Implicit mapping of pointers inside C++ Lambda closure objects in OpenMP target offload regions

David R. Truby, Carlo Bertolli, Steven A. Wright, Gheorghe-Teodor Bercea, Kevin O'Brien, Stephen A. Jarvis

Research output: Contribution to conferencePaperpeer-review


With the diversification of HPC architectures beyond traditional CPU-based clusters, a number of new frameworks for performance portability across architectures have arisen. One way of implementing such frameworks is to use C++ templates and lambda expressions to design loop-like functions. However, lower level programming APIs that these implementations must use are often designed with C in mind and do not specify how they interact with C++ features such as lambda expressions. This paper proposes a change to the behavior of the OpenMP specification with respect to lambda expressions such that when functions generated by lambda expressions are called inside GPU regions, any pointers used in the lambda expression correctly refer to device pointers. This change has been implemented in a branch of the Clang C++ compiler and demonstrated with two representative codes. Our results show that the implicit mapping of lambda expressions always exhibits identical performance to an explicit mapping but without breaking the abstraction provided by the high level frameworks, and therefore also reduces the burden on the application developer.
Original languageEnglish
Publication statusAccepted/In press - 1 Feb 2018
EventUK OpenMP Users' Conference 2018 - St Catherine's College, Oxford, United Kingdom
Duration: 21 May 201822 May 2018


ConferenceUK OpenMP Users' Conference 2018
Country/TerritoryUnited Kingdom
Internet address


  • OpenMP, C++

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