Mask results from flow-sensitive resolver with in_any_value_of_ty

We relied previously on the caller (e.g. `Q::in_operand`) to ignore
`Local`s that were indirectly mutable (and thus assumed to be
qualified). However, it's much clearer (and more efficient) to do this
in the resolver itself.

This does not yet remove the masking done in `Q::in_operand` and others
for safety's sake, although I believe that should now be possible.

Author: ecstatic-morse

src/librustc_mir/transform/check_consts/resolver.rs

@@ -188,6 +188,9 @@ where
     indirectly_mutable_locals: &'a RefCell<IndirectlyMutableResults<'mir, 'tcx>>,
     cursor: dataflow::ResultsCursor<'mir, 'tcx, FlowSensitiveAnalysis<'a, 'mir, 'tcx, Q>>,
     qualifs_per_local: BitSet<Local>,
+
+    /// The value of `Q::in_any_value_of_ty` for each local.
+    qualifs_in_any_value_of_ty: BitSet<Local>,
 }
 
 impl<Q> FlowSensitiveResolver<'a, 'mir, 'tcx, Q>
@@ -208,10 +211,18 @@ where
             dataflow::Engine::new(item.body, dead_unwinds, analysis).iterate_to_fixpoint();
         let cursor = dataflow::ResultsCursor::new(item.body, results);
 
+        let mut qualifs_in_any_value_of_ty = BitSet::new_empty(item.body.local_decls.len());
+        for (local, decl) in item.body.local_decls.iter_enumerated() {
+            if Q::in_any_value_of_ty(item, decl.ty) {
+                qualifs_in_any_value_of_ty.insert(local);
+            }
+        }
+
         FlowSensitiveResolver {
             cursor,
             indirectly_mutable_locals,
             qualifs_per_local: BitSet::new_empty(item.body.local_decls.len()),
+            qualifs_in_any_value_of_ty,
             location: Location { block: mir::START_BLOCK, statement_index: 0 },
         }
     }
@@ -242,16 +253,23 @@ where
 
         self.qualifs_per_local.overwrite(indirectly_mutable_locals.get());
         self.qualifs_per_local.union(self.cursor.get());
+        self.qualifs_per_local.intersect(&self.qualifs_in_any_value_of_ty);
         &self.qualifs_per_local
     }
 
     fn contains(&mut self, local: Local) -> bool {
+        // No need to update the cursor if we know that `Local` cannot possibly be qualified.
+        if !self.qualifs_in_any_value_of_ty.contains(local) {
+            return false;
+        }
+
+        // Otherwise, return `true` if this local is qualified or was indirectly mutable at any
+        // point before this statement.
         self.cursor.seek_before(self.location);
         if self.cursor.get().contains(local) {
             return true;
         }
 
-
         let mut indirectly_mutable_locals = self.indirectly_mutable_locals.borrow_mut();
         indirectly_mutable_locals.seek(self.location);
         indirectly_mutable_locals.get().contains(local)