Clear ChunkedBitSet without reallocating

Author: Zalathar

compiler/rustc_index/src/bit_set.rs

@@ -585,8 +585,7 @@ impl<T: Idx> ChunkedBitSet<T> {
 }
 
 pubfnclear(&mutself){
-let domain_size = self.domain_size();
-*self = ChunkedBitSet::new_empty(domain_size);
+self.chunks.fill_with(|| Chunk::Zeros);
 }
 
 #[cfg(test)]
@@ -684,9 +683,7 @@ impl<T: Idx> ChunkedBitSet<T> {
 
 /// Sets all bits to true.
 pubfninsert_all(&mutself){
-for chunk inself.chunks.iter_mut(){
-*chunk = Ones;
-}
+self.chunks.fill_with(|| Chunk::Ones);
 }
 
 /// Returns `true` if the set has changed.