Sketching stencils

Abstract

Performance of stencil computations can be significantly improved through smart implementations that improve memory locality, computation reuse, or parallelize the computation. Unfortunately, efficient implementations are hard to obtain because they often involve non-traditional transformations, which means that they cannot be produced by optimizing the reference stencil with a compiler. In fact, many stencils are produced by code generators that were tediously handcrafted.In this paper, we show how stencil implementations can be produced with sketching. Sketching is a software synthesis approach where the programmer develops a partial implementationa sketch-and a separate specification of the desired functionality given by a reference (unoptimized) stencil. The synthesizer then completes the sketch to behave like the specification, filling in code fragments that are difficult to develop manually.Existing sketching systems work only for small finite programs, i.e., programs that can be represented as small Boolean circuits. In this paper, we develop a sketching synthesizer that works for stencil computations, a large class of programs that, unlike circuits, have unbounded inputs and outputs, as well as an unbounded number of computations. The key contribution is a reduction algorithm that turns a stencil into a circuit, allowing us to synthesize stencils using an existing sketching synthesizer.

Synthesis of machine code from semantics

“…CEGIS is a synthesis framework that has been widely used in synthesis tools. Sketching is a technique that uses CEGIS for completing partial programs, or sketches [Solar- Lezama et al 2005Lezama et al , 2006Lezama et al , 2007. The templatized instructionsequences enumerated by MCSYNTH can be considered as sketches, with the template operands being the holes.…”

Program sketching

“…In our PLDI 07 paper [17], we showed how synthesis could be made much more effective for programs in a particular domain by incorporating domain-specific insight into the synthesizer. We believe such domain-specific insight can make an enormous difference.…”

Synthesis modulo recursive functions

“…Program sketching has demonstrated the practicality of program synthesis by focusing its use on particular domains [40][41][42]. The algorithms employed in sketching are typically focused on appropriately guided search over the syntax tree of the synthesized program.…”