Until now, we have focused on overcoming data hazards. However, control hazards contribute greatly to reduced CPI, especially as pipelines become longer.
Branches arrive n times more frequently in a n-issue machine.
The latency of resolving a branch does not decrease, so the CPI is more significantly affected than it is for a single-issue machine. In static prediction, all decisions are made at compile time. This does not allow the prediction scheme to adapt to program behavior that changes over time. Clearly, the accuracy of a branch prediction scheme impacts CPU performance. A scheme that is not accurate may make CPU performance worse than it would be without prediction.