Author: Johannes Doerfert Date: 2020-12-22T13:05:04-06:00 New Revision: 9cb748724ef5d7d0f7d662d849423404267d532a
URL: https://github.com/llvm/llvm-project/commit/9cb748724ef5d7d0f7d662d849423404267d532a DIFF: https://github.com/llvm/llvm-project/commit/9cb748724ef5d7d0f7d662d849423404267d532a.diff LOG: [OpenMP][Docs] Add FAQ entry about math and complex on GPUs Reviewed By: tianshilei1992 Differential Revision: https://reviews.llvm.org/D93718 Added: Modified: openmp/docs/SupportAndFAQ.rst Removed: ################################################################################ diff --git a/openmp/docs/SupportAndFAQ.rst b/openmp/docs/SupportAndFAQ.rst index 37c5bcecfccc..489b66d5b4a6 100644 --- a/openmp/docs/SupportAndFAQ.rst +++ b/openmp/docs/SupportAndFAQ.rst @@ -80,3 +80,32 @@ For now, the answer is most likely *no*. Please see :ref:`build_offload_capable_ Q: Does OpenMP offloading support work in packages distributed as part of my OS? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ For now, the answer is most likely *no*. Please see :ref:`build_offload_capable_compiler`. + + +.. _math_and_complex_in_target_regions: + +Q: Does Clang support `<math.h>` and `<complex.h>` operations in OpenMP target on GPUs? +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Yes, LLVM/Clang allows math functions and complex arithmetic inside of OpenMP target regions +that are compiled for GPUs. + +Clang provides a set of wrapper headers that are found first when `math.h` and +`complex.h`, for C, `cmath` and `complex`, foc C++, or similar headers are +included by the application. These wrappers will eventually include the system +version of the corresponding header file after setting up a target device +specific environment. The fact that the system header is included is important +because they diff er based on the architecture and operating system and may +contain preprocessor, variable, and function definitions that need to be +available in the target region regardless of the targeted device architecture. +However, various functions may require specialized device versions, e.g., +`sin`, and others are only available on certain devices, e.g., `__umul64hi`. To +provide "native" support for math and complex on the respective architecture, +Clang will wrap the "native" math functions, e.g., as provided by the device +vendor, in an OpenMP begin/end declare variant. These functions will then be +picked up instead of the host versions while host only variables and function +definitions are still available. Complex arithmetic and functions are support +through a similar mechanism. It is worth noting that this support requires +`extensions to the OpenMP begin/end declare variant context selector +<https://clang.llvm.org/docs/AttributeReference.html#pragma-omp-declare-variant>`__ +that are exposed through LLVM/Clang to the user as well. _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
