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I am guessing that the compiler uses odd addresses to indicate funky function pointers, perhaps indicating indirection through the class vtable, or some other mapping, perhaps for dynamic loaded code, where r8 is the class pointer?

My best guess is this is a pointer to member function, and that could either be a simple member function, or a virtual function. If it is simple it is the raw address and if it is virtual it is the funky pointer value.

If the "pointer" is even, then it is used directly, if it is odd it plings through r8 (probably the object instance) and rdi, and I have no idea what is in rdi, before applying rax as an offset with the 1 subtracted. It will depend heavily on the calling conventions of the platform and whatever tricks the compiler is playing.