Runtime error (Eigen 3.1.1) if compile with "g++ -O3 main.cc". if -O2 instead of -O3, runtime error.does not arise.

eigenre.cc

// Runtime error if compile with "g++ -O3 main.cc"
#include <iostream>
#include <Eigen/Eigen>

using namespace std;
using namespace Eigen;

void f() {
  MatrixXd U(2,2);
  U = U*U; // runtime error
}
int main() {
  MatrixXd U(2,2);
  U = U*U; // ok

  f();
}