local-method-hotpath

🌳 Sustainable Code - Small Hotpath Methods 📊

This example shows how to improve the performance of methods with the help of local functions. Inlining is an optimization

In this case, the contents of the local functions are detached from the actual method ("AnyHotPathMethod") and moved into a compiler-generated method. Thus the "HotPathMethod" is smaller and the compiler has the possibility to inline.

// Generated code without local function
public void AnyHotPathMethod()
{
    if (_b1)
    {
        _sb.Append("aaa");
    }
    if (_b2)
    {
        _sb.Append("bbb");
    }
}

// Generated code with local function
public void AnyHotPathMethodWithFunction()
{
    if (_b1)
    {
        <AnyHotPathMethodWithFunction>g__Core|4_0();
    }
    if (_b2)
    {
        <AnyHotPathMethodWithFunction>g__Core|4_1();
    }
}

[CompilerGenerated]
private void <AnyHotPathMethodWithFunction>g__Core|4_0()
{
    _sb.Append("aaa");
}

[CompilerGenerated]
private void <AnyHotPathMethodWithFunction>g__Core|4_1()
{
    _sb.Append("bbb");
}

🔥 Benchmark

BenchmarkDotNet v0.13.9+228a464e8be6c580ad9408e98f18813f6407fb5a, Windows 10 (10.0.19045.3570/22H2/2022Update)
AMD Ryzen 9 5950X, 1 CPU, 32 logical and 16 physical cores
.NET SDK 8.0.100-rc.2.23502.2
  [Host]   : .NET 7.0.13 (7.0.1323.51816), X64 RyuJIT AVX2
  .NET 7.0 : .NET 7.0.13 (7.0.1323.51816), X64 RyuJIT AVX2
  .NET 8.0 : .NET 8.0.0 (8.0.23.47906), X64 RyuJIT AVX2

| Method       | Runtime  | Iterations | Mean         | Error      | StdDev     | Allocated |
|------------- |--------- |----------- |-------------:|-----------:|-----------:|----------:|
| WithoutLocal | .NET 7.0 | 10         |    15.991 ns |  0.1620 ns |  0.1436 ns |         - |
| WithoutLocal | .NET 8.0 | 10         |     4.089 ns |  0.0171 ns |  0.0160 ns |         - |
|              |          |            |              |            |            |           |
| WithLocal    | .NET 7.0 | 10         |     6.928 ns |  0.1270 ns |  0.1126 ns |         - |
| WithLocal    | .NET 8.0 | 10         |     4.894 ns |  0.0300 ns |  0.0266 ns |         - |
|              |          |            |              |            |            |           |
| WithoutLocal | .NET 7.0 | 100        |   152.300 ns |  0.7867 ns |  0.6569 ns |         - |
| WithoutLocal | .NET 8.0 | 100        |    47.345 ns |  0.6740 ns |  0.6304 ns |         - |
|              |          |            |              |            |            |           |
| WithLocal    | .NET 7.0 | 100        |    67.067 ns |  0.3281 ns |  0.3069 ns |         - |
| WithLocal    | .NET 8.0 | 100        |    47.956 ns |  0.6337 ns |  0.5928 ns |         - |
|              |          |            |              |            |            |           |
| WithoutLocal | .NET 7.0 | 1000       | 1,504.512 ns | 29.8548 ns | 34.3809 ns |         - |
| WithoutLocal | .NET 8.0 | 1000       |   426.727 ns |  4.8606 ns |  4.5467 ns |         - |
|              |          |            |              |            |            |           |
| WithLocal    | .NET 7.0 | 1000       |   644.801 ns | 12.6167 ns | 11.8016 ns |         - |
| WithLocal    | .NET 8.0 | 1000       |   430.170 ns |  5.7188 ns |  5.3494 ns |         - |

🏁 Results

• 🚀 The local functions are x3 faster

Remarks

• Local functions do not make sense everywhere and also not with every hot path method
• However, for methods with simple decisions and subsequent actions, this method has proven to be very effective.
• All cases are at least twice, sometimes three times as performant in .NET 8.

⌨️ Run this sample

dotnet run -c Release

Updates

• 2023/11 - Add .NET 8

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Thanks to gfoidl.