how to use cargo in the benchmarks game

[BurntSushi]

I just went through the process of getting the regex benchmark updated (because it recently got a lot of optimizations), and this required Cargo because regex now has four total dependencies: regex-syntax, aho-corasick, memchr and libc.

It was a little tricky to get working because the maintainer still needs to be able to run rustc on the submitted benchmark.

Here is the thread: https://alioth.debian.org/tracker/index.php?func=detail&aid=315089&group_id=100815&atid=413122

The approach we finally settled on was to set up a blank Cargo project with regex as a dependency, cargo build --release it, and then use rustc with -L with the ./target/release/deps directory:

$ ls
regex-dna.rs
$ cargo new regex-deps
$ printf '[dependencies]\nregex = "=0.1.38"\n' >> regex-deps/Cargo.toml 
$ cargo build --release --manifest-path regex-deps/Cargo.toml 
$ rustc -C opt-level=3 -C lto -L ./regex-deps/target/release/deps/ regex-dna.rs -o regex-dna
$ ./regex-dna < /data/regex-dna.fasta

This does fail on 32 bit unfortunately, as can be seen here at the bottom of the list: http://benchmarksgame.alioth.debian.org/u32/performance.php?test=regexdna I filed a bug with rustc: rust-lang/rust#26541

I'm hoping this info is useful enough so that we can:

1. Get this build process setup in this repo so that the regex benchmark can be maintained here.
2. Possibly do something similar for other benchmarks that are allowed to use a library.

[BurntSushi]

I talked to @alexcrichton on IRC, and he seems to think the 32 bit problem is an LTO related bug. Perhaps we could open a new thread in the benchmark game forum and ask the maintainer to not use LTO? (I guess this might be a question that must be answered for all Rust benchmarks.)

[BurntSushi]

@TeXitoi The maintainer has stated that we can selectively disable LTO on certain benchmarks. I'm in favor of disabling it for regex-dna at least, but we can't go back and forth on it with the Benchmark Game as the intermediate. Is there anyone else I should speak with?

[TeXitoi]

I'm OK to disable lto everywhere.

I'll look for the cargo installation with dependencies.

Sorry I'm quite busy now, I don't know when I'll have time to do that.

[llogiq]

I think I have it working now. I'll push a PR shortly.

[TeXitoi]

closed by #13