add new rval, pull deref early

compiler/rustc_mir_transform/src/const_prop.rs

@@ -621,6 +621,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
             // There's no other checking to do at this time.
             Rvalue::Aggregate(..)
             | Rvalue::Use(..)
+            | Rvalue::CopyForDeref(..)
             | Rvalue::Repeat(..)
             | Rvalue::Len(..)
             | Rvalue::Cast(..)