JIT Optimizations in .NET 10 : Performance Improvements

With .NET 10, Microsoft has introduced significant Just-In-Time (JIT) compiler optimizations that improve performance by reducing iteration overhead, memory allocations, and loop inefficiencies.

This article provides a detailed overview of three key improvements: Array Interface Method Devirtualization, Stack Allocation of Value-Type Arrays, and Loop Optimizations, with before and after code comparisons.

1. Array Interface Method Devirtualization

Before .NET 10, iterating over an IEnumerable-backed array caused virtual method calls, which increased overhead. .NET 10 eliminates this by optimizing iteration directly.

Before .NET 10 (Higher Overhead)

using System;
using System.Collections;

class Program
{
    static void Main()
    {
        int[] numbers = { 1, 2, 3, 4, 5 };
        IEnumerable enumerable = numbers; // Casting to IEnumerable
        foreach (int num in enumerable) // Virtual call to GetEnumerator()
        {
            Console.Write(num + " ");
        }
    }
}

After .NET 10 (Optimized) 🚀🔥

using System;
using System.Collections;

class Program
{
    static void Main()
    {
        int[] numbers = { 1, 2, 3, 4, 5 };
        foreach (int num in numbers) // JIT now eliminates the virtual call!
        {
            Console.Write(num + " ");
        }
    }
}

2. Stack Allocation of Value-Type Arrays

Previously, small arrays of value types (like int[] and double[]) were always heap-allocated. In .NET 10, the JIT can now allocate them on the stack, reducing memory overhead.

Before .NET 10 (Heap Allocation)

using System;

class Program
{
    static void Main()
    {
        int[] numbers = new int[4] { 1, 2, 3, 4 }; // Always heap-allocated
        Console.WriteLine(numbers[0]);
    }
}

After .NET 10 (Stack Allocation) 🚀🔥

using System;
using System.Runtime.CompilerServices;

class Program
{
    [SkipLocalsInit] // Helps ensure stack allocation
    static void Main()
    {
        Span<int> numbers = stackalloc int[4] { 1, 2, 3, 4 }; // Stack allocation
        Console.WriteLine(numbers[0]);
    }
}

3. Loop Optimization Enhancements

Before .NET 10, loops checked array lengths on every iteration. Now, loop hoisting and unrolling reduce unnecessary operations.

Before .NET 10 (Unoptimized Loop)

using System;

class Program
{
    static void Main()
    {
        int sum = 0;
        int[] numbers = { 1, 2, 3, 4, 5 };
        for (int i = 0; i < numbers.Length; i++) // Condition checked every iteration
        {
            sum += numbers[i];
        }
        Console.WriteLine(sum);
    }
}

After .NET 10 (Optimized Loop Hoisting) 🚀🔥

using System;

class Program
{
    static void Main()
    {
        int sum = 0;
        int[] numbers = { 1, 2, 3, 4, 5 };
        int length = numbers.Length; // Loop hoisting: moving condition outside
        for (int i = 0; i < length; i++) // Now length is cached
        {
            sum += numbers[i];
        }
        Console.WriteLine(sum);
    }
}

Summary of .NET 10 JIT Optimizations

Conclusion

With these JIT optimizations in .NET 10, applications benefit from improved performance, reduced memory usage, and faster iteration over data structures.