forked from OSchip/llvm-project
83ddfa0d22
This patch implements Clang support for an original OpenMP extension we have developed to support OpenACC: the `ompx_hold` map type modifier. The next patch in this series, D106510, implements OpenMP runtime support. Consider the following example: ``` #pragma omp target data map(ompx_hold, tofrom: x) // holds onto mapping of x { foo(); // might have map(delete: x) #pragma omp target map(present, alloc: x) // x is guaranteed to be present printf("%d\n", x); } ``` The `ompx_hold` map type modifier above specifies that the `target data` directive holds onto the mapping for `x` throughout the associated region regardless of any `target exit data` directives executed during the call to `foo`. Thus, the presence assertion for `x` at the enclosed `target` construct cannot fail. (As usual, the standard OpenMP reference count for `x` must also reach zero before the data is unmapped.) Justification for inclusion in Clang and LLVM's OpenMP runtime: * The `ompx_hold` modifier supports OpenACC functionality (structured reference count) that cannot be achieved in standard OpenMP, as of 5.1. * The runtime implementation for `ompx_hold` (next patch) will thus be used by Flang's OpenACC support. * The Clang implementation for `ompx_hold` (this patch) as well as the runtime implementation are required for the Clang OpenACC support being developed as part of the ECP Clacc project, which translates OpenACC to OpenMP at the directive AST level. These patches are the first step in upstreaming OpenACC functionality from Clacc. * The Clang implementation for `ompx_hold` is also used by the tests in the runtime implementation. That syntactic support makes the tests more readable than low-level runtime calls can. Moreover, upstream Flang and Clang do not yet support OpenACC syntax sufficiently for writing the tests. * More generally, the Clang implementation enables a clean separation of concerns between OpenACC and OpenMP development in LLVM. That is, LLVM's OpenMP developers can discuss, modify, and debug LLVM's extended OpenMP implementation and test suite without directly considering OpenACC's language and execution model, which can be handled by LLVM's OpenACC developers. * OpenMP users might find the `ompx_hold` modifier useful, as in the above example. See new documentation introduced by this patch in `openmp/docs` for more detail on the functionality of this extension and its relationship with OpenACC. For example, it explains how the runtime must support two reference counts, as specified by OpenACC. Clang recognizes `ompx_hold` unless `-fno-openmp-extensions`, a new command-line option introduced by this patch, is specified. Reviewed By: ABataev, jdoerfert, protze.joachim, grokos Differential Revision: https://reviews.llvm.org/D106509 |
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design | ||
openacc | ||
optimizations | ||
remarks | ||
CMakeLists.txt | ||
README.txt | ||
ReleaseNotes.rst | ||
SupportAndFAQ.rst | ||
conf.py | ||
doxygen-mainpage.dox | ||
doxygen.cfg.in | ||
index.rst |
README.txt
OpenMP LLVM Documentation ================== OpenMP LLVM's documentation is written in reStructuredText, a lightweight plaintext markup language (file extension `.rst`). While the reStructuredText documentation should be quite readable in source form, it is mostly meant to be processed by the Sphinx documentation generation system to create HTML pages which are hosted on <https://llvm.org/docs/> and updated after every commit. Manpage output is also supported, see below. If you instead would like to generate and view the HTML locally, install Sphinx <http://sphinx-doc.org/> and then do: cd <build-dir> cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_HTML=true <src-dir> make $BROWSER <build-dir>/projects/openmp/docs//html/index.html The mapping between reStructuredText files and generated documentation is `docs/Foo.rst` <-> `<build-dir>/projects/openmp/docs//html/Foo.html` <-> `https://openmp.llvm.org/docs/Foo.html`. If you are interested in writing new documentation, you will want to read `llvm/docs/SphinxQuickstartTemplate.rst` which will get you writing documentation very fast and includes examples of the most important reStructuredText markup syntax. Manpage Output =============== Building the manpages is similar to building the HTML documentation. The primary difference is to use the `man` makefile target, instead of the default (which is `html`). Sphinx then produces the man pages in the directory `<build-dir>/docs/man/`. cd <build-dir> cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_MAN=true <src-dir> make man -l >build-dir>/docs/man/FileCheck.1 The correspondence between .rst files and man pages is `docs/CommandGuide/Foo.rst` <-> `<build-dir>/projects/openmp/docs//man/Foo.1`. These .rst files are also included during HTML generation so they are also viewable online (as noted above) at e.g. `https://openmp.llvm.org/docs/CommandGuide/Foo.html`.