Support for Thread-Level Speculation into OpenMP

Abstract

Software-based, thread-level speculation (TLS) systems allow the parallel execution of loops that can not be analyzed at compile time. TLS systems optimistically assume that the loop is parallelizable, and augment the original code with functions that check the consistency of the parallel execution. If a dependence violation is detected, offending threads are restarted to consume correct values. Although many TLS implementations have been developed so far, robustness issues and changes required to existent compiler technology prevent them to reach the mainstream. In this paper we propose a different approach: To add TLS support to OpenMP. A new OpenMP speculative clause would allow to execute in parallel loops whose dependence analysis can not be done at compile time.