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llvm / llvm-project / pstl / 7989575255543967a1935a1b4a7063aee4a330c8
commit7989575255543967a1935a1b4a7063aee4a330c8[log] [tgz]
authorLouis Dionne <ldionne@apple.com>Thu Aug 08 12:43:13 2019 +0000
committerCopybara-Service <copybara-worker@google.com>Tue Sep 01 14:44:18 2020 -0700
treead0fcba1d70cf9b18cda3f8d41a5309023a96da6
parent0b9cff1058f8fb2122ae55ea9253f074048a568a [diff]
[pstl] Error out when the backend is left unspecified

Instead of silently falling back to the serial backend, it's better if
we fail loudly when the parallel backend is left unspecified. Since we
have a __pstl_config_site header, a backend should always be specified.

llvm-svn: 368285
GitOrigin-RevId: a8a436ef95908a560ddca8c5f7c5349d2dc2f977
1 file changed
tree: ad0fcba1d70cf9b18cda3f8d41a5309023a96da6
  1. cmake/
  2. docs/
  3. include/
  4. test/
  5. .arcconfig
  6. .clang-format
  7. CMakeLists.txt
  8. CREDITS.txt
  9. LICENSE.txt
  10. README.md
README.md

Parallel STL

Parallel STL is an implementation of the C++ standard library algorithms with support for execution policies, as specified in ISO/IEC 14882:2017 standard, commonly called C++17. The implementation also supports the unsequenced execution policy specified in Parallelism TS version 2 and proposed for the next version of the C++ standard in the C++ working group paper P1001. Parallel STL offers efficient support for both parallel and vectorized execution of algorithms. For sequential execution, it relies on an available implementation of the C++ standard library.

Prerequisites

To use Parallel STL, you must have the following software installed:

  • C++ compiler with:
    • Support for C++11
    • Support for OpenMP* 4.0 SIMD constructs
  • Threading Building Blocks (TBB) which is available for download at https://github.com/01org/tbb/

Known issues and limitations

  • unseq and par_unseq policies only have effect with compilers that support #pragma omp simd or #pragma simd.
  • Parallel and vector execution is only supported for the algorithms if random access iterators are provided, while for other iterator types the execution will remain serial.
  • The following algorithms do not allow efficient SIMD execution: includes, inplace_merge, merge, nth_element, partial_sort, partial_sort_copy, set_difference, set_intersection, set_symmetric_difference, set_union, sort, stable_partition, stable_sort, unique.
  • The initial value type for exclusive_scan, inclusive_scan, transform_exclusive_scan, transform_inclusive_scan shall be DefaultConstructible. A default constructed-instance of the initial value type shall be the identity element for the specified binary operation.
  • For max_element, min_element, minmax_element, partial_sort, partial_sort_copy, sort, stable_sort the dereferenced value type of the provided iterators shall be DefaultConstructible.
  • For remove, remove_if, unique the dereferenced value type of the provided iterators shall be MoveConstructible.
  • The following algorithms require additional O(n) memory space for parallel execution: copy_if, inplace_merge, partial_sort, partial_sort_copy, partition_copy, remove, remove_if, rotate, sort, stable_sort, unique, unique_copy.