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R2R image of SPC has many costly ValueTuple methods · Issue #76513 · dotnet/runtime · GitHub
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R2R image of SPC has many costly ValueTuple methods #76513

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R2R image of SPC has many costly ValueTuple methods#76513
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area-crossgen2-coreclr
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@jakobbotsch

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@jakobbotsch
jakobbotsch
opened on Oct 2, 2022

I noticed that we spend a lot of JIT time and image size on ValueTuple methods in R2R:
https://gist.github.com/jakobbotsch/84a4525207268577fddb1b174b8ea63d

It seems these end up being rooted due to e.g.

runtime/src/libraries/System.Private.CoreLib/src/System/TupleExtensions.cs

Lines 679 to 689 in 144a33a

/// <summary>
/// Make a properly nested <see cref="ValueTuple"/> from a properly nested <see cref="Tuple"/> with 21 elements.
/// </summary>
public static ValueTuple<T1, T2, T3, T4, T5, T6, T7, ValueTuple<T8, T9, T10, T11, T12, T13, T14, ValueTuple<T15, T16, T17, T18, T19, T20, T21>>>
ToValueTuple<T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19, T20, T21>(
this Tuple<T1, T2, T3, T4, T5, T6, T7, Tuple<T8, T9, T10, T11, T12, T13, T14, Tuple<T15, T16, T17, T18, T19, T20, T21>>> value)
{
return CreateLong(value.Item1, value.Item2, value.Item3, value.Item4, value.Item5, value.Item6, value.Item7,
CreateLong(value.Rest.Item1, value.Rest.Item2, value.Rest.Item3, value.Rest.Item4, value.Rest.Item5, value.Rest.Item6, value.Rest.Item7,
ValueTuple.Create(value.Rest.Rest.Item1, value.Rest.Rest.Item2, value.Rest.Rest.Item3, value.Rest.Rest.Item4, value.Rest.Rest.Item5, value.Rest.Rest.Item6, value.Rest.Rest.Item7)));
}

Skipping ToValueTuple and ToTuple methods avoids the root and reduces the size of SPC by around 2% on win-x64. It feels like a safe bet that most of these overloads are not going to be used in most applications, so skipping them would be fruitful in terms of deployment size.

It would also be nice to collect some data such as "X method is responsible for rooting Y bytes in the final image" and see if there are more cases like this that we should consider skipping.

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