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.

[1]  John Paul Shen,et al.  Processor Monitoring Using Asynchronous Signatured Instruction Streams , 1995, Twenty-Fifth International Symposium on Fault-Tolerant Computing, 1995, ' Highlights from Twenty-Five Years'..

[2]  Anne Parry.  WHEN YOU COME TO A FORK IN THE ROAD , 1998 .

[3]  D. J. Wheeler,et al.  A Block-sorting Lossless Data Compression Algorithm , 1994 .

[4]  Charles Consel,et al.  A general approach for run-time specialization and its application to C , 1996, POPL '96.

[5]  Doug Burger,et al.  Evaluating Future Microprocessors: the SimpleScalar Tool Set , 1996 .

[6]  Ravishankar K. Iyer,et al.  Characterization of linux kernel behavior under errors , 2003, 2003 International Conference on Dependable Systems and Networks, 2003. Proceedings..

[7]  Scott A. Mahlke,et al.  Integrated predicated and speculative execution in the IMPACT EPIC architecture , 1998, ISCA.

[8]  Kunle Olukotun,et al.  The case for a single-chip multiprocessor , 1996, ASPLOS VII.

[9]  S. McFarling.  Combining Branch Predictors , 1993 .

[10]  Eric Rotenberg,et al.  Slipstream processors: improving both performance and fault tolerance , 2000, SIGP.

[11]  Eric Rotenberg,et al.  Exploiting Large Ineffectual Instruction Sequences , 1999 .

[12]  Yogi Berra,et al.  When You Come to a Fork in the Road, Take It! , 2001 .

[13]  Daniel P. Siewiorek,et al.  Effects of transient gate-level faults on program behavior , 1990, [1990] Digest of Papers. Fault-Tolerant Computing: 20th International Symposium.