automatically exploiting cross-invocation parallelism using runtime ...

Chapter 4Speculatively ExploitingCross-Invocation ParallelismDOMORE provides a non-speculative solution to exploiting cross-invocation parallelismusing runtime information. However, DOMORE’s transformation requires the constructionof a scheduler thread. If the code duplication causes any side effect, DOMORE cannot beapplied. Figure 4.1 demonstrates such a loop nest. The cross-invocation dependence patternbetween loop invocations L1 1 and L1 0 is determined by the index array C. However,array C itself is updated in Loop L2, preventing the inspector from getting the addressesaccessed in L1 without updating the values in array C. Among the candidate benchmarkprograms, we observe that two of them cannot be parallelized by DOMORE because ofthis limitation. Alternatively, since speculative solutions do not check the accessed memoryaddresses before scheduling and executing a loop iteration, they do not have the sameconstraints and can achieve better applicability.This motivates the idea of SPECCROSS, the first automatic parallelization techniquedesigned to aggressively exploit cross-invocation parallelism using high-confidence speculation.SPECCROSS parallelizes independent loops and replaces the barrier synchronizationbetween two loop invocations with its speculative counterpart. Unlike non-speculative49