Trimming Tools in .NET 8

[agocke]

There are two categories of tools that would help users with trimming

1. App size
2. Trimming roots

For (1), users could use the tool to examine the size of items after trimming and see what's taking up the most space.

For (2), users could find out what's keeping a particular type or member around, and then remove the roots.

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Issue Details

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There are two categories of tools that would help users with trimming

1. App size
2. Trimming roots

For (1), users could use the tool to examine the size of items after trimming and see what's taking up the most space.

For (2), users could find out what's keeping a particular type or member around, and then remove the roots.

Author:	agocke
Assignees:	-
Labels:	untriaged, area-Tools-ILLink
Milestone:	8.0.0

[eerhardt]

In case this helps drive features/solutions here, the most helpful tools I've found are:

App Size

0. Set <PublishAot>true</PublishAot> in the .csproj
1. Set <IlcGenerateMstatFile>true</IlcGenerateMstatFile> in the .csproj
2. Publish your app
3. In obj\<Configuration>\<Target_Framework>\<RID>\native\ there will be an <AppName>.mstat file. This file contains information about what methods, types, etc. were left in the app. And gives a rough size of the methods in the app.
4. The mstat file is a binary file and has an interesting format. It can be read by a tool like: https://gist.github.com/MichalStrehovsky/2c7cb3d623c7f8901541914dab04238d. Just change the file path on line 12 to your app's.
   • The mstat tool needs <PackageReference Include="Mono.Cecil" Version="0.11.4" /> in order to build/run.
   • I have also modified this code to dump all the methods and their sizes in a specific namespace. This allows me to see "what's so big in namespace 'X'?". It also allows you to visualize things like generic expansions, as you will see the generic methods filled with each ValueType. Code for this is here, with the diff being the code in #if TRUE. Change the namespaceName as needed.

Trimming roots

For seeing "why" a chunk of code is included in the app, the easiest approach I found is:

1. Set the following properties in the .csproj

    <PublishAot>false</PublishAot>
    <PublishTrimmed>true</PublishTrimmed>
    <SelfContained>true</SelfContained>
    <TrimMode>full</TrimMode>
    <DynamicCodeSupport>false</DynamicCodeSupport>
    <EventSourceSupport>false</EventSourceSupport>

3. Publish your app
4. Open all the published bin\<Configuration>\<Target_Framework>\<RID>\publish\*.dll files in ILSpy (or similar)
5. Find the code you are interested in analyzing and use the (right-click) Analyze feature to see what is calling it.

This usually finds 80-90% of the reasons why a certain method/class is required by the app. When this doesn't tell me why, then I end up using https://github.com/dotnet/linker/tree/main/src/analyzer as my next option.