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Optimization: parse manifest only once by mkeeter · Pull Request #2898 · rust-la...
source link: https://github.com/rust-lang/rustup/pull/2898
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I was building a project which invoked cargo multiple times, and noticed that a no-op build (i.e. a build with no local changes) was surprisingly slow.
Generating a flamegraph of one cargo call, I noticed the following:
About half the work is done in Manifestation::load_manifest, which is called twice to parse the same 700K TOML file (here and here).
This PR adds a new struct in toolchain.rs which encapsulates this parsed manifest plus other relevant data. This struct is then used in config.rs to eliminate the double-parsing.
I also use this struct to clean up duplicate code in toolchain.rs, e.g. this comment:
// Overlapping code with get_manifest :/.
I see a 15-25% speedup in a no-op build, depending on the project!
- Tests all pass (at least on my machine!)
-
No new
clippylints (there are a few pre-existing lints in areas I haven't touched) -
rustfmtrun
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