Hi Richard,

after giving it a second thought, and seeing that most of the changes to 
existing code are not strictly necessary anymore, I figured it could be 
easier not changing the current control flow too much like in the 
attached patch.

The changes remaining are to "outsource" the maybe_expand_insn part and 
making the emit_conditional_move with full comparison and rev_comparsion 
externally available.

I suppose straightening of the arguably somewhat baroque parts, we can 
defer to a separate patch.

On s390 this works nicely but I haven't yet done a bootstrap on other archs.

Regards
  Robin