Factor out a recurring pattern as count_ones.

Author: nnethercote

compiler/rustc_index/src/bit_set.rs

@@ -160,7 +160,7 @@ impl<T: Idx> DenseBitSet<T> {
 
     /// Count the number of set bits in the set.
     pub fn count(&self) -> usize {
-        self.words.iter().map(|e| e.count_ones() as usize).sum()
+        count_ones(&self.words)
     }
 
     /// Returns `true` if `self` contains `elem`.
@@ -817,10 +817,8 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
                             op,
                         );
                         debug_assert!(has_changed);
-                        *self_chunk_count = self_chunk_words[0..num_words]
-                            .iter()
-                            .map(|w| w.count_ones() as ChunkSize)
-                            .sum();
+                        *self_chunk_count =
+                            count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
                         if *self_chunk_count == chunk_domain_size {
                             *self_chunk = Ones;
                         }
@@ -871,10 +869,7 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
                     let self_chunk_count = chunk_domain_size - *other_chunk_count;
                     debug_assert_eq!(
                         self_chunk_count,
-                        self_chunk_words[0..num_words]
-                            .iter()
-                            .map(|w| w.count_ones() as ChunkSize)
-                            .sum()
+                        count_ones(&self_chunk_words[0..num_words]) as ChunkSize
                     );
                     *self_chunk = Mixed(self_chunk_count, Rc::new(self_chunk_words));
                 }
@@ -897,10 +892,8 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
                             op,
                         );
                         debug_assert!(has_changed);
-                        *self_chunk_count = self_chunk_words[0..num_words]
-                            .iter()
-                            .map(|w| w.count_ones() as ChunkSize)
-                            .sum();
+                        *self_chunk_count =
+                            count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
                         if *self_chunk_count == 0 {
                             *self_chunk = Zeros;
                         }
@@ -956,10 +949,8 @@ impl<T: Idx> BitRelations<ChunkedBitSet<T>> for ChunkedBitSet<T> {
                             op,
                         );
                         debug_assert!(has_changed);
-                        *self_chunk_count = self_chunk_words[0..num_words]
-                            .iter()
-                            .map(|w| w.count_ones() as ChunkSize)
-                            .sum();
+                        *self_chunk_count =
+                            count_ones(&self_chunk_words[0..num_words]) as ChunkSize;
                         if *self_chunk_count == 0 {
                             *self_chunk = Zeros;
                         }
@@ -1046,21 +1037,12 @@ impl Chunk {
                 assert!(0 < count && count < chunk_domain_size);
 
                 // Check the number of set bits matches `count`.
-                assert_eq!(
-                    words.iter().map(|w| w.count_ones() as ChunkSize).sum::<ChunkSize>(),
-                    count
-                );
+                assert_eq!(count_ones(words.as_slice()) as ChunkSize, count);
 
                 // Check the not-in-use words are all zeroed.
                 let num_words = num_words(chunk_domain_size as usize);
                 if num_words < CHUNK_WORDS {
-                    assert_eq!(
-                        words[num_words..]
-                            .iter()
-                            .map(|w| w.count_ones() as ChunkSize)
-                            .sum::<ChunkSize>(),
-                        0
-                    );
+                    assert_eq!(count_ones(&words[num_words..]) as ChunkSize, 0);
                 }
             }
         }
@@ -1542,7 +1524,7 @@ impl<R: Idx, C: Idx> BitMatrix<R, C> {
     /// Returns the number of elements in `row`.
     pub fn count(&self, row: R) -> usize {
         let (start, end) = self.range(row);
-        self.words[start..end].iter().map(|e| e.count_ones() as usize).sum()
+        count_ones(&self.words[start..end])
     }
 }
 
@@ -1753,6 +1735,11 @@ fn max_bit(word: Word) -> usize {
     WORD_BITS - 1 - word.leading_zeros() as usize
 }
 
+#[inline]
+fn count_ones(words: &[Word]) -> usize {
+    words.iter().map(|word| word.count_ones() as usize).sum()
+}
+
 /// Integral type used to represent the bit set.
 pub trait FiniteBitSetTy:
     BitAnd<Output = Self>