gistfile1.txt

void ShenandoahBarrierSetAssembler::resolve_forward_pointer_not_null(MacroAssembler* masm, Register dst, Register tmp) {
  assert(ShenandoahCASBarrier || ShenandoahLoadRefBarrier, "should be enabled");
  // The below loads the mark word, checks if the lowest two bits are
  // set, and if so, clear the lowest two bits and copy the result
  // to dst. Otherwise it leaves dst alone.
  // Implementing this is surprisingly awkward. I do it here by:
  // - Inverting the mark word
  // - Test lowest two bits == 0
  // - If so, set the lowest two bits
  // - Invert the result back, and copy to dst

  bool pp = (tmp == noreg);
  if (pp) {
    // No free registers available. Make one useful.
    tmp = rscratch1;
    __ push(tmp);
  }

  Label done;
  __ movptr(tmp, Address(dst, oopDesc::mark_offset_in_bytes()));
  __ notptr(tmp);
  __ testb(tmp, markOopDesc::marked_value);
  __ jccb(Assembler::notZero, done);
  __ orptr(tmp, markOopDesc::marked_value);
  __ notptr(tmp);
  __ mov(dst, tmp);
  __ bind(done);

  if (pp) {
    __ pop(tmp);
  }
}