The pochoir stencil compiler

  • Authors:

  • Yuan Tang;Rezaul Alam Chowdhury;Bradley C. Kuszmaul;Chi-Keung Luk;Charles E. Leiserson

  • Affiliations:

  • Fudan University, MIT, Cambridge, MA, USA;Boston University, MIT, Cambridge, MA, USA;MIT, Cambridge, MA, USA;Intel Corp., Hudson, MA, USA;MIT, Cambridge, MA, USA

  • Venue:
  • Proceedings of the twenty-third annual ACM symposium on Parallelism in algorithms and architectures
  • Year:
  • 2011

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Abstract

A stencil computation repeatedly updates each point of a d-dimensional grid as a function of itself and its near neighbors. Parallel cache-efficient stencil algorithms based on "trapezoidal decompositions" are known, but most programmers find them difficult to write. The Pochoir stencil compiler allows a programmer to write a simple specification of a stencil in a domain-specific stencil language embedded in C++ which the Pochoir compiler then translates into high-performing Cilk code that employs an efficient parallel cache-oblivious algorithm. Pochoir supports general d-dimensional stencils and handles both periodic and aperiodic boundary conditions in one unified algorithm. The Pochoir system provides a C++ template library that allows the user's stencil specification to be executed directly in C++ without the Pochoir compiler (albeit more slowly), which simplifies user debugging and greatly simplified the implementation of the Pochoir compiler itself. A host of stencil benchmarks run on a modern multicore machine demonstrates that Pochoir outperforms standard parallelloop implementations, typically running 2-10 times faster. The algorithm behind Pochoir improves on prior cache-efficient algorithms on multidimensional grids by making "hyperspace" cuts, which yield asymptotically more parallelism for the same cache efficiency.