<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/55738>55738</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            LLVM rebuild is slower than a clean build when -DLLVM_ENABLE_MOULDES=Yes
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang:modules
      </td>
    </tr>

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

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

<pre>
    ```
$ cmake -G Ninja -S llvm -B build \
    -DCMAKE_BUILD_TYPE=Release    \
    -DLLVM_ENABLE_LIBCXX=Yes      \
    -DLLVM_ENABLE_LLD=Yes         \
    -DLLVM_ENABLE_MODULES=Yes     \
    -DLLVM_ENABLE_PROJECTS=clang  \
    -DLLVM_ENABLE_ZLIB=Yes
$ time ninja -C build
<snip>
[4493/4493] Linking CXX executable bin/c-index-test
real    4m40.843s
user    247m42.595s
sys     16m34.862s
```
```
$ touch clang/include/clang/Sema/Sema.h
$ time ninja -C build
ninja: Entering directory `build'
[350/350] Creating library symlink lib/libclang-cpp.so

real    11m13.765s
user    51m32.644s
sys     5m5.875s
```
I've observed this for the past few months. It shouldn't take 3x as long to build only a twelfth of the files.
</pre>
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