void MacroAssembler::store_check_part_2(Register obj) {

  {- -------------------------------------------
  (1) (変数宣言など)
      ---------------------------------------- -}

      BarrierSet* bs = Universe::heap()->barrier_set();
      assert(bs->kind() == BarrierSet::CardTableModRef, "Wrong barrier set kind");
      CardTableModRefBS* ct = (CardTableModRefBS*)bs;
      assert(sizeof(*ct->byte_map_base) == sizeof(jbyte), "adjust this code");

  {- -------------------------------------------
  (1) movb で書き込んだアドレスに対応する card table のエントリに 0 を書き込む.
      (0 が dirty を示す (See: dirty_card))

      なお, 対応するエントリは以下のようにして算出 
      (ただし card_shift 分だけ右シフトする処理は MacroAssembler::store_check_part_1() で行っている)
        _byte_map - (uintptr_t(low_bound) >> card_shift)
      ---------------------------------------- -}

      // The calculation for byte_map_base is as follows:
      // byte_map_base = _byte_map - (uintptr_t(low_bound) >> card_shift);
      // So this essentially converts an address to a displacement and
      // it will never need to be relocated. On 64bit however the value may be too
      // large for a 32bit displacement

      intptr_t disp = (intptr_t) ct->byte_map_base;
      if (is_simm32(disp)) {
        Address cardtable(noreg, obj, Address::times_1, disp);
        movb(cardtable, 0);
      } else {
        // By doing it as an ExternalAddress disp could be converted to a rip-relative
        // displacement and done in a single instruction given favorable mapping and
        // a smarter version of as_Address. Worst case it is two instructions which
        // is no worse off then loading disp into a register and doing as a simple
        // Address() as above.
        // We can't do as ExternalAddress as the only style since if disp == 0 we'll
        // assert since NULL isn't acceptable in a reloci (see 6644928). In any case
        // in some cases we'll get a single instruction version.

        ExternalAddress cardtable((address)disp);
        Address index(noreg, obj, Address::times_1);
        movb(as_Address(ArrayAddress(cardtable, index)), 0);
      }
    }