Plan to test parallel rustc

[est31]

This reminds me of the discussion to add a nightly-alt channel to rustup: Add support for a nightly-alt toolchain · Issue #1099 · rust-lang/rustup · GitHub

Disabling LLVM assertions in Nightly builds?

Building rustc (usually) involves building LLVM. One of LLVM’s compile-time configuration is whether to enable assertions. Currently, in rust-lang’s official builds, LLVM assertions are enabled in the Nightly channel, and disabled on Beta and Stable. I imagine that these assertions help catch some rustc bugs, but they also have a compiler performance cost. In one particular benchmark, they added 16% to Servo’s compilation time in debug mode and 53% in release mode. “Rust should have a pleasant…

The proposal didn't materialize as the LLVM assertions were disabled unconditionally.