It always did feel like a weird hack to me to avoid parts of the CPU to be idle. I mean the performance benefits are there, but it's at the cost of power usage in the end.
Can branch prediction be turned off on a compiler or application level? If you're optimizing for energy use that is. Disclaimer: I don't actually know if disabling branch prediction is more energy efficient.
Disabling branch prediction would have such a catastrophic effect on performance, there is no way it would pay for itself. Actually this is true for most parts of a CPU; Apple's little cores are extremely power efficient and yet they are fairly impressive out-of-order designs. It would take a very meaningful redesign of how a CPU works to beat a processor like that, at least at useful speeds.
At the cost of power doesn't necessarily mean at the cost of energy. If it takes a minimum of 1 gazillion electrons to do something useful then it's better to move those electrons quickly and return to idle than it is to eke them out slowly over a longer time despite the latter having a lower power usage.
Clocks and leakage burn most of the power. So the most power efficient thing to do is to get as much work done per clock as possible, and if a small fraction turns out to be wasted, you still come out ahead.
Turning off branch prediction sounds like a weird hack that serves no purpose, just underclock and undervolt your CPU if you care about power consumption that much.
Can branch prediction be turned off on a compiler or application level? If you're optimizing for energy use that is. Disclaimer: I don't actually know if disabling branch prediction is more energy efficient.