On 2018-08-02, at 11:27:28, Charles Mills wrote: >> Can EX modify the CC mask in a target branch instruction? > > You bet! > Branch prediction is always ... well, like any other prediction. > It was mentioned in IBM-MAIN that BCT(R) is predicted to always branch; BC is predicted to never branch. I hope there's an exception for BC 15: EX targets, syscall arguments, etc.
If so, I wondered if: BC cond,target Highly probable branch, but predicted not to branch Might be better optimized as: BC 15-cond,*+8 Probable not branch; correctly predicted BC 15,target Predictably certain to branch. (JIT compilation is supposed to fix things like this.) -- gil