Neither. I'm claiming that UB allows a transform that violates or ignores the additional guards put in place by Fil-C, and by the definition of UB that is not a bug in the compiler, as any behavior is allowable.

To assert that something specific always happens under UB is counter to the definition of UB. Fil-C carefully defines away UB for some operations, but to make full guarantee of safety, even by their definition and modulo bugs, I believe it necessary to fully remove UB.