When does Eigen matrix release heap memory?

I would like to write a very very tiny matrix/tensor library with minimal features, and API like Eigen.

What confused me is, setting a debug break point, does not take me into some destructor function, I get nothing.

To reproduce, use this snippet that uses Eigen:

#include <Eigen/Dense>
#include <stdio.h>
#include <iostream>
using namespace Eigen;

int main()
{
    printf("hello Eigen\n");
    {
        MatrixXf m1(300, 400);
        MatrixXf m2(300, 400);
        MatrixXf m3 = m1 + m2;
        std::cout << m3.rows() << std::endl;
        printf("bye\n"); 
    }  // set a debug break point in this line, expecting going into its destructor and free memory, but there isn't
    printf("-----------------\n");

    return 0;
}

As a comparison, I simple created a Tensor template class, and when leaving its scope, its destructor is called:


template<class T>
class Tensor {
public:
    int c, h, w;
    int len;
    T* data;
    Tensor(int _c, int _h, int _w): c(_c), h(_h), w(_w) {
        len = c * h * w;
        data = new T[len];
    }
    ~Tensor() {
        if (data) {
            free(data);
        }
    }
};


int main() {

    // Tensor
    {
        printf("hello tensor\n");
        Tensor<float> tensor(3, 2, 2);
        printf("bye tensor\n");
    } // set a debug break point here, Tensor class's destructor is called
    
    return 0;
}

My question: when and where does Eigen's big matrix (with heap memory allocated) free its heap memory? And how can I see that?

update: I forget to mention that I was using Visual Studio 2019 Debug mode.

Solution

This is the compiler and debugger difference, after tried difference tools and methods from comments in this problem description.

The Visual Studio 2019 (until 2021-4-9, version 16.9.3) still can't debug step into DenseStorage class's destruction function.

While, Visual Studio 2019 with clang-cl, and lldb/gdb with clang-10/g++-9.3 on Linux, all can debug into DenseStorage class's destruction function.