[CSL-1002] Link project with gold linker

[chshersh]

This PR uses gold linker for cardano-sl (should speed up build time).

Details in the answer to this question:
http://stackoverflow.com/questions/43243322/how-to-link-with-the-gnu-gold-linker-instead-of-ld-in-haskell/43243323#43243323

[mention-bot]

@chshersh, thanks for your PR! By analyzing the history of the files in this pull request, we identified @neongreen, @gromakovsky and @flyingleafe to be potential reviewers.

[neongreen]

• does it work on macOS?
• does it work on Windows?

[gromakovsky]

We have CI to answer this question 😉 .
I will test it on MacOS by myself though.

[gromakovsky]

Doesn't work on Windows.

[neongreen]

Beda.

@chshersh can you use cabal conditionals to disable it on Windows?

@gromakovsky so does it work on macOS or not? Travis tests on macOS, right?

[gromakovsky]

Yes, Travis does test MacOS, but builds failed.

[gromakovsky]

clang-3.7: error: invalid linker name in argument '-fuse-ld=gold' (in travis, macos)

[chshersh]

It was expected that won't work on windows. Okay, I'll add cabal options to enable this only on linux.

[chshersh]

@neongreen @gromakovsky @domenkozar Seems like we can get even faster linking with lld
http://stackoverflow.com/questions/43243322/how-to-link-with-the-gnu-gold-linker-instead-of-ld-in-haskell/43243323#43243323

[domenkozar]

You'd use lld on macOS and gold on Linux.

[chshersh]

I'm not sure it works properly on macOS because probably project should be configured in different way for lld to work according to this example:
https://github.com/nh2/link-with-lld-example/blob/master/link-with-lld-example.cabal

[gromakovsky]

MacOS build in CI: https://travis-ci.org/input-output-hk/cardano-sl/jobs/221020730

clang-3.7: error: unsupported option '--cpp'

`clang' failed in phase `C pre-processor'. (Exit code: 1)

[gromakovsky]

Seems to be broken on MacOS which is bad I think.

[gromakovsky]

Same error on my macbook, btw (I don't use nix).

[chshersh]

I'm not a macOS expert and I don't even have macOS :(
It works now on windows and linux. So somebody with mac should try to investigate problems and fix this.

[neongreen]

@chshersh can you try without "-pgmP clang"?

[chshersh]

@neongreen What do you mean by saying _ try without "-pgmP clang"_? Just remove this code, commit and wait untill somebody with mac build this?

[neongreen]

Remove, commit and wait until CI builds this

[neongreen]

I'll do it by myself actually

[neongreen]

@domenkozar how can I install lld conditionally on macOS? There's stdenv.isLinux but I haven't found a corresponding var for macOS.

Also, blocked by NixOS/nixpkgs#24744.

[neongreen]

Niklas is going to fix NixOS/nixpkgs#24744, but while we're waiting it'd be nice to get just gold on Linux. @chshersh can you split lld into a separate PR?

[domenkozar]

stdenv.isDarwin. I think this PR is premature optimization for what we're doing since compilation itself is long including dependencies. This is why @jmitchell is working on stack2nix

[neongreen]

I think this PR is premature optimization for what we're doing since compilation itself is long including dependencies.

It's not for CI, it's for developers.

[domenkozar]

Ah, excuse my ignorance. That does make sense.

Ideally you could use stack to only build one executable instead of all of them, but that's waiting on next Cabal release.

Since lld seems like a long shot, we might give it a try with LLVM 4.0 and gold:

• Merge LLVM 4.0 Darwin stdenv NixOS/nixpkgs#24294
• http://stackoverflow.com/questions/40536508/is-it-possible-to-compile-link-clang-llvm-using-the-gold-linker

[chshersh]

can you split lld into a separate PR?

Yes, I can. Will to it today then.

[chshersh]

@neongreen I'll open PR with lld linker after this PR is merged to avoid further conflicts.