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

src/x64/lithium-codegen-x64.h

Index: src/x64/lithium-codegen-x64.h
diff --git a/src/x64/lithium-codegen-x64.h b/src/x64/lithium-codegen-x64.h
index 071ba6683035462536f8304d0d5489653cce0cd6..e749711075f9eb2a17dde059dff77a1bb3846a56 100644
--- a/src/x64/lithium-codegen-x64.h
+++ b/src/x64/lithium-codegen-x64.h
@@ -43,6 +43,7 @@ namespace internal {
 // Forward declarations.
 class LDeferredCode;
 class SafepointGenerator;
+class LithiumSmiInstructionWrapper;
 
 class LCodeGen BASE_EMBEDDED {
  public:
@@ -122,6 +123,7 @@ class LCodeGen BASE_EMBEDDED {
 
   // Deferred code support.
   void DoDeferredNumberTagD(LNumberTagD* instr);
+  void DoDeferredNumberTagI(LNumberTagI* instr);
   void DoDeferredNumberTagU(LNumberTagU* instr);
   void DoDeferredTaggedToI(LTaggedToI* instr);
   void DoDeferredMathAbsTaggedHeapNumber(LMathAbs* instr);
@@ -268,7 +270,7 @@ class LCodeGen BASE_EMBEDDED {
       uint32_t additional_index = 0);
 
   void EmitIntegerMathAbs(LMathAbs* instr);
-  void EmitInteger64MathAbs(LMathAbs* instr);
+  void EmitSmiMathAbs(LMathAbs* instr);
 
   // Support for recording safepoint and position information.
   void RecordSafepoint(LPointerMap* pointers,
@@ -406,6 +408,7 @@ class LCodeGen BASE_EMBEDDED {
   friend class LDeferredCode;
   friend class LEnvironment;
   friend class SafepointGenerator;
+  friend class LithiumSmiInstructionWrapper;
   DISALLOW_COPY_AND_ASSIGN(LCodeGen);
 };