Y-Branches: When You Come to a Fork in the Road, Take It

In this paper, 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.

• Type: Conference
• Year: 2003
• Where: IEEEPACT
• Authors: Nicholas J. Wang, Michael Fertig, Sanjay J. Patel
• Keywords: Coding Constructs, Conditional Branches, Dynamic Branches, Hardware, IEEEPACT 2003