Value Speculation for VLIW and EPIC Architectures

该项目致力于解决打破水平(EPIC，VLIW)微体系结构的纯依赖关系的新技术。通过计算，明细表长度的最终限制是最长的链。这项研究提出了依赖链分裂的技术，该技术使用先前提出的超标量微体系结构的方法攻击纯依赖链。超标量处理器的技术并不直接适用于VLIW或EPIC体系结构，因为这种体系结构没有或几乎没有动态推测机制。本质上，它们执行由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割点打破一条链，然后投机性地执行链的后半部分。这个项目开发了寻找代码区域的最佳分割点(S)的技术，开发基于硬件的极低开销值剖析，研究VLIW/EPIC特定的值预测器设计，调查启发式方法以解决修补代码的惩罚分支，研究为VLIW/EPIC值推测添加置信度预测的方法，以及研究仅软件价值推测的可能性。还在探索寄存器压力影响和跨控制流值投机的分支插入等问题。

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.