SHF: AF: Medium: Collaborative Research: The Pochoir Stencil Compiler

许多高端科学应用程序在其内部循环中执行模板计算。模板将时间t时d维空间网格中网格点的值定义为t之前最近时间相邻网格点的函数。使用嵌套循环实现模板计算在概念上很简单，但是循环实现在多核处理器上受到缓存性能差的影响。与循环实现相比，与缓存无关的分治模板代码可以在缓存效率方面实现一个数量级的改进，但是大多数程序员发现编写与缓存无关的模板代码很困难。此外，在使这些算法适应缺乏简单示例的完美规律性的实际应用方面，仍然存在一些开放的问题。本项目对无关缓存的模板编译的研究使普通的模板计算程序员能够享受多核技术的好处，而无需编写比简单嵌套循环更复杂的代码。该研究项目正在开发一种嵌入c++的语言，该语言可以简洁地表达模板计算，并可以自动编译成多核处理器和其他平台的高效算法代码。Pochoir模板编译器编译具有复杂边界条件的模板计算，如周期、常数、狄利克雷、诺伊曼、镜像和相位因子；不规则性，包括宏观和微观的不均匀性，以及不规则的形状；一般的复杂依赖关系，例如推送依赖关系、水平依赖关系和动态依赖关系。为了实现这些目标，研究人员正在为复杂的模板计算开发可证明的良好算法；探索领域特定的编译器技术如何从高效的缓存管理、处理器管道调度和并行计算中实现加速；研究如何在各种架构上高效运行模板，如多核、分布式内存集群、图形处理单元、FPGA和未来的百亿亿次机器；通过开发生产质量的模板编译器来展示其研究的有效性；开发一套评估Pochoir的基准测试套件和基准测试系统。这项研究使科研人员和其他人能够轻松地为复杂的模板计算生成高效的代码。这些代码很好地利用了多核处理器特有的内存层次结构和处理器管道，并在各种硬件平台上快速运行。这项研究简化了各种基于模板的应用程序的开发和维护。涵盖物理、生物、化学、能源、气候、机电工程、金融等领域？使这些应用领域以及整个社会受益。

Many high-end scientific applications perform stencil computations in their inner loops. A stencil defines the value of a grid point in a d-dimensional spatial grid at time t as a function of neighboring grid points at recent times before t. Stencil computations are conceptually simple to implement using nested loops, but looping implementations suffer from poor cache performance on multicore processors. Cache-oblivious divide-and-conquer stencil codes can achieve an order of magnitude improvement in cache efficiency over looping implementations, but most programmers find it difficult to write cache-oblivious stencil codes. Moreover, open problems remain in adapting these algorithms to realistic applications that lack the perfect regularity of simple examples. This project's investigation of cache-oblivious stencil compilation enables ordinary programmers of stencil computations to enjoy the benefits of multicore technology without requiring them to write code any more complex than naive nested loops.The research project is developing a language embedded in C++ that can express stencil computations concisely and can be compiled automatically into highly efficient algorithmic code for multicore processors and other platforms. The Pochoir stencil compiler compiles stencil computations that exhibit complex boundary conditions, such as periodic, constant, Dirichlet, Neumann, mirrored, and phase factors; irregularities, including macroscopic and microscopic inhomogeneities, as well as irregular shapes; general complex dependencies, such as push dependencies, horizontal dependencies, and dynamic dependencies.To achieve these goals, the researchers are developing provably good algorithms for complex stencil computations; exploring how domain-specific compiler technology can achieve speedups from efficient cache management, processor-pipeline scheduling, and parallel computation; investigating how to run stencils efficiently on a wide variety of architectures such as multicore, distributed-memory clusters, graphical processing units, FPGA's, and future exascale machines; demonstrating the effectiveness of their research by developing a production-quality stencil compiler; developing a benchmark suite and benchmarking system for evaluating Pochoir.This research enables scientific researchers and others to easily produce highly efficient codes for complex stencil computations. The codes make good use of the memory hierarchy and processor pipelines endemic to multicore processors and run fast on a diverse set of hardware platforms. This research eases the development and maintenance of a wide variety of stencil-based applications ? ranging across physics, biology, chemistry, energy, climate, mechanical and electrical engineering, finance, and other areas ? benefiting these application areas, as well as society at large.