Y-branches: when you come to a fork in the road, take it

We study the effects of manipulating the architected direction of conditional branches. Through the use of statistical sampling, we find that about 40% of all dynamic branches and about 50% of mispredicted branches do not affect correct program behavior when forced down the incorrect path. We call such branches Y-branches. To further examine this unexpected phenomenon, we provide a characterization of the coding constructs that give rise to such branches. Examples of such coding constructs include short-circuits and ineffectual loop iterations. We provide a statistical breakdown of the frequency of these branches and their constructs. Finally, we suggest some techniques for exploiting this behavior, particularly when it results from short-circuit constructs.