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Clacc: OpenACC for C/C++ in Clang

Journal Article · · International Journal of High Performance Computing Applications
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  1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
  2. Universidad Politecnica de Cataluña, Barcelona (Spain)
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The Clacc project has developed OpenACC compiler, runtime, and profiling interface support for C/C++ by extending Clang and LLVM. A key Clacc design feature is that it translates OpenACC to OpenMP to leverage the OpenMP offloading support that is actively being developed for Clang and LLVM. A benefit of this design is support for two compilation modes: traditional compilation mode produces a binary, and source-to-source mode produces OpenMP source. Clacc has been deployed on Oak Ridge National Laboratory’s (ORNL’s) Frontier, on which Clacc is the only OpenACC implementation for C/C++. Clacc supports x86_64, POWER9, AMD GPUs, and NVIDIA GPUs. Clacc’s OpenACC profiling interface support has been integrated with TAU, which is also deployed on Frontier. While Clacc has always supported C as a base language, Clacc also has increasing C++ support, including support for Kokkos’s OpenACC back end. Clacc itself is hosted publicly on GitHub. In this paper, we describe Clacc’s design and mapping from OpenACC directives to OpenMP. We also present a performance evaluation on ORNL’s Frontier (AMD MI250x GPU offload) and Argonne National Laboratory’s (ANL’s) Polaris (NVIDIA A100 GPU offload) for various SPEC ACCEL and Kokkos OpenACC back end benchmarks.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR). Scientific Discovery through Advanced Computing (SciDAC)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
2438826
Journal Information:
International Journal of High Performance Computing Applications, Journal Name: International Journal of High Performance Computing Applications Vol. 0; ISSN 1094-3420
Publisher:
SAGECopyright Statement
Country of Publication:
United States
Language:
English

References (7)

OpenACC Profiling Support for Clang and LLVM using Clacc and TAU conference November 2020
OpenACC to FPGA: A Framework for Directive-Based High-Performance Reconfigurable Computing conference May 2016
CLACC: Translating OpenACC to OpenMP in Clang conference November 2018
Understanding Portability of a High-Level Programming Model on Contemporary Heterogeneous Architectures journal July 2015
KokkACC: Enhancing Kokkos with OpenACC conference November 2022
OpenARC: open accelerator research compiler for directive-based, efficient heterogeneous computing conference January 2014
The Tau Parallel Performance System journal May 2006

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Related Subjects

97 MATHEMATICS AND COMPUTING
Clang
Kokkos
LLVM
OpenACC
OpenMP