Introduce MaybeUnreachable.

1 files changed, 17 insertions, 1 deletions

diff --git a/compiler/rustc_mir_dataflow/src/framework/mod.rs b/compiler/rustc_mir_dataflow/src/framework/mod.rs
index 8ccd57802d7..b40cf9f4691 100644
--- a/compiler/rustc_mir_dataflow/src/framework/mod.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/mod.rs
@@ -48,7 +48,7 @@ mod visitor;
 pub use self::cursor::{AnalysisResults, ResultsClonedCursor, ResultsCursor, ResultsRefCursor};
 pub use self::direction::{Backward, Direction, Forward};
 pub use self::engine::{Engine, EntrySets, Results, ResultsCloned};
-pub use self::lattice::{JoinSemiLattice, MeetSemiLattice};
+pub use self::lattice::{JoinSemiLattice, MaybeUnreachable, MeetSemiLattice};
 pub use self::visitor::{visit_results, ResultsVisitable, ResultsVisitor};
 
 /// Analysis domains are all bitsets of various kinds. This trait holds
@@ -524,6 +524,22 @@ impl<T: Idx> GenKill<T> for ChunkedBitSet<T> {
     }
 }
 
+impl<T, S: GenKill<T>> GenKill<T> for MaybeUnreachable<S> {
+    fn gen(&mut self, elem: T) {
+        match self {
+            MaybeUnreachable::Unreachable => {}
+            MaybeUnreachable::Reachable(set) => set.gen(elem),
+        }
+    }
+
+    fn kill(&mut self, elem: T) {
+        match self {
+            MaybeUnreachable::Unreachable => {}
+            MaybeUnreachable::Reachable(set) => set.kill(elem),
+        }
+    }
+}
+
 impl<T: Idx> GenKill<T> for lattice::Dual<BitSet<T>> {
     fn gen(&mut self, elem: T) {
         self.0.insert(elem);