analysis-stats: allow parallel type inference

[jonas-schievink]

This is mostly just for testing/fun, but it looks like type inference can be sped up massively with little to no effort (since it runs after the serial phases are already done).

Without --parallel:

Item Collection: 16.43597698s, 683mb allocated 720mb resident
Inference: 25.429774879s, 1720mb allocated 1781mb resident
Total: 41.865866352s, 1720mb allocated 1781mb resident

With --parallel:

Item Collection: 16.380369815s, 683mb allocated 735mb resident
Parallel Inference: 7.449166445s, 1721mb allocated 1812mb resident
Inference: 143.437157ms, 1721mb allocated 1812mb resident
Total: 23.973303611s, 1721mb allocated 1812mb resident

[flodiebold]

That's pretty cool! Is there any reason except comparison purposes to make this optional?

[bjorn3]

I don't think the lsp server uses parallel type inference.

[jonas-schievink]

Is there any reason except comparison purposes to make this optional?

Single-threaded inference is deterministic (I think?), while multi-threaded inference isn't. This can be a helpful property when trying to narrow down bugs, and also makes benchmarks more reproducible.

I don't think the lsp server uses parallel type inference.

Yeah, this is just an experiment for analysis-stats. Interactive use is unlikely to benefit from this as types are only inferred for function bodies visible in the editor.

[lnicola]

Single-threaded inference is deterministic

Nope: #1552

[jonas-schievink]

Ah, that's unfortunate. But adding threads on top makes it even more noisy.

[flodiebold]

Well, it's supposed to be deterministic, yeah. And analysis-stats is a good tool for finding non-determinism (which I should do sometime again...), you're right.

[matklad]

bors r+

[matklad]

Just seeing rayon in Cargo.toml creates an impression of speed 👍 !

[bors]

Build succeeded:

• TypeScript (windows-latest)
• Rust (windows-latest)
• Rust (ubuntu-latest)
• TypeScript (macos-latest)
• Rust (macos-latest)
• TypeScript (ubuntu-latest)