Method group allocates when it shouldn't

[smoogipoo]

The following code:

[MemoryDiagnoser]
public class MethodGroupBenchmarks
{
    [Benchmark]
    public int ByMethodGroup()
    {
        int res = 0;

        for (int i = 0; i < 1000; i++)
            res += doSomething(getValue);

        return res;
    }

    [Benchmark]
    public int ByDelegate()
    {
        int res = 0;

        for (int i = 0; i < 1000; i++)
            res += doSomething(v => getValue(v));

        return res;
    }

    private static int doSomething(Func<int, int> del) => 0;

    private static int getValue(int v) => 0;
}

Outputs:

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
ByMethodGroup	9,006.7 ns	71.83 ns	67.19 ns	12.2375	-	-	64000 B
ByDelegate	546.7 ns	1.12 ns	0.94 ns	-	-	-	-

The delegate generated by the by-method-group form is allocated every time, even though it's functionally identical to the by-delegate form.

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[stephentoub]

Dup of dotnet/roslyn#5835