An improved scheme for effective execution of nested loops with irregular dependence constraints

• Main Authors: Hwu,Ming-Jinn, 胡明進
• Other Authors: Daniel J. Buehrer
• Format: Others
• Language: en_US
• Published: 1993
• Online Access: http://ndltd.ncl.edu.tw/handle/30435791031635791519

碩士 === 國立中正大學 === 資訊工程研究所 === 81 === In nested loops, the dependence pattern is usually com- plicated, especially in the case of coupled subscripts in mul- tidimensional array references. When the dependences of nested loops contain irregular dependence relations, it is very dif- ficult to extract parallelism from the loops. In this thesis, we present an improved scheme which is based on the static strip scheduling scheme. Our scheme differs from the previous scheme in that if we have known ma- ximal and minimal slopes of all the possible dependence vec- tors, we directly select the adequate synchronization vectors and strip direction of static strip scheduling to exploit more parallelism. In our method, when the strip direction is along the outer loop direction, we can use the synchronization vectors (1,1) to replace the synchronization vectors (1,0) in many cases. When the strip direction is along the inner loop direction, we can also use the synchronization vectors (1,1) to replace the synchronization vectors (0,1) in many cases.If the slopes of the dependence vectors are between 0 and 1 ,or between 0 and -1, we can change the execution order in the inner loop from bottom-up to top-down ,or from top-down to bottom-up respec- tively. Because the longer dependence distance between a source and a sink reduces the busy-wait time required the sink . It will make the probability of the synchronization being wait- free higher.