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[Offload] Provide a CMake cache file to easily build offloading #115074

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merged 3 commits into from
Nov 7, 2024
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[Offload] Provide a CMake cache file to easily build offloading #115074

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[Offload] Provide a CMake cache file to easily build offloading
jhuber6 Nov 5, 2024
7f8d612
Update SupportAndFAQ.rst
jhuber6 Nov 6, 2024
445e395
Update Offload.cmake
jhuber6 Nov 7, 2024
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12 changes: 12 additions & 0 deletions offload/cmake/caches/Offload.cmake
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
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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