<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/128870>128870</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            OpenMP dylib not found on MacOS
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          vincentloechner
      </td>
    </tr>
</table>

<pre>
    Hi,

Compiling LLVM with the OpenMP project activated, it builds fine and everything seems to be installed ok, including the libomp.dylib.

But, when compiling an OpenMP C program using the newly built clang, the dylib is not found at runtime as I would expect it to be:
```
% /opt/llvm/bin/clang toto.c
% otool -L a.out
a.out:
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1351.0.0)
% ./a.out
1 threads
% /opt/llvm/bin/clang toto.c -fopenmp
% otool -L a.out
a.out:
        @rpath/libomp.dylib (compatibility version 5.0.0, current version 5.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1351.0.0)
% ./a.out
dyld[73817]: Library not loaded: @rpath/libomp.dylib
  Referenced from: <05684888-4242-32CB-9806-AE5BAF37FD0C> ./a.out
  Reason: no LC_RPATH's found
zsh: abort      ./a.out
% DYLD_LIBRARY_PATH=/opt/llvm/lib ./a.out
14 threads
% 
```

Using the DYLD_LIBRARY_PATH environment variable is not satisfactory, and it is not possible when using this toolchain in another Cmake-enabled project.

This patch fixes the issue:
```
% git diff
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 2b916f000336..9e2a8cf798ec 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1104,6 +1104,10 @@ void tools::addOpenMPRuntimeLibraryPath(const ToolChain &TC,
 llvm::sys::path::parent_path(TC.getDriver().Dir);
 llvm::sys::path::append(DefaultLibPath, CLANG_INSTALL_LIBDIR_BASENAME);
 CmdArgs.push_back(Args.MakeArgString("-L" + DefaultLibPath));
+  #if defined(__APPLE__)
+ CmdArgs.push_back(Args.MakeArgString("-rpath"));
+ CmdArgs.push_back(Args.MakeArgString(DefaultLibPath));
+  #endif
 }

 void tools::addArchSpecificRPath(const ToolChain &TC, const ArgList &Args,
```

I ran this on an Apple M4Pro, MacOS Sequoia 15.3.1.
This is my cmake configuration (tried various things, the 2 last lines do not seem to change anything):
```
% cmake -G Ninja ../llvm \
 -DLLVM_ENABLE_PROJECTS="clang;openmp" \
  -DLLVM_BUILD_EXAMPLES=OFF \
 -DLLVM_TARGETS_TO_BUILD="host" \
  -DCMAKE_BUILD_TYPE=Release \
 -DLLVM_ENABLE_ASSERTIONS=ON \
  -DLLVM_ENABLE_LLD=ON \
 -DDEFAULT_SYSROOT="$(xcrun --show-sdk-path)" \
 -DCMAKE_INSTALL_PREFIX=/opt/llvm \
  -DLLVM_INSTALL_UTILS=ON \
 -DCMAKE_INSTALL_RPATH_USE_LINK_PATH=ON \
 -DCMAKE_INSTALL_RPATH=/opt/llvm/lib \
  -DCMAKE_MACOSX_RPATH=TRUE
```

</pre>
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