HPhis with HParameter inputs must have Tagged representation

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HYDROGEN_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include <iosfwd>
 
 #include "src/v8.h"
@@ skipping 5294 matching lines @@
 
   unsigned index() const { return index_; }
   ParameterKind kind() const { return kind_; }
 
   virtual std::ostream& PrintDataTo(std::ostream& os) const OVERRIDE;  // NOLINT
 
   virtual Representation RequiredInputRepresentation(int index) OVERRIDE {
     return Representation::None();
   }
 
+  virtual Representation KnownOptimalRepresentation() OVERRIDE {
+    // If a parameter is an input to a phi, that phi should not
+    // choose any more optimistic representation than Tagged.
+    return Representation::Tagged();
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(Parameter)
 
  private:
   explicit HParameter(unsigned index,
                       ParameterKind kind = STACK_PARAMETER)
       : index_(index),
         kind_(kind) {
     set_representation(Representation::Tagged());
   }
 
@@ skipping 2586 matching lines @@
 };
 
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_