[Clr-dev] Weird compiler errors with -O0 -fopenmp and Eigen

Hi, I am experiencing a weird problem, while developping C++ on clearlinux with gcc and Eigen. The following code-snippet: #include <eigen3/Eigen/Dense> template<typename TInputBlock, typename TOutputBlock> static void encode(const TInputBlock& input, TOutputBlock& output) { Eigen::MatrixXf mul0(8, 8); Eigen::MatrixXf mul1(8, 8); output = (mul0 * input * mul1); } int main() { Eigen::MatrixXf input(8, 8); Eigen::MatrixXf output(8, 8); encode(input, output); } compiles fine with the following gcc-invocation on Gentoo and OpenSUSE (using GCC-7.2.0 and GCC-7.2.1 respectively): g++ -g -O0 -fopenmp ./main.cpp However, using this invocation on clearlinux spouts a bunch of weird errors I can't track down, from one of the SIMD intrinsics headers. This error is specific to this special combination of gcc-arguments: "-O0 -fopenmp". Removing either one of them results in a successfull compilation. Another way to get it to build on clearlinux, is by adding "-ftree-fre" to the gcc-invocation. I tried the current master of Eigen, as well as the version that comes with clearlinux. Might this come from clearlinux-specific changes to the gcc codebase? Thanks!