When calculating post-compaction destination addresses during sliding heap compaction, a block of contiguous memory objects may be treated as a single unit by adding the offset of each object in the block to the post-compaction address for the first object in the block. Additionally contiguous blocks of reachable objects may be constructed by creating deadwood objects, such as non-referenced, placeholder objects, into gaps between objects. Thus, post-compaction destination addresses for the object in the resulting contiguous block may be determined by adding the offset of an object within the block to the destination address for the first object in the block.