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[Offload] Provide a CMake cache file to easily build offloading (llvm…
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…#115074)

Summary:
This patch adds a cache file that will automatically enable openpm,
offload, and all the fancy GPU libraries.
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jhuber6 authored and Groverkss committed Nov 15, 2024
1 parent 62067e7 commit 2ff2a83
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Showing 2 changed files with 29 additions and 1 deletion.
12 changes: 12 additions & 0 deletions offload/cmake/caches/Offload.cmake
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set(LLVM_ENABLE_PROJECTS "clang;clang-tools-extra;compiler-rt;lld" CACHE STRING "")
set(LLVM_ENABLE_RUNTIMES "libunwind;libcxx;libcxxabi;openmp;offload" CACHE STRING "")
set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR ON CACHE BOOL "")

set(CLANG_DEFAULT_CXX_STDLIB "libc++" CACHE STRING "")
set(CLANG_DEFAULT_LINKER "lld" CACHE STRING "")

set(LLVM_RUNTIME_TARGETS default;amdgcn-amd-amdhsa;nvptx64-nvidia-cuda CACHE STRING "")
set(RUNTIMES_nvptx64-nvidia-cuda_CACHE_FILES "${CMAKE_SOURCE_DIR}/../libcxx/cmake/caches/NVPTX.cmake" CACHE STRING "")
set(RUNTIMES_amdgcn-amd-amdhsa_CACHE_FILES "${CMAKE_SOURCE_DIR}/../libcxx/cmake/caches/AMDGPU.cmake" CACHE STRING "")
set(RUNTIMES_nvptx64-nvidia-cuda_LLVM_ENABLE_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi" CACHE STRING "")
set(RUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES "compiler-rt;libc;libcxx;libcxxabi" CACHE STRING "")
18 changes: 17 additions & 1 deletion openmp/docs/SupportAndFAQ.rst
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Expand Up @@ -51,7 +51,23 @@ All patches go through the regular `LLVM review process

Q: How to build an OpenMP GPU offload capable compiler?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
To build an *effective* OpenMP offload capable compiler, only one extra CMake

The easiest way to create an offload capable compiler is to use the provided
CMake cache file. This will enable the projects and runtimes necessary for
offloading as well as some extra options.

.. code-block:: sh
$> cd llvm-project # The llvm-project checkout
$> mkdir build
$> cd build
$> cmake ../llvm -G Ninja \
-C ../offload/cmake/caches/Offload.cmake \ # The preset cache file
-DCMAKE_BUILD_TYPE=<Debug|Release> \ # Select build type
-DCMAKE_INSTALL_PREFIX=<PATH> \ # Where the libraries will live
$> ninja install
To manually build an *effective* OpenMP offload capable compiler, only one extra CMake
option, ``LLVM_ENABLE_RUNTIMES="openmp;offload"``, is needed when building LLVM (Generic
information about building LLVM is available `here
<https://llvm.org/docs/GettingStarted.html>`__.). Make sure all backends that
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