OpenMP

This page contains information on GCC's implementation of the OpenMP specification and related functionality like the auto parallelizer (-ftree-parallelize-loops).

As of GCC 4.2, the compiler implements version 2.5 of the OpenMP specification, as of 4.4 it implements version 3.0 and since GCC 4.7 it supports the OpenMP 3.1 specification. GCC 4.9 supports OpenMP 4.0 for C/C++, GCC 4.9.1 also for Fortran. GCC 5 adds support for Offloading.

OpenMP Documentation

• Documentation on libgomp (GNU Offloading and Multi Processing Runtime Library).

• OpenMP v2.5 specification

• OpenMP v3.0 specification

• OpenMP v3.1 draft specification (forum for draft comments)

• OpenMP v3.1 specification (July 2011) (OpenMP 3.1 API forum)

• OpenMP v4.0 specification (July2013) (Official OpenMP 4.0 Examples, OpenMP 4.0 API forum)

Automatic Parallelization

(-ftree-parallelize-loops)

• Streamization

Test Suites and Benchmarks

• OpenMP Validation Suite by HLRS, Univ. Stuttgart and Univ. of Houston (2007 version at UH: README, Download)

• OpenMP task test suite by BSC

• SPEC OMP

• EPCC Microbenchmarks

• NAS Benchmarks (unofficial C version)

• LLNL benchmark

• Rodinia Benchmark suite (2): OpenMP, OpenCL, CUDA benchmark

TODO List

Feel free to add new items to this list as you run into issues or features that would be interesting to add. Send mail to the list and/or the GCC OpenMP maintainers if any item in this list sounds interesting but is hard to understand.

• Fix PR 35423 (missing parts of OpenMP WORKSHARE).

• Fine tune the auto scheduling feature for parallel loops.

• Implement untied tasks (no compliance issue; needs to be well tuned to be actually faster; cf. page 53 of pdf) - see also next item

• Tasks need some tuning in taskwait. Cf. GCC email, comparison. Algorithms: PDF 1, PDF 2, PDF 3

  • A comparison for tasks between libgomp, another library (gcc+libKOMP) and Intel (cf. benchmark on p. 10); see also another IOMP 2012 comparison

• taskyield is a stub and mergeable task clonning could be optimized

• OpenMP 4.0 (specifications released on July 2013). Cf. slides at the IWOMP, the International Workshop for OpenMP (slides and tutorials) in June 2010 and the OWOMP 2010 proceedings. There is also a blog entry. See also IWOMP 2012's talks and the committee report. SC2011 (November 2011): OpenMP Lang Committee Report, CEO report

  • And the 2012 slides: IWOMP program, Language Committee report

  • And the OpenMP 4.0 release candidate documents: OpenMP v4.0rc2 specification (March 2013) (OpenMP 4.0 API forum, rc2 changes)

  • And a comment prior to the final release: OpenMP 4.0 about to be released and IWOMP 2013, by Michael Wong (May 2013)