McGill University School of Computer Science Sable Research Group Memory Abstractions for Speculative Multithreading

Speculative multithreading is a promising technique for automatic parallelization. However, our experience with a software implementation indicates that there is significant overhead involved in managing the heap memory internal to the speculative system and significant complexity in correctly managing the call stack memory used by speculative tasks. We first describe a specialized heap management system that allows the data structures necessary to support speculation to be quickly recycled. We take advantage of constraints imposed by our speculation model to reduce the complexity of this otherwise general producer/consumer memory problem. We next provide a call stack abstraction that allows the local variable requirements of in-order and out-of-order nested method level speculation to be expressed and hence implemented in a relatively simple fashion. We believe that heap and stack memory management issues are important to efficient speculative system design. We also believe that abstractions such as ours help provide a framework for understanding the requirements of different speculation models.