Vectorization of the program increases the execution time

Question

I am asked to vectorize a large program. Before starting with a large program, I wanted to see the effect of vectorization in a separate case. To do this, I created two programs that should show the idea of ​​an outstanding transformation. One with an array of structures (without vec) and an array structure (with vec). I expected Soa to be far ahead of AOS, but it is not.

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measured program cycle A

for (int i = 0; i < NUM; i++) {
    ptr[i].c = ptr[i].a + ptr[i].b;
}

full program:

#include <cstdlib>
#include <iostream>
#include <stdlib.h>

#include <chrono>
using namespace std;
using namespace std::chrono;


struct myStruct {
    double a, b, c;
};
#define NUM 100000000

high_resolution_clock::time_point t1, t2, t3;

int main(int argc, char* argsv[]) {
    struct myStruct *ptr = (struct myStruct *) malloc(NUM * sizeof(struct myStruct));

    for (int i = 0; i < NUM; i++) {
        ptr[i].a = i;
        ptr[i].b = 2 * i;
    }
    t1 = high_resolution_clock::now();
    for (int i = 0; i < NUM; i++) {
        ptr[i].c = ptr[i].a + ptr[i].b;
    }
    t2 = high_resolution_clock::now();
    long dur = duration_cast<microseconds>( t2 - t1 ).count();
    cout << "took "<<dur << endl;
    double sum = 0;
    for (int i = 0; i < NUM; i++) {
        sum += ptr[i].c;
    }
    cout << "sum is "<< sum << endl;

}

---

measured program cycle B

#pragma simd 
for (int i = 0; i < NUM; i++) {
    C[i] = A[i] + B[i];
}

full program:

#include <cstdlib>
#include <iostream>
#include <stdlib.h>
#include <omp.h>
#include <chrono>

using namespace std;
using namespace std::chrono;

#define NUM 100000000

high_resolution_clock::time_point t1, t2, t3;

int main(int argc, char* argsv[]) {
    double *A = (double *) malloc(NUM * sizeof(double));
    double *B = (double *) malloc(NUM * sizeof(double));
    double *C = (double *) malloc(NUM * sizeof(double));
    for (int i = 0; i < NUM; i++) {
        A[i] = i;
        B[i] = 2 * i;
    }


    t1 = high_resolution_clock::now();
    #pragma simd
    for (int i = 0; i < NUM; i++) {
        C[i] = A[i] + B[i];
    }
    t2 = high_resolution_clock::now();
    long dur = duration_cast<microseconds>( t2 - t1 ).count();
    cout << "Aos "<<dur << endl;

    double sum = 0;
    for (int i = 0; i < NUM; i++) {
        sum += C[i];
    }
    cout << "sum "<<sum;
}

---

I compile with

icpc vectorization_aos.cpp -qopenmp --std=c++11 -cxxlib=/lrz/mnt/sys.x86_64/compilers/gcc/4.9.3/

icpc (v16) compiled and executed on Intel (R) Xeon (R) processor E5-2697 v3 @ 2.60 GHz

A 300 , B 350 . A, ( ) -O3 #pragma simd . , -, .

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• / , vecotrization , .