Redundant logical operations left after early splitting

[Jeff Law]

Paolo Bonzini wrote:
> 
>> Propagating  REG_EQUIV notes across register-register moves would seem 
>> to a obviously simple way to fix this. Thoughts?
>> I am not sure local-alloc is the best place to address the overall 
>> problem, I doubt it is intended to provide such optimizations.
>> An additional cse pass after split would seem a better way perhaps?
> 
> You could try adding another fwprop run after splitting.  I wouldn't 
> like a third instance of the pass, but it could help.
I think we should at least look at how ugly it would be to do the
propagation in local.  I don't particularly like either solution --
extending local to do something other passes do quite well is
duplication, but adding another pass isn't ideal either.

Jeff