Support string add in crankshaft:

src/hydrogen-instructions.h

 // Copyright 2011 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(Simulate)                                  \
   V(StackCheck)                                \
   V(StoreContextSlot)                          \
   V(StoreGlobalCell)                           \
   V(StoreGlobalGeneric)                        \
   V(StoreKeyedFastElement)                     \
   V(StoreKeyedSpecializedArrayElement)         \
   V(StoreKeyedGeneric)                         \
   V(StoreNamedField)                           \
   V(StoreNamedGeneric)                         \
+  V(StringAdd)                                 \
   V(StringCharCodeAt)                          \
   V(StringCharFromCode)                        \
   V(StringLength)                              \
   V(Sub)                                       \
   V(Test)                                      \
   V(Throw)                                     \
   V(ToFastProperties)                          \
   V(Typeof)                                    \
   V(TypeofIs)                                  \
   V(UnaryMathOperation)                        \
@@ skipping 1532 matching lines @@
   virtual bool IsCheckInstruction() const { return true; }
 
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::Tagged();
   }
 
 #ifdef DEBUG
   virtual void Verify();
 #endif
 
+  virtual HValue* Canonicalize() {
+    if (!value()->type().IsUninitialized() &&
+        value()->type().IsString() &&
+        first() == FIRST_STRING_TYPE &&
+        last() == LAST_STRING_TYPE) {
+      return NULL;
+    }
+    return this;
+  }
+
   static HCheckInstanceType* NewIsJSObjectOrJSFunction(HValue* value);
 
   InstanceType first() const { return first_; }
   InstanceType last() const { return last_; }
 
   DECLARE_CONCRETE_INSTRUCTION(CheckInstanceType, "check_instance_type")
 
  protected:
   // TODO(ager): It could be nice to allow the ommision of instance
   // type checks if we have already performed an instance type check
@@ skipping 21 matching lines @@
   virtual Representation RequiredInputRepresentation(int index) const {
     return Representation::Tagged();
   }
 
   virtual HType CalculateInferredType();
 
 #ifdef DEBUG
   virtual void Verify();
 #endif
 
+  virtual HValue* Canonicalize() {
+    HType value_type = value()->type();
+    if (!value_type.IsUninitialized() &&
+        (value_type.IsHeapNumber() ||
+         value_type.IsString() ||
+         value_type.IsBoolean() ||
+         value_type.IsNonPrimitive())) {
+      return NULL;
+    }
+    return this;
+  }
+
   DECLARE_CONCRETE_INSTRUCTION(CheckNonSmi, "check_non_smi")
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
 };
 
 
 class HCheckPrototypeMaps: public HTemplateInstruction<0> {
  public:
   HCheckPrototypeMaps(Handle<JSObject> prototype, Handle<JSObject> holder)
@@ skipping 1640 matching lines @@
 
   virtual void PrintDataTo(StringStream* stream);
 
   DECLARE_CONCRETE_INSTRUCTION(StoreKeyedGeneric, "store_keyed_generic")
 
  private:
   bool strict_mode_;
 };
 
 
+class HStringAdd: public HBinaryOperation {
+ public:
+  HStringAdd(HValue* left, HValue* right) : HBinaryOperation(left, right) {
+    set_representation(Representation::Tagged());
+    SetFlag(kUseGVN);
+    SetFlag(kDependsOnMaps);
+  }
+
+  virtual Representation RequiredInputRepresentation(int index) const {
+    return Representation::Tagged();
+  }
+
+  virtual HType CalculateInferredType() {
+    return HType::String();
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(StringAdd, "string_add")
+
+ protected:
+  virtual bool DataEquals(HValue* other) { return true; }
+};
+
+
 class HStringCharCodeAt: public HBinaryOperation {
  public:
   HStringCharCodeAt(HValue* string, HValue* index)
       : HBinaryOperation(string, index) {
     set_representation(Representation::Integer32());
     SetFlag(kUseGVN);
     SetFlag(kDependsOnMaps);
   }
 
   virtual Representation RequiredInputRepresentation(int index) const {
@@ skipping 249 matching lines @@
   HValue* object() { return left(); }
   HValue* key() { return right(); }
 };
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_