Test out parallel frontend via crater

[zetanumbers]

I would like to help push progress on parallel compiler. I think it will be necessary at some point to test compiler in its multi-threaded mode (we already "have" parallel compiler but it is single-threaded by default) via crater. It would allow us to diagnose new issues, measure impact on the ecosystem and estimate amount of remaining work.

I have modified compiler to use "num_cpus" number of 8 threads by default. But I am not sure if there's better value for the cloud environment, so please tell if there is one. I am also not aware of any other nuances of cloud computing, but @Mark-Simulacrum on zulip have confirmed it should be fine.

I believe build-and-test crater mode should provide us with more useful information than the other modes, but if necessary you can scale it down to just build only.

Related zulip thread: #t-compiler/parallel-rustc > Run crater with `-Zthreads=$NUM_CPUS` set

EDIT: Switched from num_cpus to 8 threads

[rustbot]

r? @petrochenkov

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[lqd]

@bors try

[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

warning: spurious network error (1 try remaining): [28] Timeout was reached (Operation too slow. Less than 10 bytes/sec transferred the last 30 seconds)
error: failed to get `wasm-encoder` as a dependency of package `rustc_codegen_ssa v0.0.0 (/checkout/compiler/rustc_codegen_ssa)`

Caused by:
  download of wa/sm/wasm-encoder failed

Caused by:
  failed to download from `https://index.crates.io/wa/sm/wasm-encoder`

Caused by:
  [28] Timeout was reached (Operation too slow. Less than 10 bytes/sec transferred the last 30 seconds)
Bootstrap failed while executing `check`
Build completed unsuccessfully in 0:02:43

[bjorn3]

@bors try spurious failure

[rust-bors]

Unknown argument "spurious". Run @bors2 help to see available commands.

[bjorn3]

Never mind, that was PR CI, not the try job.

[rust-bors]

☀️ Try build successful (CI)
Build commit: d79d87d (d79d87d4c0f7f0d0785ad6e493cf8cf718ed89a6, parent: ad85bc524b1ad696e42061ad8338d382dffbdbe5)

[petrochenkov]

@craterbot build-and-test

[craterbot]

🚨 Error: failed to parse the command

🆘 If you have any trouble with Crater please ask in t-infra on Zulip
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[petrochenkov]

@craterbot run mode=build-and-test

[craterbot]

👌 Experiment pr-146237 created and queued.
🤖 Automatically detected try build d79d87d
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more