src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/codegen/OptimisticTypesCalculator.java

*** 128,138 ****
          return true;
      }
  
      @Override
      public boolean enterForNode(final ForNode forNode) {
!         if(forNode.isForIn()) {
              // for..in has the iterable in its "modify"
              tagNeverOptimistic(forNode.getModify());
          } else {
              // Test is never optimistic (always coerced to boolean).
              tagNeverOptimisticLoopTest(forNode);
--- 128,138 ----
          return true;
      }
  
      @Override
      public boolean enterForNode(final ForNode forNode) {
!         if(forNode.isForInOrOf()) {
              // for..in has the iterable in its "modify"
              tagNeverOptimistic(forNode.getModify());
          } else {
              // Test is never optimistic (always coerced to boolean).
              tagNeverOptimisticLoopTest(forNode);