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[docs] Prefer --gcc-install-dir= to deprecated GCC_INSTALL_PREFIX #85458

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Mar 18, 2024
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[docs] Prefer --gcc-install-dir= to deprecated GCC_INSTALL_PREFIX #85458

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17 changes: 10 additions & 7 deletions clang/www/get_started.html
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Expand Up @@ -86,13 +86,16 @@ <h3 id="buildNix">On Unix-like Systems</h3>
</ul>
</li>

<li>If you intend to use Clang's C++ support, you may need to tell it how
to find your C++ standard library headers. In general, Clang will detect
the best version of libstdc++ headers available and use them - it will
look both for system installations of libstdc++ as well as installations
adjacent to Clang itself. If your configuration fits neither of these
scenarios, you can use the <tt>-DGCC_INSTALL_PREFIX</tt> cmake option
to tell Clang where the gcc containing the desired libstdc++ is installed.
<li>On Linux, you may need GCC runtime libraries (e.g. <tt>crtbeginS.o,
libstdc++.so</tt>) and libstdc++ headers. In general, Clang will detect
well-known GCC installation paths matching the target triple (configured at
build time (see <tt>clang --version</tt>); overriden by
<tt>--target=</tt>) and use the largest version. If your configuration fits
none of the standard scenarios, you can set <tt>--gcc-install-dir=</tt> to
the GCC installation directory (something like
<tt>/usr/lib/gcc/$triple/$major</tt>). If your GCC installation is under
<tt>/usr/lib/gcc</tt> but uses a different triple, you can set
<tt>--gcc-triple=$triple</tt>.
</li>
<li>Try it out (assuming you add llvm/build/bin to your path):
<ul>
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7 changes: 4 additions & 3 deletions openmp/docs/SupportAndFAQ.rst
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Expand Up @@ -279,11 +279,12 @@ Q: How to build an OpenMP offload capable compiler with an outdated host compile

Enabling the OpenMP runtime will perform a two-stage build for you.
If your host compiler is different from your system-wide compiler, you may need
to set the CMake variable `GCC_INSTALL_PREFIX` so clang will be able to find the
correct GCC toolchain in the second stage of the build.
to set ``CMAKE_{C,CXX}_FLAGS`` like
``--gcc-install-dir=/usr/lib/gcc/x86_64-linux-gnu/12`` so that clang will be
able to find the correct GCC toolchain in the second stage of the build.

For example, if your system-wide GCC installation is too old to build LLVM and
you would like to use a newer GCC, set the CMake variable `GCC_INSTALL_PREFIX`
you would like to use a newer GCC, set ``--gcc-install-dir=``
to inform clang of the GCC installation you would like to use in the second stage.

Q: How can I include OpenMP offloading support in my CMake project?
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