Despite extremely capable branch predictors in modern out-of-order (OOO) processors, the problem is still open for hard-to-predict branches such as data-dependent ones. We briefly review branch-prediction in modern OOO micro-architectures, and then present our co-designed BOSS (Branch-Outcome Side-channel Stream) mechanism where the compiler insight into the program structure allows to pre-resolve the direction of the branch. This talk should allow you to review how the processor frontend works, and give you insights into how compiler-microarchitecture collaboration can help to address pressing modern issues.