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};
 useChunk::*;
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_NoContext,Encodable_NoContext};
-use smallvec::{SmallVec, smallvec};
 
 usecrate::{Idx,IndexVec};
 
@@ -118,7 +117,7 @@ macro_rules! bit_relations_inherent_impls {
 #[derive(Eq,PartialEq,Hash)]
 pubstructDenseBitSet<T>{
 domain_size:usize,
-words:SmallVec<[Word;2]>,
+words:Vec<Word>,
 marker:PhantomData<T>,
 }
 
@@ -134,15 +133,15 @@ impl<T: Idx> DenseBitSet<T> {
 #[inline]
 pubfnnew_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]
 pubfnnew_filled(domain_size:usize) -> DenseBitSet<T>{
 let num_words = num_words(domain_size);
 letmut 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> {
 pubstructBitMatrix<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,
 }
 }