It seems like you would benefit from having reproducible and hermetic builds with a good caching layer so you don't do the same work again and again.
Then you can just use the latest built version to build mold and the next version of rust.
Then you can just use the latest built version to build mold and the next version of rust.
The problem is changing any dependency of rust, even python or perl or musl or openssl or the llvm stack or any dependencies of the llvm stack have the potential of resulting in a different hash for rust.
Any time a dependency is changed all decedents must be rebuilt. Which we must do very frequently. That is where mold saved us a ton of time.
Your stage1 will be based on whatever version is your stage0, but your stage2 should end up identical to any other build with any other stage0. So you don't have to rebuild the full chain all the time.
And then preferably you build a stage3 with FDO, you can easily get 20% more speed with a good corpus of tests.
Do you have at least a distributed cache with I guess sccache to save time for each rebuild?
Our goal is to allow people to reproduce the entire tree from source in the shortest time possible, so no one has to trust us, thus encouraging as many people to do it as possible, thus preventing us from having the means to inject supply chain attacks without anyone noticing.
It is literally a goal for new users to be able to run a server that bootstraps itself, and then bootstraps and signs all future releases, with remote attestation proofs. The shorter that initial build window is the better, which is why things like fast linkers written in early-bootstrappable-languages are so important.
In any case, people could be using the stage2 or stage3 binary and still get the same binaries in the end, they are just alternative versions of the same package that should be compatible.
And using a 192 core CPU is a bit futile, have you looked at how well the work can parallelize? Isn't there some good remote worker solution you could use to have more cores available for the whole fleet without locking a 192 cores machine for a single build? It doesn't look very efficient to me as it is.
Building rust that far to build mold to then build rust again faster negates any benefits.