Value Speculation for VLIW and EPIC Architectures

该项目解决了为水平（EPIC， VLIW）微架构打破纯依赖的新技术。调度长度的最终限制是通过计算的最长链。研究提出了依赖链分裂技术，该技术使用先前针对超标量微体系结构提出的方法来攻击纯依赖链。超标量处理器的技术不能直接应用于VLIW或EPIC体系结构，因为这类体系结构没有或很少有动态推测机制。本质上，它们执行编译器静态推测的代码。这项工作的核心思想是在一个有利的分裂点打破一个链，然后投机地执行链的后半部分。该项目开发了寻找代码区域最佳分割点的技术，开发基于硬件的非常低开销的价值分析，研究VLIW/EPIC特定价值预测器设计，研究启式方法以解决补丁代码的惩罚分支，研究为VLIW/EPIC价值推测添加置信预测的方法，并研究仅软件价值推测的潜力。在整个控制流程中，诸如注册压力影响和分支插入价值投机等问题也正在探索中。

This project addresses new techniques to break pure dependencies for horizontal (EPIC, VLIW) microarchitectures. The ultimate limit to schedule length is the longest chain through the computation. The research presents techniques for dependence chain splitting, which attack pure dependence chains using methods presented earlier for superscalar microarchitectures. The techniques for superscalar processors are not directly applicable to VLIW or EPIC architectures, since such architectures have no or little dynamic speculation mechanisms. Essentially, they execute code that is statically speculated by the compiler. The core idea of this work is to break a chain at a beneficial split point, and then speculatively execute the second half of the chain. This project develops techniques to find the best split point(s) of a region of code, develop hardware-based very low overhead value profiling, study VLIW/EPIC-specific value predictor designs, investigate heuristics to address the penalty branches to patch-up code, look into methods for adding confidence prediction for VLIW/EPIC value speculation, and study the potential of software-only value speculation. Issues such as register pressure impact and branch insertion for value speculation across control flow are also being explored.