Optionally use 31-bits SMI value for 64-bit system

src/x64/lithium-x64.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 1908 matching lines @@
     temps_[0] = temp;
   }
 
   LOperand* value() { return inputs_[0]; }
   LOperand* temp() { return temps_[0]; }
 
   DECLARE_CONCRETE_INSTRUCTION(Uint32ToDouble, "uint32-to-double")
 };
 
 
+#if !V8_USE_31_BITS_SMI_VALUE
 class LNumberTagI: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LNumberTagI(LOperand* value) {
     inputs_[0] = value;
   }
 
   LOperand* value() { return inputs_[0]; }
 
   DECLARE_CONCRETE_INSTRUCTION(NumberTagI, "number-tag-i")
 };
+#else
+class LNumberTagI: public LTemplateInstruction<1, 1, 1> {
+ public:
+  explicit LNumberTagI(LOperand* value, LOperand* temp) {
+    inputs_[0] = value;
+    temps_[0] = temp;
+  }
+
+  LOperand* value() { return inputs_[0]; }
+  LOperand* temp() { return temps_[0]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(NumberTagI, "number-tag-i")
+};
+#endif
 
 
 class LNumberTagU: public LTemplateInstruction<1, 1, 1> {
  public:
   explicit LNumberTagU(LOperand* value, LOperand* temp) {
     inputs_[0] = value;
     temps_[0] = temp;
   }
 
   LOperand* value() { return inputs_[0]; }
@@ skipping 757 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::int
 
 #endif  // V8_X64_LITHIUM_X64_H_