Current CDS archive ships multiple bitmaps. Archival/loading code makes a useful optimization: it truncates the bitmaps at the beginning when it is known the prefix contains many zeroes. The object sorting code additionally sorts the pointer-rich objects at the end of the archive, increasing the zero-prefix length.

This optimization works less efficiently after JDK-8338912, which moved the (pointer-rich) roots array at the beginning of the archive. We need to enhance current bitmap handling mechanism to truncate bitmaps better.