Use flags setting rdffrs instead of rddfr.
RDFFR_P has to be handled differently from the other optimizations in
optimizePTestInstr: It requires introducing an additional operand, since
there is no RDFFRS_P, only RDFFRS_PP. In order to use a flag setting
version, we need to move the mask operand from the PTest into the
The mask therefore needs to be defined before the RDFFR. If it is not,
bail out for now, which seems to be sufficient for typical code where
this is encountered. This could be extended to move the definition of
the mask up so long as there are no other users.