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Section: New Results

PolyCheck: Dynamic Verification of Iteration Space Transformations on Affine Programs

Participants : Sriram Krishnamoorthy [PNNL] , Bao Wenlei [OSU] , Louis-Noël Pouchet [UCLA] , P. Sadayappan [OSU] , Fabrice Rastello.

High-level compiler transformations, especially loop transformations, are widely recognized as critical optimizations to restructure programs to improve data locality and expose parallelism. Guaranteeing the correctness of program transformations is essential, and to date three main approaches have been developed: proof of equivalence of affine programs, matching the execution traces of programs, and checking bit-by-bit equivalence of program outputs. Each technique suffers from limitations in the kind of transformations supported, space complexity, or the sensitivity to the testing dataset. In this work, we take a novel approach that addresses all three limitations to provide an automatic bug checker to verify any iteration reordering transformations on affine programs, including non-affine transformations, with space consumption proportional to the original program data and robust to arbitrary datasets of a given size. We achieve this by exploiting the structure of affine program control- and data-flow to generate at compile-time lightweight checker code to be executed within the transformed program. Experimental results assess the correctness and effectiveness of our method and its increased coverage over previous approaches.

This work is the fruit of the collaboration 8.4 with OSU and was presented at ACM POPL'16 [14].