Add RuntimeHelpers.IsRuntimeAsync intrinsic

[jakobbotsch]

The interpreter and JIT fold this intrinsic to a constant based on whether the calling function is runtime async.

The motivation is cases like #130872 and #130689 where there is a worry about potentially regressing async1 callers, especially for .NET 11 where runtime async is opt-in in Roslyn.

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[Copilot]

Pull request overview

This PR introduces a new RuntimeHelpers.IsRuntimeAsync() intrinsic in System.Private.CoreLib, and wires it up so both the CoreCLR JIT and the CoreCLR interpreter fold it to a compile-time constant based on whether the current compilation is for an async-calling-convention method (runtime-async).

Changes:

• Add RuntimeHelpers.IsRuntimeAsync() as an [Intrinsic] internal API stub in CoreLib.
• Extend CoreCLR JIT named-intrinsic plumbing to recognize the method and expand it to true / false during import based on compIsAsync().
• Extend CoreCLR interpreter named-intrinsic plumbing to recognize and constant-fold the method based on sig.isAsyncCall().

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.cs	Adds the new internal [Intrinsic] method stub IsRuntimeAsync().
src/coreclr/jit/namedintrinsiclist.h	Adds a new NamedIntrinsic enum value for RuntimeHelpers.IsRuntimeAsync.
src/coreclr/jit/importercalls.cpp	Recognizes and expands the intrinsic during import to a constant using compIsAsync().
src/coreclr/jit/fgbasic.cpp	Marks the intrinsic as foldable during IL stack simulation for jump target discovery.
src/coreclr/interpreter/intrinsics.cpp	Maps RuntimeHelpers.IsRuntimeAsync to the new NamedIntrinsic.
src/coreclr/interpreter/compiler.cpp	Expands the intrinsic to an ldc.i4 constant based on isAsyncCall(), and treats it as “must expand” for interpretation.

[jakobbotsch]

@EgorBot -intel -amd -arm --envvars DOTNET_JitDisasm:ReadLineAsync

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading.Tasks;
using BenchmarkDotNet.Attributes;

public class StreamReaderReadLineTests
{
    private string _text;
    private byte[] _bytes;

    [ParamsSource(nameof(GetLineLengthRanges))]
    public Range LineLengthRange { get; set; }

    public static IEnumerable<Range> GetLineLengthRanges()
    {
        yield return new Range() { Min = 0, Max = 0 };
        yield return new Range() { Min = 1, Max = 1 };
        yield return new Range() { Min = 1, Max = 8 };
        yield return new Range() { Min = 9, Max = 32 };
        yield return new Range() { Min = 33, Max = 128 };
        yield return new Range() { Min = 129, Max = 1024 };
        yield return new Range() { Min = 1025, Max = 2048 };
        yield return new Range() { Min = 0, Max = 1024 };
    }

    public class Range
    {
        public int Min { get; set; }
        public int Max { get; set; }
        public override string ToString() => $"[{Min,4}, {Max,4}]";
    }

    [GlobalSetup]
    public void GlobalSetup()
    {
        _text = GenerateLinesText(LineLengthRange, 16 * 1024);
        _bytes = Encoding.UTF8.GetBytes(_text);
    }

    [Benchmark]
    public async Task ReadLineAsync()
    {
        using (StreamReader reader = new StreamReader(new MemoryStream(_bytes)))
        {
            while (await reader.ReadLineAsync() != null) ;
        }
    }

    private static string GenerateLinesText(Range lineLengthRange, int textTargetLength)
    {
        int min = lineLengthRange.Min;
        int max = lineLengthRange.Max;
        string newLine = Environment.NewLine;
        var sb = new StringBuilder(textTargetLength + max + newLine.Length);
        var random = new Random(42);
        while (sb.Length < textTargetLength)
        {
            int charsCount = random.Next(min, max);
            for (int c = 0; c < charsCount; c++)
                sb.Append((char)random.Next('0', 'z'));
            sb.Append(newLine);
        }
        return sb.ToString();
    }
}

[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

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[jakobbotsch]

cc @dotnet/jit-contrib PTAL @EgorBo @BrzVlad

Reverted the StreamReader change, I will fold it into #130689 instead, I was just checking that the intrinsic worked.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

[tannergooding]

Is this something we're going to consider making public longer term, or is it one of the internal-only APIs? -- Mostly wondering if I need to be tracking something for api-review, not asking for it to be or not.

[jakobbotsch]

Is this something we're going to consider making public longer term, or is it one of the internal-only APIs? -- Mostly wondering if I need to be tracking something for api-review, not asking for it to be or not.

I'm not sure yet. I think if everything was runtime async by default we would not need it. I think time will tell how often we end up needing this.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.