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Ruslan Arutyunyan 843c12d6a0 [libc++][pstl] Implement tag dispatching mechanism for Parallel STL 
Implement the mechanism that simplifies the execution policy/iterator
category dispatching and allows to implement customizations for
the parallel algorithms with adding custom tags

Reviewed By: rodgert, MikeDvorskiy

Differential Revision: https://reviews.llvm.org/D104492
 		2022-01-28 04:09:51 +03:00
..
cmake [pstl] Rename PARALLELSTL_BACKEND to PSTL_PARALLEL_BACKEND 2019-08-13 11:50:26 +00:00
docs Bump the trunk major version to 14 2021-07-27 21:58:25 -07:00
include [libc++][pstl] Implement tag dispatching mechanism for Parallel STL 2022-01-28 04:09:51 +03:00
test [libc++][pstl] Implement tag dispatching mechanism for Parallel STL 2022-01-28 04:09:51 +03:00
.clang-format
…
CMakeLists.txt [cmake] Make include(GNUInstallDirs) always below project(..) 2022-01-20 18:59:17 +00:00
CREDITS.txt [pstl] Initial implementation of OpenMP backend, on behalf of Christopher Nelson nadiasvertex@gmail.com 2021-10-15 15:36:07 +03:00
LICENSE.TXT Rename top-level LICENSE.txt files to LICENSE.TXT 2021-03-10 21:26:24 -08:00
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.