.NET (Core and Framework)

ldc.r8     10000.
stloc.s    VB$CG$t_double$S0
ldloc.s    VB$CG$t_double$S0
ble.s      IL_001b

Public Class Form1
    Inherits System.Windows.Forms.Form
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Button1.Enable = False
        Application.DoEvents()
 
        Dim i, j, t As Double
        Dim StartTime As DateTime = DateTime.Now
 
        For i = 0 to 10000
            For j = 0 to 10000
                t += i + j
            Next
        Next
 
        Dim EndTime As DateTime = DateTime.Now
        Dim TotalTime As TimeSpan = EndTime - StartTime
        Console.WriteLine("TotalTime: " & TotalTime.TotalMilliseconds)
 
        Button1.Enabled = True
End Sub

using System;
using System.Collections.Generic;
using System.Windows.Forms;
blah, blah, blah
 
namespace Double_Performance_Test
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitalizeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            button1.Enabled = false;
            Application.DoEvents();
 
            double i, j, t = 0.0;
 
            DateTime StartTime = DateTime.Now;
 
            for (i=0; i < 10000; i++)
                for (j=0; j < 10000; j++)
                    t += i + j;
 
            DateTime EndTime = DateTime.Now;
            TimeSpan TotalTime = EndTime - StartTime;
            Console.WriteLine("Total Time: " + TotalTime.TotalMilliseconds);
 
            button1.Enabled = true;
        }
    }
}

  Debug: avg of 3460 ms
Release: avg of 820 ms