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llvm-project/pstl
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Louis Dionne 04c5bc989a [pstl] Default to the serial backend when unspecified 
This is a stopgap measure to make it easier to integrate the PSTL into
libc++. In the future, we should have a system similar to what libc++
does, where we specify settings at configuration time and generate a
__config_site header that is part of the PSTL.

llvm-svn: 363958
 		2019-06-20 17:56:51 +00:00
..
cmake [pstl] Remove our custom FindTBB CMake file 2019-04-11 17:23:18 +00:00
docs [pstl] Setup the _PSTL_VERSION macro like _LIBCPP_VERSION, and add release notes 2019-04-11 17:08:55 +00:00
include/pstl/internal [pstl] Default to the serial backend when unspecified 2019-06-20 17:56:51 +00:00
test [pstl] Mark pstl tests as unsupported before C++17 2019-06-20 16:22:06 +00:00
.arcconfig
…
.clang-format [pstl] Indent preprocessor directives as part of the clang-format rules 2019-04-01 15:21:46 +00:00
CMakeLists.txt [pstl] Make the default backend be the serial backend and always provide parallel policies 2019-04-24 20:12:36 +00:00
CREDITS.txt
…
LICENSE.txt Fix typos throughout the license files that somehow I and my reviewers 2019-01-21 09:52:34 +00:00
README.md A test commit from Mikhail Dvorskiy (blank line, to pstl/trunk) according 'Obtaining Commit Access' rules (https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access) 2019-06-03 08:23:30 +00:00

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.