Do not allow generic inlining of ldftn requiring a fat function pointer

[agocke]

Fixes #129093.

When ldftn targets a method that needs a hidden generic context argument, ILC asks the JIT to build a fat function pointer and creates a ReadyToRunHelperId.MethodEntry generic lookup helper for it. Unlike every other lookup path in CorInfoImpl (ComputeLookup, and the delegate ctor path fixed in #102299), this one did not check whether the token came from an inlinee's generic context.

The result is that the runtime determined method - expressed in terms of the inlinee's generic parameters - ends up recorded in the inliner's dictionary. ShadowMethodNode.GetStaticDependencies then substitutes it with the inliner's instantiations, which throws IndexOutOfRangeException in GetNonRuntimeDeterminedTypeFromRuntimeDeterminedSubtypeViaSubstitution when the arities don't line up (and would silently look up the wrong dictionary slot when they do).

Repro (crashes ilc with the stack reported in #129093):

class Gen<T>
{
    [MethodImpl(MethodImplOptions.NoInlining)]
    public static Type Method() => typeof(T);
}

static unsafe nint GetPtr<U>() => (nint)(delegate*<Type>)&Gen<U>.Method;

class Caller<X>
{
    [MethodImpl(MethodImplOptions.NoInlining)]
    public static nint Run() => GetPtr<X>();
}

The fix aborts the inline in that case, which the JIT already knows how to handle (impLookupToTree notes CALLSITE_GENERIC_DICTIONARY_LOOKUP for CORINFO_LOOKUP_NOT_SUPPORTED, and both impMethodPointer callers check compDonotInline).

Validation:

• The added smoke test fails with the reported Index was outside the bounds of the array error without the compiler change, and passes with it.
• Full src/tests/nativeaot tree builds and the produced binaries run clean on linux-x64.

Cc @dotnet/ilc-contrib

Note

This change was authored with GitHub Copilot.

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[Copilot]

Pull request overview

Prevents NativeAOT/ILC from allowing inlining when importing an ldftn that would require a fat function pointer lookup expressed in the inlinee’s generic context, by reporting the lookup as unsupported in that situation. Adds a NativeAOT smoke-test regression to cover the crash scenario.

Changes:

• In CorInfoImpl.getCallInfo, detect ldftn fat-function-pointer runtime lookups coming from an inlinee token context and return CORINFO_LOOKUP_NOT_SUPPORTED to force the JIT to abort the inline.
• Add a NativeAOT smoke-test regression (Test129093Regression) that takes a function pointer to a generic method requiring a generic context and validates correctness for multiple instantiations.

Show a summary per file

File	Description
src/coreclr/tools/aot/ILCompiler.RyuJit/JitInterface/CorInfoImpl.RyuJit.cs	Returns CORINFO_LOOKUP_NOT_SUPPORTED for fat-function-pointer ldftn lookups when the token context doesn’t match the method being compiled (inlining case).
src/tests/nativeaot/SmokeTests/UnitTests/Generics.cs	Adds Test129093Regression and wires it into the NativeAOT Generics smoke test run list.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0 new

[MichalStrehovsky]

Good catch! Seems like not async specific and not a .NET 11 regression. Looks like I almost fixed this in #129560 when someone on Discord was asking why we're even doing a R2R helper here (we shouldn't be doing a R2R helper in the first place, but the R2R helper is an easier way out considering everything else).

[flucas1]

Bravo!