JIT: GDV does not handle delegates pointing to generic methods correctly

[jakobbotsch]

For delegates, we currently retain the context from the IL (similarly to how we used to do it for type-based GDV before #87847). For example:

[MethodImpl(MethodImplOptions.NoInlining)]
static int Foo(Func<int, int> test)
{
    return test(3);
}

public static int Main()
{
    for (int i = 0; i < 100; i++)
    {
        Foo(new Runtime_87597().Id<int>);

        if (i >= 30)
        {
            Thread.Sleep(10);
        }
    }

    return 100;
}

private T Id<T>(T val) => val;

results in

Importing BB01 (PC=000) of 'Runtime_87597:Foo(System.Func`2[int,int]):int'
    [ 0]   0 (0x000) ldarg.0
    [ 1]   1 (0x001) ldc.i4.3 3
    [ 2]   2 (0x002) callvirt 0A000001
 (Implicit Tail call: prefixFlags |= PREFIX_TAILCALL_IMPLICIT)
In Compiler::impImportCall: opcode is callvirt, kind=0, callRetType is int, structSize is 0
Considering guarded devirtualization at IL offset 2 (0x2)
Likely methods for call [000002] to method System.Func`2[int,int]:Invoke(int):int:this
  1) 00007FFAF0A1B5E8 (Runtime_87597:Id[int](int):int:this) [likelihood:100%]
delegate call would invoke method Runtime_87597:Id[int](int):int:this
Marking call [000002] as guarded devirtualization candidate; will guess for method Runtime_87597:Id[int](int):int:this

info.compCompHnd->canTailCall returned false for call [000002]

CheckCanInline: fetching method info for inline candidate Id -- context 00007FFAF0A63C99
Class context: System.Func`2[int,int]
INLINER: during 'impMarkInlineCandidate for GDV' result 'CheckCanInline Success' reason 'CheckCanInline Success' for 'Runtime_87597:Foo(System.Func`2[int,int]):int' calling 'System.Func`2[int,int]:Invoke(int):int:this'
INLINER: during 'impMarkInlineCandidate for GDV' result 'CheckCanInline Success' reason 'CheckCanInline Success'

The Class context: System.Func`2[int,int] is not right. This is presumably a correctness issue similar to #87847.

[ghost]

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Issue Details

---

For delegates, we currently retain the context from the IL (similarly to how we used to do it for delegate GDV before #87847). For example:

[MethodImpl(MethodImplOptions.NoInlining)]
static string Foo(Func<string, string> test)
{
    return test("abc");
}

public static int Main()
{
    for (int i = 0; i < 100; i++)
    {
        Foo(new Runtime_87597().Id<string>);

        if (i >= 30)
        {
            Thread.Sleep(10);
        }
    }

    return 100;
}

private T Id<T>(T val) => val;

results in

Importing BB01 (PC=000) of 'Runtime_87597:Foo(System.Func`2[System.String,System.String]):System.String'
    [ 0]   0 (0x000) ldarg.0
    [ 1]   1 (0x001) ldstr 70000001
    [ 2]   6 (0x006) callvirt 0A000001
 (Implicit Tail call: prefixFlags |= PREFIX_TAILCALL_IMPLICIT)
In Compiler::impImportCall: opcode is callvirt, kind=0, callRetType is ref, structSize is 0
Considering guarded devirtualization at IL offset 6 (0x6)
Likely methods for call [000002] to method System.Func`2[System.__Canon,System.__Canon]:Invoke(System.__Canon):System.__Canon:this
  1) 00007FFAF0DDB600 (Runtime_87597:Id[System.String](System.String):System.String:this) [likelihood:100%]
delegate call would invoke method Runtime_87597:Id[System.String](System.String):System.String:this
Marking call [000002] as guarded devirtualization candidate; will guess for method Runtime_87597:Id[System.String](System.String):System.String:this

info.compCompHnd->canTailCall returned false for call [000002]

CheckCanInline: fetching method info for inline candidate Id -- context 00007FFAF0E23EE9
Class context: System.Func`2[System.String,System.String]
INLINER: during 'impMarkInlineCandidate for GDV' result 'failed this callee' reason 'cannot get method info' for 'Runtime_87597:Foo(System.Func`2[System.String,System.String]):System.String' calling 'System.Func`2[System.__Canon,System.__Canon]:Invoke(System.__Canon):System.__Canon:this'

INLINER: Marking System.Func`2[System.__Canon,System.__Canon]:Invoke(System.__Canon):System.__Canon:this as NOINLINE because of cannot get method info
INLINER: during 'impMarkInlineCandidate for GDV' result 'failed this callee' reason 'cannot get method info'

Beyond just resulting in us not being able to inline it presumably also is a correctness issue similar to #87847, though I'm not familiar enough with that problem to construct a test case.

Author:	jakobbotsch
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-