Introduce PushInt64AsTwoSmis and PopInt64AsTwoSmis macro instructions for X64

src/x64/macro-assembler-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 702 matching lines @@
   void Move(Register dst, Smi* source) {
     LoadSmiConstant(dst, source);
   }
 
   void Move(const Operand& dst, Smi* source) {
     Register constant = GetSmiConstant(source);
     movq(dst, constant);
   }
 
   void Push(Smi* smi);
+
+  // Push a 64-bit integer as two "general" Smis on stack so that the garbage

[danno, 2013/08/19 22:00:40]

I find the comments a bit confusing. I think the following is probably clearer:

Save away a 64-bit integer on the stack as two 32-bits integers masquerading as
smis so that the garbage collector skips visiting them.

[haitao.feng, 2013/08/20 13:20:15]

Done.

+  // collector could iterate stack safely. The Smis are general, i.e., all the
+  // lower kSmiShift bits are zero.
+  void PushInt64AsTwoSmis(Register src, Register scratch = kScratchRegister);
+  // Reconstruct a 64-bit integer from two "general" Smis from stack.

[danno, 2013/08/19 22:00:40]

// Reconstruct a 64-bit integer from two 32-bits integers masquerading as smis
on the top of stack.

[haitao.feng, 2013/08/20 13:20:15]

Done.

+  void PopInt64AsTwoSmis(Register dst, Register scratch = kScratchRegister);
+
   void Test(const Operand& dst, Smi* source);
 
 
   // ---------------------------------------------------------------------------
   // String macros.
 
   // If object is a string, its map is loaded into object_map.
   void JumpIfNotString(Register object,
                        Register object_map,
                        Label* not_string,
@@ skipping 810 matching lines @@
     masm->popfq();                                                           \
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_