travis: Add builders without assertions

[alexcrichton]

This commit adds three new builders, one OSX, one Linux, and one MSVC, which
will produce "nightlies" with LLVM assertions disabled. Currently all nightly
releases have LLVM assertions enabled to catch bugs before they reach the
beta/stable channels. The beta/stable channels, however, do not have LLVM
assertions enabled.

Unfortunately though projects like Servo are stuck on nightlies for the near
future at least and are also suffering very long compile times. The purpose of
this commit is to provide artifacts to these projects which are not distributed
through normal channels (e.g. rustup) but are provided for developers to use
locally if need be.

Logistically these builds will all be uploaded to rustc-builds-alt instead of
the rustc-builds folder of the rust-lang-ci bucket. These builds will stay
there forever (until cleaned out if necessary) and there are no plans to
integrate this with rustup and/or the official release process.

[rust-highfive]

r? @aturon

(rust_highfive has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

Would we prefer utilizing these for the perf infrastructure too? Or do assertions produce a relatively equivalent increase in compile time from commit to commit (and as such don't affect percentages)?

[alexcrichton]

Perhaps! I suspect it wouldn't matter too much though

[aturon]

r? @brson

Thanks for doing this, @alexcrichton!

cc @larsbergstrom @metajack @nox

[larsbergstrom]

Thank you very much for doing this! It'll have a huge positive impact on both our staff and contributors on Servo.

[nox]

Yep, thanks everyone for this! (Sorry I'm too oldschool to just put a thumbsup emoji.)

[brson]

@bors r+

It is a poor situation for us to be running 3 builders to produce builds just for servo, and I will be looking for alternatives.

[bors]

📌 Commit 0340dde has been approved by brson

[SimonSapin]

It is a poor situation for us to be running 3 builders to produce builds just for servo

Is Servo really the only project that runs on Nigthly and wants better compile times?

[alexcrichton]

For posterity, these are the builds that are uploaded on each commit now:

• https://s3.amazonaws.com/rust-lang-ci/rustc-builds-alt/e8154a092558d79f13d7dd48abbfcc4e9d4ed44c/rust-nightly-i686-unknown-linux-gnu.tar.gz
• https://s3.amazonaws.com/rust-lang-ci/rustc-builds-alt/e8154a092558d79f13d7dd48abbfcc4e9d4ed44c/rust-nightly-x86_64-apple-darwin.tar.gz
• https://s3.amazonaws.com/rust-lang-ci/rustc-builds-alt/e8154a092558d79f13d7dd48abbfcc4e9d4ed44c/rust-nightly-x86_64-pc-windows-msvc.tar.gz
• https://s3.amazonaws.com/rust-lang-ci/rustc-builds-alt/e8154a092558d79f13d7dd48abbfcc4e9d4ed44c/rust-nightly-x86_64-unknown-linux-gnu.tar.gz

There are other components and such (and alternate installers) but those are probably the ones you're interested in.

[aturon]

@SimonSapin

Is Servo really the only project that runs on Nigthly and wants better compile times?

Likely not, but to make these more readily available we'd need to adapt rustup, which would require significantly more work -- and we'd also like to keep as much of the nightly ecosystem as we can with assertions on, as they do catch bugs.

I'll bring up to the core team tomorrow whether to consider making these available via rustup.

[SimonSapin]

I got some numbers: servo/servo#15559 (comment)

With an empty incremental compilation cache (or, presumably, with incremental compilation disabled), LLVM assertions add 16% to the compilation time in debug mode, 53% (!) in release mode.