It is of extreme relevance for us as we have to re-bootstrap every time we change any dependency of rust, and rust depends on almost everything that is expensive to build in a toolchain tree.
Use the mold binary from the last rebuild and only rebuild again if the new one is different?
If 80% of the tree is in the parent list for mold, the cache hit rate would be 20% - assuming the change distribution is even, which it won’t be.