[release/8.0] Emit less metadata for not-reflection-visible types #91703
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In .NET 8 we massively regressed the size of an empty WinForms app. A WinForms app now brings in a big chunk of WPF with it. I traced it down to the `ICommand` interface having a WPF `TypeConverter` and `ValueSerializer` attribute on it: https://github.com/dotnet/runtime/blob/04bd438844482c907062583153a43a9e3b37dbb8/src/libraries/System.ObjectModel/src/System/Windows/Input/ICommand.cs#L13-L16. An empty app will have a call to a method on `ICommand`, but nothing actually implements `ICommand`. Previously this would mean we generate an unconstructed `MethodTable` for `ICommand`, the unconstructed `MethodTable`s get no reflection metadata, and that's the end of the story. After #85810 however, the reflection stack can no longer reason about `MethodTable`s that don't have reflection metadata, so we need to generate it. This means we end up with the custom attribute and all the reflection dataflow that comes out of it. But this metadata is not actually visible in trim safe apps (the only place where reflection could see these method tables in trim safe code is if they're used in a type comparison `x == typeof(Foo)` and we were able to optimize the method table to the unconstructed version because of that). So we can generate less of it and still get away with it. In this PR I'm adding support for skipping generation of custom attribute metadata for such types. The size of an empty WinForms app goes from 50-something MB to 20-something MB. I think we'll be able to further reduce this number to ~7 MB or less because 12 MB of this are embedded resources that look designer related.
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Tagging subscribers to this area: @agocke, @MichalStrehovsky, @jkotas Issue DetailsBackport of #91660 to release/8.0 Customer ImpactTestingRiskIMPORTANT: If this backport is for a servicing release, please verify that:
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/azp run runtime-extra-platforms |
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Azure Pipelines successfully started running 1 pipeline(s). |
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@MichalStrehovsky / @agocke can y'all take a look at the PR failures and let me know when we are ready to merge. |
This looks good to merge. runtime-extra-platforms haven't been fully green in years. We're separating out native aot testing into a separate pipeline that we can better keep green. |
ghost
locked as resolved and limited conversation to collaborators
Backport of #91660 to release/8.0
/cc @MichalStrehovsky
Customer Impact
In .NET 8.0 we deleted the concept of reflection-not-visible types. In pathological situations such as the one found in WinForms, this can result in massive size on disk regression compared to .NET 7. In WinForms, the regression doubles the size of the app. Impact on non-WinForms scenarios is hard to estimate but it will likely be a small size improvement everywhere.
There are people using NativeAOT in WinForms even though it's not officially supported, through e.g. https://github.com/kant2002/WinFormsComInterop project.
Testing
Manual test on WinForms, plus all of our CI testing.
Risk
This is a low risk compiler fix. The fix will result in small dependency graph size increase within the compiler due to extra analysis and associated increase in memory use/log size. The increase is negligible.
IMPORTANT: If this backport is for a servicing release, please verify that:
The PR target branch is
release/X.0-staging, notrelease/X.0.If the change touches code that ships in a NuGet package, you have added the necessary package authoring and gotten it explicitly reviewed.