register classes, predicates, constraints...

[Jim Wilson]

There isn't enough info here to tell what went wrong.  It is probably 
easier for you try to debug reload than to try to explain things to us.

The key info you need to know is
1) What did the insn look like before reload started?
2) What did reload try do to the instruction to try to make it valid? 
This is the debug_reload() output which should be in the .greg dump file.
3) What did the insn look like after reload was done with it?  This 
would be the original insn and all reload insns generated before and 
after it.

Reload looks only at the constraint letters, so the behaviour of the 
predicates is irrelevant here.

You didn't define all of the constraint letters that you are using in 
the pattern, so I am unable to interpret the insn pattern.

Jim