Pointers inside lambda closure objects in OpenMP target offload regions

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

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

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 discusses 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. This change has also been accepted into the draft OpenMP®specification for inclusion in OpenMP 5. 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.

Original languageEnglish
Title of host publicationProceedings of LLVM-HPC 2018
Subtitle of host publication5th Workshop on the LLVM Compiler Infrastructure in HPC, Held in conjunction with SC 2018: The International Conference for High Performance Computing, Networking, Storage and Analysis
PublisherInstitute of Electrical and Electronics Engineers (IEEE)
Pages10-17
Number of pages8
ISBN (Electronic)9781728101880
DOIs
Publication statusPublished - 11 Feb 2019
Event5th IEEE/ACM Workshop on the LLVM Compiler Infrastructure in HPC, LLVM-HPC 2018 - Dallas, United States
Duration: 12 Nov 2018 → …

Publication series

NameProceedings of LLVM-HPC 2018: 5th Workshop on the LLVM Compiler Infrastructure in HPC, Held in conjunction with SC 2018: The International Conference for High Performance Computing, Networking, Storage and Analysis

Conference

Conference5th IEEE/ACM Workshop on the LLVM Compiler Infrastructure in HPC, LLVM-HPC 2018
Country/TerritoryUnited States
CityDallas
Period12/11/18 → …

ASJC Scopus subject areas

  • Hardware and Architecture
  • Software

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