On 2 October 2012 16:29, Maciej Stachowiak <m...@apple.com> wrote: > > Note, despite the stackoverflow thread cited, I would be highly surprised > if static branch predicition had no effect ever, even on modern > architectures. While recent intel CPUs have very good dynamic branch > prediction, the basic block reordering should still have a significant > impact in some cases due to cache effects. > > Aside: interestingly, the Core2 family of CPUs doesn't do 'static branch prediction' in the traditional sense. When they encounter a branch not already in the BTB, a BTB index is assigned to it. The prediction now proceeds as though it were dynamic - meaning that this first time, it predicts based on the previous data in that index. That is, it's effectively a 50% chance of taken/not taken the first time the branch is encountered (source: http://www.agner.org/optimize/microarchitecture.pdf, Section 3.15).
mike
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