Introduce `MixedBitSet`.

It just uses `BitSet` for small/medium sizes (<= 2048 bits) and
`ChunkedBitSet` for larger sizes. This is good because `ChunkedBitSet`
is slow and memory-hungry at smaller sizes.

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/rustc_mir_dataflow/src/framework/lattice.rs b/compiler/rustc_mir_dataflow/src/framework/lattice.rs
index e2b56aedca3..852099e2ac8 100644
--- a/compiler/rustc_mir_dataflow/src/framework/lattice.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/lattice.rs
@@ -40,7 +40,7 @@
 
 use std::iter;
 
-use rustc_index::bit_set::{BitSet, ChunkedBitSet};
+use rustc_index::bit_set::{BitSet, ChunkedBitSet, MixedBitSet};
 use rustc_index::{Idx, IndexVec};
 
 use crate::framework::BitSetExt;
@@ -132,6 +132,12 @@ impl<T: Idx> JoinSemiLattice for ChunkedBitSet<T> {
     }
 }
 
+impl<T: Idx> JoinSemiLattice for MixedBitSet<T> {
+    fn join(&mut self, other: &Self) -> bool {
+        self.union(other)
+    }
+}
+
 /// Extends a type `T` with top and bottom elements to make it a partially ordered set in which no
 /// value of `T` is comparable with any other.
 ///