Improve array to string conversion.

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 137 matching lines @@
   V(OsrEntry)                                  \
   V(OuterContext)                              \
   V(Parameter)                                 \
   V(Power)                                     \
   V(PushArgument)                              \
   V(Random)                                    \
   V(RegExpLiteral)                             \
   V(Return)                                    \
   V(Ror)                                       \
   V(Sar)                                       \
+  V(SeqStringSetChar)                          \
   V(Shl)                                       \
   V(Shr)                                       \
   V(Simulate)                                  \
   V(SoftDeoptimize)                            \
   V(StackCheck)                                \
   V(StoreContextSlot)                          \
   V(StoreGlobalCell)                           \
   V(StoreGlobalGeneric)                        \
   V(StoreKeyed)                                \
   V(StoreKeyedGeneric)                         \
@@ skipping 5037 matching lines @@
     return Representation::Tagged();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(DateField)
 
  private:
   Smi* index_;
 };
 
 
+class HSeqStringSetChar: public HTemplateInstruction<3> {
+ public:
+  HSeqStringSetChar(bool is_one_byte,
+                    HValue* string,
+                    HValue* index,
+                    HValue* value) : is_one_byte_(is_one_byte) {
+    SetOperandAt(0, string);
+    SetOperandAt(1, index);
+    SetOperandAt(2, value);
+  }
+
+  bool is_one_byte() { return is_one_byte_; }
+  HValue* string() { return OperandAt(0); }
+  HValue* index() { return OperandAt(1); }
+  HValue* value() { return OperandAt(2); }
+
+  virtual Representation RequiredInputRepresentation(int index) {
+    return Representation::Tagged();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(SeqStringSetChar)
+
+ private:
+  bool is_one_byte_;
+};
+
+
 class HDeleteProperty: public HBinaryOperation {
  public:
   HDeleteProperty(HValue* context, HValue* obj, HValue* key)
       : HBinaryOperation(context, obj, key) {
     set_representation(Representation::Tagged());
     SetAllSideEffects();
   }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
@@ skipping 165 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_