Implemented FastAsciiStringJoin in X64 full codegen.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index eb1f42d244b35deec43fa8225e2beb9ec4a84150..fca46cc93c7283a7c627f0749fc9773397402a02 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -470,6 +470,11 @@ class MacroAssembler: public Assembler {
               Register src1,
               Register src2,
               LabelType* on_not_smi_result);
+  template <typename LabelType>
+  void SmiAdd(Register dst,
+              Register src1,
+              const Operand& src2,
+              LabelType* on_not_smi_result);
 
   void SmiAdd(Register dst,
               Register src1,
@@ -590,6 +595,10 @@ class MacroAssembler: public Assembler {
   // Converts a positive smi to a negative index.
   SmiIndex SmiToNegativeIndex(Register dst, Register src, int shift);
 
+  // Add the value of a smi in memory to an int32 register.
+  // Sets flags as a normal add.
+  void AddSmiField(Register dst, const Operand& src);
+
   // Basic Smi operations.
   void Move(Register dst, Smi* source) {
     LoadSmiConstant(dst, source);
@@ -1022,6 +1031,18 @@ class MacroAssembler: public Assembler {
 
   Handle<Object> CodeObject() { return code_object_; }
 
+  // Copy length bytes from source to destination.
+  // Uses scratch register internally (if you have a low-eight register
+  // free, do use it, otherwise kScratchRegister will be used).
+  // The min_length is a minimum limit on the value that length will have.
+  // The algorithm has some special cases that might be omitted if the string
+  // is known to always be long.
+  void CopyBytes(Register destination,
+                 Register source,
+                 Register length,
+                 int min_length = 0,
+                 Register scratch = kScratchRegister);
+
 
   // ---------------------------------------------------------------------------
   // StatsCounter support
@@ -1273,6 +1294,26 @@ void MacroAssembler::SmiAdd(Register dst,
 
 
 template <typename LabelType>
+void MacroAssembler::SmiAdd(Register dst,
+                            Register src1,
+                            const Operand& src2,
+                            LabelType* on_not_smi_result) {
+  ASSERT_NOT_NULL(on_not_smi_result);
+  if (dst.is(src1)) {
+    movq(kScratchRegister, src1);
+    addq(kScratchRegister, src2);
+    j(overflow, on_not_smi_result);
+    movq(dst, kScratchRegister);
+  } else {
+    ASSERT(!src2.AddressUsesRegister(dst));
+    movq(dst, src1);
+    addq(dst, src2);
+    j(overflow, on_not_smi_result);
+  }
+}
+
+
+template <typename LabelType>
 void MacroAssembler::SmiSub(Register dst,
                             Register src1,
                             Register src2,