Fix Issue 1234.

src/x64/assembler-x64.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 377 matching lines @@
 
   // Offset from existing memory operand.
   // Offset is added to existing displacement as 32-bit signed values and
   // this must not overflow.
   Operand(const Operand& base, int32_t offset);
 
   // Checks whether either base or index register is the given register.
   // Does not check the "reg" part of the Operand.
   bool AddressUsesRegister(Register reg) const;
 
+  // Queries related to the size of the generated instruction.
+  // Whether the generated instruction will have a REX prefix.
+  bool requires_rex() const { return rex_ != 0; }
+  // Size of the ModR/M, SIB and displacement parts of the generated
+  // instruction.
+  int operand_size() const { return len_; }
+
  private:
   byte rex_;
   byte buf_[6];
   // The number of bytes of buf_ in use.
   byte len_;
 
   // Set the ModR/M byte without an encoded 'reg' register. The
   // register is encoded later as part of the emit_operand operation.
   // set_modrm can be called before or after set_sib and set_disp*.
   inline void set_modrm(int mod, Register rm);
@@ skipping 1167 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_H_