Enables LTO for Travis Release Builds

[daniel-j-h]

LTO builds for Travis release jobs. Let's wait for Travis and see how it goes.

[TheMarex]

Would omit this one, I don't think need we need this for the sanitzer build.

[daniel-j-h]

Hm having the same build setup sanitizes that we're using for releases would be nice though - without lto things like undefined behavior due to e.g. ODR violations can behave differently. I don't have a strong opinion here, though. Removed it for now.

[daniel-j-h]

Urgh I've just seen the Clang error with LTO builds on Travis

clang-3.9: error: unable to execute command: Segmentation fault (core dumped)
clang-3.9: error: linker command failed due to signal (use -v to see invocation)

[TheMarex]

@daniel-j-h weird, we are using clang 3.9.1 in node-osrm as well and we use it to compile osrm-backend. Any specifics about our setup?

[daniel-j-h]

Hm no, we are using the exact same Clang version in node-osrm:
https://github.com/Project-OSRM/node-osrm/blob/master/scripts/build.sh#L17

The failing build is Mason+Clang3.9.1+LTO specifically. I can try to reproduce locally.

[TheMarex]

/cc @springmeyer You might have some experience with clang 3.9 vs. LTO linking here? Anything that we do in node-osrm that we don't here?

[springmeyer]

Thanks for the ping. I recall that clang 3.9.0 and binutils 2.27 had a bad interaction that was fixed in clang 3.9.1: #3389 (comment). The fact that this is happening now with 3.9.1 is curious. I'll attempt to replicate later today and see if I see any clues.

[daniel-j-h]

I just spawned up a local Trusty Docker container, replicating the build environment with binutils, clang and really all deps. from Mason - except for zlib and libstdc++ (from ubuntu toolchain ppa, as we do on Travis).

But I can not replicate the segfault.

What I tried is clearing the Travis caches primarily for ccache and restarting the build.
But we still hit the Clang 3.9.1 segfault.

[daniel-j-h]

It works with Clang 4.0. Argh. At least we are unblocked by it now.

@springmeyer as soon as we merge this PR we depend on Clang 4.0 for all our production builds. Can you make sure to bundle a recent Clang 4.0 RC and once the release is out (should be a matter of days) bundle this.

[daniel-j-h]

Blocked by having LLVM 4 in Mason mapbox/mason#385

[springmeyer]

Blocked by having LLVM 4 in Mason mapbox/mason#385

llvm 4.0 packages are now available via mason. This includes separate packages:

• llvm (all tools in one download)
• clang++ - just the compiler + libraries needed for -fsanitize=* and -flto
• llvm-cov
• clang-tidy
• clang-format
• lldb
• include-what-you-use