Avoid memmove when emitting operands in the assembler ...

src/assembler-ia32.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 242 matching lines @@
                              ScaleFactor scale,
                              const ExternalReference& arr) {
     return Operand(index, scale, reinterpret_cast<int32_t>(arr.address()),
                    RelocInfo::EXTERNAL_REFERENCE);
   }
 
   // Returns true if this Operand is a wrapper for the specified register.
   bool is_reg(Register reg) const;
 
  private:
-  // Mutable because reg in ModR/M byte is set by Assembler via set_reg().
-  mutable byte buf_[6];
+  byte buf_[6];
   // The number of bytes in buf_.
   unsigned int len_;
   // Only valid if len_ > 4.
   RelocInfo::Mode rmode_;
 
-  inline void set_modrm(int mod,  // reg == 0
-                        Register rm);
+  // Set the ModRM byte without an encoded 'reg' register. The
+  // register is encoded later as part of the emit_operand operation.
+  inline void set_modrm(int mod, Register rm);
+
   inline void set_sib(ScaleFactor scale, Register index, Register base);
   inline void set_disp8(int8_t disp);
   inline void set_dispr(int32_t disp, RelocInfo::Mode rmode);
-  inline void set_reg(Register reg) const;
 
   friend class Assembler;
 };
 
 
 // -----------------------------------------------------------------------------
 // A Displacement describes the 32bit immediate field of an instruction which
 // may be used together with a Label in order to refer to a yet unknown code
 // position. Displacements stored in the instruction stream are used to describe
 // the instruction and to chain a list of instructions using the same Label.
@@ skipping 544 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ASSEMBLER_IA32_H_