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Emit less metadata for not-reflection-visible types #91660

Merged
merged 2 commits into from
Sep 6, 2023
Merged

Emit less metadata for not-reflection-visible types #91660

merged 2 commits into from
Sep 6, 2023

Commits on Sep 6, 2023

  1. Emit less metadata for not-reflection-visible types 

    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 dotnet#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.
    @MichalStrehovsky
    MichalStrehovsky committed Sep 6, 2023
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  2. CR feedback

    @MichalStrehovsky
    MichalStrehovsky committed Sep 6, 2023
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