How much does RegexOptions.Compiled improve performance in .NET?

Just how much does the RegexOptions.Compiled flag improve regular expression performance in .NET? The answer: a lot! People have spoken about this before, but below are some more numbers to how you just how much it matters!

Performance Stats

Character Count	Regex Pattern
1	[a-z]
3	[b-y].[1-8]
5	[b-y].[c-x].[1-8].[2-7]
7	[b-y].[c-x].[d-w].[1-8].[2-7].[3-6]
9	[b-y].[c-x].[d-w].[e-v].[1-8].[2-7].[3-6].[4-5]

RegexOptions	1	3	5	7	9
None	234176	285067	653016	690282	687343
Compiled	193945	235213	430609	452483	454625
Percent Gain	17%	17%	34%	34%	34%

Test Code

public class RegexPerformanceTests

{

    [Fact]

    public void Test()

    {

        TestPattern("[a-z]");

        TestPattern("[b-y].[1-8]");

        TestPattern("[b-y].[c-x].[1-8].[2-7]");

        TestPattern("[b-y].[c-x].[d-w].[1-8].[2-7].[3-6]");

        TestPattern("[b-y].[c-x].[d-w].[e-v].[1-8].[2-7].[3-6].[4-5]");

    }

    private void TestPattern(string pattern)

    {

        Console.WriteLine("--- " + pattern + " ---");

        var regex1 = new Regex(pattern);

        TestRegex(regex1);

        Console.WriteLine("--- Compiled ---");

        var regex2 = new Regex(pattern, RegexOptions.Compiled);

        TestRegex(regex2);

    }

    private void TestRegex(Regex regex)

    {

        const int count = 100000;

        var sw = Stopwatch.StartNew();

        for (var x = 0; x < count; x++)

        {

            var guid = Guid

                .NewGuid()

                .ToString();

            regex.IsMatch(guid);

        }

        sw.Stop();

        Console.WriteLine(sw.ElapsedTicks);

    }

}

Enjoy,
Tom