SHF: AF: Medium: Collaborative Research:The Ponchoir Stencil Complier

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处的d维空间网格中的网格点的值定义为t之前最近时间的相邻网格点的函数。模板计算在概念上易于使用嵌套循环来实现，但是循环实现在多核处理器上受到较差的高速缓存性能的影响。与循环实现相比，缓存无关的分而治之模板代码可以在缓存效率上实现数量级的改进，但大多数程序员发现很难编写缓存无关的模板代码。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悬而未决的问题。该项目对模板缓存无关的模板编译的研究使模板计算的普通程序员能够享受到多核技术的好处，而不需要编写比朴素嵌套循环更复杂的代码。该研究项目正在开发一种嵌入C语言的语言，该语言可以简洁地表达模板计算，并可以自动编译为适用于多核处理器和其他平台的高效算法代码。Pochoir模板编译器编译模板计算，这些模板计算显示复杂的边界条件，如周期、常量、狄利克雷、诺伊曼、镜像和相位因子；不规则，包括宏观和微观不均匀，以及不规则形状；一般复杂依赖关系，如推依赖关系、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公认的良好算法；探索特定领域的编译器技术如何从高效的高速缓存管理、处理器流水线调度和并行计算中实现加速；研究如何在各种架构上高效地运行模板，如多核、分布式内存集群、图形处理单元、现场可编程门阵列和未来的亿级机器；通过开发生产质量的模板编译器来展示他们研究的有效性；开发用于评估Pochoir的基准测试套件和基准测试系统。这项研究使科学研究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流水线，并在不同的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，涉及物理、生物、化学、能源、气候、机械和电气工程、金融和其他领域，使这些应用程序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.