Ignore errors re: unreachable blocks in dataflow cursor unit tests

compiler/rustc_mir_dataflow/src/framework/cursor.rs

@@ -64,6 +64,13 @@ where
         }
     }
 
+    /// Allows inspection of unreachable basic blocks even with `debug_assertions` enabled.
+    #[cfg(test)]
+    pub(crate) fn allow_unreachable(&mut self) {
+        #[cfg(debug_assertions)]
+        self.reachable_blocks.insert_all()
+    }
+
     /// Returns the underlying `Results`.
     pub fn results(&self) -> &Results<'tcx, A> {
         &self.results.borrow()

compiler/rustc_mir_dataflow/src/framework/tests.rs

@@ -268,6 +268,8 @@ fn test_cursor<D: Direction>(analysis: MockAnalysis<'tcx, D>) {
     let mut cursor =
         Results { entry_sets: analysis.mock_entry_sets(), analysis }.into_results_cursor(body);
 
+    cursor.allow_unreachable();
+
     let every_target = || {
         body.basic_blocks()
             .iter_enumerated()