Optimize '[Guid]' parsing on Native AOT

[Sergio0694]

We're going to need to use [Guid] in some scenarios in CsWinRT 3.0 (see #114179), and while looking at the Type.GUID logic in Native AOT I saw some potential small perf improvements we could do. Figured I'd give it a shot and see if it's well received 😄

[Copilot]

Pull Request Overview

This PR aims to optimize the parsing of [Guid] in Native AOT by improving the underlying UTF8 string decoding and Guid parsing logic. Key changes include:

• Adding a new DecodeStringUtf8 method in NativeFormatReader.String.cs to efficiently decode UTF8 strings.
• Introducing a GetRawStringDataUtf8 helper in ConstantStringValue to leverage the new decoding method.
• Refactoring Guid parsing in NativeFormatRuntimeNamedTypeInfo.cs to use a static local method that processes UTF8 data for performance gains.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/coreclr/tools/Common/Internal/NativeFormat/NativeFormatReader.String.cs	Added method for decoding UTF8 strings with boundary checks and copying to a destination span
src/coreclr/tools/Common/Internal/Metadata/NativeFormat/NativeFormatReaderGen.cs	Added a helper that uses the new decode method to extract UTF8 encoded string data
src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeNamedTypeInfo.cs	Replaced direct Guid creation with a static local method that decodes and parses UTF8 data for Guid construction

Comments suppressed due to low confidence (1)

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/NativeFormat/NativeFormatRuntimeNamedTypeInfo.cs:88

• [nitpick] Consider using a parameter name in the exception call that more clearly reflects the null context of the handle value rather than 'utf8Text', which might be misleading.

ArgumentNullException.Throw("utf8Text");

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @MichalStrehovsky, @jkotas
See info in area-owners.md if you want to be subscribed.

[jkotas]

Any perf numbers?

[jkotas]

This is dead ifdef. You can delete it

[Sergio0694]

There's another one in the method above, should I remove that one too?

[Sergio0694]

Mmh if I remove it, building fails with this at the Guid.Parse call:

D:\git\runtime\src\coreclr\tools\Common\Internal\NativeFormat\NativeFormatReader.String.cs(75,31): error CS1503: Argume
nt 1: cannot convert from 'System.ReadOnlySpan<byte>' to 'System.ReadOnlySpan<char>' [D:\git\runtime\src\coreclr\tools\
aot\ILCompiler.MetadataTransform\ILCompiler.MetadataTransform.csproj]

[jkotas]

Hmm, that's because we have not picked up #105654 in the LKG SDK yet.

It should be fixed by https://github.com/dotnet/runtime/pull/116328/files#diff-8df3cd354bc584349d04ad5675b33c042d8b99b741b8b95af394c55e0f5001bfR3

[Sergio0694]

It seems like it's fine now after doing the changes Michal suggested. I removed that ifdef 👍

[jkotas]

Could you please delete the ifdef (and the define in .csproj) while you are on in, even though it is not strictly required for the rest?

[Sergio0694]

Yup, of course, but just to clarify, I need to wait for that PR you linked to be merged first, and then to update this branch, right?

[jkotas]

I do not think you need to wait for that PR. The earlier build break was caused by the new code that you have introduced. The existing code should compile just fine with the ifdef deleted.

[jkotas]

Where was this exception thrown before?

[Sergio0694]

By the Guid constructor I think. The code was getting a ConstantStringValue value, which immediatley returns in the constructor if the input handle is null. That leaves the string field set to default, and that's then directly passed to the Guid constructor. I added this check here to try to match the semantics in case of failures as close as possible.

[MichalStrehovsky]

/azp run runtime-nativeaot-outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jkotas]

Could you please measure the perf improvement for Type.GUID?

[Sergio0694]

Yup yup, will set some time aside to whip together a small benchmark. Was chatting with @EgorBo who said he might look into adding NAOT support to the bot, but I might just do a simple thing locally for now to unblock this sooner 🙂