1 Introduction

CLooG is a free software and library generating loops for scanning Z-polyhedra. That is, it finds a code (e.g. in C, FORTRAN...) that reaches each integral point of one or more parameterized polyhedra. CLooG has been originally written to solve the code generation problem for optimizing compilers based on the polytope model. Nevertheless it is used now in various area, e.g., to build control automata for high-level synthesis or to find the best polynomial approximation of a function. CLooG may help in any situation where scanning polyhedra matters. It uses the best state-of-the-art code generation algorithm known as the Quilleré et al. algorithm (see Qui00) with our own improvements and extensions (see Bas04). The user has full control on generated code quality. On one hand, generated code size has to be tuned for sake of readability or instruction cache use. On the other hand, we must ensure that a bad control management does not hamper performance of the generated code, for instance by producing redundant guards or complex loop bounds. CLooG is specially designed to avoid control overhead and to produce a very efficient code.

CLooG stands for Chunky Loop Generator: it is a part of the Chunky project, a research tool for data locality improvement (see Bas03a). It is designed also to be the back-end of automatic parallelizers like LooPo (see Gri04). Thus it is very compilable code oriented and provides powerful program transformation facilities. Mainly, it allows the user to specify very general schedules where, e.g., unimodularity or invertibility of the transformation doesn’t matter.

The current version is still under evaluation, and there is no guarantee that the upward compatibility will be respected (but the previous API has been stable for two years, we hope this one will be as successful -and we believe it-). A lot of reports are necessary to freeze the library API and the input file shape. Most API changes from 0.12.x to 0.14.x have been requested by the users themselves. Thus you are very welcome and encouraged to post reports on bugs, wishes, critics, comments, suggestions or successful experiences in the forum of http://www.CLooG.org or to send them to cedric.bastoul@inria.fr directly.

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