We needed a stricter version of m_Not for D114462, but I wasn't sure if that was going to be required anywhere else, so I didn't bother to make that reusable.
It turns out we have one more existing simplification that needs this (currently miscompiles):
And there's at least one more fold in that family that we could add.
I copied from existing code to implement this, but I'm definitely open to suggestions if there's a better way. I don't know C++ template magic well at all.