HeapWord* PSParallelCompact::first_src_addr(HeapWord* const dest_addr,
                                            SpaceId src_space_id,
                                            size_t src_region_idx)
{

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

      assert(summary_data().is_region_aligned(dest_addr), "not aligned");

  {- -------------------------------------------
  (1) 
      ---------------------------------------- -}

      const SplitInfo& split_info = _space_info[src_space_id].split_info();
      if (split_info.dest_region_addr() == dest_addr) {
        // The partial object ending at the split point contains the first word to
        // be copied to dest_addr.
        return split_info.first_src_addr();
      }

      const ParallelCompactData& sd = summary_data();
      ParMarkBitMap* const bitmap = mark_bitmap();
      const size_t RegionSize = ParallelCompactData::RegionSize;

      assert(sd.is_region_aligned(dest_addr), "not aligned");
      const RegionData* const src_region_ptr = sd.region(src_region_idx);
      const size_t partial_obj_size = src_region_ptr->partial_obj_size();
      HeapWord* const src_region_destination = src_region_ptr->destination();

      assert(dest_addr >= src_region_destination, "wrong src region");
      assert(src_region_ptr->data_size() > 0, "src region cannot be empty");

      HeapWord* const src_region_beg = sd.region_to_addr(src_region_idx);
      HeapWord* const src_region_end = src_region_beg + RegionSize;

      HeapWord* addr = src_region_beg;
      if (dest_addr == src_region_destination) {
        // Return the first live word in the source region.
        if (partial_obj_size == 0) {
          addr = bitmap->find_obj_beg(addr, src_region_end);
          assert(addr < src_region_end, "no objects start in src region");
        }
        return addr;
      }

      // Must skip some live data.
      size_t words_to_skip = dest_addr - src_region_destination;
      assert(src_region_ptr->data_size() > words_to_skip, "wrong src region");

      if (partial_obj_size >= words_to_skip) {
        // All the live words to skip are part of the partial object.
        addr += words_to_skip;
        if (partial_obj_size == words_to_skip) {
          // Find the first live word past the partial object.
          addr = bitmap->find_obj_beg(addr, src_region_end);
          assert(addr < src_region_end, "wrong src region");
        }
        return addr;
      }

      // Skip over the partial object (if any).
      if (partial_obj_size != 0) {
        words_to_skip -= partial_obj_size;
        addr += partial_obj_size;
      }

      // Skip over live words due to objects that start in the region.
      addr = skip_live_words(addr, src_region_end, words_to_skip);
      assert(addr < src_region_end, "wrong src region");
      return addr;
    }