Move the cache for the marshaler methods to be stored on the RuntimeType instead of in a ConditionalWeakTable

[jkoritzinsky]

Should fix #126608

[jkoritzinsky]

@MihuBot benchmark Interop.StructureToPtr

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[Copilot]

Pull request overview

This PR moves the cache for Marshal.LayoutTypeMarshalerMethods from a ConditionalWeakTable<Type, …> to the per-RuntimeType generic cache infrastructure to address the reported interop performance regressions (issue #126608).

Changes:

• Adds LayoutTypeMarshalerMethods storage to RuntimeType.CompositeCacheEntry so it can live in the existing RuntimeType generic cache.
• Refactors LayoutTypeMarshalerMethods to implement RuntimeType.IGenericCacheEntry<T> and retrieves it via RuntimeType.GetOrCreateCacheEntry<T>().
• Switches from delegate creation (CreateDelegate) to caching raw function pointers (MethodHandle.GetFunctionPointer) for the marshaler methods.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/System.Private.CoreLib/src/System/RuntimeType.GenericCache.cs	Adds a new composite-cache field to hold the marshaler-methods cache on RuntimeType.
src/coreclr/System.Private.CoreLib/src/System/Runtime/InteropServices/Marshal.CoreCLR.cs	Reworks LayoutTypeMarshalerMethods to use RuntimeType cache entries and cached function pointers instead of a ConditionalWeakTable.

[Copilot]

GetMarshalMethodsForType takes a Type but now unconditionally casts to RuntimeType. This can throw InvalidCastException if any internal caller passes a non-RuntimeType (e.g., TypeBuilder), which is a behavior change from the prior ConditionalWeakTable<Type, ...> implementation.

Consider tightening the contract by changing the parameter type to RuntimeType, or adding a fast check/throw with an ArgumentException message that clearly states the requirement (or keeping a fallback path for non-RuntimeType).

Suggested change

	return ((RuntimeType)t).GetOrCreateCacheEntry<LayoutTypeMarshalerMethods>();
	if (t is not RuntimeType runtimeType)
	{
	throw new ArgumentException("Type must be a RuntimeType.", nameof(t));
	}
	return runtimeType.GetOrCreateCacheEntry<LayoutTypeMarshalerMethods>();

[MihuBot]

Interop.StructureToPtr

BenchmarkDotNet v0.16.0-nightly.20260320.467, Linux Ubuntu 24.04.4 LTS (Noble Numbat)
AMD EPYC 9V74 2.60GHz, 1 CPU, 8 logical and 4 physical cores
Memory: 31.34 GB Total, 2.07 GB Available
  Job-TPEJOW : .NET 11.0.0 (11.0.0-dev, 42.42.42.42424), X64 RyuJIT x86-64-v4
  Job-HKHXHK : .NET 11.0.0 (11.0.0-dev, 42.42.42.42424), X64 RyuJIT x86-64-v4
EvaluateOverhead=False  OutlierMode=Default  PowerPlanMode=
IterationTime=250ms  MaxIterationCount=20  MemoryRandomization=Default
MinIterationCount=15  WarmupCount=1

Method	Toolchain	Mean	Error	Ratio	Allocated	Alloc Ratio
MarshalStructureToPtr	Main	53.46 ns	0.045 ns	1.00	24 B	1.00
MarshalStructureToPtr	PR	41.83 ns	0.073 ns	0.78	24 B	1.00
MarshalPtrToStructure	Main	57.27 ns	0.111 ns	1.00	24 B	1.00
MarshalPtrToStructure	PR	43.72 ns	0.169 ns	0.76	24 B	1.00
MarshalDestroyStructure	Main	109.19 ns	0.141 ns	1.00	96 B	1.00
MarshalDestroyStructure	PR	87.02 ns	0.241 ns	0.80	96 B	1.00