PyPS a programmable pass manager

International audiencePIPS4U :1- Complex Environment2- Source-to-Source3- Model for Code Transformations4- Based on a Scripting Language5- Abstractions6- Control Structures7- Target

Polyèdres et Compilation

22 pagesInternational audienceLa première utilisation de polyèdres pour résoudre un problème de compilation, la parallélisation automatique de boucles en présence d'appels de procédure, a été décrite et implémenté il y a près de trente ans. Le modèle polyédrique est maintenant reconnu internationalement et est en phase d'intégration dans le compilateur GCC, bien que la complexité exponentielle des algorithmes associés ait été pendant très longtemps un motif justifiant leur refus pur et simple. L'objectif de cet article est de donner de nombreux exemples d'utilisation des polyèdres dans un compilateur optimiseur et de montrer qu'ils permettent de poser des conditions simples pour garantir la légalité de transformations

PIPS Is not (just) Polyhedral Software Adding GPU Code Generation in PIPS

6 pagesInternational audienceParallel and heterogeneous computing are growing in audience thanks to the increased performance brought by ubiquitous manycores and GPUs. However, available programming models, like OPENCL or CUDA, are far from being straightforward to use. As a consequence, several automated or semi-automated approaches have been proposed to automatically generate hardware-level codes from high-level sequential sources. Polyhedral models are becoming more popular because of their combination of expressiveness, compactness, and accurate abstraction of the data-parallel behaviour of programs. These models provide automatic or semi-automatic parallelization and code transformation capabilities that target such modern parallel architectures. PIPS is a quarter-century old source-to-source transformation framework that initially targeted parallel machines but then evolved to include other targets. PIPS uses abstract interpretation on an integer polyhedral lattice to represent program code, allowing linear relation analysis on integer variables in an interprocedural way. The same representation is used for the dependence test and the convex array region analysis. The polyhedral model is also more classically used to schedule code from linear constraints. In this paper, we illustrate the features of this compiler infrastructure on an hypothetical input code, demonstrating the combination of polyhedral and non polyhedral transformations. PIPS interprocedural polyhedral analyses are used to generate data transfers and are combined with non-polyhedral transformations to achieve efficient CUDA code generation

Par4All: From Convex Array Regions to Heterogeneous Computing

2 pagesInternational audienceRecent compilers comprise an incremental way for converting software toward accelerators. For instance, the pgi Accelerator [14] or hmpp [3] require the use of directives. The programmer must select the pieces of source that are to be executed on the accelerator, providing optional directives that act as hints for data allocations and transfers. The compiler generates all code automatically. [...] Unlike these approaches, Par4All [13] is an automatic parallelizing and optimizing compiler for C and Fortran sequential programs funded by the hpc Project startup. The purpose of this source-to-source compiler is to integrate several compilation tools into an easy-to-use yet powerful compiler that automatically transforms existing programs to target various hardware platforms

Interprocedural Array Region Analyses

. Many program optimizations require exact knowledge of the sets of array elements that are referenced in or that flow between statements or procedures. Some examples are array privatization, generation of communications in distributed memory machines, or compile-time optimization of cache behavior in hierarchical memory machines. Exact array region analysis is introduced in this article. These regions exactly represent the effects of statements and procedures upon array variables. To represent the flow of these data, we also introduce two new types of array region analyses: IN and OUT regions. The intraprocedural propagation is presented, as well as a general linear framework for interprocedural analyses, that handles array reshapes. Introduction The efficient compilation of scientific programs for massively parallel machines, hierarchical memory machines or fault-tolerant computing environments requires a precise intra- and inter-procedural analysis of array data flow. A recent type..

Exact vs. Approximate Array Region Analyses

Advanced program optimizations, such as array privatization, require precise array data flow analyses, usually relying on conservative over- (or may) and under- (or must) approximations of array element sets [26, 32, 21]. In a recent study [14], we proposed to compute exact sets whenever possible. But the advantages of this approach were still an open issue which is discussed in this paper. It is first recalled that must array region analyses cannot be defined on lattices. It implies that there exists no better solution for such data flow problems, and that ad-hoc solutions must be defined. For that purpose, it is suggested to perform under- and over-approximate analyses at the same time, and to enhance the results of must analyses with those of may analyses, when the latter can be proved exact according to an exactness criterion. This is equivalent to our previous approach, and is more effective than using only traditional techniques such as widening and narrowing operators which may..

Interprocedural Analyses of Fortran Programs

Interprocedural analyses (IPA) are becoming more and more common in commercial compilers. But research on the analysis of Fortran programs is still going on, as a number of problems are not yet satisfactorily solved and others are emerging with new language dialects. This paper presents a survey of the main interprocedural analysis techniques, with an emphasis on the suitability of the analysis framework for the characteristics of the original semantic problem. Our experience with the pips interprocedural compiler workbench is then described. pips includes a make-like mechanism, PipsMake, which takes care of the interleavings between top-down and bottom-up analyses and allows a quick prototyping of new interprocedural analyses. Intensive summarization is used to reduce storage requirements and achieve reasonable analysis times when dealing with real-life applications. The speed/accuracy tradeoffs made for pips are discussed in the light of other interprocedural tools. Key ..

Program Sequentially, Carefully, and Benefit from Compiler Advances for Parallel Heterogeneous Computing

International audienceThe current microarchitecture trend leads toward heterogeneity. This evolution is driven by the end of Moore's law and the frequency wall due to the power wall. Moreover, with the spreading of smartphone, some constraints from the mobile world drive the design of most new architectures. An immediate consequence is that an application has to be executable on various targets. Porting and maintaining multiple versions of the code base requires different skills and the efforts required in the process as well as the increased complexity in debugging and testing are time consuming, thus expensive. Some solutions based on compilers emerge. They are based either on directives added to C like in openhmpp or openacc or on automatic solution like pocc, Pluto, ppcg, or Par4All. However compilers cannot retarget in an efficient way any program written in a low-level language such as unconstrained C. Programmers should follow good practices when writing code so that compilers have more room to perform the transformations required for efficient execution on heterogeneous targets. This chapter explores the impact of different patterns used by programmers, and defines a set of good practices allowing a compiler to generate efficient code