Improve SeqStringSetChar implementation.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 6248 matching lines @@
 
 class HSeqStringSetChar: public HTemplateInstruction<3> {
  public:
   HSeqStringSetChar(String::Encoding encoding,
                     HValue* string,
                     HValue* index,
                     HValue* value) : encoding_(encoding) {
     SetOperandAt(0, string);
     SetOperandAt(1, index);
     SetOperandAt(2, value);
+    set_representation(Representation::Tagged());
   }
 
   String::Encoding encoding() { return encoding_; }
   HValue* string() { return OperandAt(0); }
   HValue* index() { return OperandAt(1); }
   HValue* value() { return OperandAt(2); }
 
   virtual Representation RequiredInputRepresentation(int index) {
-    return Representation::Tagged();
+    return (index == 0) ? Representation::Tagged()
+                        : Representation::Integer32();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(SeqStringSetChar)
 
  private:
   String::Encoding encoding_;
 };
 
 
 class HDeleteProperty: public HBinaryOperation {
@@ skipping 174 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_