Register Communication Strategies for the Multiscalar Architecture

This paper considers the problem of register communication in the Multiscalar architecture, a novel paradigm for exploiting instruction level parallelism. The Multiscalar architecture employs a combination of hardware and software mechanisms to partition a sequential program into tasks, and uses control and data speculation to execute such tasks in parallel. Inter-task register dependencies represent register communication in the architecture. The two primary issues in register communication for a Multiscalar processor are correctness and performance. Not only must proper values be directed from producers to consumers, these values must be sent as early as possible from producing tasks to consuming task in order to avoid execution stalls which may have a critical impact on overall performance. We present a simple model to ensure that register communication obeys the sequential semantics of the program. To this model, we apply a progression of hardware techniques (including register dat..

A Dynamic Approach to Improve the Accuracy of Data Speculation

Data speculation is used in instruction-level parallel (ILP) processors to allow early execution of an instruction before a logically preceding instruction on which it may be data dependent. If the instruction is independent, data speculation succeeds; if not, it fails, and the two instructions must be synchronized. This paper considers dynamic techniques to improve the accuracy with which data speculation is carried out. We propose dynamic techniques: (i) to predict if the execution of an instruction is likely to result in a data misspeculation, and (ii) to provide the synchronization needed to avoid a misspeculation. Experimental results evaluating the effectiveness of the proposed techniques are presented within the context of a Multiscalar processor. 1 Introduction Speculative execution is an integral part of modern ILP processors, be they statically- or dynamically-scheduled designs. Speculation takes on two forms: control speculation and data speculation. Control speculation imp..