<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/84724>84724</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Wrong result of llvm_config macro with USE_SHARED and default llvm build
        </td>
    </tr>

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

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

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

<pre>
    The `llvm_config` makro with the `USE_SHARED` flag returns the shared library instead of the static libraries when used with LLVM compiled with static component libraries (`LLVM_BUILD_LLVM_DYLIB` = off). This of course causes linking projects using llvm to fail:
```
[2/2] Linking CXX executable simple-tool
FAILED: simple-tool 
: && /usr/bin/c++  -Wl,--gc-sections CMakeFiles/simple-tool.dir/tool.cpp.o -o simple-tool -L/root/llvmtest/llvm-project/build/./lib -Wl,-rpath,"\$ORIGIN/../lib:/root/llvmtest/llvm-project/build/./lib" -lLLVM && :
/usr/bin/ld: cannot find -lLLVM: No such file or directory
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
```

The wrong result is caused by inconsistency between `LLVM_BUILD_LLVM_DYLIB` (default off) and `LLVM_DYLIB_COMPONENTS` (default=all). 
https://github.com/llvm/llvm-project/blob/35b784379e707423f3b4f5a2cfedabcfa6f5b47d/llvm/CMakeLists.txt#L819-L823
https://github.com/llvm/llvm-project/blob/35b784379e707423f3b4f5a2cfedabcfa6f5b47d/llvm/CMakeLists.txt#L804

`LLVM_DYLIB_COMPONENTS` is used by the `llvm_config` makro to filter the passed components, assuming that all components listed there are available in the shared library, even when no shared library was created. 
https://github.com/llvm/llvm-project/blob/35b784379e707423f3b4f5a2cfedabcfa6f5b47d/llvm/cmake/modules/LLVM-Config.cmake#L88-L92

Until now this probably hasn't caused many problems because the documentation still recomends to use `llvm_map_components_to_libnames`, which works fine for static libraries.
https://github.com/llvm/llvm-project/blob/d8d2dea7fc6f452ac6a24948fe3ff99920f81c99/llvm/docs/CMake.rst?plain=1#L1059-L1066

People using `llvm_config` probably use it because they have an llvm that uses shared libraries and therefore the macro works fine for them. But when the documentation is updated to recommend to use `llvm_config` macro (e.g. by https://github.com/llvm/llvm-project/pull/82769/) more people could get problems.

Possible solutions probably would be to either:
- always set `LLVM_DYLIB_COMPONENTS` to empty when `LLVM_BUILD_LLVM_DYLIB` is `false` or
- check `LLVM_BUILD_LLVM_DYLIB` in the `llvm_makro`.

</pre>
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