• Upgrade the Glibc library to version 2.22 or higher. It supports SIMD directives in OpenMP* 4.0 or higher.
• Upgrade the GNU* gcc compiler to version 4.9 or higher. It supports vectorized math function options.
• Use the -fopenmp and -ffast-math compiler options to enable vector math functions.
• Use appropriate OpenMP SIMD directives to enable vectorization.

Note : Also use the -I/path/to/glibc/install/include and -L/path/to/glibc/install/lib compiler options if you have multiple Glibc libraries installed on the host.

Example

gcc program.c -O2 -fopenmp -ffast-math -lrt -lm -mavx2 -I/opt/glibc-2.22/include -L/opt/glibc-2.22/lib -Wl,--dynamic-linker=/opt/glibc-2.22/lib/ld-linux-x86-64.so.2

...
#pragma omp simd
for (i = 0; i < N; i++)
...

gcc program.c -O2 -fopenmp -ffast-math -lrt -lm -mavx2 -I/opt/glibc-2.22/include -L/opt/glibc-2.22/lib -Wl,--dynamic-linker=/opt/glibc-2.22/lib/ld-linux-x86-64.so.2

#include "math.h"
#include "stdio.h"
#define N 100000

int main()
{
    double angles[N], results[N];
    int i;
    srand(86456);

    for (i = 0; i < N; i++)
    {
        angles[i] = rand();
    }

    #pragma omp simd
    for (i = 0; i < N; i++)
    {
        results[i] = cos(angles[i]);
    }

   return 0;
}