From 0dc5b52e8eef98e973d9935c45e8dc3d7fbd6a1d Mon Sep 17 00:00:00 2001
From: Usman Akinyemi <usmanakinyemi202@gmail.com>
Date: Fri, 16 Jan 2026 04:25:12 +0530
Subject: [PATCH] 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.

Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
---
 compiler/rustc_index/src/bit_set.rs | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/compiler/rustc_index/src/bit_set.rs b/compiler/rustc_index/src/bit_set.rs
index a9bdf597e128f..184fa409d9605 100644
--- a/compiler/rustc_index/src/bit_set.rs
+++ b/compiler/rustc_index/src/bit_set.rs
@@ -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.