X64 implementation starts using virtual frame and register allocators.

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 464 matching lines @@
   }
 
   void addq(const Operand& dst, Immediate src) {
     immediate_arithmetic_op(0x0, dst, src);
   }
 
   void addl(const Operand& dst, Immediate src) {
     immediate_arithmetic_op_32(0x0, dst, src);
   }
 
+  void cmpb(const Operand& dst, Immediate src) {
+    immediate_arithmetic_op_8(0x7, dst, src);
+  }
+
   void cmpq(Register dst, Register src) {
     arithmetic_op(0x3B, dst, src);
   }
 
   void cmpq(Register dst, const Operand& src) {
     arithmetic_op(0x3B, dst, src);
   }
 
   void cmpq(const Operand& dst, Register src) {
     arithmetic_op(0x39, src, dst);
@@ skipping 456 matching lines @@
   inline void emit_code_relative_offset(Label* label);
 
   // Emit machine code for one of the operations ADD, ADC, SUB, SBC,
   // AND, OR, XOR, or CMP.  The encodings of these operations are all
   // similar, differing just in the opcode or in the reg field of the
   // ModR/M byte.
   void arithmetic_op(byte opcode, Register dst, Register src);
   void arithmetic_op(byte opcode, Register reg, const Operand& op);
   void immediate_arithmetic_op(byte subcode, Register dst, Immediate src);
   void immediate_arithmetic_op(byte subcode, const Operand& dst, Immediate src);
+  // Operate on a 32-bit word in memory.
   void immediate_arithmetic_op_32(byte subcode,
                                   const Operand& dst,
                                   Immediate src);
+  // Operate on a byte in memory.
+  void immediate_arithmetic_op_8(byte subcode,
+                                  const Operand& dst,
+                                  Immediate src);
   // Emit machine code for a shift operation.
   void shift(Register dst, Immediate shift_amount, int subcode);
   // Shift dst by cl % 64 bits.
   void shift(Register dst, int subcode);
 
   // void emit_farith(int b1, int b2, int i);
 
   // labels
   // void print(Label* L);
   void bind_to(Label* L, int pos);
@@ skipping 52 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_H_