Analysis of interprocedural side effects in a parallel programming environment

Abstract

This paper addresses the analysis of subroutine side effects in the ParaScope programming environment, an ambitious collection of tools for developing, understanding, and compiling parallel programs. In spite of significant progress in the optimization of programs for execution on parallel and vector computers, compilers must still be very conservative when optimizing the code surrounding a call site, due to the lack of information about the code in the subroutine being invoked. This has resulted in the development of algorithms for interprocedural analysis of the side effects of a subroutine, which summarize the body of a subroutine, producing approximate information to improve optimization. This paper reviews the effectiveness of these methods in preparing programs for execution on parallel computers. It is shown that existing techniques are insufficient and a new technique, called regular section analysis, will be described.Regular section analysis extends the lattice used in previous interprocedural analysis methods to a one that is rich enough to represent common array access patterns: elements, rows, columns and their higher dimensional analogues. Regular sections are defined, their properties are established and the modifications to existing interprocedural analysis algorithms required to handle regular sections are presented. Among these modifications are methods for dealing with language features that reshape array parameters at call sites.In addition to improved precision of summary information, we also examine two problems crucial to effective parallelization. The first addresses the need for information about which variables are always redefined as a side-effect of a call and the second addresses the requirement that, for parallel programming, information about side effects must be qualified by information about any critical regions in which those side effects take place. These problems are solved by extensions to existing interprocedural dataflow analysis frameworks.KeywordsFormal ParameterData DependenceSummary InformationCall GraphInduction VariableThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.