Developer Voices podcast question: Tips and tricks to speed up compilation time

[laundmo]

Hi, i just saw the Developer Voices podcast with Keavon and Dennis, where @Keavon asked for tips/tricks to speed up the development workflow regarding Rust compile times (specifically, at 1:02:54). I have some ideas which work for other projects, though i have not compiled graphite yet - i can't say any of these will actually help, though i plan on testing it next time i get the chance.

• Implement something like the dynamic_linking feature of Bevy engine docs which re-exports the engine (which in your case would be the core crates and dependencies) using a dylib to allow for less code needing to be statically linked. source (kinda)
• cargo configs to test and document/recommend to contributors:
  • Using the mold linker. I see you have a shell.nix which uses mold as a linker, but nothing else. (note: the mold linker is entirely separate from the npm/node tool also called mold)
  • Using the multithreaded frontend with Rustflags -Zthreads=0 (automatic thread count) or -Zthreads=8 (important to test this, it can be slower)
  • Using the cranelift codegen backend, at least for some crates. You can compile dependencies and performance-critical crates with llvm while compiling other crates with cranelift. IME, Cranelift is not noticeably slower with opt-level=3, and generates worse performing binaries, so i always set opt-level=3 for building with cranelift.
  • Compiling proc-macros and their dependencies with opt-level=3 by setting it in [profile.dev.build-override] and [profile.dev.package.syn] (or just ..package."*" for setting it for all dependencies)

Of course it always makes sense to try various settings with cargo build --timings to see where time is spent, and maybe cargo build --verbose which logs out reasons why a crate might be re-built (Fresh/Dirty).

The above represent the options i've used across various projects, mostly Bevy (with these, i get 0.5s incremental compile times for bevy-based projects!). Theres various other ways to improve compile times, heres a few helpful links. These also discuss some code changes, which i don't have experience with:

• https://burn.dev/blog/improve-rust-compile-time-by-108x/
• https://corrode.dev/blog/tips-for-faster-rust-compile-times/