cfg(feature = "nightly") branch and the temporary zeroed array on stable. This avoids copying a potentially large [Word; CHUNK_WORDS] into the Rc.
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Matthias Krüger 2026-01-16 13:57:46 +01:00 • committed by GitHub
commit 4227404a04
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1 changed files with 0 additions and 20 deletions
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20
compiler/rustc_index/src/bit_set.rs
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@ -634,22 +634,12 @@ impl<T: Idx> ChunkedBitSet<T> {
match *chunk {
Zeros => {
if chunk_domain_size > 1 {
#[cfg(feature = "nightly")]
let mut words = {
// We take some effort to avoid copying the words.
let words = Rc::<[Word; CHUNK_WORDS]>::new_zeroed();
// SAFETY: `words` can safely be all zeroes.
unsafe { words.assume_init() }
};
#[cfg(not(feature = "nightly"))]
let mut words = {
// FIXME: unconditionally use `Rc::new_zeroed` once it is stable (#129396).
let words = mem::MaybeUninit::<[Word; CHUNK_WORDS]>::zeroed();
// SAFETY: `words` can safely be all zeroes.
let words = unsafe { words.assume_init() };
// Unfortunate possibly-large copy
Rc::new(words)
};
let words_ref = Rc::get_mut(&mut words).unwrap();
let (word_index, mask) = chunk_word_index_and_mask(elem);
@ -695,22 +685,12 @@ impl<T: Idx> ChunkedBitSet<T> {
Zeros => false,
Ones => {
if chunk_domain_size > 1 {
#[cfg(feature = "nightly")]
let mut words = {
// We take some effort to avoid copying the words.
let words = Rc::<[Word; CHUNK_WORDS]>::new_zeroed();
// SAFETY: `words` can safely be all zeroes.
unsafe { words.assume_init() }
};
#[cfg(not(feature = "nightly"))]
let mut words = {
// FIXME: unconditionally use `Rc::new_zeroed` once it is stable (#129396).
let words = mem::MaybeUninit::<[Word; CHUNK_WORDS]>::zeroed();
// SAFETY: `words` can safely be all zeroes.
let words = unsafe { words.assume_init() };
// Unfortunate possibly-large copy
Rc::new(words)
};
let words_ref = Rc::get_mut(&mut words).unwrap();
// Set only the bits in use.