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Cranelift code generation comes to Rust

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Re: Cranelift code generation comes to Rust

#11

Post by diggan »

Tried out the instructions from the article on a tiny Bevy project, and compared it to a "normal" build:

> cargo build --release 23.93s user 22.85s system 66% cpu 1:09.88 total

> cargo +nightly build -Zcodegen-backend 23.52s user 21.98s system 68% cpu 1:06.86 total

Seems just marginally faster than a normal release build. Wonder if there is something particular with Bevy that makes this so? The author of the article mentions 40% difference in build speed, but I'm not seeing anything near that.

Edit: just realized I'm caching my release builds with sccache and a local NAS, hence the release builds being as fast as Cranelift+debug builds. Trying it again with just debug builds and without any caching:

> cargo +nightly build 1997.35s user 200.38s system 1878% cpu 1:57.02 total

> cargo +nightly build -Zcodegen-backend 280.96s user 73.06s system 657% cpu 53.850 total

Definitely an improvement once I realized what I did wrong, about half the time spent compiling now :) Neat!

Re: Cranelift code generation comes to Rust

#12

Post by nindalf »

k_bx wrote: post #2

Any fresh compilation time benchmarks and comparisons to LLVM?

Few reports comparing Cranelift to LLVM from this day old reddit thread [1]

- 29.52s -> 24.47s (17.1%)

- 27s -> 19s (29.6%)

- 11.5s -> 8.4s (26.9%)

- 37.5s -> 29.6s (28.7%) - this measurement from TFA.

To put these numbers in context, all the perf improvements over the last 4 years have helped the compiler become faster on a variety of workloads by 7%, 17%, 13% and 15%, for an overall speed gain of 37% over 4 years. [2] So one large change providing a 20-30% improvement is very impressive.

When you add that to the parallel frontend [3] and support for linking with LLD [4], Rust compilation could be substantially faster by this time next year.

[1] - https://old.reddit.com/r/rust/comments/1bgyo8a/try_cranelift...

[2] - https://nnethercote.github.io/2024/03/06/how-to-speed-up-the...

[3] - https://blog.rust-lang.org/2023/11/09/parallel-rustc.html

[4] - https://github.com/rust-lang/rust/issues/39915

Re: Cranelift code generation comes to Rust

#13

Post by naasking »

diggan wrote: post #11

Tried out the instructions from the article on a tiny Bevy project, and compared it to a "normal" build: > cargo build --release 23.93s user 22.85s system 66% cpu 1:09.88 total > cargo +nightly build -Zcodegen-backend 23.52s user 21.98s system 68% cpu 1:06.86 total Seems just marginally faster than a normal release build. Wonder if there is something particular with Bevy that makes this so? The author of the article…

Maybe your build is not limited by code generation, which seems like the only thing that changed here. There was a good thread recently about the variation in what slows down compilation:

https://news.ycombinator.com/item?id=39721922

Re: Cranelift code generation comes to Rust

#14

Post by diggan »

naasking wrote: post #13
diggan wrote: post #11

Tried out the instructions from the article on a tiny Bevy project, and compared it to a "normal" build: > cargo build --release 23.93s user 22.85s system 66% cpu 1:09.88 total > cargo +nightly build -Zcodegen-backend 23.52s user 21.98s system 68% cpu 1:06.86 total Seems just marginally faster than a normal release build. Wonder if there is something particular with Bevy that makes this so? The author of the article…

Maybe your build is not limited by code generation, which seems like the only thing that changed here. There was a good thread recently about the variation in what slows down compilation: https://news.ycombinator.com/item?id=39721922

Edited my comment now, forgot I was caching the release builds with sccache so wasn't actually compiling all the units, but fetching a lot of them instead :/

Re: Cranelift code generation comes to Rust

#18

Post by Findecanor »

AlexErrant wrote: post #6
k_bx wrote: post #2

Any fresh compilation time benchmarks and comparisons to LLVM?

Not quite fresh, but > A paper from 2020 [0] showed that Cranelift was an order of magnitude faster than LLVM, while producing code that was approximately twice as slow on some benchmarks. [0] https://arxiv.org/pdf/2011.13127.pdf

The changes in Cranelift since 2020 have been quite significant so I would not put any trust in those benchmarks.

Re: Cranelift code generation comes to Rust

#19

Post by mrklol »

Dowwie wrote: post #15

Would it be naive to assume a general compile-time reduction of 20% for all Rust projects by swapping llvm with cranelift?

There are still projects out there which won’t hit 20% or even some %, if the bottleneck isn’t code gen (for example). So the part with"all" can be wrong, but beside that 20% is a good number.

Re: Cranelift code generation comes to Rust

#20

Post by Tehnix »

Very excited for Cranelift for debug builds to speed up development iteration - in particular for WASM/Frontend Rust where iteration speed is competing with the new era of Rust tooling for JS which lands in the sub 1 second builds sometimes (iteration speed in Frontend is crucial).

Sadly, it does not yet support ARM macOS, so us M1-3 users will have to wait a bit :/

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