llvm-project
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
andunseq
policies only have effect with compilers that supportpar_unseq
or#pragma omp simd
.#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
shall be DefaultConstructible. A default constructed-instance of the initial value type shall be the identity element for the specified binary operation.transform_inclusive_scan - For
,max_element
,min_element
,minmax_element
,partial_sort
,partial_sort_copy
,sort
the dereferenced value type of the provided iterators shall be DefaultConstructible.stable_sort - For
,remove
,remove_if
the dereferenced value type of the provided iterators shall be MoveConstructible.unique - 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