RFA: loop optimization bug

[Paolo Bonzini]

> The ("old") RTL loop optimizer believes that loops either fall through 
> into the top, or start with a branch to the bottom, and is getting confused 
> when handed this loop. Before I get too deep, is it the intent of the
 > tree optimizers to  produce only CFGs that conform to the loop 
optimizer's
 > expectations, or should the RTL opts be handling this?  Thanks.

My understanding is that the RTL code that produces loop notes should 
not spit them out in this case, so that the loop optimizer will not do 
anything on this loop.

Paolo