Metabug for Rust-related issues

[jonathandturner]

This metabug tracks issues across multiple repos that impact Servo and Servo-related projects. The hope here is to have a way to coordinate possible fixes and to raise awareness of the specific impact of each issue.

High priority

add thiscall calling convention support
rust-lang/rust#42058 (done!)
Reason: blocks Stylo from working on 32-bit Windows

Medium-high priority

Rayon 0.7.0: unbounded spins in Sleep::no_work_found
https://github.com/nikomatsakis/rayon/issues/343 (done!)
Reason: CI build-time impact. Regression of 20% (possibly even upward of 50%) in build times

trans/LLVM: Don't keep all LLVM modules in memory at the same time
rust-lang/rust#39280 (done!)
Reason: Blocks incremental compilation for Servo

Disabling assertions in nightly builds
https://internals.rust-lang.org/t/disabling-llvm-assertions-in-nightly-builds/5388 (fixed with rust-lang/rust#43167!)
Reason: build times improve noticeably when assertions are disabled

Medium-low priority

Build instruction profiler runtime as part of compiler-rt
rust-lang/rust#42524
Reason: blocks some of the coverage tools

[jonathandturner]

cc @aturon @nikomatsakis

[jonathandturner]

cc @cpeterso, who may have other items

[jonathandturner]

Woohoo! Looks like we are finished with this batch (the last issue looks like it's no longer needed in that form)

[SimonSapin]

rust-lang/rust#43167 fixed the "alternative" compiler builds that have LLVM assertions disabled (they broke cross-compilation at some point), but Nightly still has these slow assertions. https://internals.rust-lang.org/t/disabling-llvm-assertions-in-nightly-builds/5388 did not come to a conclusion, as far as I can tell.

[jonathandturner]

@SimonSapin - I thought the issue now was around rustup support for the no-assertions build. The original issue of Servo not having a no-assertions build to use is fixed, I thought.

[SimonSapin]

Alternative compiler builds were first added with rust-lang/rust#39754 in February, in order to make it possible at all to use unstable features without LLVM assertions.

They were broken for cross-compilation for a while in July: rust-lang/rust#42967, then fixed with rust-lang/rust#43167.

This issue is about neither of these things. The original message links to https://internals.rust-lang.org/t/disabling-llvm-assertions-in-nightly-builds/5388, which proposes disabling assertions in "normal" Nightly and making "alternative" builds completely unnecessary. That thread is unresolved. If the compiler team since came to a decision on the subject, they forgot to communicate it. I’ll ping the thread.