[compiler] Properly guard the speculative optimizations for instanceof.

src/ast/ast.cc

Index: src/ast/ast.cc
diff --git a/src/ast/ast.cc b/src/ast/ast.cc
index 18e88310002a7ba497e1f2fa4356db68c445408c..c4808ca840500bd89c9c4b1498d2f5f16733ad2e 100644
--- a/src/ast/ast.cc
+++ b/src/ast/ast.cc
@@ -735,12 +735,16 @@ void CompareOperation::AssignFeedbackVectorSlots(
   // Feedback vector slot is only used by interpreter for binary operations.
   // Full-codegen uses AstId to record type feedback.
   switch (op()) {
-    // instanceof and in do not collect type feedback.
     case Token::INSTANCEOF:
+      // instanceof collects feedback in a general slot (for now).
+      type_feedback_slot_ = spec->AddGeneralSlot();
+      return;
     case Token::IN:
+      // in does not collect type feedback.
       return;
     default:
       type_feedback_slot_ = spec->AddInterpreterCompareICSlot();
+      return;
   }
 }