The FP_EXTEND combine done to remove extra EXTRACT_SUBVECTORs can also
be done on legal types. In this case there are no EXTRACT_SUBVECTORs
involved, but as a side effect we will end up folding the UUNPKLO generated
by the FP_EXTEND lowering into the load feeding it.
This is a very specific fix that will likely be temporary until a more
general approach is decided upon.
Depends on D110237