static void cpuid(int32_t out[4], int32_t eax, int32_t ecx);

mov eax,1
cpuid
and ecx,18000000h
cmp ecx,18000000h
jne no_AVX
xor ecx,ecx
xgetbv
and eax,110b
cmp eax,110b
jne no_AVX
.....
.....

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace DetectAVX
{
   public partial class Form1 : Form
   {
       [DllImport(@"C:\DLL\AVX\AVX.DLL")]
       private static extern uint AVX();

       public Form1()
       {
           InitializeComponent();
       }

       private void button1_Click(object sender, EventArgs e)
       {
           if (AVX() == 1)
               textBox1.Text = "AVX Support: No";
           else if (AVX() == 2)
               textBox1.Text = "AVX Support: Yes";
           else
               textBox1.Text = "AVX Support: Unknown";
       }
   }
}

BOOL IsProcessorFeaturePresent(
 [in] DWORD ProcessorFeature
);

PF_AVX_INSTRUCTIONS_AVAILABLE
39

using System;
using System.Runtime.InteropServices;
namespace Exercise
{
   internal class Program
   {
       [DllImport("kernel32.dll")]
       private static extern bool IsProcessorFeaturePresent(uint ProcessorFeature);
       static void Main(string[] args)
       {
           Console.WriteLine("PF_SSSE3_INSTRUCTIONS_AVAILABLE " + IsProcessorFeaturePresent(36));
           Console.WriteLine("PF_AVX_INSTRUCTIONS_AVAILABLE " + IsProcessorFeaturePresent(39));
           Console.ReadLine();
       }
   }
}

using System;
using System.Runtime.Intrinsics.X86;

namespace AvxSupportCheck
{
   class Program
   {
       static void Main(string[] args)
       {
           Console.WriteLine("AVX Support: " + Avx.IsSupported);
           Console.WriteLine("AVX2 Support: " + Avx2.IsSupported);
       }
   }
}