Section: Software

OpenScop

Participant : Cédric Bastoul.

OpenScop is an open specification which defines a file format and a set of data structures to represent a static control part (SCoP for short), i.e., a program part that can be represented in the polyhedral model, an algebraic representation of programs used for automatic parallelization and optimization (used, e.g., in GNU GCC, LLVM, IBM XL or Reservoir Labs R-Stream compilers). The goal of OpenScop is to provide a common interface to various polyhedral compilation tools in order to simplify their interaction.

OpenScop provides a single format for tools that may have different purposes (e.g., as different as code generation and data dependence analysis). We could observe that most available polyhedral compilation tools during the last decade were manipulating the same kind of data (polyhedra, affine functions...) and were actually sharing a part of their input (e.g., iteration domains and context concepts are nearly everywhere). We could also observe that those tools may rely on different internal representations, mostly based on one of the major polyhedral libraries (e.g., Polylib, PPL or isl), and this representation may change over time (e.g., when switching to a more convenient polyhedral library). OpenScop aims at providing a stable, unified format that offers a durable guarantee that a tool can use an output or provide an input to another tool without breaking a compilation chain because of some internal changes in one element of this chain. The other promise of OpenScop is the ability to assemble or replace the basic blocks of a polyhedral compilation framework at no, or at least low engineering cost. The OpenScop Library (licensed under the 3-clause BSD license) has been developped as an example, yet powerful, implementation of the OpenScop specification.