X64 implementation: Add high_bit() and low_bits() to register methods.

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 74 matching lines @@
   // The byte-register distinction of ai32 has dissapeared.
   bool is_byte_register() const  { return false; }
   int code() const  {
     ASSERT(is_valid());
     return code_;
   }
   int bit() const  {
     return 1 << code_;
   }
 
+  // Return the high bit of the register code as a 0 or 1.  Used often
+  // when constructing the REX prefix byte.
+  int high_bit() const {
+    return code_ >> 3;
+  }
+  // Return the 3 low bits of the register code.  Used when encoding registers
+  // in modR/M, SIB, and opcode bytes.
+  int low_bits() const {
+    return code_ & 0x7;
+  }
+
   // (unfortunately we can't make this private in a struct when initializing
   // by assignment.)
   int code_;
 };
 
 extern Register rax;
 extern Register rcx;
 extern Register rdx;
 extern Register rbx;
 extern Register rsp;
@@ skipping 871 matching lines @@
   // Optionally do as emit_rex_32(const Operand&) if the operand register
   // numbers have a high bit set.
   inline void emit_optional_rex_32(const Operand& op);
 
 
   // Emit the ModR/M byte, and optionally the SIB byte and
   // 1- or 4-byte offset for a memory operand.  Also encodes
   // the second operand of the operation, a register or operation
   // subcode, into the reg field of the ModR/M byte.
   void emit_operand(Register reg, const Operand& adr) {
-    emit_operand(reg.code() & 0x07, adr);
+    emit_operand(reg.low_bits(), adr);
   }
 
   // Emit the ModR/M byte, and optionally the SIB byte and
   // 1- or 4-byte offset for a memory operand.  Also used to encode
   // a three-bit opcode extension into the ModR/M byte.
   void emit_operand(int rm, const Operand& adr);
 
   // Emit a ModR/M byte with registers coded in the reg and rm_reg fields.
   void emit_modrm(Register reg, Register rm_reg) {
-    emit(0xC0 | (reg.code() & 0x7) << 3 | (rm_reg.code() & 0x7));
+    emit(0xC0 | reg.low_bits() << 3 | rm_reg.low_bits());
   }
 
   // Emit a ModR/M byte with an operation subcode in the reg field and
   // a register in the rm_reg field.
   void emit_modrm(int code, Register rm_reg) {
-    ASSERT((code & ~0x7) == 0);
-    emit(0xC0 | (code & 0x7) << 3 | (rm_reg.code() & 0x7));
+    ASSERT(is_uint3(code));
+    emit(0xC0 | code << 3 | rm_reg.low_bits());
   }
 
   // Emit the code-object-relative offset of the label's position
   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);
@@ skipping 78 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_H_