Using Pattern Matching in C# for Performance Optimization

The C# compiler is smart enough to understand some constructs and generates optimized code. However, C# gives you multiple ways to express the same intent. The compiler is not always smart enough to optimize every single ways. In this post, I will show you how to use pattern matching syntax to improve the performance of your code in some cases.

Here's an example that checks if a version number is one of several specific values. You can use different syntaxes to express this check, such as using if statements, switch expressions, or pattern matching syntax.

private static bool Sample1(short version)
    => version == 0x0002
    || version == 0x0300
    || version == 0x0301
    || version == 0x0302
    || version == 0x0303
    || version == 0x0304;

private static bool Sample2(short version)
    => version is 0x0002
               or 0x0300
               or 0x0301
               or 0x0302
               or 0x0303
               or 0x0304;

private static bool Sample3(short version)
    => version switch
    {
        0x0002 or 0x0300 or 0x0301 or 0x0302 or 0x0303 or 0x0304 => true,
        _ => false
    };

You can see that the compiler generates an optimized code for the method that use pattern matching syntax.

private static bool Sample1(short version)
{
    if (version != 2 && version != 768 && version != 769 && version != 770 && version != 771)
    {
        return version == 772;
    }
    return true;
}

private static bool Sample2(short version)
{
    if (version == 2 || (uint)(version - 768) <= 4u)
    {
        return true;
    }
    return false;
}

private static bool Sample3(short version)
{
    if (version == 2 || (uint)(version - 768) <= 4u)
    {
        return true;
    }
    return false;
}

Last but not least, even if the compiler is not able to optimize some code, the JIT can still do the job. Be sure to run a benchmark using BenchmarkDotNet to validate the performance benefits.

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