whiteblackgoose/codegenanalysis

Library for obtaining and analyzing the codegen of JIT for .NET. Can be used for both tests (assertions) and making reports (benchmarks).

CodegenAnalysis

Library for analyzing the machine code generated by JIT (codegen). Has API for obtaining the codegen, verifying the characteristics for tests (in a similar manner to xUnit), and generating reports as benchmarks (in a similar manner to BenchmarkDotNet). Supports x86_64 on three major platforms (Windows, MacOS, Linux).

Why should I use it?

First of all, most .NET developers don't need this library. If you want to measure performance of your code, use BenchmarkDotNet.

If you're working on low-level, often HW-related project, where it's crucial if a branch or call or etc. is optimized or not, this library is for you.

Table of contents

• CodegenAnalysis
• CodegenAnalysis.Assertions
• CodegenAnalysis.Benchmarks

CodegenAnalysis

static int AddAndMul(int a, int b) => a + b * a;

...

var ci = CodegenInfo.Obrain(() => AddAndMul(3, 5));
Console.WriteLine(ci);

Output:

00007FFD752E42F0 8BC2                 mov       eax,edx
00007FFD752E42F2 0FAFC1               imul      eax,ecx
00007FFD752E42F5 03C1                 add       eax,ecx
00007FFD752E42F7 C3                   ret

CodegenAnalysis.Assertions

Verifying the size of the codegen

using CodegenAssertions;
using Xunit;

public class CodegenSizeTest
{
    public static int SomeMethod(int a, int b)
        => a + b;

    [Fact]
    public void Test1()
    {
        CodegenInfo.Obtain(() => SomeMethod(4, 5), CompilationTier.Tier1)
            .ShouldBeNotLargerThan(20);
    }
}

Having calls in the codegen

public class Tests
{
    public class A
    {
        public virtual int H => 3;
    }

    public sealed class B : A
    {
        public override int H => 6;
    }

    // this will get devirtualized at tier1, but not at tier0
    static int Twice(B b) => b.H * 2;

    [Fact]
    public void NotDevirtTier0()
    {
        CodegenInfo.Obtain(() => Twice(new B()), CompilationTier.Default)
            .ShouldHaveCalls(c => c >= 1);
    }

    [Fact]
    public void DevirtTier1()
    {
        CodegenInfo.Obtain(() => Twice(new B()), CompilationTier.Tier1)
            .ShouldHaveCalls(0);
    }
}

Testing if we have branches

    private static readonly bool True = true;

    static int SmartThing()
    {
        if (True)
            return 5;
        return 10;
    }

    [Fact]
    public void BranchElimination()
    {
        CodegenInfo.Obtain(() => SmartThing())
            .ShouldHaveBranches(0);
    }

    [MethodImpl(MethodImplOptions.NoOptimization)]
    static int StupidThing()
    {
        if (True)
            return 5;
        return 10;
    }

    [Fact]
    public void NoBranchElimination()
    {
        CodegenInfo.Obtain(() => StupidThing(), CompilationTier.Default)
            .ShouldHaveBranches(b => b > 0);
    }

CodegenAnalysis.Benchmarks

CodegenBenchmarkRunner.Run<A>();

[CAJob(Tier = CompilationTier.Default),
 CAJob(Tier = CompilationTier.Tier1)]

[CAColumn(CAColumn.Branches),
 CAColumn(CAColumn.Calls), 
 CAColumn(CAColumn.CodegenSize), 
 CAColumn(CAColumn.StaticStackAllocations)]

[CAExport(Export.Html),
 CAExport(Export.Md)]
public class A
{
    [CAAnalyze(3.5f)]
    [CAAnalyze(13.5f)]
    public static float Heavy(float a)
    {
        var b = Do1(a);
        var c = Do1(b);
        if (a > 10)
            c += Aaa(a);
        return c + b;
    }

    [CAAnalyze(6f)]
    public static float Square(float a)
    {
        return a * a;
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    public static float Do1(float a)
    {
        return a * 2;
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    public static float Aaa(float h)
    {
        return h * h * h;
    }
}

See the output.