I am adding CI to Boost.Rational and the unit tests are failing for different levels of optimization on different compilers. Before I dig into it further, does anybody have any idea what this might be? https://github.com/boostorg/rational/issues/18 See issue for error output. Ubuntu Bionic gcc unit test succeeds: -O0, -O1 unit test fails: -O2, -O3 boost@17b66a9efac4:/boost/libs/rational/test$ g++ --version g++ (Ubuntu 7.3.0-16ubuntu3) 7.3.0clang unit test succeeds: -O0 unit test fails: -O1, -O2, -O3 boost@17b66a9efac4:/boost/libs/rational/test$ clang++-6.0 --version clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final) Target: x86_64-pc-linux-gnu Thread model: posix InstalledDir: /usr/bin To reproduce, try: boost@17b66a9efac4:/boost/libs/rational/test$ ../../../b2 toolset=clang variant=release rational_test I am using the ubuntu bionic docker container to do the build in. See boostorg/boost#184 <https://github.com/boostorg/boost/pull/184>