While testing a minor optimization on the H8 my builds failed due to 
failure to split a zero-extended memory load.    That particular pattern 
is a bit special on the H8 in that it's split at assembly time primarily 
to get the length computations correct.  Arguably that alternative 
should go away completely, but I haven't really looked into that.

Anyway, with the final-asm split we obviously need to match a 
define_split somewhere.  But none was ever written after adding CCZN 
optimizations.  So if we had a zero extend of a memory operand and it 
was used to eliminate a compare, then we'd abort at final asm time.


Regression tested (in conjunction with various other in-progress 
patches) on H8 without regressions.


Installed on the trunk.


Jeff