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I think the purpose of this project isn't to change the LLVM build system, but rather to integrate LLVM better into Bazel. Bazel offers deterministic builds (wh

I think the purpose of this project isn't to change the LLVM build system, but rather to integrate LLVM better into Bazel. Bazel offers deterministic builds (which allows things like content-based caching and early stopping), but for that to work well, you often need to build the toolchain itself using Bazel as well—since the object files depend on the compiler too, not just the source files. Currently, the system is kind of broken: if you upgrade your compilers, Bazel doesn't catch the changes, and your build cache ends up potentially breaking as a result. That said, I'm not sure why they don't just hash the compiler and library binaries instead of building them from scratch... but that's a different question.

justicezyx 6y ago
Right, the Google monorepo is more monolithic than anyone can imagine. The compiler was part of the repo as well. I forgot how does the bootstrap work, but it definitely builds a compiler if needed (most often there is a cached version somewhere already, so no risk of small changes result into gigantic builds)
- Joky 6y ago
  The bootstrap isn't too much of an issue, a binary release of the compiler is committed inside the repo itself.
- dleslie 6y ago
  How many dozens of gigabytes is it, excluding art artifacts?
  - gravypod 6y ago
    No idea about excluding binary/artifacts but it was ~80TB [0]. A better comparison is available here: https://www.visualcapitalist.com/wp-content/uploads/2017/02/1276_lines_of_code_sep2015_fb.png https://www.visualcapitalist.com/wp-content/uploads/2017/02/... [0] - https://cacm.acm.org/magazines/2016/7/204032-why-google-stores-billions-of-lines-of-code-in-a-single-repository/fulltext#:~:text=Google%2DScale&text=The%20Google%20codebase%20includes%20approximately,Google's%20entire%2018%2Dyear%20existence https://cacm.acm.org/magazines/2016/7/204032-why-google-stor....
    - dleslie 6y ago
      Wild! Thanks for the info.

justicezyx 6y ago

Right, the Google monorepo is more monolithic than anyone can imagine. The compiler was part of the repo as well. I forgot how does the bootstrap work, but it definitely builds a compiler if needed (most often there is a cached version somewhere already, so no risk of small changes result into gigantic builds)

Joky 6y ago
The bootstrap isn't too much of an issue, a binary release of the compiler is committed inside the repo itself.
dleslie 6y ago
How many dozens of gigabytes is it, excluding art artifacts?
- gravypod 6y ago
  No idea about excluding binary/artifacts but it was ~80TB [0]. A better comparison is available here: https://www.visualcapitalist.com/wp-content/uploads/2017/02/1276_lines_of_code_sep2015_fb.png https://www.visualcapitalist.com/wp-content/uploads/2017/02/... [0] - https://cacm.acm.org/magazines/2016/7/204032-why-google-stores-billions-of-lines-of-code-in-a-single-repository/fulltext#:~:text=Google%2DScale&text=The%20Google%20codebase%20includes%20approximately,Google's%20entire%2018%2Dyear%20existence https://cacm.acm.org/magazines/2016/7/204032-why-google-stor....
  - dleslie 6y ago
    Wild! Thanks for the info.