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[OpenMP][NFC] Added release note for new `deviceRTLs` and hidden helper task 

Added release note for new `deviceRTLs` and hidden helper task for LLVM
12.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D95584
This commit is contained in:
Shilei Tian 2021-01-29 13:12:47 -05:00
parent 5565092faa
commit 7bc31018f7
1 changed files with 25 additions and 1 deletions
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26
openmp/docs/ReleaseNotes.rst
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@ -7,7 +7,7 @@ OpenMP 12.0.0 Release Notes
These are in-progress notes for the upcoming LLVM 12.0.0 release.
Release notes for previous releases can be found on
`the Download Page <https://releases.llvm.org/download.html>`_.
Introduction
============
@ -44,3 +44,27 @@ Non-comprehensive list of changes in this release
``LIBOMPTARGET_INFO`` allows the user to request certain information from the
``libomptarget`` runtime using a 32-bit field. A full description of each
environment variable is described :ref:`here <libopenmptarget_environment_vars>`.
- ``target nowait`` was supported via hidden helper task, which is a task not
bound to any parallel region. A hidden helper team with a number of threads is
created when the first hidden helper task is encountered. The number of threads
can be configured via the environment variable
``LIBOMP_NUM_HIDDEN_HELPER_THREADS``. By default it is 8. If
``LIBOMP_NUM_HIDDEN_HELPER_THREADS=0``, hidden helper task is disabled and
falls back to a regular OpenMP task. It can also be disabled by setting the
environment variable ``LIBOMP_USE_HIDDEN_HELPER_TASK=OFF``.
- ``deviceRTLs`` for NVPTX platform is CUDA free now. It is generally OpenMP code.
Target dependent parts are implemented with Clang/LLVM/NVVM intrinsics. CUDA
SDK is also dropped as a dependence to build the device runtime, which means
device runtime can also be built on a CUDA free system. However, it is
disabled by default. Set the CMake variable
``LIBOMPTARGET_BUILD_NVPTX_BCLIB=ON`` to enable the build of NVPTX device
runtime on a CUDA free system. ``gcc-multilib`` and ``g++-multilib`` are
required. If CUDA is found, the device runtime will be built by default.
- Static NVPTX device runtime library (``libomptarget-nvptx.a``) was dropped.
A bitcode library is required to build an OpenMP program. If the library is
not found in the default path or any of the paths defined by ``LIBRARY_PATH``,
an error will be raised. User can also specify the path to the bitcode device
library via ``--libomptarget-nvptx-bc-path=``.