Release build taking forever on 1.34.1

[fizyk20]

I'm trying to build my crate at this commit: https://github.com/fizyk20/atm-refraction/tree/a7f38e582d507345f0f6bddbf769244caee0fe70

cargo build --release ran on Rust 1.34.1 doesn't finish for at least a few minutes (I admit I haven't been too patient with letting it run for a long time, as I knew it used to compile quite quickly, but I can safely say that it wasn't able to finish for me in at least 5 minutes). A debug build (cargo build) finishes in about 15 seconds.

I checked on another Rust version to make sure that it's different, and indeed, compilation of the same commit on 1.31.0 in release mode takes 24 seconds. Nightly 1.36.0 2019-05-03 can't finish just like 1.34.1.

I haven't tried versions other than 1.31.0, 1.34.1 and 1.36.0 nightly so far, but I can do so if needed.

I'm on Gentoo Linux on x86_64. All tested Rust versions installed via rustup.

If any other information is required, please let me know.

[ohsayan]

@fizyk20 Can you reproduce this frequently?

[fizyk20]

It happens every time I try to build this specific crate using 1.34.1. I haven't encountered the problem with any other piece of code yet, though.

I'm not sure if I answered the question.

[jonas-schievink]

I've given the crate a cursory look and nothing stood out as being particularly difficult for the compiler (except a few nom parsers perhaps?). Build is stuck somewhere in LLVM, probably running module passes on a cgu. I'll try to bisect, but it's likely that it will just point us to an LLVM upgrade.

[jonas-schievink]

Good: 1.33.0
Bad: 1.34.0

Good: rustc 1.34.0-nightly (097c04cf4 2019-02-24)
Bad: rustc 1.34.0-nightly (00aae71f5 2019-02-25)

Commits in range: 097c04c...00aae71

Likely cause: #57609 (since it touches MIR lowering)
cc @matthewjasper

[jonas-schievink]

It's something in air/parser.rs – if parse_atmospheres body is replaced with unimplemented!() the issue disappears.

[ohsayan]

@jonas-schievink
✔️ Verified on Rust 1.31.0 -> Build okay stable
✔️ Verified on Rust 1.33.0 -> Build okay stable
✔️ Verified on Rust 1.34.0 -> Slow Build nightly
✔️ Verified on Rust 1.34.1 -> Slow Build nightly
(Likely commits causing problems: c15437c...5ffc919