Auto merge of #147644 - cjgillot:bitsetvec, r=jackh726

Use regular Vec in BitSet.

That code is hot enough for the branch in all accesses to `SmallVec` to appear in profiles.

Author: bors

compiler/rustc_index/src/bit_set.rs

@@ -8,7 +8,6 @@ use std::{fmt, iter, slice};
 use Chunk::*;
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_NoContext, Encodable_NoContext};
-use smallvec::{SmallVec, smallvec};
 
 use crate::{Idx, IndexVec};
 
@@ -118,7 +117,7 @@ macro_rules! bit_relations_inherent_impls {
 #[derive(Eq, PartialEq, Hash)]
 pub struct DenseBitSet<T> {
     domain_size: usize,
-    words: SmallVec<[Word; 2]>,
+    words: Vec<Word>,
     marker: PhantomData<T>,
 }
 
@@ -134,15 +133,15 @@ impl<T: Idx> DenseBitSet<T> {
     #[inline]
     pub fn new_empty(domain_size: usize) -> DenseBitSet<T> {
         let num_words = num_words(domain_size);
-        DenseBitSet { domain_size, words: smallvec![0; num_words], marker: PhantomData }
+        DenseBitSet { domain_size, words: vec![0; num_words], marker: PhantomData }
     }
 
     /// Creates a new, filled bitset with a given `domain_size`.
     #[inline]
     pub fn new_filled(domain_size: usize) -> DenseBitSet<T> {
         let num_words = num_words(domain_size);
         let mut result =
-            DenseBitSet { domain_size, words: smallvec![!0; num_words], marker: PhantomData };
+            DenseBitSet { domain_size, words: vec![!0; num_words], marker: PhantomData };
         result.clear_excess_bits();
         result
     }
@@ -1384,7 +1383,7 @@ impl<T: Idx> From<DenseBitSet<T>> for GrowableBitSet<T> {
 pub struct BitMatrix<R: Idx, C: Idx> {
     num_rows: usize,
     num_columns: usize,
-    words: SmallVec<[Word; 2]>,
+    words: Vec<Word>,
     marker: PhantomData<(R, C)>,
 }
 
@@ -1397,7 +1396,7 @@ impl<R: Idx, C: Idx> BitMatrix<R, C> {
         BitMatrix {
             num_rows,
             num_columns,
-            words: smallvec![0; num_rows * words_per_row],
+            words: vec![0; num_rows * words_per_row],
             marker: PhantomData,
         }
     }