Speedup compilation time ? Precompiled header ? c++20 modules ? extern template ?

Hi all,

Did anyone has found a trick to lower the compilation time of eigen ? Precompiled headers ? c++20 modules ? extern template ?

The following program for example takes 4s just for one expression. It would be great if we could precompile all the arithmetics operators so the compile time does not go crazy on large projects.

#include <eigen3/Eigen/Dense>
int main() {
  Eigen::Matrix<float, 4, 4> m;
  m = m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m*m;
}

Cheers, Matthieu