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===========================
OpenMP 12.0.0 Release Notes
===========================
.. warning::
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
============
This document contains the release notes for the OpenMP runtime, release 12.0.0.
Here we describe the status of OpenMP, including major improvements
from the previous release. All OpenMP releases may be downloaded
from the `LLVM releases web site <https://llvm.org/releases/>`_.
Non-comprehensive list of changes in this release
=================================================
- Extended the ``libomptarget`` API functions to include source location
information and OpenMP target mapper support. This allows ``libomptarget`` to
know the source location of the OpenMP region it is executing, as well as the
name and declarations of all the variables used inside the region. Each
function generated now uses its ``mapper`` variant. The old API calls now call
into the new API functions with ``nullptr`` arguments for backwards
compatibility with old binaries. Source location information for
``libomptarget`` is now generated by Clang at any level of debugging
information.
- Added improved error messages for ``libomptarget`` and ``CUDA`` plugins. Error
messages are now presented without requiring a debug build of
``libomptarget``. The newly added source location information can also be used
to identify which OpenMP target region the failure occurred in. More
information can be found :ref:`here <libopenmptarget_errors>`.
- Added additional environment variables to control output from the
``libomptarget`` runtime library. ``LIBOMPTARGET_PROFILE`` to
generate time profile output similar to Clang's ``-ftime-trace`` option.
``LIBOMPTARGET_MEMORY_MANAGER_THRESHOLD`` sets the threshold size for which
the ``libomptarget`` memory manager will handle the allocation.
``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=``.
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