A speculative execution scheme of macrotasks for parallel processing systems

This paper considers the high‐speed execution of FORTRAN programs on parallel processing systems and proposes the parallelizing scheme of the program and execution based on the speculative execution over multiple conditional branches. Several techniques have been proposed that parallelize the program including conditional branches. A method which does not use the speculative execution is: (1) the method called earliest execution condition determination. As the methods which use the speculative execution are: (2) speculative evaluation scheme for a single conditional branch for the superscalar processor or VLIW computer; and (3) multiple speculative execution scheme assuming particular loops. There are the following problems: (1) sufficient parallelism is not extracted only by determining the earliest execution condition; (2) the speed improvement that can be realized by the speculative execution of a single conditional branch is at most twofold; and (3) the scheme can be applied only to particular loops. This paper divides the program into macrotasks, and defines the multiple stage speculative execution scheme between macrotasks on the general parallel processing system. Then, the macrotask execution control for the individual macrotask is proposed, using the execution start condition, the control establishment condition and the execution stop condition.