Optimize access to the default FuncPtrStub

[davidwrighton]

Caches the default-type FuncPtrStub precode directly on the MethodDesc (in MethodDescCodeData) so the common FuncPtrStubs::GetFuncPtrStub path avoids taking the FuncPtrStubs hash-table critical section.

A new DefaultFuncPtrStub field plus SetDefaultFuncPtrStub/GetDefaultFuncPtrStub accessors store and retrieve the cached precode using an interlocked publish. For the default precode type, lookup and insertion now go through the cached field instead of the hash table + m_hashTableCrst.

This was extracted from #129019 to keep the optimization independent of the preemptive-mode changes in that PR.

(It's not clear to me this is worth it, but it's certainly not a good part of that original PR).

Note

This PR was generated with the assistance of GitHub Copilot.

[davidwrighton]

@EgorBot -arm64

using System;
using System.Reflection;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

public interface IFoo
{
    void Bar();
}

public class Foo : IFoo
{
    public void Bar() { }
}

public class DelegateBindBenchmarks
{
    private static readonly MethodInfo s_method = typeof(IFoo).GetMethod(nameof(IFoo.Bar))!;
    private static readonly Type s_delegateType = typeof(Action);
    private readonly Foo _target = new Foo();

    [Benchmark(Baseline = true)]
    public Delegate BindToMethodInfo_InterfaceInstanceMethod()
{
        return Delegate.CreateDelegate(s_delegateType, _target, s_method);
}
}

Note

This comment was generated with the assistance of GitHub Copilot.

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[Copilot]

Pull request overview

This PR adds a per-MethodDesc cache for the default FuncPtrStub (stored in MethodDescCodeData) so the common FuncPtrStubs::GetFuncPtrStub(pMD) path can avoid taking the FuncPtrStubs hash-table lock.

Changes:

• Adds a DefaultFuncPtrStub field to MethodDescCodeData plus interlocked publish/accessors on MethodDesc.
• Updates FuncPtrStubs::GetFuncPtrStub to use the cached stub for the default PrecodeType instead of locking and querying the hash table.
• Uses an interlocked “first-wins” publish so concurrent stub creation races converge on a single cached stub.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/coreclr/vm/method.hpp	Adds MethodDescCodeData::DefaultFuncPtrStub and declares MethodDesc accessors.
src/coreclr/vm/method.cpp	Implements interlocked set/get helpers for the cached default funcptr stub.
src/coreclr/vm/fptrstubs.cpp	Uses the per-MethodDesc cached stub for default PrecodeType and avoids the hash-table lock on that path.

[jkotas]

Can we reuse TemporaryEntryPoint as DefaultFuncPtrStub instead of tracking is separately?

This was not possible originally when we had compact temporary entrypoints that were not back patchable, but it should be possible now.