Benchmark hang with `lto = true` and `target-cpu=native`

[TheIronBorn]

I'm benchmarking some code and often get hangs with $ RUSTFLAGS='-C target-cpu=native' cargo bench.

My Cargo.toml:

[profile.bench]
lto = true

It only happens when both LTO and target-cpu=native are enabled.

A typical output looks like this, where it hangs for as long as I've left it:

$ RUSTFLAGS='-C target-cpu=native' cargo bench
    Finished release [optimized] target(s) in 0.0 secs
     Running target/release/deps/bench-88a75a65bb7327e4

I'm using cargo 1.26.0-nightly (b70ab13b3 2018-04-04), and rustc 1.27.0-nightly (eeea94c11 2018-04-06). The code requires nightly so I can't test whether this happens on stable.
$ rustc --print target-cpus says my processor is sandybridge.

[TheIronBorn]

It doesn't seem to happen when using target-cpu=westmere, the preceding Intel CPU microarchitecture.

[alexcrichton]

I think this is likely a LLVM bug so the best place to report this is likely rustc, but can you get a minimized and/or reproducible test case?

[ehuss]

Closing in favor of the rust issue.