How to install/use CrossGen to optimize .NET Core Library as part of ci/cd?

I am attempting to pre-jit/Ahead-Of-Time (AOT) compile a .NET Core 5 Library to a Native Image using the CrossGen utility as described here to improve start up time.

However the instructions for Getting CrossGen are vague:

If you install CoreCLR using a NuGet package, you can find CrossGen in the tools folder of the NuGet package.

How do I install CrossGen via NuGet?

What I’ve tried so far:

1. Create a build script that writes deleteme.csproj to disk and has a <PackageReference Include="Microsoft.NETCore.App.Runtime.win-x64" Version="3.1.6" />

2. Run dotnet restore deleteme.csproj. This will download the Crossgen nuget package to local cache.

3. I can now run ~/.nuget/packages/microsoft.netcore.app.runtime.win-x64\3.1.6\tools\crossgen.exe

NOTE: I know I can use the ReadyToRun feature for Self-Contained Deployment executable (as described here) HOWEVER I need to optimize a Class Library, so ReadyToRun doesn’t work.

Problem

1. The Nuget package has a big warning:

Internal implementation package not meant for direct consumption. Please do not reference directly.

1. Installation like this seems incorrect. I’d expect CrossGen to be installed as a dotnet tool rather than needing to create a dummy project and run dotnet restore in order to download a copy of a nuget package in cache.

Is there a correct way to pre-jit a .NET Core 5 Library during a ci/cd build?

[mangod9]

R2R should work on libraries, for context all the .net libraries are crossgened themselves. Note that if R2R code is determined to be invalid for the platform, then the runtime should fall back to JITing. In .net 6 with crossgen2 we will also support a composite mode where apps can we published with all app+library code included in a single composite image.

[AntonLapounov]

<PublishReadyToRun>true</PublishReadyToRun> does work for libraries when targeting netcoreapp3.1, net5.0, and the upcoming net6.0 framework. If you run the following commands in an empty directory:

dotnet new classlib
dotnet publish -p:PublishReadyToRun=True -c Release -r win-x64 -v:n

you will see the crossgen.exe command line. The r2rdump.exe utility can be used to see generated native code placed into the managed DLL.