Different codegen for pinning GetPinnableReference vs GetReference after a length check

[MihaZupan]

public static void Foo(ReadOnlySpan<char> span)
{
    if (!span.IsEmpty)
    {
        fixed (char* ptr = span)
            Consume(ptr);
    }
}

public static void Bar(ReadOnlySpan<char> span)
{
    if (!span.IsEmpty)
    {
        fixed (char* ptr = &MemoryMarshal.GetReference(span))
            Consume(ptr);
    }
}

[MethodImpl(MethodImplOptions.NoInlining)]
private static void Consume(char* ptr) { }

https://www.diffchecker.com/cAaIxNr9/

-mov       ecx,[rcx+8]
-test      ecx,ecx
+cmp       dword ptr [rcx+8],0

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[EgorBo]

I guess the difference is that both _reference and _length fields are loaded into temp before IsEmpty check. if the span is not empty than it has no impact since later we re-use _reference from that temp instead of loading it from memory