Boosting C# Performance with [MethodImpl(AggressiveInlining)]

When writing high-performance applications in C#, every millisecond counts. One lesser-known yet powerful tool is the [MethodImpl(MethodImplOptions.AggressiveInlining)] attribute.

In this article, we’ll explore what inlining is, why it matters, and how to use [MethodImpl] effectively in your .NET applications.

What is Inlining?

Inlining is an optimization performed by the JIT (Just-In-Time) compiler.

Instead of calling a method through a normal function call, the JIT replaces the call site with the actual method body.

int result = Add(3, 5); // Without inlining int result = 3 + 5; // With inlining 

Inlining removes method call overhead and sometimes allows the JIT to apply further optimizations.

Forcing Inlining with [MethodImpl]

By default, JIT decides whether to inline a method.
Sometimes, we want to force the JIT to inline. Use [MethodImpl]:

using System.Runtime.CompilerServices; public class Calculator { [MethodImpl(MethodImplOptions.AggressiveInlining)] public int Add(int a, int b) => a + b; } 

This instructs the JIT:

"Please inline this method whenever possible."

Other Useful MethodImplOptions

MethodImplAttribute offers several options:

When to Use Aggressive Inlining?

Inlining is not a silver bullet. Use it wisely:

Good use cases:

• Small, frequently called methods (Add, Multiply, IsNullOrEmpty)
• Performance-sensitive code (game loops, real-time calculations)
• Utility functions used millions of times

Avoid when:

• Method is large (increases binary size)
• Method is rarely called
• Overuse may hurt CPU cache efficiency

Example: Math Utility

public static class MathUtils { [MethodImpl(MethodImplOptions.AggressiveInlining)] public static int Square(int value) => value * value; [MethodImpl(MethodImplOptions.AggressiveInlining)] public static int Cube(int value) => value * value * value; } 

Small, frequently used methods are perfect candidates for inlining.

Conclusion

• [MethodImpl(MethodImplOptions.AggressiveInlining)] gives you control over JIT optimizations.
• Use it on small, performance-critical methods.
• Avoid overuse, as excessive inlining can negatively affect performance.

Sample Code

Check out a simple project demonstrating [MethodImpl] usage with benchmarks:
GitHub Repository

Tags

#csharp #dotnet #performance #jit #clr #softwaredevelopment

I’m Morteza Jangjoo and “Explaining things I wish someone had explained to me”