The runtime location of a CDS heap region is calculated using this field:

https://github.com/openjdk/jdk/blob/4999f2cb164743ebf4badd3848a862609528dde3/src/hotspot/share/include/cds.h#L53-L55

typedef struct CDSFileMapRegion {
  size_t  _mapping_offset;    // This region should be mapped at this offset from the base address
                              // - for non-heap regions, the base address is SharedBaseAddress
                              // - for heap regions, the base address is the compressed oop encoding base

using very convoluted code:

https://github.com/openjdk/jdk/blob/4999f2cb164743ebf4badd3848a862609528dde3/src/hotspot/share/cds/filemap.cpp#L2063-L2071

address FileMapInfo::decode_start_address(FileMapRegion* spc, bool with_current_oop_encoding_mode) {
  size_t offset = spc->mapping_offset();
  narrowOop n = CompressedOops::narrow_oop_cast(offset);
  if (with_current_oop_encoding_mode) {
    return cast_from_oop<address>(CompressedOops::decode_raw_not_null(n));
  } else {
    return cast_from_oop<address>(ArchiveHeapLoader::decode_from_archive(n));
  }
}

=========================
This can be greatly simplified:

For each heap region, save its dumptime address in CDSFileMapRegion.

At runtime, the address for this region = (dumptime address) + ArchiveHeapLoader::runtime_delta();